CN1230328A - Method and appts. for inter-system handoff within plural hyperband supporting cellular telephone network - Google Patents

Abstract

A cellular telephone network (10) includes plural system areas (32) each having a plurality of cells (12). The system areas do not support cellular communications in all of the same hyperbands. When a verification signal strength measurement (118, 218) is needed, a message (114, 116) is sent from a first one of the system areas to a second one of the system areas, with the message including not only an identification for measurement of the traffic channel currently being used by a mobile station, but also an identification of the hyperband within which that traffic channel exists. The report (120, 122) on the results of the requested measurement and hyperband capabilities of target cell is then sent from the second system area to the first system area. From this information, the first system area may confirm (124, 224) that the measurement was made or was attempted in the proper hyperband and thus determine whether the second system would be able to support mobile station operation with respect to hyperband in the event of an inter-system hand off.

Description

Method and apparatus for handover between systems in a cellular telephone network supported by multiple hyperbands

This invention relates to cellular telephone networks, and more particularly to intersystem handover of mobile stations associated with multiple hyperband supported cellular telephone networks.

North American cellular communications have historically been implemented only in the 800 MHZ cellular hyperband, to which two frequency bands (commonly referred to as the A-band and B-band) are allocated for transmission and control communications. Recent developments in cellular communication services have adopted three additional hyperbands for handling mobile and personal communications. Of these additional hyperbands, only the Personal Communications Service (PCS) hyperband in the 1900 MHZ frequency range has been fully defined, designated The PCS Hyperband includes six different frequency bands (A, B, C, D, E, and F).

Each of the frequency bands designated for the cellular and PCS hyperbands is assigned a plurality of voice or speech (traffic) channels and access or control channels. The control channel is used to control or supervise the operation of the mobile station using information sent to and received from the mobile station. Such information may include incoming call signals, outgoing call signals, paging signals, page answer signals, location registration signals, voice channel assignments, maintenance instructions and moving out of the radio coverage area of one cell and into another Cell selection or reselection commands for radio coverage areas. Traffic channels are used to carry subscriber telephony communications and messages requesting mobile station assistance in making handoff evaluations and controlling handoff operations. Control and traffic channels can operate in analog, digital or combined modes.

As cellular telephone networks have been upgraded to accommodate newly available hyperbands, there have been instances where one cellular system region does not support the same hyperband as its adjacent cellular system region. Thus, for example, a first cellular system region may support cellular operation in both cellular and PCS hyperbands, while an adjacent second cellular system region inconsistently supports cellular operation only in cellular Communication problems arise when roaming between service areas because the mobile station may become obliged to switch between hyperbands and switch traffic channels when handing off. Also, perhaps an even more concerning communication issue is that the check process involved may not be performed correctly, or the results may be wrong, if the service area does not support the hyperband in which the mobile station is currently operating, because Signal strength measurements are made based on the target cell on the traffic channel currently used by the mobile station. Accordingly, there is a need for a system and method for supporting inter-system handoff, and in particular a system and method for supporting check processing involving the differences between the hyperbands supported by the systems and contradiction.

In a cellular telephone network that includes multiple non-uniform hyperband supported system areas, a message sent from a first system area to a second system area requesting a verification signal strength measurement includes not only the The identification of the traffic channel, but also the identification of the hyperband in which that traffic channel exists. In response to this, measurements are made, if possible, from the second system area in the identified hyperband on the traffic channel currently being used by the mobile station. A report on the requested calibration measurements is then sent from the second system area to the first system area for further processing. This report preferably includes an indication of the hyperband in which the calibration measurements were made, if any. From this report, the first system area can confirm the hyperband capability of the second system area and thereby determine whether the second system area supports mobile station operation during inter-system handover.

Upon handover of the mobile station from the first system area to the second system area, the first system area requests the second system area to allocate a traffic channel. In response to that request, the second system area selects to the first system area a traffic channel within a supported hyperband and reports the selected channel and the hyperband in which that selected traffic channel exists. From that report, the first system area can confirm the hyperband capabilities of the second system area and thereby determine whether the second system area supports mobile station operation in the event of an inter-system handover.

A more complete understanding of the methods and apparatus of the present invention may be obtained by referring to the following detailed description when taken in conjunction with the accompanying drawings, in which:

1 is a cell diagram representing an exemplary cell structure of a multiple hyperband supported cellular telephone network in which the present invention may be implemented;

2A-2B are signal flow and network operation diagrams representing the operation of the network of FIG. 1 in connection with a mobile station handover from a cell verification type handover in a first system area to a cell in a second system area; and

3A-3B are signal flow and network operation diagrams illustrating the operation of the network of FIG. 1 as a mobile station transitions from a blind handoff type cell in a first system area to a cell in a second system area.

