MXPA98009788A - Method and apparatus for transfer of hard transmission in a system c - Google Patents

Abstract

The present invention relates to a telecommunications network, a network user communicates through a remote unit (30) with another user, using at least one base station (100). The communication network includes a first mobile switching center (MSC-I) that controls communications through a first set of base stations that includes a first base station (199). The remote unit (30) stores a list of active base stations that has an entry corresponding to each base station with which active communication is established. The first base station (100) has an entry on the list of active base functions. The first base station (100) measures a round trip delay of an active communication signal between the first base station (100) and the remote unit (30). A communication transfer of the active communication signal is initiated if the round trip delay of the active communication exceeds a threshold, if the first base station (100) is designated as a reference station. Alternatively, the remote unit (30) also stores a list of candidate base stations comprising an entry corresponding to each base station through which active communication can be possible pin is established. A transmission transfer of the active communication signal is initiated if the list of candidate base stations comprises an input corresponding to an activated pilot signal

Description

METHOD AND APPARATUS FOR TRANSFER OF HARD TRANSFER IN A CDMA SYSTEM FIELD OF THE INVENTION The present invention relates generally to cellular communication systems, in which multiple base stations are located. In particular, the present invention relates to a novel and improved technique for the transfer of communication between base stations of different cellular systems.

BACKGROUND OF THE INVENTION The use of code division multiple access modulation (CDMA) techniques is just one of several techniques for facilitating communications in which a large number of users of the system are present.

Although other techniques such as time division multiple access (TDMA) and frequency division multiple access (FDMA) are known, CDMA has significant advantages over these other modulation techniques. The use of CDMA techniques in a multiple access communication sisterr.a is disclosed in U.S. Patent No. 4,901,307, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING P1752 / 98MX SATELLITE OR TERRESTRIAL REPEATERS ", assigned to the assignee of the present invention, which disclosure is incorporated herein by reference. In the just mentioned patent, a multiple access technique wherein a large number of users is revealed mobile telephone system, each have a transceiver (also known as a remote unit), communicate through satellite repeater stations or land base stations (also known as base stations or cell sites) using CDMA wide-spectrum communication signals. By using CDMA communications, the frequency spectrum can be reused multiple times.The use of CDMA techniques results in a much higher spectral efficiency than can be achieved using other multiple access techniques, thus allowing an increase in the capacity of the user system: conventional FM cellular telephone systems used within the United States, are commonly called Advanced Mobile Phone Service (AMPS), and are detailed in the Electronic Industry standard Association EIA / TIA-553"Mobile Station - Land Station Compatibility Specification. "In this conventional FM cell phone system, the available frequency band is divided into channels that normally have P1752 / 98MX a bandwidth of 30 Kilo Hertz (kHz). The service area of the system is geographically divided into base station coverage areas that can vary in size. The available frequency channels are divided together. The frequency sets are assigned to the coverage areas in such a way as to minimize the possibility of co-channel interference. For example, consider a system in which there are seven frequency sets and the coverage areas are hexagons of the same size. The frequency set used in a coverage area is not used in the six closest neighboring coverage areas. In conventional cellular systems, a communication transfer scheme is used to allow a communication connection to continue when a remote unit crosses or crosses the boundary between coverage areas of two different base stations. In the system with AMPS, the transfer of communication from one base station to another is initiated when the receiver in the active base station is handling the call note that the signal strength received from the remote unit has fallen below a value default threshold. The indication of low signal intensity implies that the remote unit must be close to the boundary of the coverage area of the base station. When the level of the signal P1752 / 98 X falls below the predetermined threshold value, the active base station requests the system controller to determine if a neighboring base station receives the signal from the remote unit with a better signal strength than the current base station. The system controller in response to the inquiry of the active base station sends messages to neighboring base stations with a communication transfer request. Each of the neighboring base stations of the active base station employs a special scanning or scanning receiver that searches for the signal from the remote unit in the channel in which it is operating. If one of the neighboring base stations reports an adequate signal level to the system controller, the transfer is attempted to that neighboring base station which is now labeled as the target base station. The transfer of the communication is then initiated by selecting a free or unoccupied channel from the set of channels used in the target base station. A control message is sent to the remote unit that commands it to switch from the current or present channel to the new channel supported by the target base station. At the same time, the system controller switches the call connection of the active base station to the objective base station. This process is referred to as communication transfer P1752 / 98MX hard. The hard term is used to characterize the particularity of "cutting before establishing" the transfer. In the conventional system, a call connection is lost (i.e., discontinued or interrupted) if the transfer to the target base station is unsuccessful. There are many reasons why a failure in the hard transfer of communication can occur. The transfer may fail if a free or unoccupied channel is not available at the target base station. The transfer may also fail if one of the neighboring base stations reports receiving a signal from the remote unit, when in fact, the base station is actually receiving the signal from a different remote unit, using the same channel to communicate with a station. distant base. This reporting error results in the transfer of the call connection to a wrong base station, usually one in which the signal strength of the remote unit present is insufficient to maintain communications. Also, if the remote unit fails to receive the command to switch channels, the transfer fails. Actual operating experience indicates that transfer failures occur frequently, which significantly decreases the reliability of the system.

P1752 / 98MX Another common problem in the conventional AMPS telephone system occurs when the remote unit remains for an extended period of time near the border between two coverage areas. In this situation, the level of the signal tends to fluctuate with respect to each base station, as the remote unit changes position or as other reflective or attenuating objects within the coverage area change position. Fluctuations in the level of the signal can result in a "bounce or ping-pong" situation in which repeated round-trip requests are made to transfer the call between the two base stations. These unnecessary additional transfers increase the probability of the call being inadvertently discontinued. In addition, repeated transfers, even if successful, can adversely affect the quality of the signal. In U.S. Patent No. 5,101,501, entitled "METHOD AND SYSTEM FOR PROVIDING A SOFT HANDOFF IN COMMUNICATIONS IN A CDMA CELLULAR TELEPHONE SYSTEM", issued March 31, 1992, which was assigned to the assignee of the present invention, a method and system for providing communication with the remote unit through more than one base station during the transfer of a CDMA call are disclosed. The use of this type of communication transfer within the cellular system P1752 / 98MX is not interrupted by the transfer of the active base station to the target base station. This type of transfer can be considered as a "soft" transfer in which concurrent communications are established with the target base station that becomes the second active base station before communication with the first active base station is terminated. An improved soft transfer technique is disclosed in U.S. Patent No. 5,267,261, entitled "MOBILE STATION ASSISTED SOFT HANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM", granted on November 30, 1993, hereinafter referred to as the 'patent'. 261, which is also assigned to the assignee of the present invention. In the system of the '261 patent, the process of soft transfer is controlled on the basis of the measurements of the intensity of the "pilot" signals in the remote unit, transmitted by each base station within the system. These measurements of the pilot intensity help the smooth transfer process by facilitating the identification of viable base stations candidates for the transfer. More specifically, in the system of the '261 patent, the remote unit monitors the signal strength of the pilot signals of the neighboring base stations. The coverage area of the neighboring base stations really P1752 / 98MX does not need to merge with the coverage area of the base station with which active communication is established. When the measured intensity of the pilot signal from one of the neighboring base stations exceeds a given threshold, the remote unit sends a signal strength message to the system controller via the active base station. The system controller commands a target base station to establish communication with the remote unit and commands the remote unit through the active base station to establish contemporary communication through the target base station, while maintaining communication with the remote base station. the active base station. This process can continue for other base stations. When the remote unit detects that the signal strength of a pilot corresponding to one of the base stations through which the remote unit is communicating has fallen below a predetermined level, the remote unit reports the measured intensity of the remote unit. the signal from the corresponding base station to the system controller via the active base stations. The system controller sends an order message to the identified base station and to the remote unit to terminate communication through the identified base station while maintaining communications to P1752 / 98MX through the other or other active base stations. Although the preceding techniques are well adapted for call transfers between base stations of the same cellular system, which are controlled by the same system controller, a more difficult situation is presented due to the movement of the remote unit towards a coverage area served by a base station of another cellular system. A complicating factor in these "intersiste a" transfers is that each system is controlled by a different system controller and that, normally, there is no direct link between the base stations of the first system and the system controller of the second system and vice versa . In this way, the two systems are prevented from simultaneously communicating with the remote unit through more than one base station during the transfer process. Although the existence of an intersystem link between the two systems is available to facilitate soft intersystem transfer, the dissimilar characteristics of the two systems often complicate the smooth transfer process. When resources are not available to conduct soft intersystem transfers, the execution of a "hard" transfer of the connection between P1752 / 98MX call from one system to another, it becomes critical if the service should be maintained uninterrupted. The intersystem transfer must be executed at a convenient time and location to result in a successful transfer of the connection between the systems. It follows that the transfer should only be attempted when, for example: (i) a free channel is available at the target base station, (ii) the remote unit is within the range of the target base station and the active base station and ( iii) the remote unit is in a position where it is assured the reception of the command to switch channels. Ideally, each hard intersystem transfer should be conducted in a manner that minimizes the potential for "bounce or ping-pong" transfer requests between base stations of different systems. These and other disadvantages of existing intersystem transfer techniques impair the quality of cellular communications, and can be expected to further degrade performance as competing cellular systems continue to proliferate. In accordance with the above, there is a resultant need for an intersystem transfer technique that P1752 / 98 X has the ability to reliably execute the transfer of a call between the base stations of different systems.

SUMMARY OF THE INVENTION The present invention uses two different techniques to facilitate hard transfer from a first base station controlled by a first system controller to a second base station controlled by a second system controller. The detection rule activates a transfer when a remote unit located within the coverage area of a designated base station reports the detection of an activating pilot signal. The action taken depends on the coverage area in which the remote unit is located and the activating pilot signal that is perceived. The donation rule activates a transfer when the active set of the remote unit contains only one base station and that base station is designated as a reference base station and the round trip delay between the remote unit and the reference base station exceeds a certain threshold. The detection and donation rules can be used together with the physical configurations of the coverage area that provide both the intra-system hysteresis and the intersystem spatial hysteresis. The P1752 / 98MX rules can also be combined with other network planning configurations to provide maximum benefit such as the use of a frequency transfer different from CDMA to CDMA.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURES The features, objects and advantages of the present invention will be more evident from the detailed description set forth below when considered with the drawings, wherein: Figure 1 provides an exemplary illustration of an LL system cellular, PCS or wireless PBX; Figure 2 shows a cellular communications network comprised of a first and a second cellular system controlled respectively by the mobile switching centers first (MSC-I) and second (MSC-II); Figure 3 shows a cellular communication system co-located in a microwave link from point to point between two directional microwave antennas; Figure 4A shows a very idealized representation of the hard transfer region of an FM system; Figure 4B shows a very idealized representation of the hard and soft transfer region of a P1752 / 98MX CDMA system; Figure 4C shows a highly idealized representation of the transfer region corresponding to a different frequency transfer from CDMA to CDMA; Figure 5 shows a set of indoor, transition and second base stations and is used to illustrate the function of the remote unit measurement directed to the hard transfer table; Figure 6 shows an antenna pattern for a three-sector base station; Figure 7 illustrates the use of the detection rule in a transfer of the same frequency from CDMA to CDMA; Figure 8 illustrates the use of the stop rule in a frequency transfer different from CDMA to CDMA; Figure 9 illustrates two base stations placed in a configuration that provides for the transfer of different frequency from CDMA to CDMA; Figure 10 illustrates the transfer of a CDMA system to a system that provides the service using a different technology; Figure 11 illustrates an alternative configuration that provides a different frequency transfer from CDMA to CDMA using a single base station P1752 / 98MX of multiple sectors; Figure 12 is a block diagram of a prior art base station comprising reception diversity; Figure 13 is a block diagram of a border base station having transmission diversity to produce a diversity of trajectories; Figure 14 depicts the use of base stations placed to effect hard transfer; Figure 15 represents the use of very closely located base stations that have a significant portion of overlap in the coverage area to effect the hard transfer; Figure 16 illustrates the use of a "Cone of Silence" in a CDMA system intersected by a point-to-point microwave link; and Figure 17 illustrates the use of a "Cone of Silence "in a CDMA system intersected by a point-to-point microwave link in which the coverage area of the silent cone and the coverage area of the microwave link is substantially the same.

