MXPA97007844A - System, method and apparatus for transfer bla - Google Patents

Abstract

The present invention relates to a wireless communication device (100) that continues with the measurement of intensities of pilot signals while in the System Access Status (220) and provides at least one of the current pilot signal intensities measured to the station base in each access test (210). A base station (102) receives the information about the pilot signal intensities (3508; 320) and the system specifies the base stations for soft transfer according to the intensities of current measured pilot signals (315; 34

Description

SYSTEM, METHOD AND APPARATUS FOR SOFT TRANSFER Field of the Invention The present invention relates generally to the field of digital communications, and more particularly to a system, method and apparatus for soft handoff in a Personal Communications System (PCS) or cellular that employs Code Division Multiple Access (CDMA). . Although the invention has a wide range of applications, it is especially suitable for use in cellular radiotelephones and base stations and is described in particular in relation thereto.

Antecedaoias of the. Invention Provisional Standard IS-95-A (IS - l &) - has been adopted by the Association of Telecommunications Industries to implement the CDMA_ in a cellular system. In the CDMA system, a mobile station communicates with one or more than a number of base stations in a geographical region. Each base station continuously transmits a pilot channel signal which has the same code as widens but with a different code phase shift. The phase shift allows the pilot signals to be distinguished from each other, which in turn allows the base stations to be distinguished from one another. Thereafter r a pilot signal from a base station will simply receive the name of pilot. The mobile station monitors the pilots and measures the energy received from the pilots.

IS-95 defines a number of states and channels for communication between the mobile station and the base station.

For example, in the Mobile Station Control in. the Traffic State, the base station communicates with the mobile station through the One Way Traffic Channel and the mobile station communicates with the base station by the Return Traffic Channel- During a call ^ la. The mobile station must constantly monitor and maintain four sets of pilots collectively referred to as the Joint-Pilot Set, the Active Set, the Candidate Set, the Neighbor Set, and the Remaining Set. The Active Set are pilots associated with. The Ida Traffic Channel assigned to the mobile station. The Candidate Set are pilots who are not currently in the Active Set but have been received by a particular mobile station with sufficient intensity to indicate that the One Way Traffic Channel could demodulate them successfully. The Neighbor Set are pilots who are not currently in the Active Set or in the Candidate Set but with possible candidates for the transfer. The Remaining Set are all possible pilots in the current system in the current CMA frequency assignment, excluding the pilots in the Neighbor Set, the Candidate Set and in the Active Set.

The mobile station constantly searches for a Pilot Channel from the neighboring base stations for a pilot having intensity sufficiently greater than a threshold value.

When the mobile station moves from one region covered by a base station to another, the mobile station advances certain pilots from the Set Neighbor to the Set Candidate and notify the base station or base stations of the advance of the Neighbor Set to the Candidate Set by means of a Pilot Intensity Measurement Message. The base station determines an Active Set according to the Pilot Intensity Measurement Message and notifies the mobile station of the Active Set-up by means of a Transfer Address Message. When the mobile station starts the. camunrication with a new base station in the Active Set prior to terminating communications with the previous base station, - a "soft transfer" has occurred.

In the Inactive State of the Station. Mobile The mobile station monitors a Paging Channel, transmitted from a single base station of the Active Set for control and call information. Moreover, the mobile station continues the search of the Pilot Channel of the neighboring base stations for a pilot having an intensity sufficiently greater than the pilot of the base station monitored at this time. When a pilot is found having intensity, substantially greater, an "inactive transfer" occurs to the base station having the pilot with the highest intensity and the mobile station monitors the Pager Channel from this base station.

In a System Access State ^ the mobile station continues with the reception of control information by the Pager Channel and also transmits short message signals, such as call origination, - calls and registers responses, - by Access Channel at the monitored base station. While in the System Access State, the mobile station continues its pilot search and updates its Neighbor Set, - but, according to article 6.-6.-3.1.3- of IS --- 15- and unlike the Mobile Station Control in the State of Traffic and the Inactive State of Mobile Station, the mobile station is not allowed to transfer to another base station.

Each time the mobile station sends a message in the System Access State, it must perform an "access attempt" to the single base station that is monitored. Attempt to access is the process of repeatedly transmitting the message until an acknowledgment of the message from the base station is received. Each transmission in the access attempt is called an "access test" r which is composed of an Access Channel Preamble and an Access Channel Message, The content of the Access Channel Message depends on the type of signal broadcast message . According to article 6-.6.3-.1.1.1 of IS-9-5, - the same message is sent in each message test.