Referring now to FIG. 1, there is shown a cell diagram representing an exemplary cell structure for a multiple hyperband supported cellular telephone network 10 in which the present invention may be practiced. Cellular telephone network 10 operates according to one of many well-known air interface types including, for example, the digital Time Division Multiple Access (TDMA) protocol. For example, in a digital TDMA cellular telephone network, each cell 12 operates using an assigned set of transmission frequencies selected from one or more available hyperbands, the set of frequencies assigned to each cell 12 including the support Frequency of at least one control channel and a plurality of traffic channels, the control and traffic channels being operable in either analog digital mode or both analog and digital modes. The assigned frequency groups are different for adjacent cells 12, and such frequency groups are not reused by other cells except those cells that are sufficiently far from each other to make adjacent or co-channel interference possible Sex is the least.

In the network 10, each cell 12 is provided with a base station 14. The base station 14 is in simultaneous communication with a plurality of mobile stations 16 operating substantially within the area of the associated cell 12 . The control channels assigned to each cell 12 are used to carry system control signals between the base station 14 and adjacently located mobile stations 16, and are also used to assist the network in mobile station cell reselection. Such control signals include call origination, paging signals, page answer signals, location registration signals, traffic channel assignments, maintenance instructions and cell selection or reselection instructions. Traffic channels are provided in each cell 12 for carrying user voice or data communications between the base station 14 and adjacently located mobile stations 16 and also for assisting in handoff operations.

A base station 14 is shown located at or near the center of each cell 12 . However, base stations 14 may instead be located at or near the periphery of each cell 12, or otherwise remote from the center of each cell 12, depending on geographic area and other well-known factors. In this case, base station 14 may broadcast and communicate with mobile stations 16 located within cell 12 using directional rather than omnidirectional antennas. Each base station 14 includes a transmitter, a receiver and a base station controller (none shown) connected to an antenna (not shown) in a manner known in the art and having a structure known in the art.

Base station 14 also communicates via signaling links and voice trunks 22 with a central control station, commonly referred to as a mobile switching center 18, which functions to control the operation of network 10. Mobile switching centers 18 are interconnected to each other and to the public switched telephone network (PSTN) 20 by signaling links and voice trunks 24, and the mobile switching centers 18 operate to connect subscriber voice and data communications to mobile stations 16 selectively through their base stations 14. Accordingly, the mobile switching center 18 controls system operation through the transmission of control signals on the control channel and responds to the transmission of control signals on the control channel in order to establish a call originating from or terminating at the mobile station 16 on the traffic channel. call. The mobile switching center 18 also controls the switching of user communications from the traffic channel of one cell 12 to the mobile station 16 by and in response to control and traffic channel transmissions as the user mobile station 16 roams throughout the cellular service area during ongoing communications. Traffic channel of another cell.

There are usually multiple system areas 32 (distinguished from each other by having different system identifications (SIDs) and possibly different service providers) within a general cellular service area. Boundaries 34 passing between cells 32 along the edges of the two system areas 32 are shown in bold type in FIG. 1 to delineate the actual extent of each system area shown. In the example shown here, it will be noted that the cells 12 in the two system areas 32 are served by different mobile switching centers 18 .

North American cellular communication has historically been implemented only in the 800MHZ cellular superband, and the latest solutions in the cellular communication business include the use of three additional superbands for handling mobile and personal communications. Of these additional hyperbands, only the Personal Communications Services (PCS) hyperband in the 1900 MHZ frequency range is fully defined. In network 10 shown in FIG. 1, mobile switching center 18(1) for system area 32(1) supports mobile station 16 operation in both the cellular hyperband and the PCS hyperband. However, the mobile switching center 18(2) for system area 32(2) only supports mobile station 16 operation in the cellular hyperband. Consequently, there is uncoordinated hyperband support among multiple system areas 32 in the network 10 .