DESCRIPTION OF THE PREFERRED MODALITY An exemplary illustration of a cellular telephone system, a private exchange system (PBX) Wireless P1752 / 98MX, a wireless local circuit (LL), a personal communications system (PCS) or other analog wireless communication system is provided in Figure 1. In an alternative mode, the base stations of Figure 1 may be based in satellites. The system illustrated in Figure 1 can use various multiple access modulation techniques to facilitate communications between a large number of remote units and a plurality of base stations. Various techniques for the multiple access communication system are known in the art, such as the time division multiple access scheme (TDMA), the frequency division multiple access scheme (FDMA), the multiple access scheme for code division (CDMA) and the amplitude modulation (AM) scheme, such as the compressed (expanded-compressed) amplitude of a single sideband. However, the CDMA wide-spectrum modulation technique has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Patent No. 4,901,307, issued on February 13, 1990, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS" , assigned to the assignee of this P1752 / 98MX invention, which is incorporated herein by reference. Many of the ideas described herein, can be used with a variety of communication techniques, even through the preferred embodiments disclosed herein are described with reference to a CDMA system. In U.S. Patent No. 4,901,307, referred to above, a multiple access technique is disclosed, wherein a large number of users of the mobile telephone system each have a transceiver that communicates through satellite repeater stations. or terrestrial base stations using CDMA wide-spectrum communication signals. When using CDMA communications, the same frequency spectrum can be reused multiple times to communicate a plurality of different communication signals. The use of CDMA results in a much higher spectral efficiency than can be achieved using other multiple access techniques, thus allowing an increase in the capacity of the system user. In the typical CDMA system, each base station transmits a unique pilot signal. In the preferred embodiment, the pilot signal is a broad-spectrum unmodulated and direct-sequence signal transmitted continuously by each base station, using a code P1752 / 98MX common pseudorandom (PN) noise dispersion. Each base station or base station sector transmits the time-shared pilot sequence offset from the other base stations. The remote units can identify a base station based on the displacement of the code phase of the pilot signal it receives from the base station. The pilot signal also provides a phase reference for the coherent demodulation and the bases of the signal strength measurements used in the determination of the transfer. Referring again to Figure 1, the system controller and switch 10, also referred to as the mobile switching center (MSC), typically includes an interface and processing circuitry to provide control of the system to the base stations. The controller 10 also controls the routing of telephone calls from the public switched telephone network (PSTN) to the appropriate base station for transmission to the appropriate remote unit. The controller 10 also controls the routing of the calls from the remote units, by the rr.enos a base station, to the PSTN. The controller 10 can direct calls between remote units by the appropriate base stations. A typical wireless communication system P1752 / 98MX contains some base stations that have multiple sectors. A multi-sector base station comprises multiple independent transmit and receive antennas, as well as some independent processing circuitry. The present invention also applies to each sector of a sectorized base station and independent base stations of a single sector. The term base station is assumed to refer to either a sector of a base station or a base station of a single sector. The controller 10 may be coupled to the base stations by various means such as dedicated or dedicated telephone lines, fiber optic links or microwave communication links. Figure 1 illustrates exemplary base stations 12, 14, 16 and the exemplary remote unit 18. The remote unit 18 can be a vehicle-based telephone, a portable hand-held unit, a PCS unit or. a fixed location wireless local circuit unit or any other device, voice or data conformation communication. The arrows 20A-20B illustrate the possible communication link between the base station 12 and the remote unit 18. The arrows 22A-22B illustrate the possible communication link between the base station 14 and the remote unit 18. Similarly, the arrows 24A-24B, illustrate the P1752 / 98 X possible communication link between station 16 and remote unit 18. Base station locations are designed to provide service to remote units located within their coverage areas. When the remote unit is free or unoccupied, that is, there are no calls in progress, the remote unit constantly monitors the transmissions of the pilot signal from each nearby base station. As illustrated in Figure 1, the pilot signals are transmitted to the remote unit 18 by the base stations 12, 14 and 16 with the communication links 20B, 22B and 24B, respectively. Generally speaking, the term uplink refers to the connection of the base station to the remote unit. Generally speaking, the term "downlink" refers to the connection of the remote unit to the base station. In the example illustrated in Figure 1, the remote unit 18 may be considered to be in the coverage area of the base station 16. In this way, the remote unit 18 tends to receive the pilot signal from the base station 16 to a level greater than any other pilot signal that it monitors. When the remote unit 18 initiates a traffic channel communication (ie, a telephone call) to the base station 16 a message is transmitted P1752 / 98MX control. The base station 16 upon reception of the call request message sends signals to the controller 10 and transfers the called telephone number. The controller 10 then connects the call through the PSTN to the intended container. If a call will be initiated from the PSTN, the controller 10 transmits the call information to a set of base stations located in the vicinity of the location where the presence of the remote unit was most recently recorded. The base stations in turn broadcast a radio location message. When the intended remote unit receives its signaling message, it responds with a control message that is transmitted to the nearest base station. The control message notifies the controller 10 that this particular base station is in communication with the remote unit. The controller 10 initially routes the call through this base station to the remote unit. If the remote unit 18 moves outside the coverage area of the initial base station, for example, of the base station 16, the communication is transferred to another base station. The process of transferring the communication to another base station is referred to as a transfer. In the preferred embodiment, the remote unit initiates and assists the transfer process.

P1752 / 98MX In accordance with the "Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System", TIA / EIA / IS-95, generally referred to simply as the IS-95, the same remote unit can initiate a transfer "aided or assisted by the remote unit". The remote unit is equipped with a search receiver, which is used to sweep or explore the transmission of the pilot signal from neighboring base stations in addition to performing other functions. If a pilot signal from one of the neighboring base stations, for example, the base station 12, is found to be stronger than a given threshold, the remote unit 18 transmits a message to the present base station, the base station 16. information is communicated by the base station 16 to the controller 10. The controller 10 upon receiving this information can initiate a connection between the remote unit 18 and the base station 12. The controller 10 requests that the base station 12 allocate resources for the call. In the preferred embodiment, the base station 12 assigns a channel element to process the call and reports this assignment back to the controller 10. The controller 10 informs the remote unit 18 through the base station 16 to look for a signal of the base station 12 and informs the base station 12 of the parameters of the traffic channel of the remote unit. The P1752 / 98MX remote unit 18 communicates through both base stations, 12 and 16. During this process, the remote unit continues and identifies and measures the signal strength of the pilot signals it receives. In this way, the transfer helped by remote unit is achieved. The above process can also be considered to be a "soft" transfer in which the remote unit communicates simultaneously through more than one base station. During smooth transfer, the MSC can combine or choose between the signals received from each base station and with which the remote unit is in communication. The MSC retransmits the signals from the PSTN to each base station with which the remote unit is in communication. The remote unit combines the signals it receives from each base station to produce an aggregate result. With the review of the soft transfer process, it is clear that the MSC provides centralized control of the process. The transfers aided by the remote unit tend to be more complex if it happens that the remote unit is located within the coverage area of two or more base stations that are not within the same cellular system, that is, they are not controlled by the same MSC . Figure 2 shows a communication network 30 P1752 / 98MX cells comprising first and second cellular systems under the control of first and second mobile switching centers, MSC-I and MSC-II, respectively. The MSC-I and the MSC-II are respectively coupled to the base stations of the first and second cellular systems by various means such as dedicated or exclusive telephone lines, fiber optic link or microwave communication links. In Figure 2, five of these exemplary BIA-SIE base stations provided respectively within the coverage areas C1A-C1E of the first system and five B2A-B2E base stations provided respectively within the coverage areas C2A are represented in illustrative form. -C2E of the second cellular system. For convenience of illustration, the coverage areas C1A-Cle and C2A-C2E of Figure 2, and the coverage areas shown in Figure 3, subsequently introduced therein, are shown as circular or hexagonal and are highly idealized. In the actual communication environment, the coverage areas of the base station can vary in shape and size. The coverage areas of the base station may tend to overlap with the limits of the coverage area that define coverage areas with different forms of the ideal circular or hexagonal shape. In addition, base stations can also P1752 / 98MX be sectorized, such as in three sectors, as is well known in the art. In the following, the coverage areas C1C-C1E and C2c ~ C2E can be referred to as the border or transition coverage areas, because these coverage areas are close to the boundary or boundary between the first and second cellular systems. . The rest of the coverage areas within each system are referred to as the interior of the coverage area or the internal coverage area. A quick examination of Figure 2 reveals that the MSC-II does not have direct access to communicate with the base stations B1A-B1E and the MSC-I does not have direct access to communicate with the base stations B2A-B2E. As shown in Figure 2 MSC-I and MSC-II, they can communicate with each other. For example, the EIA / TIA / IS-41, entitled "Cellular Radio Telecommunication Intersystem Operations", and the subsequent revision thereof, define a standard for communication between switches of different operating regions, as shown by the data link. intersystem 34 of Figure 2. To provide smooth transfer between one of the base stations B1C-B1E and one of the B2C-B2E base stations, a large volume of call signal information and power control must pass between the MSC-I and the MSC- P1752 / 98MX II. The continuous nature of the switch-to-switch connection and the large volume of the call signal and power control information can cause undue delay and can sacrifice excessive resources. Another difficulty in providing soft transfer is that the architecture of the system controlled by the MSC-I and the system controlled by MSC-II can be very different. Also, the power control method used by two systems can be totally different. Therefore, the present invention relates to the provision of a hard transfer mechanism between two systems to avoid complications and the expense of soft intersystem transfer. A mechanism for hard transfer can be used in different situations. For example, the system controlled by the MSC-II may not use the CDMA to communicate signals but may use FM, TDMA or another method instead. In this case, hard transfer is required even if a mechanism for smooth intersystem transfer is provided in the system controlled by the MSC-I, because soft transfer is only possible if both systems operate or operate using the CDMA. In accordance with the above, this invention could be used to make the transfer of remote units between two systems that use P1752 / 98MX different air interfaces. The second system may need to be modified to transmit a pilot signal or another CDMA radio beacon to help initiate the hard transfer process. A system using a pilot radio beacon is detailed in copending United States Patent Application Serial No. 08 / 413,306, entitled "METHOD AND APPARATUS FOR MOBILE UNIT ASSISTED CDMA TO ALTERNATIVE SYSTEM HARD HANDOFF", filed on March 30, 1995. An alternative system is detailed in copending United States Patent Application Serial No. 08 / 522,469, entitled "SAME FREQUENCY, TIME-DIVISION-DUPLEX REPEATER", filed on August 31, 1995, these two are assigned to the assignee of the present invention. A system may use a pilot beacon unit detailed in copending United States Patent Application Serial No. 08 / 322,817, entitled "METHOD AND APPARATUS FOR HANDOFF BETWEEN DIFFERENT CELLULAR COMMUNICATIONS SYSTEMS", filed October 13, 1995 and assigned to the assignee of the present invention. Another situation in which hard transfer may be useful is the case where the remote unit must change the frequency at which it works. For example, within the PCS band, point-to-point microwave links can operate in coexistence with the CDMA communication system. In Figure 3, P1752 / 98 X shows the point-to-point microwave link 140 between the directional microwave antenna 130 and the directional microwave antenna 135. The base stations 40, 100 and 110 may need to avoid using the frequency band used by the link 140 point-to-point microwave and thus avoid interference between the two systems. Because the directional microwave antenna 130 and the directional microwave antenna 135 are highly directional, the point-to-point microwave link 140 has a very narrow or closed field. In this way, the other base stations of the system, such as the base stations 115, 120 and sectors 50 and 70, can operate without interference with point-to-point microwave link 140. In this way, the remote unit 125 may be operating in a CDMA channel in the same frequency band as the point-to-point microwave link 140. If the remote unit 125 moves to the base station 110 that does not support communication on the frequency that the remote unit 125 is currently operating, it is not possible to complete the soft transfer from the base station 115 to the base station 110. Instead of that, the base station 115 may instruct the remote unit 125 to perform the hard transfer to another frequency band that is supported by the base station 110.

P1752 / 98MX Another situation in which hard transfer may be useful, is the case where the remote unit must change the frequency at which it works for a distributed load more evenly. For example, within the PCS band, the CDMA communicates with the traffic channel signals in a plurality of frequency bands, such as, for example, the frequency band i1 and the frequency band f2. If the frequency band f2 is more heavily loaded with active communication signals than the frequency band fl r it may be advantageous to download part of the active communication signal from the frequency band f2 to the frequency band f1. To perform load sharing, one or more remote units operating in the frequency band f2 are commanded to start operating in the frequency band f2 when performing a hard transfer intrasiste a. The most reliable way to effect the hard transfer may be to have the base station 115 perform a hard transfer to an alternative frequency within itself. Thus, at some point when the remote unit 125 is receiving a rather large and reliable volume of signals from the base station 115. The base station 115 instructs the remote unit 125 to operate at a different frequency supported by the station base 115. The base station 115 P1752 / 98MX starts transmitting and trying to receive the signal transmitted from the remote unit to the new frequency. Alternatively, hard transfer could occur between a first frequency of the base station 115 and a second frequency of the base station 110. Neither of the two types of hard transfer requires any intersystem communication. Referring again to Figure 2, the first mobile switching center (MSC-I) controls the routing of telephone calls from the PSTN to the appropriate base station B1A-B1E for transmission to the designated remote unit. The MSC-I also controls the routing of remote units within the coverage area, through at least one base station, to the PSTN. The MSC-II operates in a similar manner to govern the operation of the B2A-B2E base stations to route calls between the PSTN and the B2A-B2E base stations. Control messages and the like may be communicated between the MSC-I and MSC-II over an intersystem data link 34 using an industry standard, such as IS-41 or a subsequent revision standard. When a remote unit is located within the coverage area of an internal base station, the remote unit is programmed to monitor the pilot signal transmissions of a set of neighboring base stations.

