JP2011182458A - Radio access network device, mobile station and handover control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio access network device, a mobile station and a handover control method which reduce processing in the mobile station at the execution of handover, and reduce mobile station resources for use to execute the handover. <P>SOLUTION: The wireless access network device includes: a receiver for acquiring, from the mobile station, radio quality data indicative of radio quality in a communication link between the mobile station and a base station; a command generator for generating a measurement command to start measuring communication states in peripheral cells of the mobile station when the radio quality data satisfies a predetermined condition; and a transmitter for transmitting the measurement command to the mobile station. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radio access network apparatus, a mobile station, and a handover control method.

  In the conventional mobile communication system, the mobile station UE measures the communication status of links from neighboring cells, and based on the result, a radio access network (hereinafter referred to as RAN) is connected to the mobile station UE. Instructing switching of the cell connection, and the mobile station UE switches the cell connection based on the instruction from the RAN, thereby performing the handover.

  Specifically, using the compressed mode shown in FIG. 9, the mobile station UE periodically transmits the communication status (propagation loss of the link between the mobile station UE and the peripheral cell as the communication status in the peripheral cell. Measure measured value, received power, signal-to-interference power ratio, etc.). Compressed mode is one of the methods used to measure the communication status in neighboring cells to perform handover.

  The compressed mode will be further described with reference to FIG. FIG. 9 (b) is an enlarged view of a part of FIG. 9 (a).

  The mobile station UE measures the communication status in neighboring cells when performing handover. Usually, since the mobile station UE includes only one communication device, the communication status in the neighboring cells cannot be measured during data communication. Therefore, by stopping the transmission of the frame for a predetermined period on the link between the mobile station UE and the base station (stopping the transmission from the base station) and providing a transmission gap, the mobile station UE The communication status of the link between the base station to be managed and the mobile station UE is measured.

  For example, in 3GPP, the communication status of the common pilot channel transmitted from the base station is measured as the communication status in the neighboring cells.

  The mobile station UE transmits the measurement results of the communication status in its own cell and neighboring cells to the RAN via the radio interface periodically or when a certain condition (for example, the measured value exceeds a threshold value) is satisfied. It was.

  From these measurement results, the RAN determines the necessity for switching the connection of the cell to which the mobile station UE is currently connected, and transmits a command for causing the mobile station UE to switch the cell connection at an appropriate timing. . With this command, the mobile station UE switches the cell connection, so that a handover is performed in the conventional mobile communication system (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

3GPP TSG-RAN TS25.212 v6.6.0 "W-CDMA mobile communication system" supervised by Keiji Tachikawa, p. 140

  However, in the conventional mobile communication system, it is necessary for the mobile station UE to frequently measure the communication status with the own cell and the neighboring cells in order to carry out the handover. Had spent resources.

  For example, in the compressed mode shown in FIG. 9, the data for the time transmitted during the transmission gap needs to be transferred at high speed during the time when transmission is possible.

  For this reason, in the conventional mobile communication system, the spreading rate is lowered before and after the transmission gap, and the power is increased to secure the transfer rate and the line quality, thereby enabling high-speed data transfer.

  As described above, the conventional mobile communication system has a problem in that the mobile station UE consumes a large amount of power in order to perform handover, and thus the battery of the mobile station UE is quickly consumed.

  In addition, in order to implement handover, the mobile station UE needs to measure the communication status with neighboring cells and transmit the measurement result to the base station, and the base station can connect the cells based on the measurement result. There is a problem that a lot of processing is required, such as sending a command for switching between.

  Therefore, the present invention has been made in view of the above-described problems. When performing a handover, the present invention reduces the processing of the mobile station and reduces the resources of the mobile station used for performing the handover. An object is to provide a network device, a mobile station, and a handover control method.

  According to a first aspect of the present invention, a radio access network device receives radio quality data indicating radio quality in a communication link between a mobile station and a base station from a mobile station, and the radio quality data includes A command generation unit that generates a measurement command for starting measurement of a communication state in a neighboring cell of the mobile station when a predetermined condition is satisfied, and a transmission unit that transmits the measurement command to the mobile station. The gist.