A number of mobile stations 16 are shown operating within the service area of the network 10, and these mobile stations 16 may include cellular hyperband-only mobile stations, PCS hyperband-only mobile stations, or dual-frequency (cellular and PCS hyperband-capable) mobile stations. Hyperband) operating mobile stations. For cellular hyperband only mobiles, they can operate in analog only or in dual (analog and digital) mode, for PCS hyperband only mobiles, they can only operate in digital mode. Finally, for mobile stations capable of dual frequency (cellular and PCS hyperband) operation, they may operate in digital mode only or in dual (analog or digital) mode. Of course, it should be understood that cellular hyperband only mobile stations may operate within cells 12 of system areas 32(1) and 32(2) of FIG. 1 using either of the cellular hyperband traffic or control channel frequencies. . However, a PCS hyperband-only mobile station may operate within cell 12 of system area 32(1) using either of the PCS hyperband traffic or control channel frequencies. A mobile station capable of dual frequency (cellular and PCS hyperband) operation can operate within cell 12 in both system areas 32(1) and 32(2) and use both cellular and PCS overband while in system area 32(1) While in the system area 32(2), only the traffic or control channel frequencies of the cellular hyperband may be used.

When a mobile station 16 moves into the service area of network 10, this is when the mobile station will move through two cells 12 within a single system area 32 or from a cell in a first system area 32(1) to a second system The case of another cell in area 32(2). While moving between cells 12, the mobile station 16 has the opportunity to use handoffs to change the cellular radio communications through which it is being carried out, based on base station 14 information and instructions exchanged with and between the mobile switching centers 18. base station. For example, mobile station 16(1) is shown moving in the direction of arrow 26 from system area 32(1) into system area 32(2). Since network 10 supports multiple hyperbands and includes single and multiple hyperband support system areas 32, mobile station 16 may not only change traffic or control channel frequencies used for communication by moving between cells and as a result changing base stations , but also change the hyperband on which the communication is being carried out. In the case of such an intersystem handover, it is important to not only notify the mobile switching center 18 of the hyperband in which communication is being implemented in the current serving cell, but also inform the mobile switching center 18 of the hyperband used for communication in the target cell. The mobile switching center is notified of the hyperband capability.

Referring now to FIGS. 1 and 2A-2B together, wherein FIGS. 2A-2B are in conjunction with a mobile station 16(1) check-type handoff from a cell 12(1) within the first system area 32(1) to a second system Cell 12(2) within region 32(2) represents the signal flow and network operation diagram for the operation of network 10 of FIG. In this case, the mobile switching center 18(1) for system area 32(1) supports mobile station 16 operation in both the cellular hyperband and the PCS hyperband, while the mobile switching center for system area 32(2) 18(2) only supports mobile station 16 operation in the cellular hyperband. The mobile station 16(1), operating according to the well-known principles of Mobile Assisted Handoff (MAHO), periodically downlinks, if possible, on the traffic channel (of the cell 12(1)) currently in use. Signal strength measurements 100, and also periodically downlink signal strength measurements 102 are made on the control channels of cells 12 identified by the network as being adjacent to cell 12(1), including cell 12(2). These signal strength measurements are reported 104 to the base station 14(1) for the currently serving cell 12(1), while the base station 14(1) is uplink signaling on the traffic channel currently being used by the mobile station 16(1). Intensity measurement 106.

The base station 14(1) processes the downlink signal strength measurements (100 and 102) reported by the mobile station 16(1) 104, if available, and the uplink signal strength measurements made by the base station (106), to first determine Whether a handover is necessary (act 108) and then (if so) it is determined to which cell(s) the handover can and/or should preferably be handed over to (act 110). In this example, it is assumed that base station 14(1) determines 108 that a handoff is necessary from deteriorating measured uplink and/or downlink signal strengths. It is also assumed that cell 12(2) in system area 32(2) is identified as the preferred target cell for handoff. includes the traffic channel containing the currently serving cell 12(1), being used to communicate with the mobile station 16(1) in the cell 12(1), the hyperband in which that traffic channel exists, A handoff request 112 is then sent by the base station 14(1) to the serving mobile switching center 18(1) with information on the time slot of the digital traffic channel and the identification of the target cell 12(2) for the handoff. Since the target cell 12(2) is operated by a different mobile switching center (serving system area 32(2)) than the mobile switching center 18(1) serving the current cell 12(1) (serving system area 32(1)) 18(2) to provide the service, so the handover granted in this case will include an intersystem handover. The foregoing description is just one example of the procedure used when making the determination of whether to carry out handover.

The currently serving MSC 18(1) then transmits a signal 14 to the MSC 18(2) associated with the target cell 12(2) requesting a communication capability check of the base station 14(2) and the MS 16(1). Like the request 112 sent by the base station 14(1), the signal 114 also includes information about the currently serving cell 12(1), the traffic channel being used to communicate with the mobile station 16(1) in the cell 12(1), the The hyperband in which traffic channels exist, the time slots (for digital traffic channels) carrying cellular communications, the target cell 12(2) for handover, and the hyperband capabilities of the mobile station. In response to this, the mobile switching center 18(2) signals 116 to the base station 14(2) of the target cell 12(2) that the base station 14(2) in the current serving cell 12(1) is currently being used by the mobile station 16(1). A check signal strength measurement is made on the traffic channel (act 118). This measurement should take into account the hyperband in which the traffic channel exists and, if necessary, possibly the time slot (for the digital traffic channel) in which the cellular communication is carried.