IS-95 specifies a particular protocol each time the mobile station originates a call or answers a call in the System Access State and establishes the call in the Mobile Station Control in the Traffic State. Only certain parts of the protocol are described here- The mobile station first sends an Origination Message through the Access Channel. After the receipt of the Origination Message, the base station sends an Assignment Message, from the Channel to the Buscapexsanas. The Channel Assignment Message specifies a Traffic Code Channel of the monitored base station - for demodulation by the mobile station. The mobile station tunes the Canal de Tráfi CQ Code as expected and receives the Traffic Channel from Ida. The base station acquires the mobile station in the Canal de Tráfico-de Vuelta. The mobile station sends, by the Return Traffic Channel, the Measurement Message, gives Intensity, gives Pilot, indicating the current Candidate Set. The base station transmits - via the Idar Traffic Channel an Extended Transfer Address Message to the mobile station specifying the Active Set - when the Extended Transfer Address Message specifies the unique monitored base station and other stations of baser a soft transfer is made to the different base stations and the so-called demods the Code Traffic Channels of the base stations represented by the pilots of the Active Set- Interrupted calls and poor call quality reception have been observed using this protacaio- As a consequence, the mobile station communicates with only one base station through the Traffic Channel until the soft transfer is performed.

As a solution to this problem, a proposed modification of the IS-95 would move more quickly (the mobile station towards soft handoff reporting the intensities of piloting and speci fi c signals from certain members of the Candidate Set by the Access Channel instead of waiting until the Traffic Channel is acquired, that is, the mobile station would measure the pilot intensities and add to the Mansaja da Canal da Acceso the entities of the base stations that are suitable for a soft transfer. Active Set in the Channel Assignment Message In consequence, the mobile station will know its Active Set before acquiring the Traffic Channel and will immediately be able to acquire the Traffic Channel of multiple base stations instead of one.

This solution is a problem when multiple access tests are needed to make a successful access attempt and the conditions change. - The time between the successive access tests is in the order of hundreds of days - Duxanta up to this time the intensities of pilots can change. But, because the same message is sent in each accessor test the same pilot intensity measurement reported by the station, mobile in the initial access test is reported in. subsequent access tests. Since the base station receives obsolete pilot intensity information in ^ The following access tests, you can not specify the best base stations suitable for the transfer in the Active Set. As a result, poor call quality or call interruptions ensue- ^ Accordingly, there is a need for a system, method and apparatus for soft transfer that provides current information in intensities of pilot signals to the base station.

Breva Description, gives the Drawings Fig. 1 is an electrical block diagram of a communication system, including a block diagram of a radiotelephone. Fig. -2 is a flow diagram illustrating a method for reporting intensities of pilot signals used by the radiotelephone shown in Fig. 1- Fig. 1 is a flow diagram illustrating a method for specifying suitable base stations © for transfer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The system, method and apparatus described herein perform the soft transfer by providing active information about the intensities of pilot signals to a base station. According to the invention, a mobile station continues with the measurement of intensities of pilot signals while in the System Access State and provides the intensities of current measured pilot signals to the base station in each access test. , The base station receives current information about the intensities of pilot signals and the system specifies the base stations for soft transfer according to the intensities of pilot signals.- The invention offers an advantage over the conventional system, method and apparatus, that interrupted calls are reduced and call quality improves. Other advantages and novel features of the invention will be set forth in part in the following description, wherein the embodiments of the invention are shown and described and, in part, become apparent to those skilled in the art upon review of the following description. detailed or may be known by putting the invention into practice.

Next, reference will be made in detail to the embodiment configured in accordance with the present invention.

Fig.L is a branch, in. electric blocks gives a. wireless communication system, including a block diagram of a communications device, - eg a radiotelephone 100. This figure illustrates, among other elements, a 1QL antenna for ra i bi_ signs, gives a number of base stations 102 ( only one is shown) and transmit signals originated by the radiotelephone 1Q-Q--. An analogue front end 103 processes the received signals and provides them to an analogue to digital conversation (ADC) 105. The digitized received signals are provided to a rake receiver composed of a number of indicator receivers 107 and at least one receiver receiver 1Q9 conactador an_ paralalo.- La. operation of the indicator receivers 107 and at least one searcher receiver 109- connected in parallel. The operation of the indicator receivers and the search receiver is controlled in part by the logic circuit and gives control 113. The output of the indicator receivers and the search receiver is provided to the logic and control circuit 113 for further processing.