P17? 2/98 X Consider the case in which the remote unit is located within the coverage area C1D but is approaching the coverage area C2D. In this case, the remote unit could begin to reside usable signal levels of the base station B2D, which will then be reported to the base station B1D and to any other base stations with which the remote unit is currently in communication. The time in which usable signal levels are received by a remote unit can be determined by measuring one or more quantifiable parameters (eg, signal strength, signal-to-noise ratio, frame error rate, erase rate) of the frame, bit error rate and / or relative time delay) of the received signal. In the preferred embodiment, the measurement is based on the intensity of the pilot signal as it is received by the remote unit. After this detection of the usable levels of the signal received in the remote unit and of the report thereof to the base station B1D using a message of quality or signal strength, it could then proceed as follows a hard transfer assisted or assisted per remote unit at the same frequency from base station Blc to base station B2D; (i) Base station B1D delays the level of the reported signal of the remote unit received from the station P1752 / 98MX base B2D to the MSC-I, which is prevented that the base station B2D is controlled by the MSC-II; (ii) The MSC-I requests channel resources and intersystem trunk facilities between the two systems in the base station B2D of the MSC-II over the intersystem data link 34; (iii) The MSC-II responds to the request by providing information to the MSC-I, through the intersystem data link 34, which identifies the channel in which the communication will be established as well as other information. In addition, the controller reserves within the base station B2D the channel designated for communication with the remote unit and the trunk resources; (iv) The MSC-I supplies the new channel information to the remote unit via the base station B1D, and specifies the time at which the remote unit will begin communication with the base station B2D; (v) The communication is established by hard transfer between the remote unit and the B2D base station at the specified time; and (vi) The MSC-II recognizes or sends the acknowledgment to the MSC-I of the successful transition of the remote unit in the system. One difficulty with this approach is that the MSC-I is not aware of whether the signal from the remote unit is received by the base station B2D at a sufficient level to P1752 / 98MX support communication at that time. The MSC-I instructs the remote unit to establish a communication with the base station B2D. Similarly, the base station B2D may not yet be receiving a usable signal level from the remote unit. As a result, the call connection may be lost during the process of transferring the control to the MSC-II. If the call connection is lost, an error message will be sent from the MSC-II to the MSC-I instead of an acknowledgment or acknowledgment message. Another difficulty in providing hard transfer is the nature of the boundaries of the coverage areas of the CDMA system. In an FM system, such as the AMPS, the overlap regions of the coverage areas are very broad. The overlap region of • the coverage areas is the area in which the communication can be supported between a remote unit and a single one of two different base stations. In the FM system, these regions of overlap of coverage areas must be broad, because hard transfers can only occur successfully when the remote unit is located in a region of overlap of coverage areas. For example, Figure 4A is a highly idealized representation of an FM system. The base station 150 and the base station 165 have the ability to provide the P1752 / 98MX uplink and downlink FM communication to remote unit 155. (The uplink refers to the connection of the base station to the remote unit.) The downlink refers to the connection of the remote unit to the station. base) . Within region 160, the signal strength from both base stations, 150 and 165, is at a level sufficient to support communication with remote unit 155. Note that due to the nature of the FM system, the stations base 150 and 165 can not communicate simultaneously with remote unit 155. When hard transfer from base station 150 to base station 165 occurs within region 160, for communication a new frequency is used between the base station 165 and the base station 165. remote unit 155 which was used between the base station 150 and the remote unit 155. The base station 165 never transmits on any frequency used by the base station 150 and, thus, the base station 165 nominally does not provide interference to the communication between the base station 150 and any remote unit with which it is in communication. The boundary 182 indicates the location beyond which the communication of the base station 165 with the remote unit 155 is not possible. Similarly, the boundary 188 indicates the location beyond which the communication of the base station 150 with the P1752 / 98MX remote unit 155. Obviously, Figure 4A, as well as Figures 4B and 4C, are not drawn to scale and, in reality, the overlapping regions of the coverage areas are relatively narrow compared to the coverage area total of each base station. With the soft transfer of CDMA, the existence of a region of overlap of coverage areas in which communication can be fully supported by one or two base stations is not critical. In the region where the soft transfer occurs, it is sufficient that reliable communication can be maintained if communication is established simultaneously with two or more base stations. In the CDMA system, normally active and neighboring base stations operate at the same frequency. In this way, as the remote unit approaches or approaches a coverage area of a neighboring base station, the levels of the active base station signal fall and the interference levels of the neighboring base station increase. Due to the increased interference from neighboring base stations, if a smooth transfer is not established, the connection between the active base station and the remote unit may be invalidated. The connection is especially invalidated if the signal vanishes with respect to the active base station and not with respect to the neighboring base station.