The base station 14(2) then reports 120 the calibration signal strength measurement to the mobile switching center 18(2), which in turn transmits 122 the result back to the mobile switching center 18(1). This report not only identifies whether the verification signal strength measurement was successful, but also identifies the specific hyperband in which the verification measurement (if any) was made, along with identifying the cell hyperband capability. The results are then processed (act 124) by the mobile switching center 18(1) to determine whether a handoff should be made to the target cell 12(2). This determination takes into account not only the success and strength of the verification measurements, but also the hyperband capabilities of the mobile station 16(1) and the target cell 12(2). If the determination is affirmative, the mobile switching center 18(1) transmits 126 a request for allocation (and reservation) of traffic channels (and therein time slots for digital traffic channels) for handoff to the target cell 12(2) ) signal to the mobile switching center 18(2). The base station 14(2) and the mobile switching center 18(1) are then notified of the traffic channel (and the hyperband in which that traffic channel exists) in the target cell 12(2) assigned by the mobile switching center 18(2), and the mobile The switching center 18(1) then confirms ownership of the assigned traffic channel and hyperband based on the mobile station 16(1) communication capabilities (act 130), and passes through the base station 14(1) for the current serving cell 12(1) The mobile station 16(1) is signaled 132 with a transfer order directing the mobile station to switch to the assigned traffic channel (and time slot therein, if appropriate) in the target cell 12(2). Mobile station 16(1) then tunes to and accesses 134 the assigned traffic channel (in the correct time slot). When the base station 14(2) detects a mobile station access (action 136), the mobile switching centers 18(1) and 18(2) are notified 138 and the call is transferred 140 to the mobile switching center 18(2) for further processing to complete the handover procedure.

The operation of network 10 with respect to the check-type handoff procedure shown in FIG. 2 may be better understood with reference to the following example.

In a first example, mobile station 16(1) comprises a PCS hyperband-only mobile station capable of operating in digital mode only, and is currently using the digital traffic channel number of cell 12(1) in the PCS hyperband 1. As the mobile station 16(1) moves, the base station 14(1) processes available signal strength measurements (100, 102 and/or 106) and determines that a handoff is necessary (108). The cell 12(1) other than the other adjacent cell 12 comprises a candidate target cell for that handoff. The base station 14(1) then requests 112 a handoff from the mobile switching center 18(1). This request includes not only the identification of traffic channel number 1, but also the identification of the PCS hyperband in which that traffic channel number 1 is located. This is important because cellular hyperbands also include traffic channel number 1, and if the hyperband identification is absent, the traffic channel number identification provided may confuse system areas 32 that support multiple hyperbands.

The mobile switching center 18(1) then requests (using signals 114 and 116) that the base station 14(2) of the target cell 12(2) operate in the PCS hyperband on traffic channel number 1 currently being used by the mobile station 16(1). Perform a check signal strength measurement (act 118) within the PCS hyperband, the base station 14(2) cannot make the requested check signal strength measurement within the PCS hyperband since the service area 32(2) only supports cellular operation in the cellular hyperband . Accordingly, base station 14(2) may report 120 and 122 that it cannot make the requested verification signal strength measurements. Alternatively, the base station 14(2) may have erroneously made a calibration signal strength measurement on traffic channel number 1 of the cellular hyperband, and the reports 120 and 122 would include the (albeit inappropriate) measurements made in the cellular hyperband. instruct. In either case, the reported process 124 confirms the capability of the target cell 12(2) to operate only in the cellular hyperband and determines that, for the PCS hyperband mobile station 16(1), handoff to the target cell Hole 12(2) is not possible. That cell is then discarded as a viable target cell for handover. Thus, for a mobile station 16(1) that is only capable of PCS hyperband operation, no handoff is attempted to a cell in the service area 32(2) that supports only cellular hyperband operation.