  A second feature of the present invention is that a radio access network acquires radio quality data indicating radio quality in a communication link between a mobile station and a base station from a mobile station, and the radio quality data includes: If a predetermined condition is satisfied, a command generation unit that generates a switching command for handing over the mobile station from a first cell to which the mobile station is currently connected to a second cell different from the first cell; A gist is provided with a transmission unit that transmits the switching command to the mobile station.

  A third feature of the present invention is that a wireless quality measuring unit that measures wireless quality in a communication link with a base station and obtains wireless quality data indicating the wireless quality, and a communication status in a neighboring cell from the wireless access network device A reception unit that acquires a measurement command for starting measurement of the radio frequency, a measurement unit that measures a communication status in a neighboring cell after acquiring the measurement command, and the radio access to the wireless quality data and the measurement result of the communication status The gist of the present invention is to include a transmission unit that transmits to a network device.

  A fourth feature of the present invention is a handover control method in which a mobile station acquires radio quality data indicating radio quality in a communication link between the mobile station and a base station, and a radio access network apparatus However, when the wireless quality data satisfies a predetermined condition and the wireless quality data satisfies a predetermined condition, the wireless access network device communicates with the mobile station in a neighboring cell of the mobile station. Generating a measurement command for starting the measurement, a step in which the radio access network apparatus transmits the measurement command to the mobile station, and a measurement of a communication status in a peripheral cell of the mobile station. Including the step of performing.

  As described above, according to the present invention, when performing a handover, the radio access network apparatus, the mobile station, and the mobile station reduce the processing of the mobile station and reduce the resources of the mobile station used for performing the handover. A handover control method can be provided.

1 is an overall configuration diagram of a mobile communication system according to a first embodiment of the present invention. It is a functional block diagram in the base station of the mobile communication system which concerns on the 1st Embodiment of this invention. It is a functional block diagram in the mobile station of the mobile communication system which concerns on the 1st Embodiment of this invention. It is a functional block diagram of the base station of the mobile communication system which concerns on the 2nd Embodiment of this invention. It is a functional block diagram of the base station of the mobile communication system which concerns on the modification of this invention. It is a functional block diagram of the mobile station of the mobile communication system which concerns on the modification of this invention. FIG. 5 is a sequence pattern diagram showing an operation of a handover control method in the mobile communication system according to the embodiment of the present invention. It is a sequence pattern figure which shows operation | movement of the handover control method in the mobile communication system which concerns on the modification of this invention. It is a figure of the compressed mode for demonstrating conventional invention.

(Mobile communication system according to the first embodiment of the present invention)
A radio access network apparatus according to the first embodiment of the present invention will be described with reference to FIGS.

  In the example of FIG. 1, a mobile station UE that has a link formed with a cell managed by the radio base station NodeB # 1 is a cell managed by the radio base station NodeB # 1 in which the mobile station UE is located. The radio quality of the cell managed by the radio base station NodeB # 2 is measured, and CQI (Channel Quality Indicator) indicating the radio quality is transmitted from the mobile station UE to the radio base station NodeB # 1.

  In the example of FIG. 1, the mobile station UE is connected to the cell of the radio base station NodeB # 1 via a link. However, the radio base station NodeB # 1 acquires the CQI from the mobile station UE, and when the CQI satisfies a predetermined condition, the mobile base station UE, the radio base station NodeB # 1, and the radio base station NodeB # 2 Measurement of the communication status of a plurality of links connecting the two is started. Receiving the measurement result of the radio quality from the mobile station UE, the radio base station NodeB # 1 selects an optimal cell to be connected to the mobile station UE and instructs the mobile station UE to switch the cell connection. The mobile station UE instructed to switch the connection by the radio base station NodeB # 1 switches the connection from the currently connected cell to a different cell. Thereby, it is comprised so that a handover may be implemented.

  The radio network controller RNC according to the present embodiment is an apparatus positioned above the radio base station NodeB, and is configured to control radio communication between the radio base station NodeB and the mobile station UE. In the present embodiment, the radio network controller RNC and the radio base station NodeB are combined to form a radio access network device.