P1752 / 98MX Figure 4B is a highly idealized representation of a CDMA system. The CDMA base station 200 and the CDMA base station 205 have the ability to provide uplink and downlink CDMA communication with the remote unit 155. Within the darkest region 170, the signal strength of the two stations base, 200 and 205, is at a level sufficient to support communication with remote unit 155, even if communication is established only with one of the base stations, 200 or 205. Beyond boundary 184, the communication through only the base station 205 is not reliable. Similarly, beyond boundary 186, communication through only the base station 200 is not reliable. Regions 175A, 170 and 175B represent the areas where a remote unit is likely to be in soft handoff between the base stations 200 and 205. When establishing communication through the two base stations, 200 and 205, it improves the overall reliability of the system even if the communication link with a remote unit within the region 175A with the base station 205 is not reliable alone to support communication. Beyond boundary 180, the signal levels of base station 205 are insufficient to support communication with remote unit 155 still in transfer P1752 / 98MX soft. Beyond boundary 190, the signal levels of base station 200 are insufficient to support communication with remote unit 155 even in soft handoff. Note that Figures 4A and 4B are drawn one with reference to the other. The reference numbers used to designate the borders 180, 182, 184, 186, 188, and 190, increase in value with the increase in distance from the base station 150 and the base station 200. Thus, the transfer region Smooth between the 180 and 190 borders is the widest region. The region of overlap of FM coverage areas between borders 182 and 188 falls or remains within the soft CDMA transfer region. The "hard transfer" region of CDMA is the narrowest or most closed region between borders 184 and 186. Note that if the base station 200 belongs to a first system and the base station 205 belongs to a second system, the base station 200 and the base station 205 may not have the ability to communicate simultaneously with the remote unit 155. Thus, if the communication needs to be transferred from a base station 200 to the base station 205, the hard transfer of the base station 200 needs to be executed. to base station 205. Note that the remote unit must be located P1752 / 98MX in the hard transfer region of CDMA between boundary 184 and 186 of region 170 so that the hard transfer has a high probability of success. The difficulty lies in the fact that the hard transfer region 170 may be narrowly narrow and the time it takes the remote unit 155 to move in and out of the hard transfer region 170 may be very small. Furthermore, it is difficult to discern whether the remote unit 155 is within the hard transfer region 170. Once it has been determined that the remote unit 155 is in the hard transfer region 170, the decision must be made with which base station and when the hard transfer should occur. The present invention focuses on these problems. The first aspect of the present invention is a system and method for determining the regions within the coverage area, where the hard transfer is both necessary and probable to be achieved successfully and with which base stations the hard transfer should be attempted. The hexagonal mosaic arrangement shown in Figure 3 is highly idealized. When the systems actually deploy, the resulting coverage areas take many different forms. Figure 5 shows a more realistic representation of a set of base stations. Base stations Tx - T3 and Ix base stations P1752 / 98MX I3, are part of a first communication system controlled by the controller 212 of the system 1. The base stations Ix-I3 are indoor base stations that limit only with other base stations of the same system. The Tx-T3 base stations are transition or border base stations that have coverage areas that are spliced with the coverage areas of base stations that belong to a different operating system. The base stations St-S3 are part of a second system controlled by the controller 214 of system 2. The outermost thick concentric circles enclosing the base station S] _-S3, the base stations 1-I3 and the base stations T2 - T3, indicate the idealized coverage areas of the base stations in which it is possible to establish communication with the corresponding base station. The outermost thick wavy lines enclosing the base stations S-S2 and the Ti station show more realistic coverage areas of the corresponding base stations. For example, wavy line 228 represents the coverage area of the base station Si. The shape of the coverage area is affected to a large extent by the terrain in which the base station resides, such as the height at which the antennas are mounted, the number, the reflectivity and the height of the elevated buildings in the area of coverage, as well as P1752 / 98MX trees, hills and other obstacles within the coverage area. The actual coverage areas of each base station are not shown to simplify the drawing. In a real system, some of the base stations may be sectorized, such as, for example, in three sectors. Figure 6 shows an antenna pattern of a three-sector base station. To simplify the drawing, in Figure 5 three-sector base stations are not shown. The concepts of the present invention are directly applicable to sectorized base stations. In Figure 6, the coverage area 300A is represented by the line with the thinnest width. The coverage area 300B is represented by the medium width line. The coverage area 300C is represented by the thickest line. The shape of the three coverage areas shown in Figure 6 is the shape produced by standard directional dipole antennas. The edges of the coverage areas can be imagined as the location in which a remote unit receives the minimum level of signal necessary to support communication through that sector. As a remote unit moves to the sector, the intensity of the signal received from the base stations as perceived by the remote unit increases. A remote unit at point 302 can communicate through sector 300A. A remote unit at point 303 can P1752 / 98 X communicate through sector 300A and sector 300B. A remote unit at point 304 communicates through sector -300B. As a remote unit moves or moves beyond the edge of the sector, communication can be degraded through that sector. A remote unit operating in a soft transfer mode between the base station of Figure 6 and a neighboring base station not shown will probably be located near the edge of one of the sectors. The base station 60 of Figure 3 represents a more idealized three-sector base station. The base station 60 has three sectors, each of which covers more than 120 degrees of coverage area of the base station. The sector 50 has a coverage area indicated by the non-separated lines 55, overlaps with the coverage area of the sector 70, which has a coverage area indicated by the thick lines 75. The sector 50 also overlaps with the sector 80, which has a coverage area as indicated by the thin line lines 85. For example, location 90 as indicated by X is located both in the coverage area of sector 50 and sector 70. In general , a base station is sectorized to reduce the total power of interference with the remote units located within the coverage area of the P1752 / 98MX base station, while increasing the number of remote units that can communicate through the base station. For example, sector 80 does not transmit a signal intended for a remote unit at location 90 and, thus, no remote unit located in sector 80 is significantly interfered by the communication of a remote unit at location 90 with the base station 60. For a remote unit placed at location 90, the total interference has contributions from sectors 50 and 70 and from base stations 115 and 120. U to remote unit at location 90 may be in a smoother transfer with sectors 50 and 70. A remote unit at location 90 may simultaneously be in soft handoff with either or both of the base stations 115 and 120. The soft handoff aided by remote unit operates on the basis of the intensity of the pilot signal of several sets of base stations, as measured by the remote unit. The Active Set is the set of base stations through which active communication is established. The Neighbor Set is the set of base stations that surround an active base station that comprises the base stations that have a high probability of having a level signal strength P1752 / 98MX enough to establish communication. The Candidate Set is a set of base stations that has a pilot signal strength at a sufficient signal level to establish communication. When communications are initially established, a remote unit communicates through a first base station and the Active Set contains only the first base station. The remote unit monitors the intensity of the pilot signal from the base stations of the Active Set, the Candidate Set and the Neighbor Set. When a pilot signal from a base station in the Neighbor Set exceeds a predetermined threshold level, the base station is added to the Candidate Set and removed from the Neighbor Set in the remote unit. The remote unit communicates a message to the first base station that identifies the new base station. The system's controller decides whether to establish a communication between the new base station and the remote unit. If the system controller decides to do so, the system controller sends a message to the new base station with the identification information about the remote unit and a command to establish communications with it. A message is also transmitted to the remote unit through the first base station. The message identifies a new Active Set that P1752 / 98MX includes the first and new base stations. The remote unit looks for the information signal transmitted from the new base station and communication with the new base station is established without terminating the communication through the first base station. This process can continue with additional base stations. When the remote unit is communicating through multiple base stations, it continues to monitor the signal strength of the base stations of the Active Set, the Candidate Set and the Neighbor Set. If the intensity of the signal corresponding to a base station of the Active Set falls below a predetermined threshold for a predetermined period of time, the remote unit generates and transmits a message to report this event. The system controller receives this message through at least one of the base stations with which the remote unit is communicating. The system controller may decide to terminate communications through the base station that has a low pilot signal strength. The system controller, in deciding to terminate communications through a base station, generates a message identifying a new Active Set of base stations. The new active set does not contain the base station by means of which the P17S2 / 98MX communication. The base stations through which communication is established, send a message to the remote unit. The system controller also communicates information to the base station to terminate communications with the remote unit. Communications from the remote unit are thus routed only through the base stations identified in the new Active Set. When a remote unit is in soft handoff, the system controller receives decoded packets from each of the base stations that are members of the Active Set. From the set of signals, the system controller must create a single signal for transmission to the PSTN. Within each base station, the signals received from a common remote unit can be combined before they are decoded, thus obtaining the full advantage of the multiple signals received. The decoded result of each base station is supplied to the system controller. Once a signal has been decoded, it can not easily and advantageously be "combined" with other signals. In the preferred embodiment, the system controller must select among the plurality of decoded signals corresponding one by one to a base station with which communication is established. The signal The most advantageous decoded P1752 / 98MX is selected from the set of signals from the base stations and the other signals are simply discarded. In addition, for smooth transfer, the system can also use the "softer" transfer. The smoother transfer generally refers to a transfer between sectors of a common base station. Because the sectors of a common base station are much more intimately connected, inter-sector transfer of a common base station can be accomplished by combining non-decoded data rather than by selecting decoded data. The present invention applies equally regardless of whether or not the smoothest transfer is used within any system. The process of the smoother transfer is described in U.S. Patent Application No. 08 / 405,611, entitled "METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMON BASE STATION" filed March 13, 1995 which is a continuation of U.S. Patent Application No. 08 / 144,903, filed October 10, 1993, now abandoned, each of which is assigned to the assignee of the present invention. In the preferred mode, the selection process is performed by the system controller P1752 / 98MX within a selector bank subsystem (SBS). The SBS is comprised of a set of selectors. Each selector handles the active communication of a remote unit. At the end of a call connection, the selector can be assigned to another active remote unit. The selector provides all forms of control functions to both the remote unit and the base stations. The selector sends and receives messages from the base stations. An example of this message is the message sent by the base station each time the round trip delay between the base station and the remote unit changes by a threshold amount. The selector can also command the base station to send a message to the remote unit. An example of this message is a message sent to the base station ordering it to order the remote unit to provide a Pilot Intensity Measurement Message (PSMM). The use of these two signals is explained more fully below. In the most general mode, it does not need to be a selector that controls the transfer process and any form of communication the control unit can perform the functions that in the preferred embodiment are delegated to the selector. When a remote unit has established communication with a base station, the base station can measure the round trip delay (RTD), associated with the P1752 / 98MX remote unit. The base station aligns its transmission to the remote unit over time based on universal time. The signal is transmitted from the base station to the remote unit over the wireless air link. The transmitted signal requires some time to travel from the base station to the remote unit. The remote unit uses the signal it receives from the base station to align the transmission it sends back or back to the base station. By comparing the alignment time of the signal received by the base station from the remote unit with the alignment of the signal sent by the base station to the remote unit, the base station can determine the round trip delay. The round trip delay can be used to estimate the distance between the base station and the remote unit. In accordance with the preferred embodiment, the base station reports the round trip delay to the selector each time the round trip delay changes by more than a predetermined amount. One aspect of the present invention utilizes the round trip delay between the remote unit and the base stations that are members of the Active and Candidate Sets, to identify the location of a remote unit. Obtaining the round trip delay between the remote unit and a base station that is a member of the Active Set is a bit more complicated than determining the P1752 / 98MX round trip delay of a member of the Active Set. Because a base station that is a member of the active set does not demodulate the signal of the remote unit, the round trip delay can not be measured directly by the candidate base stations. The message sent from the remote unit to the base station comprising the pilot signal information of the members of the Candidate and Active Sets is referred to as a Pilot Intensity Measurement Message (PSMM). A PSMM is sent by the remote unit either in response to a request from the base station or, because the signal strength of a Neighbor Station base station has exceeded a threshold or signal strength of a base station of the Candidate Set has exceeded the intensity of one of the base stations of the Active Set by a predetermined amount or, due to the expiration or termination of a drop or transfer loss timer. Four parameters control the smooth transfer process. The first, the pilot detection threshold, T_ADD, specifies the level that must exceed the intensity of the pilot signal of a base station that is a member of the Neighbor Set to be classified as a member of the Candidate Set. The drop or pilot loss threshold, T_DROP, specifies the level below which P1752 / 98MX should drop the intensity of the pilot signal from a base station that is a member of the Active Set or the Candidate Set to activate a timer. The duration of the activated timer is specified by TDROP T. After the time specified by T_TDROP has elapsed, if the intensity of the pilot signal is still below the T_DROP level, the remote unit initiates the removal of the corresponding base station from the set to which it currently belongs. The comparison of the threshold of the Active Set against that of the Candidate Set, T_COMP, sets the amount by which the intensity of the pilot signal of a member of the Candidate Set must exceed the intensity of the pilot signal of a member of the Active Set to activate a PSMM. Each of these four parameters is' stored in the remote unit. Each of these four parameters can be reprogrammed into a new value by means of a message sent from the base station. The PSMM includes two parts of information that are relevant to the present invention. The PSMM comprises a record for each pilot signal corresponding to a base station that is a member of the Active Set or Candidate. First, the PSMM comprises a measurement of the intensity of the signal. Second, the PSMM comprises a measure of the phase of the pilot signal. The P1752 / 98MX remote unit measures the phase of the pilot signal for each pilot signal of the Candidate Set. The phase of the pilot signal is measured in the remote unit by comparing the phase of the usable multipath component that arrives earlier from the signal (candidate pilot for the usable multipath component that arrives earlier from a member of the Active Set. can be measured in relative PN chips The pilot signal from the base station in the Active Set that provides the most anticipated arrival signal is referred to as the reference pilot signal.The system controller can convert the phase of the pilot signal into an estimated of the round trip delay using the following equation: RTDcanl = RTDref + 2 * (PilotPhasecanl - ChannelOffsetcan_ * Pilotlnc) Equation 1 where: RTDcanl = calculated estimate of the round trip delay of a base station having an entry in the Candidate Set; RTDref = the round trip delay reported for the reference pilot signal; PilotPhasecan? = The relay phase the universal time perceived by the remote unit reported in the PSMM in units of PN chips; P1752 / 98MX ChannelOffsetcan] _ = the channel offset of the candidate base station which is a number without units; and Pilotlnc = the increase in the System's wide pilot sequence shift Index in PN chip units per channel. The round trip delay reported for the reference pilot signal, RTDref, is supplied by the corresponding base station to the selector. The round trip delay of the reference pilot signal serves as a basis for estimating the round trip delay between the remote unit and the base station that is a member of the Candidate Set. Remember that in the preferred embodiment, each base station transmits the same pilot sequence shift in time, such that the remote unit can identify a base station based on the code phase shift of the pilot signal. The increase in the pilot sequence shift index, Pilotlnc, is the increment of the code phase shift by means of which the pilot signals of the base station are moved. The channel offset, ChannelOffsetcanj_, of the candidate base station, designates which of the code phases is assigned to the candidate base station. The relative phase of the candidate base station, PilotPhasecan, is the P1752 / 98MX code phase shift of the cante base station as measured by the remote unit compared to the reference pilot signal in PN chip units. The PilotPhasecanj_ is reported to the base station in the PSMM. The ChannelOffsetcan? _ And the Pilotlnc are known by the selector. If there was no transmission delay in the system, the phase of the cante base station would be the product of the channel offset, ChannelOffsetcanj_, and the increase in the system's wide pilot sequence shift index, Pilotlnc. Because there are transmission delays in the system, the remote unit senses both the reference pilot signal and the pilot signal from the cante base station with different and variable delay. By subtracting the PN offset induced by the system (= the product of ChannelOffsetcan2 and Pilotlnc) from the perceived PN shift (= PilotPhasecan] _), it produces the relative displacement between the reference pilot signal and the pilot signal of the cante base station. If the difference is negative, the RTD between the reference base station and the remote unit is greater than the RTD between the cante base station and the remote unit. The difference perceived by the remote unit reflects only the relative delay of the uplink. The relative delay of the uplink is doubled to compensate for P1752 / 98MX full round trip delay. For the example, assume that the increase in the displacement index of the large system pilot sequence is 64 PN chips and that the following information is used on the basis of a round trip delay measurement. PilotPhaseref = 0 RTD = 137 (Base station ID = 12) PilotPhase] _ = 948 RTD = 244 (Base station ID = 14, relative offset 52 PN). PilotPhase] _g = 1009 (Base station ID = 16 relative offset -15 PN). Because in the preferred embodiment, each base station or base station sector transmits the same time shift of the pilot sequence, the identification of the base station can be pressed as that of the channel PN shift used by the base station to transmit the pilot signal. Assume further that the base stations 12 and 14 (which can be assumed refer to the base stations shown in Figure 1) are members of the active set and the RTD measurements as measured by the base stations 12 and 14 will be reported respectively as 137 and 244 PN chips. Annotated to the right of the pilot phase and of the round trip delay data of the base station 14 is the calculated relative displacement. The pilot phase P1752 / 98MX measured from base station 14 is 948 PN chips. The fixed displacement of the base station 14 is equal to the ID of the base station (14) by the increment in the displacement of the pilot sequence (64), which is equal to 896 PN chips. The difference between the measured pilot phase and the displacement of the pilot phase of the base station is the relative displacement between the base station and the remote unit which in this case is 52 PN chips (= 948 -896). It is unnecessary to use these numbers to calculate the round trip delay between the base station 14 and the remote unit, because the base station 14 makes a measurement of the round trip delay directly because the base station 14 is a member of the set. Active. However, because the base station 16 is a member of the Cante Set, no measurement of the round trip delay is made directly by the base station 16 and Equation 1 above should be used to determine the round trip delay. For the base station 16, the parameters are: RTDref = 137 PN chips; PilotPhasecan_ = 1009 PN chips; ChannelOffsetcan] _ = 16; and Pilotlnc = 64 PN chips per channel. Placing these numbers directly in Equation 1 produces a round trip delay between the P1752 / 98MX remote unit and base station 16 of 107 PN chips. As indicated above, to find the absolute displacement of the candidate base station, the product of ChannelOffsetcan? and the Pilotlnc, is subtracted from the PilotPhasecan] _ which in this case produces -15 PN chips. An interesting observation is that the round trip delay between the base station 16 and the remote unit is less than the round trip delay between the base station 12. A first method for identifying the location of the remote unit depends on the use of the state of Directed hard transfer (MDHO) measurement of the special remote unit. To minimize the impact of processing, the system enters the MDHO state only when a member of the Active Set is marked as a transition base station. In an alternative mode, the system enters the MDHO state only when all members of the Active Set are transition base stations. In a third embodiment, the system enters the MDHO state only when there is a single station based on the Active Set and that base station is a transition base station. In a fourth mode, there are sufficient processing resources in such a way that the MDHO state is always active. While in the MDHO state, the selector monitors the round trip delay of the members of the Set P1752 / 98MX Active and calculate the round trip delay of the members of the Candidate Set. After the conditions that activate the MDHO state have changed, you can exit the MDHO state. The state of MDHO is based on the use of an MDHO table. In the MDHO table, each row represents a section of the region of the coverage area that is a region of overlap of the coverage area. As defined above, a region of overlap of the coverage area is an area in which communication between a remote unit and only one of two different base stations could be supported. Each row contains a list of pairs of identification numbers of the base station and the intervals of the round trip delay. The round trip delay interval is specified in terms of a minimum and a maximum round trip delay. In order to use the MDHO table, either a network planning tool or empirical data is used to identify a set of regions and the corresponding action or measure appropriate for each region. Alternatively, a rule based or an expert system could be used to generate the MDHO table. As indicated above, Figure 5 shows a set of interior, transition and second base stations P1752 / 98MX system and is used to illustrate the function of the hard drive measurement table directed from the remote unit. The shaded lines around the base stations indicate the measurement thresholds for the round trip delay. For example, the shaded line 222 enclosing the base station S2 represents the location in which a direct path from the base station S2 to a remote unit located on the shaded line 222 exhibits a round trip delay of 200 PN chips. . The shaded line 220 enclosing the base station S2 represents the location in which a direct path from the base station S2 to a remote unit located on the shaded line 222 exhibits a round trip delay of 220 PN chips. Therefore, any remote unit located between the shaded line 220 and the shaded line 222 would exhibit a round trip delay between 200 and 220 PN chips. In the same way, the shaded line 226 that encloses the base station? , represents the location in which a direct path from the base station T] _ to a remote unit located on the shaded line 226 exhibits a round trip delay of 160 PN chips. The shaded line 224 that encloses the base station? represents the location in which a direct path from the base station T] _ to a remote unit located P1752 / 98MX on shaded line 224 exhibits a round trip delay of 180 PN chips. Therefore, any remote unit located between the shaded line 224 and the shaded line 226 would exhibit a round trip delay of between 160 and 180 PN chips. Also, the shaded line 232 enclosing the base station S] _ represents the location in which a direct path from the base station S ^ to a remote unit located on the shaded line 232 exhibits a round trip delay of 170 PN chips . The shaded line 230 enclosing the base station Sj_ represents the location in which a direct path from the base station S] _ to a remote unit located on the shaded line 230, exhibits a round trip delay of 180 PN chips. Therefore, any remote unit located between the shaded line 230 and the shaded line 232 would exhibit a round trip delay between 170 and 180 PN chips with respect to the base station Sj_. As indicated above, multipath or multipath signals that do not take a direct path between the remote unit and the base station are produced by the reflective elements within the environment. If the signal does not take a direct path, the round trip delay increases. The signal that arrived most early, is the P1752 / 98MX signal that has taken the shortest path between the remote unit and the base station. This signal that arrived earlier is measured together with the present invention to estimate the round trip delay. Observe what specific regions can be identified by the round trip delays between the various base stations. For example, coverage regions 240 and 242 can be identified by the fact that the round trip delay between the remote unit and the base station is between 160 and 180 PN chips and the round trip delay between the remote unit and the remote unit. Base station S2 is between 200 and 220 PN chips. The coverage area 242 is further defined by the fact that a pilot signal from the base station Sj_ may still be perceived, regardless of the round trip delay. Assume that the appropriate action or measure for a remote unit located within the region 240 and currently in communication with the base station T] _, is to execute a hard transfer at the same frequency to the base station S2 of CDMA. Assume further that in the region 242 the total interference is so high that the only alternative is to execute a hard transfer to an AMPS system supported by the base station S_. Table I illustrates a portion of an exemplary MDHO table. The first column indicates which regions P1752 / 98MX overlap of the coverage area correspond to the row of the MDHO table. For example, coverage area 242 corresponds to coverage region N in Table I and coverage area 240 corresponds to coverage area N + l in Table I. Note that a remote unit located in coverage area 242 the parameters given for the coverage area 240 are equal. In the illustrative mode, the MDHO table is traversed in numerical order and the first region that has the given parameters equal is selected, so that the only way in which a set of parameters given is compared to the region N + l is if the region N has already been eliminated as a possible location. The second column contains an ID of the first base station. The third column contains the range of round trip delays that correspond to the coverage region designated by the row. The fourth and fifth columns show an ID of the second base station and a pair of the round trip delay as do the sixth and seventh columns. More columns may be added that designate the base station ID and the round trip delay pairs, as necessary. In the preferred embodiment, the MDHO table is stored in the selector bank subsystem controller (SBSC). The SBSC already stores the pilot database that provides the neighboring lists and the P1752 / 98MX pilot displacement and other data necessary for normal operation. In the preferred embodiment, the selector requests that the SBSC have access to the MDHO table each time a new PSMM is received and each time the RTD measurement for any active base station changes by a significant amount.