In a second example, mobile station 16(1) comprises a cellular hyperband only mobile station operating in analog mode only or operating in dual analog/digital mode, and is currently using a traffic channel in the cellular hyperband No. 2, while the mobile station 16(1) is moving, the base station 14(1) processes the available signal strength measurements (100, 102 and/or 106) and determines that a handoff is necessary (108), the base station 14(1) also It is determined that cell 12(1), in addition to possibly other neighboring cells 12, also includes candidate target cells for that handover. The base station 14(1) then requests 112 a handoff from the mobile switching center 18(1), this request including not only the identification of traffic channel number 2, but also the identification of the cellular hyperband in which traffic channel number 2 is located. This is important because the PCS hyperband may also include traffic channel number 2, and if the identification of the hyperband is absent, the traffic channel identification provided may confuse system regions 32 that support multiple hyperbands.

The mobile switching center 18(1) then requests (using signals 114 and 116) that the base station 14(2) of the target cell 12(2) operate in the cellular hyperband on traffic channel number 2 currently being used by the mobile station 16(1). A calibration signal strength measurement is performed (act 118). Since the service area 32(2) only supports cellular operation in the cellular hyperband, the base station 14(2) should be able to make the requested verification signal strength measurements in the cellular hyperband. This measurement can then be made but is unsuccessful, indicating that the mobile station 16(1) has insufficient signal strength to communicate with the base station 14(2). This measurement may also not be possible, possibly because the base station 14(2) is not functioning properly. Alternatively, this measurement may be made and successful, indicating that the signal strength of the mobile station 16(1) is sufficient to communicate with the base station 14(2). In either of the foregoing cases, reports 120 and 122 from base station 14(2) include indications confirming that cellular hyperband measurements were taken.

If the measurements were made and were successful, or if the measurements could not be made, process 124 confirms the cellular hyperband operation capability of the target cell 12(2), and may then result in the selection and approval of the target cell 12(2) for use in Handover. The mobile switching center 18(2) then signals 126 to request allocation (and reservation) of a traffic channel for handoff to the target cell 12(2). To maximize the chance of a successful handoff, the assigned traffic channels typically include analog traffic channels within the cellular hyperband. After confirmation 130 of the selected channel, a transfer order is broadcast 132 by the base station 14(1) to the mobile station 16(1), the assigned traffic channel is then accessed 134 by the mobile station 16(1), and the call is transferred 140 to Mobile Switching Center 18(2) for further processing to complete the handoff procedure. Alternatively, if measurements were made but were unsuccessful (indicating insufficient signal strength), then process 124 again confirms the cellular hyperband-only operation capability of target cell 12(2) and determines that handoff is not possible. Subsequently, the cell discards that cell 12(2) as a viable target for handover, and no handoff is attempted to that cell.

In a third example, mobile station 16(1) comprises a dual frequency (cellular and PCS hyperband) capable mobile station operating in digital mode only or in analog digital mode, and is currently using the cellular hyperband traffic channel number 3. As mobile station 16(1) moves, base station 14(1) processes available signal strength measurements (100, 102 and/or 106) and determines 108 that a handoff is necessary. The base station 14(1) also determines that the cell 12(1), in addition to possibly other neighboring cells 12, also includes candidate target cells for that handoff. The base station 14(1) then requests 112 a handoff from the mobile switching center 18(1), this request including not only the identification of traffic channel number 3, but also the identification of the cellular hyperband in which traffic channel number 3 is located. This is important because the PCS hyperband may also include traffic channel number 3, and if the identification of the hyperband is absent, the traffic channel identification provided may confuse system areas 32 that support multiple hyperbands.

The mobile switching center 18(1) then requests (using signals 114 and 116) that the base station 14(2) of the target cell 12(2) operate in the cellular hyperband on traffic channel number 3 currently being used by the mobile station 16(1). A calibration signal strength measurement is performed (act 118). Since the service area 32(2) only supports cellular operation in the cellular hyperband, the base station 14(2) should be able to make the requested verification signal strength measurements in the cellular hyperband, which can then be made but unsuccessfully, Indicates that the signal strength of the mobile station 16(1) is insufficient to communicate with the base station 14(2). This measurement may also not be possible, possibly because the base station 14(2) is not functioning properly. Alternatively, this measurement may be made and successful, indicating that the signal strength of the mobile station 16(1) is sufficient to communicate with the base station 14(2). In either case, reports 120 and 122 from base station 14(2) include indications confirming that cellular hyperband measurements were made.