  The function of the radio access network apparatus that acquires the CQI from the mobile station UE and instructs the mobile station UE to measure the communication status will be further described with reference to FIG. 2 illustrates the radio base station NodeB # 1, but in the access network apparatus according to the present invention, some functions may be provided in the radio network controller RNC, and other radio base stations NodeB may be provided. Has the same function.

  As illustrated in FIG. 2, the radio base station NodeB # 1 includes a reception unit 211, a demultiplexing unit 221, a CQI processing unit 231, a comparison unit 241, a history information unit 251, a command generation unit 261a, and a multiplexing unit. A combining unit 271 and a transmitting unit 281 are provided.

  However, these configurations do not necessarily have to exist independently as hardware. That is, the components may be combined or may be configured by a software process.

  The receiving unit 211 is configured to receive a link signal from the mobile station UE via a link from the mobile station UE.

  The demultiplexing unit 221 is configured to acquire user data included in the link signal from the receiving unit 211. Further, the demultiplexing unit 221 is configured to acquire the CQI included in the link signal from the receiving unit 211 and transfer it to the CQI processing unit 231.

  The demultiplexing unit 221 is configured to acquire the CQI from the receiving unit 211 and transfer the CQI to the radio network controller RNC via the transmitting unit 281 and the transmission / reception antenna 291.

  The CQI processing unit 231 calculates an average CQI that is an average value of CQI that is instantaneous data, and transfers the average CQI to the comparison unit 241. Thereby, the comparison unit 241 can compare with the history information of the history information unit 251 without being influenced by the instantaneous change amount of the wireless quality data. Here, the average CQI does not necessarily need to be an average value of CQI, and may be any if it is possible to smooth a change in instantaneous radio quality data.

  Here, CQI defines feedback information as a whole, and is used to follow high-speed propagation fluctuation (for example, high-speed fading) during communication. Specifically, the CQI includes a signal interference power ratio (hereinafter referred to as SIR) instantaneously measured by the mobile station UE, instantaneous received power, instantaneous propagation loss, and the like.

  For example, in WCDMA (Wideband Code Division Multiple Access), the mobile station UE is configured to measure a binary SIR and transmit the binary SIR to the radio base station NodeB # 1 that manages its own cell. .

  Similarly, in HSDPA (High-speed Downlink Packet Access), the mobile station UE is configured to measure instantaneous SIR and transmit the quantized CQI to the radio base station NodeB. Here, it is defined that when the CQI is large, the communication state between the mobile station UE and the cell of the radio base station NodeB # 1 is good, and when the CQI is small, the communication state is bad.

  The comparison unit 241 is configured to compare the average CQI acquired from the CQI processing unit 231 with the average CQI threshold acquired from the reference value database 251.

  When the average CQI is smaller than the threshold value, the comparison unit 241 starts measuring the communication status in the link between the mobile station UE and a plurality of cells where the mobile station UE is located and the mobile station UE. The measurement command generation instruction to be transferred is transferred to the command generation unit 261a.

  On the other hand, when the average CQI is larger than the threshold, the comparison unit 241 uses a measurement stop command to stop the measurement of the communication status in the link between the plurality of cells where the mobile station UE is located and the mobile station UE. The generation instruction is transferred to the command generation unit 261a.

  The reference value database 251 includes an average CQI threshold value. The threshold value of the average CQI may be a predetermined value or a reference value calculated from the past average CQI. Further, the threshold value of the average CQI may be a different value at the start and end of measurement of the communication status.

  Based on the measurement command generation command acquired from the comparison unit 241, the command generation unit 261 a communicates with the mobile station UE in the communication status in the link between the plurality of cells in which the mobile station UE is located and the mobile station UE A measurement command for starting the measurement is generated, and the measurement command is transferred to the multiplexing / combining unit 271.

  In addition, the command generation unit 261a, based on the measurement stop command generation command acquired from the comparison unit 241, is a link between the mobile station UE and a plurality of cells in which the mobile station UE is located and the mobile station UE. Is configured to generate a measurement stop command for stopping the measurement of the communication status in FIG.