The logic and control circuit 113 is capable of storing the data and the software program which specifies the instructions for executing the method according to the invention., and storing a record of the Active Set, (the Neighbor Set and the Candidate Set.) The logic and control circuit 113 provides data- to the transmission circuit path 115, which processes the data and provides the processed data to a_ analog digit circuit (DAC) 117. The analog signal emitted by the DAC 117 is provided to the analogue front end 10-3- para, its transmission to the base stations 102 by the antenna 101. An example of the rake receiver and The trajectory of the transmission circuit 115 is the Mobile Station Modem available by Qualcomm, - Inc Although the logic and control circuit 113 is shown as a separate element from the receivers, a person of ordinary skill in the art will recognize that portions of the logic and control circuit may be in the rake receiver or in other elements of the radiotelephone.

Each of the base stations 102 has a strings I similar to the radiotelephone 100 for each of the Paging / Access Channel, of the Traffic Channel, - a Synchronization Channel and the Pilot Channel (except a reception path is not necessary for the Synchronization Channel and the Pilot Channel) and may also have multiple receiving paths and antennas for reception diversity.

A person skilled in the art will recognize that the communications system needs other infrastructure equipment, not known, for switching, encapsulated. 11 loved ^ and other functions.

The method of use and operation of the wireless communication device, with the structure and description above, will be described with. referenei to the Eig-2. q e ^ is a flow chart illustrating a method for reporting signal intensities -pilot- In the System Access State, the search receiver 109 initially measures the pilot intensity of the neighboring pilots. (Step 205). The logic and control circuit 113 creates an Access Channel Message that includes the initially measured pilot intensities. (Step 210). The analog front end 1Q3 transmits the Access Closure Mage with the pilot intensities initially measured when performing the first access test (Step 215).

The steps of metering the intensities of pilot signals (step 220), creating an Access Channel Mnesage including the newly measured pilot intensities (step 210-), and transmitting the Access Channel Message in the subsequent access tests they are repeated until the radiotelephone receives an acknowledgment of the Access Channel Message from the base station within a first predetermined time duration (step 225), or until a maximum number of access tests has been transmitted (step 23.0).

The report of the intensities of pilots current measurements in subsequent access tests is an important feature of the invention, because the system has current information on pilot-intensity measurements for use in the determination of base stations for soft transfer - With reference to Fig.2, the logic and control circuit 113 determines whether the acknowledgment of the Access Channel is received within a first time of predetermined duration (step 225). If affirmative, the method ends, (step 240) If not, the logic and control circuit 113 determines whether a predetermined maximum number of transmissions of the Access Channel Message has been executed. (step 23.Q In the aff riate house, the method ends, (step 240) If not, the logic and control circuit 113 waits for a second predetermined time-duration (step 235) before creating the Message Access Channel qua includes the newly measured stack intensities (step 210).

The method of use and operation of the infrastructure, described above, will now be described with reference to Eig-3, which is a. di agrama da fluja that i lustra un. 300 method to specify base stations suitable for transfer.

With reference now to Fiq, 3- and- to the structure of the infrastructure and the base station, the analogue front end finally successfully receives a first of the access tests and therefore the Access Channel Message (step 305) that is called p-rimer Access Channel Message. The infrastructure begins by distributing the Activor Set channels by creating a first Active Set according to the first set of measured pilot intensities and begins by installing resources to handle the call, (step 310) The base station 102 sends the acknowledgment of receipt of the Access Channel Message and a Channel Assignment Message that specifies the Active Set (step 315). In some solutions, - eg, when there are connection errors in the Paging Channel, the radiotelephone can transmit another access test before receiving the acknowledgment of the Access Channel Message. Therefore, the base station 1X2 receives another Access Channel Message (step 320) called the second Access Channel Message which specifies more current, intensity measurements of the pilot than those of the first Access Channel Message. The infrastructure determines whether you need to specify a new Active Set that is different from the Active Set based on the most current measurements. For example, the infrastructure creates a second Active Set according to the second set of measured pilot intensities, compares the first Active Set and the second Active Set (step 325 -) - and determines whether the first Active Set and the second Set Active are different (step 330. The first Active Set and the second Active Set are different, eg when they specify one or more different pilots in their respective sets of pilots.When a different Active set is not necessary, - the method ends (step 345) When a different Acitvo Set is necessary, the station gives aspara bases until the subscriber unit is acquired in the Return Traffic Channel (step 335) .The infrastructure distributes the Active Set channels, creating a second Active Set. it agrees with the second active set of measured pilot intensities and begins by installing resources to manipulate the call (step 3 Q. Although, it is shown later from step 335, the distribution may come, as soon as it is determined qua. the Active Conjuncts are different. Likewise, the base station 102 sends an Extended Transfer Message through the Ida Traffic Channel, which specifies the second Active Joint Cpasa 34H. The mobile station can then execute a soft transfer to the pilots of the second Active Set.