P1752 / 98MX TABLE I The column labeled as an action or measure describes the action or measure that should be taken when the location of the remote unit is correlated with one of the coverage regions. There are several exemplary types of action that can be taken such as: Hard transfer from CDMA to AMPS of intersystem base stations; Hard transfer from CDMA to AMPS from intrasystem base stations; Hard transfer from CDMA to CDMA of intrasystem base stations; Hard transfer from CDMA to CDMA of different frequency intersystem; and Hard transfer from CDMA to CDMA of the same intersystem frequency. If more information about the round trip delay is needed to identify the location of the remote unit, the thresholds T_ADD and T_DROP may be modified when a remote unit is in the MDHO state. By decreasing both thresholds T_DROP and T_ADD, lower pilot signal strengths qualify the corresponding base stations for membership in the candidate and active sets and lower pilot signal strengths remain in the candidate and active sets P1752 / 98MX has more before they get lost. The increase in the number of base stations listed in the candidate set and active set increases the number of point round trip delay data that can be used to locate the remote unit. Decreasing the T_ADD and the T_DROP of the broad system can have a negative effect since each remote unit in transfer uses system resources from both base stations. It is desirable to minimize the number of remote units in transfer, in order to conserve resources in each base station and maximize capacity. Therefore, in the preferred embodiment, the T_ADD and the T_DR0P only decrease in value at the transition base stations. Also, the length of time designated by T_TDR0P may be increased to increase the amount of time a base station remains in the active set after falling below T_DROP. In the preferred embodiment, if the second system is not already transmitting a CDMA pilot signal from the border base stations to the frequency to be used in the first system, the second system is modified to transmit a pilot signal or another CDMA radio beacon to assist in the initiation of the hard transfer process as detailed in the aforementioned United States Patent Application Serial No.

P1752 / 98MX 08 / 413,306 and in U.S. Patent Application Serial No. 08 / 522,469. In an alternative mode, even if the system is not already transmitting the CDMA pilot signal from the border base station, the border base stations in the second system do not produce pilot signals and, there are no entries in the base station ID column of the base station. MDHO table corresponding to the Sx-S3 base stations. Pilot beacon units can also be used at indoor base stations to help identify regions that are affected by point-to-point microwave links. In some situations it may also be possible to eliminate the use of candidate base stations as a means to identify the location of the remote unit, leaving only the information of the active base station to determine the location of the remote unit. For example, through intelligent network planning, it may be that the overlapping regions of the coverage areas can be effectively identified using only the round trip delay of the Active Set members. As indicated above, to simplify the drawing, Figure 5 does not show sectorized base stations. Actually, the presence of sectorization helps the process of location by narrowing or P1752 / 98MX close the regions in which the remote unit can be located. Observe, for example, the geometry of the base station 60 of Figure 3. Even before the round trip delays are considered, the coverage area of the base station 60 is divided into 6 different regions. The area covered only by sector 50, the area covered by sector 50 and sector 70, the area covered only by sector 70, the area covered by sector 70 and sector 80, the area covered only by sector 80 and the area covered by sector 80 and sector 50. If network planning is used to orient base stations in three sectors along the border between the two systems, it may be possible to eliminate the use of pilot beacons in the border base stations of system 2 and the use of the determination of the round trip delay of the candidate base station. Each base station of the system is calibrated initially, in such a way that the sum of the noise measured in decibles of the trajectory of the unloaded receiver and the desired pilot power measured in decibels is equal to some constant. The calibration constant is consistent throughout the base station system. As the system is loaded (that is, remote units begin to communicate with base stations), the bounding or transfer border of the link Descending P1752 / 98MX moves effectively closer to the base station. Therefore, to mimic the same effect in the uplink, a compensation network maintains the constant relationship between the downlink power received at the base station and the pilot power transmitted from the base station, as the pilot power decreases as increase the load. The process of balancing the limit of the uplink transfer with the downlink transfer limit is referred to as the base station respiration, detailed in U.S. Patent No. entitled "METHOD AND APPARATUS FOR BALANCING THE FORWARD LINK HANDOFF BOUNDARY TO THE REVERSE LINK HANDOFF BOUNDARY IN A CELLULAR COMMUNICATIONS SYSTEM "granted on, 1996 and assigned to the assignee of the present invention The process of respiration may adversely affect the operation in the MDHO state. Figure 4B, if the power transmitted by the base station 200 decreases compared to the power transmitted by the base station 205, the overlap limits of the coverage areas move closer to the base station 200 and move away from the base station 200. the base station 205. The level of the signal does not affect the round trip delay between the unit Remote P1752 / 98MX in any location and base station. Therefore, the MDHO table continues to identify the same locations as appropriate for the transfer when the actual limits may have changed. A second way to address the issue of base station breathing is to deactivate or limit breathing at border base stations. The breathing mechanism operates on the uplink signal to force the uplink performance to mimic the natural reaction of the downlink to the load level. Therefore, the elimination of breathing does not eliminate the risk that the limits change with the load on the downlink and, thus, the load remains a factor even if a system does not use the breath. A third way to deal with the issue of the breathing of the base station is through the planning of the network. If the border base stations of the second system do not transmit traffic channel signals (ie, the specific signals of the active remote unit) to the frequencies used by the border base stations of the first system, the effect of respiration is minimized . If the border base station transits a pilot signal from a pilot beacon unit, the effects of respiration are also P1752 / 98MX minimize, because the traffic channel signals are not generated when using a pilot radio beacon unit. The power emitted by a pilot radio beacon unit remains constant over time. A fourth way of dealing with the matter of base station breathing is through the use of a rule-based system. If the border base stations are breathing, a breathing parameter is sent from each base station to the system controller. The system controller updates the MDHO table based on the present value of the breath. Normally, the system controller will increase the round trip delay values in the MDHO table to reflect the effects of breathing. The effects of breathing may not be an issue at all in most situations. Because these border areas have traditionally been a source of technical and business issues, network planning typically strives to place the boundaries between the two systems in low traffic areas. Lower amounts of traffic correspond to smaller breathing effects. In some cases, it may be desirable to avoid storing and having access to the MDHO table. In one of these cases, other methods can be used to effect P1752 / 98MX the transfer. For example, in an alternative embodiment, two means are used to activate a transfer. The first method is called the detection rule. Certain base stations (or certain sectors of the base station) are designated as reference base stations, R. If a remote unit is within the coverage area of a reference base station and this reports the detection of a pilot activation signal , PB, the selector activates a transfer to a target base station determined by the data set (R, PB). The detection rule is usually not always used with a pilot radio beacon unit. The second method is called the donation rule. Certain base stations are marked as boundary base stations. The selector activates a transfer if the Active Set of the remote unit contains only one base station and that base station is a boundary base station and the round trip delay of the reference pilot signal exceeds a threshold value. Alternatively, the selector activates a transfer if the active set of the remote unit contains only base stations which are boundary base stations and the round travel delay of the reference pilot signal exceeds a threshold value. Normally, the threshold varies between base stations and is independent of the rest of the active set. The action of P1752 / 98MX off-hook is determined by the reference pilot present. The off-hook rule can be the first in a set of rules to measure directed transfer. Note that it is not necessary for a base station designated as a boundary base station to have a coverage area that is spliced with the coverage area of a base station of another system. The off-hook rule can be used for both intersystem transfer and intra-system transfer. Both the detection rule and the off-hook rule may depend on the physical characteristics of the system. The use of these two rules can make the design of the network cumbersome, such as the placement of the base stations, the orientation of the sectors within a multi-sector base station and the physical placement of the antennas. If a remote unit or a base station attempts to initiate a call at a boundary base station, the remote unit and the base station exchange a source message on the access channel. In the preferred embodiment, the Air Channel Handler resides at the base station and controls the access channel. The Air Canal Manager resides in the base station and controls the access channel. The Air Canal Handler examines the estimate of the round trip delay calculated from the message of P1752 / 98MX origin. If the round trip delay exceeds the threshold value, the air channel handler notifies the mobile switching center which may instruct the base station to send a service redirect message to the remote unit. The service redirection message may direct a remote unit with AMPS capability to an AMPS system or to another CDMA system or frequency. The redirect message also depends on the type of service that will be requested by the remote unit. If a data connection is requested instead of a voice connection, the AMPS system may not be able to support the connection. For this reason, the action taken must depend in general on the capabilities and status of the remote unit. Normally, each remote unit of the system has a class designation that designates its capabilities. The present state of the remote unit can be polled by the base station and a decision can be made based on the information returned. Figure 7 illustrates the use of the detection rule in a CDMA to CDMA transfer of the same frequency. Assume that a remote unit is traveling from the Sx system to the S2 system in the C1A / C2 region. As the remote unit approaches C2, it begins to perceive the pilot signal transmitted in this way. When using the detection rule, if CiA is the base station of P1752 / 98MX reference, the selector requests a transfer to an AMPS base station that is placed with the coverage area C1A. As indicated above, the hard transfer from an AMPS FM system to another FM AMPS system can be achieved in a physical region much larger than a hard transfer from one CDMA system to another CDMA system operating at the same frequency. Note that there must be a one-to-one correlation or at least a significant overlap between the coverage areas of the CDMA base station and the coverage areas of the AMPS base station at the border base stations. Having switched to FM AMPS operation, the probability of a successful intersystem handover between the FM system is high. Figure 8 illustrates the use of the detection rule in a CDMA to CDMA transfer of different frequency. In Figure 8, the area corresponding to the system S2 is shaded to indicate that the system S2 is in communication with the signals of the traffic channel at the frequency f2 but is not in communication with the signals of the traffic channel at the frequency fx. In Figure 8, the area corresponding to the Sx system is not shaded to indicate that the Sx system is communicating with the signals of the traffic channel at the fx frequency but is not communicating with the signals of the Sx channel.