If the measurements were made and were successful, or if the measurements could not be made, then process 124 confirms the cellular hyperband operation capability of the target cell 12(2), and may then result in the selection and approval of the target cell 12(2) for use with in handover. The mobile switching center 18(2) then signals 126(1) to request allocation (and reservation) of a traffic channel for handoff to the target cell 12(2). To maximize the chance of a successful handoff, the assigned traffic channels typically include analog traffic channels in the cellular hyperband. It is necessary not to change the hyperband being used by the mobile station 16(1). After confirmation 130 of the selected channel, the transfer command 132 is then broadcast by the base station 14(1) to the mobile station 16(1), the assigned traffic channel is then accessed 134 by the mobile station 16(1), and the call is transferred 140 to the Mobile Switching Center 18(2) for further processing to complete the handoff procedure. Alternatively, if measurements were made but were unsuccessful (indicating insufficient signal strength), process 124 reconfirms the cellular hyperband-only capability of the target cell 12(2) and determines that handoff is not possible . Subsequently, that cell 12(2) is discarded as an available target cell for handover, and no handoff is attempted to that cell.

In a fourth example, mobile station 16(1) comprises a dual-frequency (cellular and PCS hyperband) capable mobile station operating in analog mode only or in dual analog/digital mode, and is currently using PCS hyperband Traffic channel number 4 in band, as mobile station 16(1) moves, base station 14(1) processes available signal strength measurements (100, 102 and/or 106) and determines 108 that a handoff is necessary. The base station 14(1) also determines that the cell 12(1), in addition to possibly other neighboring cells 12, also includes candidate target cells for handoff. The base station 14(1) then requests 112 a handover from the mobile switching center 18(1), the request including not only the identification of traffic channel number 4, but also the identification of the PCS hyperband in which traffic channel number 4 is located. This is important because cellular hyperbands may also include traffic channel number 4, and if identification of the hyperband is absent, the traffic channel identification provided may be ambiguous.

The mobile switching center 18(1) then requests (using signals 114 and 116) that the base station 14(2) of the target cell 12(2) operate in the PCS hyperband on traffic channel number 4 currently being used by the mobile station 16(1). A calibration signal strength measurement is performed (act 118). Since the service area 32(2) only supports cellular operation in the cellular hyperband, the base station 14(2) cannot make the requested verification signal strength measurements in the PCS hyperband. Accordingly, base station 14(2) may report 120 and 122 that it is unable to make the requested verification signal strength measurements. In addition, base station 14(2) may have erroneously made a verification signal strength measurement on traffic channel number 4 of the cellular hyperband, and reports 120 and 122 would include an indication that the measurements were made (albeit incorrectly) in the cellular hyperband . In either case, the processing 124 of this report confirms the cellular hyperband-only operation capability of the target cell 12(2), and thus may result in discarding the cell 12(2) as an available target cell for handoff.

Alternatively, cell 12(2) may remain the best available choice for handoff, although no verification signal strength measurements can be made on traffic channel number 4 of the PCS hyperband because mobile station 16(1) It is capable of dual frequency (cellular and PCS hyperband) operation. Through process 124, the target cell 12(2) is then selected and admitted for handoff. A signal 126 is then sent to the mobile switching center 18(2) to request allocation (and reservation) of a traffic channel for handoff to the target cell 12(2). To maximize the chance of a successful handoff, the assigned traffic channels typically include analog traffic channels in the cellular hyperband. Following confirmation 130 of the selected channel, a transfer command 132 is broadcast by the base station 14(1) to the mobile station 16(1). A hyperband transition from PCS to cellular is effected and the assigned traffic channel is accessed 134 by the mobile station 16(1). The call is then transferred 140 to the mobile switching center 18(2) for further processing to complete the handoff procedure.

Referring now to FIGS. 1 and 3A-3B together, wherein FIGS. 3A-3B are diagrams illustrating the type of blind handoff associated with a mobile station 16(1) from a cell 12(1) within the first system area 32(1) to a second system. Signal flow and network operation diagram of Figure 1 network operation for cell 12(2) within area 32(2). As can be seen, the blind handoff type differs from the check-type handover of FIGS. 2A-2B primarily in the point in time at which the check signal strength measurements are made.

Mobile switching center 18(1) for system area 32(1) supports mobile station 16 operation in both cellular hyperband and PCS hyperband, while mobile switching center 18(2) for system area 32(2) supports only The mobile station 16 operates in the cellular hyperband. The mobile station 16(1), operating according to the well known principles of Mobile Assisted Handoff (MAHO), periodically makes downlink signal strength measurements 200 on the traffic channel (of the cell 12(1)) currently being used , and also periodically make downlink signal strength measurements 202 on the control channels of the network identification cells 12 adjacent to the cell 12(1), including the cell 12(2), these signal strength measurements are reported 204 to Base station 14(1) for currently serving cell 12(1). The base station 14(1) simultaneously makes uplink signal strength measurements 206 on the traffic channel currently being used by the mobile station 16(1).