In summary, an embodiment configured in accordance with the present invention provides transference in. a wireless communication system employing CDMA providing current information on pilot signal intensities to the base station at each access test and sending an active set derived from the intensities of current pilot signals to the iri-wire radio communications device.

Claims (7)

1. A transfer method characterized by the following steps: a) measuring a pilot intensity of each neighboring pilot (205); b) creating an Access Channel Message including at least one of the measured pilot intensities (210); c) transmit the Access Channel Message (^ ISj d) repeat steps a) to c) until the acknowledgment of the Access Channel Message is received (-225) - A and e) receive a determined Active Set of agreement with at least one of the measured pilot intensities (315).

2. The method of claim 1 further characterized by the following steps: determining, - after each execution of step G) ^ if the acknowledgment of the Access Channel Message is received within a predetermined time duration- (225; determining whether a predetermined maximum number of transmissions of the Access Channel Message has been executed when the acknowledgment of the Access Channel Message is not received within the predetermined time duration (230), and waiting for a second duration of predetermined time before executing step b) - when the maximum predetermined number of transmissions of the Access Channel Message has not been executed (225) -

3. A wireless communications device (100) for use in a communication system in the wireless communication system includes a base station (102) to transmit an acknowledgment of receipt of a- Message from Access Channel and to transmit an Active Set (315), the wireless communications device (100) characterized by: a searcher receiver (10-9> to measure a pilot intensity of each neighboring pilot (205); a logic circuit and control (1134- to create an Access Channel Message that includes at least one of the measured pilot intensities (210) -; and an analogical forward end (103) to transmit the Access Channel Message (215 -) -; where the measurement of the pilto intensity of each neighboring pilot (20-5) r the creation of the Access Channel Message that includes the at least one of the measured pilot intensities (215) is repeated until the logic circuit and control (113) receives the acknowledgment of receipt of the Message of Channel Access (225-); the analogue front end (103) also receives the Active Set determined according to the at least one of the pilot intensities measured.

4- The device gives wireless commons. (.1QQ-) gives claim 3 characterized in that: the logic-and control circuit 113- also determines-, if within a first predetermined time duration after the transmission. Channel of. Access (225), determines whether a predetermined maximum number of transmissions of the Access Channel Message has been executed when the acknowledgment of the Access Channel Message is not. it is received within the first predetermined time duration (230) and waits for a second predetermined duration of time before creating the Access Channel Message when the predetermined maximum number of transmissions of the Message Channel has Access na ha. s executed (235).

5. A transfer method characterized by the following steps: receiving a first Message from the Access Channel including a first set of measured pilot intensities (305); creating a first Active Set according to the first set of measured pilot intensities (310); -receiving a second Access Channel Message including a second set of pilot intensities mediated (320); create a second Active Set according to the set of measured pilot intensities (325); determine if the first Active Set and is the second Active set are different (330); and transmit the second Active Set when the first Active Set and the second Active Set are different (340) -

6. A base station (102) for use in a wireless communication system, the wireless communication system includes a wireless communication device (100) for repeatedly transmitting an Access Channel Message that includes measured pilot intensities, the station base (102) characterized by: an analog front end (1Q3 >; to receive a first Access Channel Message including a first set of measured pilot intensities (3Q5.J. and to receive a second Access Channel Message including a second set of measured pilot intensities (320) ^ and a logic and control circuit (113) to create a first Active Set gives agreement with the primar, joint, of pilot intensities measured 3-10) - and create a second Active Set according to the second set of pilot intensities measures (.32.5.) and to determine ^ if the first Active Set and the second Active Set are different (330) the previous analogue end (10-3) - transmits the second Active Set when the first and second Set Assets are different. i

7. A transfer method in a wireless communication system characterized by the following steps: measuring a pilot intensity of each neighboring pilot (: 2 &5); create a first Access Channel Message that includes at least one of the pilot-intensities measured t2i0); transmitting the first Access Channel Message (215); receive the first Access Channel Message (305); transmitting an acknowledgment of receipt of the first Access Channel Message (225); create, a first Active Set according to the μar at least one of the measured pilot intensities (310); transmit the first Active Set (-3-15-;) measure again the pilot intensity of the neighboring pilots (2Q5); creating a second Access Channel Message that encloses at least one of the pilot intensities measured again (210); transmitting the second Access Channel Message (-215); receiving the second Access Channel Message (320); create a second Active Set according to the at least one of the pilot intensities measured again (325) -; determine whether the first Active Set and the second Active Set I are different (330); transmitting the second Active Set r-.the first Active Set are different (340).