P1752 / 98MX traffic at frequency f2. There may or may not be a pilot radio beacon unit operating at the border base stations of either the St system or the S2 system or both. If a pilot radio beacon unit exists, the detection rule can be used. Alternatively, if C1A and C? B become the only base stations in the active set, the donation rule may be applied once the measurement of the round trip delay exceeds the threshold value. In any case, a transfer to an AMPS base station placed therein could be effected. The configuration of Figure 8 has a great advantage over the configuration of Figure 7. Figure 4C illustrates the advantage of transferring using two different CDMA frequencies. Figure 4C is a highly idealized representation of a transfer region using two different CDMA frequencies that obeys the same format as Figures 4A and 4B. In Figure 4C, the base station 205 is not transmitting signals from the traffic channel at the same frequency as the base station 200 as represented by the dotted transmission arrows emanating from the base station 205 and the remote unit 155. limit 189 represents the point at which reliable communication can be established between the remote unit 155 and the base station 200 to the P1752 / 98MX frequency fL. Region 176 between boundary 180 and boundary 189 represents the area where the remote unit 155 can detect a pilot signal from the base station 205 if the base station 205 is equipped with a beacon unit, while communicating through of the base station 200. A comparison between Figures 4B and 4C, reveals the advantage of the transfer at different frequency. If the base station 205 is not transmitting a pilot signal, there is no interference from the base station 215 for the signal between the base station 200 and the tuck unit 155. If the base station 205 is transmitting a pilot signal, the amount of interference due The pilot signal of the base station 205 for the signal between the base station 200 and the remote unit 155 is significantly less than the interference produced if the base station 205 is transmitting signals from the traffic channel. Therefore, boundary 189 is much closer to base station 205 than boundary 186. Boundary 181 represents the point at which you can establish reliable communication between remote unit 155 and base station 205 at frequency f: . The region 178 between the boundary 181 and the boundary 190 represents the area where the remote unit 155 can detect a pilot signal from the base station 200 if the base station 2 0 is P1752 / 98MX equipped with a pilot radio beacon unit operating at the frequency f2 while communicating through the base station 205. Again, observe how close the limit 181 is to the base station 200 to the limit 184. The region 174 between boundary 181 and boundary 189 represents the area where transfer of communication from base station 200 to frequency lx to base station 205 at frequency f2 or vice versa can be achieved. Observe how larger the region 174 is than the region 170 in Figure 4B. The larger size of region 174 is very advantageous for the hard transfer process. The fact that two different frequencies are used does not greatly affect the hard transfer process, because in the case of either the same frequency or different frequency, the transfer of communication has the characteristic of hard transfer of "cut before setting". The only slight disadvantage of the case of the different frequency may be that the remote unit requires a certain amount of time to switch or change the operation, from the first frequency to the second frequency. In the preferred embodiment, both the base station and the remote unit have a different frequency for transmission than for reception. In Figure 4C and in other Figures and the text describing the transfer P1752 / 98MX between two different frequencies of CDMA operation, it can be assumed that both frequencies, transmission and reception, are different after the transfer is made even if the text or the drawings refer for reasons of simplicity to a single frequency (such as frequency fx) to designate the use of a set of transmit and receive frequency. Referring again to Figure 8, it is not necessary that each base station of system S2 refrain from operating at frequency fx. It is only necessary that the border base stations and, possibly, the next layer of internal base stations of the S2 system, refrain from operating at the frequency fx. The indoor or internal base stations of the S2 system can use the fx frequency for CDMA or FM or TDMA or microwave point-to-point links or for any other function. Figure 9 further shows another alternative mode for a transition area between two systems. The configuration of Figure 9 requires cooperation between the service providers of the first and second systems and may be the most applicable where systems belong to the same service provider. Figure 9 illustrates two stations Bx and B2 placed or substantially placed providing the P1752 / 98MX transfer from CDMA to CDMA at different frequency. Both base stations, the Bx and the B2, are two sector or bisectorized base stations that provide coverage of the coverage area 310. The base station B of the system Si is providing the CDMA service at the fx frequency both in the sector a as in the sector ß and the base station B2 of the system S2 is providing the CDMA service both in the sector a and in the sector ß to the frequency fa- Note that the coverage area 310 is intercepted by the motorway 312. According to a remote unit travels to the coverage area 310 of the Sx system using the frequency flr a standard soft transference system is used to transfer the control of the call to the sector ß of the base station B ^ As the remote unit continues through Highway 312, a soft or a softer transfer is used to transfer the communication from the sector ß of the base station Bx to sector a of the base station Bx. When the sector a of the base station B becomes the only sector of the active set, the donation rule activates the transfer to the sector β of the system S2 of the base station B2 at the frequency f2. The transfer of the remote unit that travels from the S2 system to the Sx system, happens in a similar way, between P1752 / 98 X sector a of base station B2 and sector ß of base station B-____. Because the sector of the base station Bi is co-located in the sector β of the base station B2 and the sector of the base station B2 is co-located in the sector β of the base station Bx, in each case it can be completed Successfully a hard transfer without fear that the remote unit is not in the coverage area of the target base station. The configuration of Figure 9 has several advantages. Because the area in which the system transfer S ± is executed to system S2 is not the same as the area in which system transfer S2 is executed to system S r, the bounce or ping situation is minimized -pong. For example, if the area in which the transfer of the Sx system is executed to the system S2 is substantially the same as the area in which the transfer of the system S2 is executed to the system Sl r a remote unit entering the transfer area and that stops or moves within the region can continuously transfer to one system and then return to the other. The configuration of Figure 9 introduces a spatial hysteresis. Once the remote unit has transitioned from the control of the Sx system to the S2 system in the lower half of the coverage area 310, the remote unit will not transition the control of the Sx system to the system S2 in the lower half of the coverage area 310.

P1752 / 98MX returns to the Sx system, unless it changes direction and is reinserted fully into the upper half of the coverage area 310, so that sector a of the base station B2 is the only member of the active set of the remote unit. As with the configuration of Figure 8, it is not necessary in the configuration of Figure 9 that each base station of the S2 system refrain from using the frequency fx. It only needs that the border base stations and, possibly, the next layer of interior or internal base stations of the S2 system refrain from using the frequency fx. The indoor base stations of the S2 system can use the frequency fL to transmit CDMA or FM or TDMA or microwave links from point to point or for any other function. Also in Figure 9, it is not necessary for the base station to comprise exactly two sectors and a larger number of sectors could be used. Figure 10 shows a situation in which a CDMA system borders or borders a system that provides the service using a different technology. This situation can be handled in a manner similar to that of Figure 8. Figure 10 shows the special topology of the city of Detroit, Michigan, USA. Detroit splices with Canada on one side. A river defines the P1752 / 98 X border or boundary between Detroit and Canada. Some bridges cross the river to unite the two countries. On the bank of the United States, the CDMA Sx system is deployed. On the Canadian bank, the TDMA S2 system is deployed. On both banks, the United States and the Canadian, AMPS systems are operating in addition to the selected digital technologies. A remote unit that travels on the Detroit side of the system is continuously in CDMA coverage. Possibly in a soft transfer and a softer one. However, when it is found that the remote unit is exclusively in the coverage area of sector a of the coverage area CA or in sector a of the coverage area Cc, a transfer to the respective AMPS base station placed once activated is activated. the round trip delay exceeds a predetermined threshold, using the donation rule. The remote units that are on the water may or may not remain within the CDMA coverage areas, depending on the selected RTD threshold. Network planning should ensure that the antennas are properly oriented and that the base stations are located in such a way that an AMPS base station can be uniquely determined based on the transition sectors and that the call will not be lost when these sectors are P1752 / 98MX become the only sectors of the active set. Figure 14 illustrates one embodiment of the present invention, wherein the providers operating the two systems can place two base stations. Figure 14 is a graphic representation. The coverage area Cu corresponds to an indoor base station of the Sx system operating at the frequency fx. The coverage area C1B corresponds to a transition base station of the system Si operating at the frequency fx. The pilot beacon Px is a pilot radio beacon unit operating or operating at the fx frequency placed with the coverage area C 2A- The coverage area C2A corresponds to an internal base station of the S2 system operating at the frequency f2. The coverage area C2B corresponds to a transition base station of the S2 system operating at the frequency f2. The pilot radio beacon P2 is a pilot radio beacon unit operating at the frequency f2 placed with the coverage area C1A. Note that in the configuration of Figure 14, a hard transfer must be made between the base station C1B and the base station C2B as a remote unit travels between the Sx system and the S2 system. Because the indoor base stations are not transmitting traffic channel signals at the frequencies from which a hard transfer is made, the reliability P1752 / 98MX communication between the base station C1B at the frequency fx and a remote unit located in the coverage areas CXB and C2B is high. Likewise, the reliability of the communication between the C28 base station at the frequency f2 and a remote unit located in the coverage areas CXB and C2B is also high. One issue with the configuration of Figure 14 is the co-location of coverage areas C1B and C2B. The placement of the base stations usually requires some degree of coordination between the two operators of the system. If the two systems are operated by different carriers, providers may not want to share a physical installation. Also, the placement may cause regulatory issues. Figure 15 is similar to Figure 14, with the exception that the CXB coverage area and the C2B coverage area are not completely placed. The principles of this modality apply to the case where the coverage areas of two base stations overlap significantly. The spatial hysteresis region is contracted by approximately the amount by which the two coverage areas are displaced from each other. With either of Figure 14 or Figure 15, the operation is the same and very simple. A remote unit traveling in the Sx system to the S2 system is initially in communication with the CXA coverage area, P1752 / 98 X using the frequency fx. As the remote unit approaches the two coverage areas placed, the soft transfer at the fx frequency is used to transfer the communication to the coverage area C1B if the remote unit continues to the S2 system, the remote unit begins to detect the Pilot radio beacon signal Px. When the active set contains only the base station corresponding to the coverage area CXB and / or the intensity of the pilot signal Px exceeds a certain threshold value, a hard transfer is made from the base station corresponding to the coverage area C1B to the station base corresponding to the coverage area C2B. As the remote unit continues to the S2 system, soft handoff is used to transition the communication between the base station corresponding to the coverage area C2B and the base station corresponding to the coverage area C2A- The reciprocal operation is used to complete the transfer from system S2 to system Si. The configurations of Figures 14 and 15 are not similar to the configuration of Figure 9, since they introduce some measurement of the spatial hysteresis. For example, the connection of a remote unit traveling from the Sx system to the S2 system is represented by dashed line 356. Note that until the remote unit P1752 / 98MX reach the location indicated by the arrow 350, it is served by the Sx system at the frequency fx by the base station corresponding to the coverage area C1B. Similarly, the connection of a remote unit traveling from system S2 to system Sx is represented by line dashes 354. Note that until the remote unit reaches or reaches the location indicated by arrow 352, it is served by the station base that corresponds to the coverage area C2B. Therefore, between arrow 350 and arrow 352, the service providing communication with the remote unit depends on which system was providing the communication when the remote unit entered the region. The remote unit can be moved within the region between. arrows 352 and 350 without effecting the transfer between the two systems. Referring again to Figure 4B, - another solution to the hard transfer dilemma is to increase the size of the hard transfer region 170. One of the reasons the region is so narrow is due to the effects of fading. Because a remote unit located within the hard transfer region 170 can only communicate with either the base station 200 or the base station 205, if the signal vanishes with respect to the active base station but does not fade with with respect to the inactive base station, the P1752 / 98 X interference from the inactive base station becomes significant. One method to increase the size of the region and the reliability of communication within the region is to minimize the amount of fading experienced by the remote unit in this area. Diversity is an approach to mitigate the damaging effects of fading. There are three main types of diversity: diversity of time, diversity of frequency and diversity of space. The diversity of time and frequency are inherently present in a broad spectrum CDMA system. The diversity of space, which is also called path diversity, is generated by multiple signal paths of a common signal. The path diversity can be advantageously exploited by means of broad spectrum processing by receiving and processing separately arriving signals with different propagation delays. Examples of • exploitation or exploitation of the diversity of trajectories are illustrated in U.S. Patent No. 5,101,501 issued March 31, 1992, entitled "SOFT HANDOFF IN A CDMA CELLÜLAR TELEPHOK? SYSTEM", and U.S. Patent No. 5,109,350 issued on April 28, 1992, entitled "DIVERSITY RECEIVER IN A CDMA CELLULAR TELEPHONE SYSTEM".