The base station 14(1) processes the downlink signal strength measurements reported 204 (200 and 202) by the mobile station 16(1) and the uplink signal strength measurements made by the base station (206), if available, to first determine handoff Whether a handover is necessary (action 208), and secondly, if so, it is determined which cell(s) should be best handed over to (action 210). In this example, it is assumed that base station 14(1) determines 208 that a handoff is necessary from progressively deteriorating measured uplink and downlink signal strengths. Assume also that cell 12(2) in system area 32(2) is identified 210 as the target cell for the handoff. A request 212 for handoff is then sent by the base station 14(1) to the serving mobile switching center 18(1) including information including the identification of the currently serving cell 12(1) at which cell 12(1) identification of the traffic channel being used to communicate with the mobile station 16(1), identification of the hyperband in which that traffic channel exists, identification of the time slot for transmitting cellular communications (for digital traffic channels) and for handoff The target mesh 12(2). Granted handoffs in this case include intersystem handoffs, since a mobile switching center 18(1) other than the one serving the current cell 12(1) (of the serving system area 32(1)) (The mobile switching center 18(2) serving the system area 32(2) provides service to the target cell 12(2). The above description is only one example of the procedure used in determining to perform a handoff.

The current serving mobile switching center 18(1) then sends 214 a letter to the mobile switching center 18(2) associated with the target cell 12(2) requesting allocation (and reservation) of traffic channels (and where used for digital traffic channels). time slot) for handover to the target cell 12(2). Like the request 212 sent by the base station 14(1), the signal 214 also includes the identification of the currently serving cell 12(1), the identification of the traffic channel used to communicate with the mobile station 16(1) in the cell 12(1) , the identification of the hyperband in which the traffic channel exists, the identification of the time slot (for the digital traffic channel) carrying the cellular communication, the identification of the target cell 12(2) for handoff, and the hyperband capability of the mobile station identified information. In response to this, the mobile switching center 18(2) signals 216 the base station 14(2) of the target cell 12(2) to be currently in use by the mobile station 16(1) in the serving cell 12(1). A check signal strength measurement is made on the traffic channel of the device (act 218). This measurement should take into account the hyperband in which the traffic channel exists and possibly the time slot (for the digital traffic channel) in which the cellular communication is carried. The base station 14(2) then reports 220 the verification signal strength measurements to the mobile switching center (812). If the verification is successful, the base station 14(2) and the mobile switching center (812) are notified 222 of the traffic channel (and the hyperband in which that traffic channel exists) in the target cell 12(2) assigned by the mobile switching center (812) Center 18(1), this differs from the processing of Figures 2A-2B in that a check is performed prior to requesting allocation of a traffic channel.

The mobile switching center 18(2) then sends back 226 the verification assignment result to the mobile switching center 18(1). This report 226 not only identifies whether the verification signal strength measurement was successful, but also correlates with the identification of the cell's hyperband capability. Together identify the particular hyperband in which the measurements (if any) were made, and the results are then processed (act 228) by the mobile switching center 18(1) to determine whether a handoff should be made to the target cell 12(2). Not only the success and strength of the verification measurements, but also the hyperband capabilities of the mobile station 16(1) and the target cell 12(2) are considered. If the determination is affirmative, the mobile switching center 18(1) then confirms the ownership of the assigned channel and hyperband based on the mobile station 16(1) communication capabilities, and passes through the base station 14(1) for the current serving cell 12(1). ) signals 232 the mobile station 16(1) with a transfer command directing the mobile station to switch to the assigned traffic channel (and the appropriate time slot therein) in the target cell 12(2). The mobile station 16(1) then tunes to and accesses 234 (in the correct time slot) the assigned traffic channel. When the base station 14(2) detects a mobile station access (action 236), the mobile switching centers 18(1) and 18(2) are notified 238, and the call is transferred 240 to the mobile switching center 18(2) for further processing to complete Handover procedure.

Operation of the network 10 shown in FIGS. 3A-3B with respect to blind handoff type procedures may be better understood by referring back to the examples discussed above in connection with FIGS. 2A-2B. The main difference from FIGS. 2A-2B and their examples involves the mobile switching center 18(1) requesting that the base station 14(2) of the target cell 12(2) be on the designated traffic channel currently being used by the mobile station 16(1). The point in time at which a calibration signal strength measurement is performed within the specified hyperband. In FIGS. 3A-3B for each of those four examples, no check signal strength measurements are taken until after a request for traffic channel allocation in the target cell 12(2) has been made. Otherwise, the handover process and results remain the same.

While preferred embodiments of the method and apparatus of the present invention have been shown in the drawings and described in the foregoing detailed description, it is to be understood that the invention is not limited to the disclosed embodiments, but can be modified without departing from the following claims Numerous rearrangements, modifications, and substitutions are made within the spirit of the invention presented and defined herein.

Claims (15)

1. A cellular telephone network comprising: a first system region having a plurality of cells including a first cell, the first system region supporting cellular communications on traffic channels in first and second hyperbands; a second system region having a plurality of cells including a second cell supporting cellular communications on traffic channels in the first hyperband but not in the second hyperband; a mobile station moving through the network from a first cell to a second cell and conducting cellular communications on either the first or second hyperband traffic channel; and A means for transmitting from a first system area to a second system area a request for a second system area to perform a verification signal strength measurement on a traffic channel being used by the mobile station, the request including the An identification of the traffic channel of , and an identification of the first or second hyperband in which that traffic channel exists. 2. 2. A network according to claim 1, wherein the first system area includes means for identifying the second cell as a target cell for handover of the mobile station. 3. The network of claim 2, wherein the second system area performs the requested verification signal strength measurement of the target second cell. 4. The network according to claim 1, further comprising means for transmitting a report from the second system area to the first system area regarding the requested verification signal strength measurement and hyperband capability results of the target cell. 5. A network according to claim 4, wherein the first system region further includes means for processing reports on requested verification signal strength measurements to determine the second cell in the event of a handoff from the first cell to the second cell. Whether the system area can support the mobile station communication device related to the hyperband. 6. In a cellular telephone network, the telephone network includes: a first system region having a plurality of cells including a first cell, the first system region supporting cellular communications on traffic channels in first and second hyperbands; and a second system region having a plurality of cells including a second cell supporting cellular communications on traffic channels in the first hyperband but not in the second hyperband; A method for performing verification signal strength measurements in relation to a possible handover from a first cell to a second cell of a mobile station in cellular communication on a traffic channel of a first or second hyperband, comprising the following step: A request is transmitted from the first system area to the second system area requesting the second system area to perform a verification signal strength measurement on the traffic channel being used by the mobile station, the request including the traffic channel being used and identification of the first or second hyperband in which that traffic channel exists; and The identified hyperband is taken into account by the second system domain in relation to the performance and reporting of the calibration signal strength measurements. 7. 6. The method of claim 6, further comprising the step of identifying the second cell as a target cell for handover of the mobile station. 8. 7. The method of claim 7, further comprising the step of performing the requested verification signal strength measurement of the target second cell. 9. 6. The method of claim 6, further comprising the step of transmitting a report from the second system area to the first system area regarding the requested verification signal strength measurement and hyperband capability results of the target cell. 10. A method according to claim 9, further comprising processing a report on the requested verification signal strength measurement to determine whether the second system area can support the relevant overclocking in the event of a handover from the first cell to the second cell Steps for communicating with a mobile station. 11. A method for operating a cellular telephone network comprising the steps of: The mobile station has certain hyperband communication capabilities in accordance with the need to perform handoff in accordance with the detection of the mobile station's communication operations in the first cell; identifying a target second cell associated with the second system as a candidate cell for handover; requesting the second cell to perform a check signal strength measurement, the request identifying the traffic channel currently being used by the mobile station in the first cell and identifying the hyperband in which that channel exists; Attempt to perform verification signal strength measurements in identified traffic channels and hyperbands; report the results of the attempted verification signal strength measurements and hyperband capabilities of the target cell; and A report on the requested verification signal strength measurements is processed to determine whether the second cell supports mobile station communications in the event of a handoff from the first cell to the second cell based on some of its hyperband communication capabilities. 12. 11. The method of claim 11, wherein the first cell supports communication between the first hyperband and the mobile station in the second hyperband. 13. The method of claim 12, wherein the second cell supports mobile station communications in the first hyperband but does not support mobile station communications in the second hyperband. 14. The method according to claim 13, wherein the processing step further comprises the steps of: determining from the requested verification signal strength measurements that the second cell supports mobile station communications in the first hyperband but not in the second hyperband; and It is determined whether the mobile station is capable of operating in the first hyperband. 15. The method according to claim 14, further comprising the steps of: requesting a traffic channel in the first hyperband for handoff of the mobile station to the second cell; and A handover command is sent to the mobile station specifying which traffic channel to operate in the first hyperband.

Images