P1752 / 98MX The existence of a multipath environment can provide the diversity of trajectories to a broadband CDMA system. If two or more signal paths with the differential path delay greater than the duration of a chip are created, two or more receivers can be used to separately receive the signals in a single base station or remote unit receiver (the required differential of the path delay of a chip is a function of the medium by which time tracking is achieved in the receiver). After the signals are received separately, they can be combined in diversity before the decoding process. In this way, the combined total energy of the plurality of trajectories is used in the decoding process, thereby increasing the energy and accuracy of the decoding process. Multipath signals typically exhibit independence in fading, i.e., different multipath signals do not normally fade together. Thus, if the output of the two receivers can be combined in diversity, a significant loss of performance will occur only when both multipath signals vanish at the same time. Referring again to Figure 4B, suppose P1752 / 98MX that the base station 200 is the active base station. If there are two different signal components of the base station 200 that are received by the remote unit 155, the two different signals vanish independently or almost independently. Therefore, the total signal from the base station 200 does not experience the deep fading that occurs when only a different signal is received. As a result, the probability that the signals from the base station 205 dominate the signal from the base station 200 to the remote unit 155 is less. Instead of relying on natural and statistically developed multipath signals, the multipath can be artificially introduced. A typical base station has two receiving antennas and a transmission antenna. Frequently, the transmitting antenna is the same as one of the receiving antennas. This base station configuration is shown in Figure 12. In Figure 12, the transmitter 330 supplies a transmit signal to the diplexer 332, which in turn supplies a signal to the antenna 334. The antenna 334 supplies a first reception signal to port 1 of receiver 338 and antenna 336 supplies a second reception signal to port 2 of receiver 338. Inside P17S2 / 98MX of receiver 338, port 1 and port 2 receive signals that are received separately and are then combined before decoding for maximum advantage. The antenna 334 and the antenna 336 are configured in such a way that the signals received from each antenna vanish independently of the signals received by the other antenna. Because the reception signals of the antennas 334 and 336 are supplied to different receivers and are not combined until after the signals have been demodulated within the receiver 338. It is not critical since the signals received in the antenna 334 are shifted from the signals received in the antenna 336 in at least one direction of 1 PN chip. To introduce the diversity in the system of Figure 12, a second diplexer can be used to couple the transmission signal to the previous receiving antenna only by means of a delay line. This configuration is shown in Figure 13. In Figure 13, the transmitter 330 supplies a transmit signal to the diplexer 332, which in turn supplies a signal to the antenna 334. In addition, the transmitter 330 supplies a transmit signal (which, in the most basic mode contains the same signals as the original transmission signal) to the delay line 340 and to the diplexer 342 and to the P1752 / 98MX antenna 336. As in Figure 12, antenna 334 and antenna 336 are configured such that the signals as received from each antenna in the remote unit vanish independently. Because the two signals are received through a single antenna in the remote unit, in addition to the independence in fading, the two signals must be separated sufficiently in time, so that the remote unit can distinguish separately the signs. The delay line adds a sufficient delay, so that the signal radiated by the antenna 336 reaches the remote unit with a delay greater than one chip with respect to the signal of the antenna 334, so that the remote unit can distinguish the signals and receive them and demodulate them separately. In the preferred embodiment, the diversity configuration of the base station of Figure 13 is used only at the border base stations. In an alternative embodiment, the delay line 340 comprises a gain adjustment element. The gain adjustment element can be used to adjust the level of the signal transmitted by the antenna 336 with respect to the signal transmitted by the antenna 334. The advantage of this configuration is that the signal of the antenna 336 does not interfere significantly with the other signals of the system. However, the signal level of P1752 / 98MX the antenna 336 with respect to the signal level of the antenna 334, becomes insufficient when the signal of the antenna 334 vanishes. Thus, in the preferred embodiment, if the antenna signal 334 experiences a deep fading with respect to the remote unit, the signal of the antenna 336 is large enough to provide reliable communication for the duration of the fading. It may be advantageous to provide a signal from the antenna 336 only when at least one remote unit is located in the hard transfer region. This technique can also be applied to any of the following alternative modalities. An additional different mode may create a separate signal path carrying a different set of signals for transmission over the antenna 336. In this mode, the base station determines which remote units need diversity (ie, which remote units are located in the hard transfer region). The set of signals transmitted on the antenna 336 can only comprise the signals of the traffic channel of the remote units in the hard transfer region and a piloted signal. Alternatively, radio location and channel transmissions could also be included.

P1752 / 98MX synchrony. As indicated directly above, it may be advantageous to provide the pilot signal and other signals from the antenna 336 only when at least one remote unit is located in the hard transfer region. Remote units that need diversity could be identified, for example, by detecting remote units that require more transmission power than a certain threshold value or based on the round trip delay. The use of two transmitters reduces the net amount of transmitted power and, thereby, will reduce the interference of the system, including interference with the remote units within the hard transfer region 170, which are in communication with the base station 205 In Figure 13, dashed line 348 illustrates the second mode where separate signal paths carrying a different set of signals are used. It is assumed that any delay between the two signals that is necessary is induced within the transmitter 330. It should also be noted that the second radiator need not be co-located in the base station. It could be separated by a great distance and can be located near the hard transfer limit. Alternatively, instead of using the previous receive-only antenna to transmit the signal in diversity, the signal could P1752 / 98MX transmitted from a different antenna. The different antenna could be a high directionality zone antenna that focuses the energy in the hard transfer region. A particularly advantageous configuration can be obtained by using a separate signal path together with a different antenna. In this case, a greater diversity can be obtained by assigning the signal to be transmitted per the different antenna and a different PN shift to the PN shift nominally assigned to the transmitter 330. In this way, the base station executes a smoother transfer when the remote unit enters the coverage area of the different antenna. The use of a different PN offset is useful for identifying when the remote unit is located in the hard transfer region. The above embodiments can be implemented with a variety of different topologies to provide the same results. It is also observed that there are different methods by which diversity is introduced into the system. For example, the effects of fading can also be minimized by fluctuation or hesitation of the signal phase of the diversity antenna. the fluctuation or hesitation of the phase alters the alignment of the amplitude and phase of the multipath signals that can create a deep P1752 / 98MX fading in the channel. An example of this system is detailed in U.S. Patent No. 5,437,055, entitled "ANTENNA SYSTEM FOR MULTIPATH DIVERSITY IN AN INDOOR MICROCELLULAR COMMUNICATION SYSTEM", which was granted on July 25, 1996 and which is assigned to the transferee of the present invention. The detrimental effects of fading can be further controlled to some degree in a CDMA system by controlling the transmission power. A fading that decreases the power received by the remote unit from the base station can be compensated by increasing the power transmitted by the base station. The function of the power control operates in accordance with a time constant. Depending on the time constant of the power control circuit and the period or extent of fading time, the system can compensate for fading by increasing the transmit power of the base station. The nominal power level transmitted from the base station to a remote unit could be increased when the remote unit is in the region where a hard transfer can be made. Again, remote units that are in need of an increase in power could be identified, for example, based on the delay of the round trip or the reporting of a pilot signal P1752 / 98MX exceeding a threshold. By increasing only the power transmitted to the remote units that need it, the net amount of power transmitted is reduced, thus reducing the total interference in the system. As indicated above together with the Figure 3, a situation in which the realization of a hard transfer may be necessary is a situation in which a remote unit must change the frequency at which it is operating within a single system. For example, this transfer can be done to avoid interference with point-to-point microwave links that operate in coexistence with the CDMA communication system or to effect a transition of all signals from the traffic channel to a single frequency, so that a CDMA to CDMA transfer of different frequency may occur within the limits of the system. In Figure 3, a point-to-point microwave link 140 between the microwave directional antenna 130 and the directional microwave antenna 135 is shown. Because the microwave directional antenna 130 and the directional microwave antenna 135 have a high directionality, the point-to-point microwave link 140 has a very narrow or closed field. In this way, the other base stations of the system such as the base stations 115, 120 and sectors 50, 70 and 80 can P1752 / 98MX operate without interference with the microwave link 140 from point to point. In the example of the preferred embodiment, the CDMA signals will be transmitted at microwave frequencies and, therefore, the point-to-point link that intersects the system will only interfere if it also operates at the same microwave frequency. The point-to-point link in the most general mode can operate at frequencies higher or lower than those generally designated as microwave frequencies. Although the techniques previously described herein can be applied to this hard transfer, hard intra-system transfer usually has an advantage over hard intersystem transfers since two base stations between which a transfer will be made are controlled by the same controller. Figure 11 illustrates an alternative configuration for providing a CDMA to CDMA transfer of different frequency, using a single multi-sector base station. Both base stations, B_ ^ and B -_Q, have two directional sectors labeled as sectors and ß. In base station B] _7A sectors a and ß operate at frequency fj_. In base station B] _ß, sectors a and ß operate at frequency f2. Both base stations BTL ^ and B] _B have an omnidirectional gamma sector, which works P1752 / 98MX a different frequency of the directional sectors in that base station. For example, in the gamma sector of the base station B] _ / ^ works at the frequency f2 and the sector? of the Bxg base station works at the frequency f] _. Figure 11 uses the 'donation rule. The sectors? omnidirectionals are marked as border sectors with a round trip delay threshold of 0, which means that whether the gamma sectors are the only base station in the active set, a transfer is immediately activated no matter what the travel delay round. Observe that the sectors? they are not really frontier sectors between two systems, but from the perspective of the remote unit, the action taken is the same. As the remote unit travels to the base station j from a splice coverage area within the system S_ to the frequency f] _, soft transfer is used to establish communication with the alpha sector of the base station Bj_ ^ and the transfer soft or softer to transfer the connection to the sector ß of the base station B] _A- The soft transfer is then used to transfer the connection to the sector? of the base station BJ_B that is marked as a base station limit. As soon as the sector? from the base station B] _B becomes the only member of the Active Set, is a hard transfer of the sector made? from P1752 / 98MX the base station B] _B to the sector ß of the base station Bj_ß. Note that this configuration also introduces the spatial hysteresis since once the operation has been transferred to the frequency f, the operation is not transferred back to the frequency fj_, unless the remote unit enters the coverage area of the section ? from base station B] _A to such an extent that it becomes the sole member of the Active Set. Note also that the choice to use three different sectors rests on the fact that most stations in multiple sectors are comprised of three sectors and, therefore, the equipment of the available base station normally supports three sectors. In this way, a design that uses three sectors has a practical meaning. Of course, a greater or lesser number of sectors could be used. There are two different types of situations in which this configuration can be used. The configuration in Figure 11 can be used in a location where all traffic must change frequency. In this case, the base stations to the left of the base station B] _j do not use the frequency I2 and the base stations to the right of the base station BJ_B do not use the frequency fj_. In this case, all the remote units that enter on one side and P1752 / 98MX left on the other side must perform the frequency transition. In an alternative situation, the base stations to the right of the BXB base station use only the frequency f such as, for example, because a microwave link prohibits the use of the frequency fx in that area. However, base stations to the left of base station B] _ may operate at frequency f] _ or at frequency f2 - In this case, either all, some or none of the remote units traveling from the base station B] _ß to the base station B ^ A can make the transition from the frequency ± 2 to the frequency f] _. A second very different method for dealing with point-to-point microwave links or with other areas where a fraction of the spectrum needs to be erased is illustrated in Figure 16. In Figure 16 around the point-to-point microwave link 140 A "Cone of silence" is constructed as shown by beams 364 and 366. The silent cone is a pilot signal that acts as a reference signal for the remote units it detects. When a remote unit reports the detection of a pilot signal corresponding to the silent cone, the system controller knows that the pilot signal is a silent cone indication instead of a viable candidate pilot signal. The controller P1752 / 98MX system uses the reception of the pilot signal corresponding to the silent cone as a stimulus to initiate a hard transfer. Normally, the transfer carried out is a transfer from CDMA to CDMA of different intrasystem frequency, although other types of transfers can be made. An interesting aspect of the cone of silence is that the pilot signal of the cone of silence is not associated with any particular base station. Normally, the pilot signal of the silence cone is generated by a pilot radio beacon unit placed with microwave directional antennas 130 and 135. There are two different topologies of the silence cone that can be used. In the first topology shown in Figure 16, beams 364 and 366 are actually narrow transmission bands that keep each side of point-to-point microwave link 140. In the second topology shown in Figure 17, beams 360 and 362 define the edges of the transmission coverage area of the pilot signal. In Figure 17, the coverage area of the pilot signal and the coverage area of the microwave link 140 from point to point can actually be superimposed on the same region. Normally, beams 364 and 366 are produced by separate antennas other than the microwave antenna. Beams 360 and 362 can be created by the same antenna P1752 / 98MX as well as the microwave signal. A different but identical antenna or an antenna that defines a coverage area slightly wider than the microwave antenna. . The first topology of Figure 16 has the advantage that the pilot signals of the silent cone do not interfere with the microwave link from point to point even if the point-to-point microwave link operates at the same frequency as the pilot signal of the cone of silence. The first topology has the disadvantage that if the remote unit passes through the beams of the pilot signal of the silent cone without detecting the signals and without changing the frequency, the connection may be lost or the connection may continue and cause interference to the link of microwave from point to point. Also, if power is applied to the remote unit while it is located within beams 364 and 366, the remote unit will not be able to detect the pilot signals and may cause interference with the microwave link. The microwave link can be bidirectional and, thus, the operation of the link may require CDMA frequency channels. In one embodiment, two CDMA downlink channels are cleared to support the microwave link from point to point. Different pilot signals from the uplink silence cone are transmitted in the coverage area of the P1752 / 98MX silent cone, each corresponding to the two clear downlink channels for the microwave link from point to point. In this way, two pilot signals can be superimposed on the coverage area of the microwave link from point to point without interfering with the actual communication between the two directional antennas, due to the frequency diversity. In a third additional embodiment, the pilot signal can coexist at the same frequency as the point-to-point microwave link without causing a significant amount of interference with the point-to-point microwave link. The CDMA pilot signal is a wide-spectrum, low-power, broadband signal. This type of signal is perceived as simple Gaussian noise for other types of communication systems. The inherent properties of the CDMA signal make it capable only of coexisting with other communication systems without inducing significant interference. The distance between two point-to-point microwave link antennas can be much greater than the distance between a typical base station and the edge of the coverage area it defines. Therefore, the delay in which the remote unit perceives the piloting signal of the silent cone, can be significantly longer or longer than the delay normally associated with P17S2 / 98MX a cellular system. In this way, it may be necessary for the pilot signal of the mute cone to be recognized as a displacement of a set of consecutive pilot signal shift. For example, the induced delay in the pilot signal of the silent cone is greater than the normal shift between the pilot signals, which causes the displacement of the perceived pilot signal to be correlated with the next consecutive pilot signal shift. This type of operation normally r-o is a problem, because a typical system only uses it every seventh or eighth PN displacement. The offset set to which the pilot signals of the cone of silence are expected can be added to the neighbor set, so that the remote unit looks for these signals in the same way that it searches for the other entries in the neighboring list. With the detection of the pilot signal of the silent cone, the action taken depends on the base stations with which the active communication was established. Because the same pilot signal from the silent cone can cross many base station coverage areas, the same pilot signal provides very little information for the location of the remote unit or the action that needs to be taken. The base station and the frequency at which the transfer must be made is based on the members of the P1752 / 98 X set active at the moment when the pilot signal is perceived. Also, the action that will be taken could be determined by the members of the active and candidate groups. Additionally, the action that will be taken could be based on the perceived PN displacement of the pilot signal of the silence cone. Also, it may be advantageous to postpone the action that will be taken until the intensity of the pilot signal of the silence cone exceeds a second higher threshold. Because the pilot signal of the silent cone provides so little information, the same displacement of the pilot signal can be used throughout the system to protect a plurality of different microwave links from point to point. In Figure 16, all beams 364 and 366 can operate at the same displacement or at four different PN displacements. If the distance between the two antennas of the microwave link from point to point becomes very large, it may be necessary to use a repeater to extend the coverage of the pilot signal. A method and apparatus for providing a repeater in a CDMA system is detailed in copending United States Patent Application No. 08 / 522,469 entitled "Same Frequency, Time-Division-Duplex Repeater" filed on August 31, 1995 , and assigned to the assignee of the present invention. Alternatively, a series of antennas that P1752 / 98MX provide the same or different pilot displacement sequences can be installed along the microwave length trajectory to define more narrowly and accurately and reliably the area of the silent cone. Many of the concepts of the present invention can be combined. For example, the detection and donation rules can be used together with the physical configurations of the coverage area that provide spatial hysteresis both intrasisteraa with intersistema. The rules can also be combined with other network planning configurations to provide maximum benefit, such as the use of a CDMA to CDMA transfer of different frequency. The parameters that control the smooth transfer process can be increased to increase the number of members of the candidate and active sets. You can also increase the breathing of the base station. The concept of the measurement of the directed hard transfer of the remote unit. it can be combined with the physical configurations of the coverage area that provide the spatial hysteresis both intrasystem and intersystem. It can also be combined with other network planning configurations to provide maximum benefit such as the use of the transfer of P1752 / 98MX CDMA to CDMA of different frequency. The prior description of the preferred embodiments is provided to enable any person skilled in the art to prepare or use the present invention. The various modifications to these modalities will be readily apparent to those skilled in the art and the generic principles defined herein may be applied to other modalities without the use of the inventive faculty. Thus, it is not intended that the present invention be limited to the embodiments shown herein but is defined in accordance with the broadest scope consistent with the principles and novel features disclosed herein.

P1752 / 98MX

Claims (24)

1. NOVELTY OF THE INVENTION Having described the present invention, it is considered as a novelty and, therefore, the content of the following CLAIMS is claimed as property: 1. In a communication network in which a user of the network communicates to Through a remote unit with another user, by means of at least one base station, the communication network includes a first mobile switching center for controlling communications through a first set of base stations including a first base station, a method for directing communications between the remote unit and the first base station, comprising the steps of: storing in the remote unit a list of active base stations comprising an entry corresponding to each base station with which an active communication is established and, wherein the first base station has an entry in the list of active base stations; measuring, at the first base station, the round trip delay of a first active communication signal between the first base station and the remote unit; and initiate the transfer of the first active communication signal if the round trip delay of the P-L752 / 98MX first active communication exceeds a threshold if the first base station is designated as a boundary base station. The method according to claim 1, wherein the step of initiating a transfer is executed when the list of active base stations comprises a single entry and, where the single entry corresponds to a base station of a set of border base stations, wherein each base station of the set of border base stations is controlled by the first mobile switching center and has a coverage area that is spliced with a coverage area corresponding to a base station controlled by the second mobile switching center. The method according to claim 1, wherein the step of initiating a transfer is executed when the entry in the list of active base stations corresponds to a set of border base stations, wherein each base station of the set of border base stations is controlled by the first mobile switching center and has a coverage area that is spliced with the coverage area corresponding to a base station controlled by the second mobile switching center. 4. The method according to claim 1, further comprising the step of determining by a unit P1752 / 98 Communication control X activates a type of transfer that must be attempted in the step of initiating a transfer. The method according to claim 5, wherein the type of transfer to be attempted is a transfer from the first base station that is in communication with the remote unit using code division multiple access (CDMA) to the first station base that works using an alternative modulation technology. The method according to claim 5, wherein the alternative modulation technology is that of frequency modulation (FM). The method according to claim 5, wherein the alternative modulation technology is the time division multiple access (TDMA). The method according to claim 4, wherein the type of transfer to be attempted is a transfer of the first base station that is in communication to a first frequency with the remote unit using the code division multiple access (CDMA) to the first base station that communicates to a second frequency using the CDMA. 9. The method according to claim 1, further comprising the step of determining the type of P1752 / 98 X transfer to be taken in the step of initiating the transfer based on the list of active base stations. The method according to claim 1, further comprising the step of determining the type of transfer to be taken in the step of initiating the transfer based on the list of active base stations and the list of candidate base stations. 11. The method according to claim 1, wherein the system further comprises a second mobile switching center that controls a second set of base stations that includes a second base station further comprising the steps of: transmitting communication signals from an alpha sector of the first base station to a first frequency that defines an alpha coverage area of the first base station where the alpha sector of the first base station is designated as a boundary base station; transmitting communication signals from a beta sector of the first base station to the first frequency defining a beta coverage area of the first base station; transmit communication signals from an alpha sector of the second base station to a second frequency that defines an alpha coverage area of the second P1752 / 98MX base station, wherein the alpha coverage area of the second base station substantially overlaps the beta coverage area of the first base station, where the alpha sector of the second base station is designated as a boundary base station; and transmitting communications signals from a beta sector of the second base station to the second frequency defining a beta coverage area of the second base station, wherein the beta coverage area of the second base station substantially overlaps with the area of the alpha coverage of the first base station. The method according to claim 1, wherein the system further comprises the steps of: transmitting communication signals from an alpha sector of the first base station to the first frequency defining an alpha coverage area of the first base station; transmitting communication signals from a beta sector of the first base station to the first frequency defining a beta coverage area of the first base station; transmitting communication signals from a range sector of the first base station to a second frequency defining a range coverage area of the P1752 / 98 X first base station, wherein the range coverage area of the first base station substantially overlaps the alpha coverage area of the first base station and the beta coverage area of the first base station and, where the The gamma sector of the first base station is designated as a boundary base station; transmitting communication signals from an alpha sector of a second base station to the second frequency defining an alpha coverage area of the second base station; transmitting communication signals from a beta sector of the second base station to the second frequency defining a beta coverage area of the second base station, and the beta coverage area of the second base station is connected to the coverage area of the second base station. first base station; and transmitting communication signals from a range sector of the second base station to the first frequency defining a range coverage area of the second base station, wherein the range coverage area of the second base station substantially overlaps the coverage area. alpha of the second base station, and wherein the gamma sector of the second base station is designated as a boundary base station. 13. In a communications network in which a P1752 / 98MX network user communicates through a remote unit with another user through at least one base station, the communications network includes a first mobile switching center to control communications through a first set of base stations that includes a first base station, a method for directing communications between the remote unit and the first and second base stations, comprising the steps of: storing in the remote unit a list of active base stations comprising an entry corresponding to each station base with which an active communication is established and, wherein the first base station has an entry in the list of active base stations and, wherein the first base station is a reference base station; storing in the remote unit a list of candidate base stations comprising an entry corresponding to each base station through which it may be possible but an active communication is not established; and initiating the transfer of the active communication signal if the list of candidate base stations comprises an input corresponding to an activating pilot signal. 14. The method according to claim 13, in P1752 / 98MX where the step of initiating a transfer is executed when the list of active base stations comprises a single entry corresponding to a reference base station. The method according to claim 13, wherein the step of initiating a transfer is executed when each entry in the list of active base stations corresponds to a base reference station. 16. The method according to claim 13, which further comprises the step of determining by means of an active communication control unit a type of transfer to be attempted in the step of initiating a transfer. The method according to claim 16, wherein the type of transfer to be attempted is a transfer from the first base station that is in communication with the remote unit using the code division multiple access (CDMA) to the first station base that operates using an alternative modulation technology. 18. The method according to claim 17, wherein the alternative modulation technology is frequency modulation (FM). 19. The method according to claim 17, wherein the alternative modulation technology is access P1752 / 98MX multiple times division (TDMA). The method according to claim 17, wherein the type of transfer to be taken is a transfer from the first base station that is communicating at a first frequency to the remote unit using the code division multiple access (CDMA) to the first base station that communicates to a second frequency using CDMA. The method according to claim 13, further comprising the step of determining a type of transfer in the step of initiating a transfer to be taken on the basis of the list of active base stations. The method according to claim 13, further comprising the step of determining the type of transfer in the step of initiating a transfer to be taken based on the list of active base stations and the activating pilot signal. The method according to claim 13, wherein the system further comprises a second mobile switching center that controls a second set of base stations including a second base station further comprising the steps of: transmitting from an alpha sector of the first base station communication signals to a first P1752 / 98MX frequency defining an alpha coverage area of the first base station, wherein the alpha sector of the first base station is designated as a reference base station; transmitting from the beta sector of the first base station communication signals to the first frequency defining a beta coverage area of the first base station; transmit from an alpha sector of the second base station communication signals to a second frequency defining an alpha coverage area of the second base station, where the alpha coverage area of the second base station substantially overlaps the coverage area beta of the first base station, wherein the alpha sector of the second base station is designated as a reference base station; and transmitting from the beta sector of the second base station communication signals to the second frequency defining a beta coverage area of the second base station, wherein the beta coverage area of the second base station overlaps substantially over the area of the alpha coverage of the first base station. The method according to claim 13, wherein the system further comprises the steps of: P1752 / 98MX transmit communication signals from an alpha sector of the first base station to a first frequency defining an alpha coverage area of the first base station; transmitting communication signals from a beta sector of the first base station to the first frequency defining a beta coverage area of the first base station; transmitting communication signals from a range sector of the first base station to a second frequency defining a range coverage area of the first base station, wherein the range coverage area of the first base station substantially overlaps the coverage area alpha of the first base station and the beta coverage area of the first base station; transmitting communication signals from an alpha sector of a second base station to the second frequency defining an alpha coverage area of the second base station; transmitting communication signals from a beta sector of the second base station to a second frequency defining a beta coverage area of the second base station, and the beta coverage area of the second base station is connected to the coverage area of the second base station. first base station; Y P1752 / 98MX transmit communication signals from a range sector of the second base station to the first frequency defining a range coverage area of the second base station, wherein the range coverage area of the second base station substantially overlaps the area alpha coverage of the second base station. P1752 / 98MX SUMMARY OF THE INVENTION In a telecommunications network, a network user communicates through a remote unit (30) with another user, using at least one base station (100). The communication network includes a first mobile switching center (MSC-I) that controls communications through a first set of base stations that includes a first base station (199). The remote unit (30) stores a list of active base stations that has an entry corresponding to each base station with which active communication is established. The first base station (100) has an entry on the list of active base stations. The first base station (100) measures a round trip delay of an active communication signal between the first base station (100) and the remote unit (30). A communication transfer of the active communication signal is initiated if the round trip delay of the active communication exceeds a threshold, if the first base station (100) is designated as a reference station. Alternatively, the remote unit (30) also stores a list of candidate base stations comprising an entry corresponding to each base station through which active communication may be possible but not established. A transfer Transmission P1752 / 98MX of the active communication signal is initiated if the list of candidate base stations comprises an input corresponding to an activating pilot signal. P1752 / 98MX