  The multiplexing unit 271 receives the control command of either the measurement command or the measurement stop command acquired from the command generation unit and the transmission data, performs multiplexing processing, and performs processing to convert the signal into a radio frequency band signal. It is configured to forward to H.281.

  The transmission unit 281 is configured to amplify the signals acquired from the multiplexing / combining unit 271 and the demultiplexing unit 221 and transmit the signals to the mobile station UE and the radio network controller RNC via the transmission / reception antenna 291.

  FIG. 3 shows a schematic configuration example of the mobile station UE according to the present embodiment. As shown in FIG. 3, the mobile station UE includes a receiving unit 10, a demultiplexing unit 11, a command processing unit 12, a CQI measuring unit 13, a handover measuring unit 14, a handover signal generating unit 15, A synthesizer 16 and a transmitter 17 are provided.

  However, these configurations do not necessarily have to exist independently as hardware. That is, the components may be combined or may be configured by a software process.

  The receiving unit 10 is configured to receive CQI and physical data from the radio access network via the downlink.

  The demultiplexing unit 11 is configured to acquire user data included in physical data from the receiving unit 10. Further, the demultiplexing unit 11 is configured to acquire a measurement command from the receiving unit 10 and transfer it to the command processing unit 12.

  The demultiplexing unit 11 is configured to acquire the CQI from the receiving unit 10 and transfer it to the CQI measuring unit and the handover measuring unit.

  When the control command acquired from the demultiplexing unit 11 is a measurement command, the command processing unit 12 starts measuring the communication status of links that respectively connect a plurality of cells in which the mobile station UE is located and the mobile station UE. The measurement command is configured to be transferred to the handover measurement unit.

  When the control command acquired from the demultiplexing unit 11 is a measurement stop command, the command processing unit 12 stops measuring the communication status of the links that respectively connect the plurality of cells in which the mobile station UE is located and the mobile station UE. The measurement stop command is transferred to the handover measurement unit.

  The CQI measurement unit 13 receives radio waves from the reception unit 10 and instantaneously measures a signal interference power ratio (hereinafter referred to as SIR), reception power, propagation loss, etc., which are radio quality in a communication link with the base station. The CQI measurement result is transferred to the multiplexing / combining unit 16.

  The handover measuring unit 14 receives radio waves from the receiving unit 10 and, when the control command received from the command processing unit 12 is a measurement command, each of the plurality of cells in which the mobile station UE is located and the mobile station UE The communication status of the link to be connected is measured, and the handover measurement result is transferred to the handover signal generation unit 15.

  The handover measuring unit 14 receives the control data from the receiving unit 10, and when the control command received from the command processing unit 12 is a measurement stop command, the handover measuring unit 14 determines a plurality of cells in which the mobile station UE is located and the mobile station UE. It is configured to stop measuring the communication status of each link.

  The handover signal generation unit 15 is configured to receive a handover measurement result from the handover measurement unit 14 and to transfer a handover measurement result or a handover command for instructing the radio access network to perform handover to the multiplexing / combining unit 16.

  The multiplexing unit 16 receives the CQI measurement result from the CQI measurement unit, the handover measurement result or the handover command, and transmission data such as user data and control data from the handover signal generation unit, multiplexes and combines them, and transmits the radio frequency band The signal is converted into a signal and transferred to the transmission unit 17.

  The transmission unit 17 is configured to amplify the signal acquired from the multiplexing / combining unit 16 and transmit the amplified signal to the radio access network apparatus via the transmission / reception antenna 18.

(Operations and effects of the mobile communication system according to the first embodiment of the present invention)
The radio access network apparatus according to the first embodiment of the present invention includes a receiving unit 211 that acquires radio quality data from the mobile station UE, and the mobile station UE and the radio base station when the radio quality data satisfies a predetermined condition. A command generation unit 261 that generates a measurement command for starting measurement of a communication state of a link connecting Node B, and a transmission unit 281 that transmits the measurement command to the mobile station UE are provided. According to this, the mobile station UE does not need to frequently measure the communication status with its own cell and neighboring cells, and only when the wireless quality data satisfies a predetermined condition, it communicates with its own cell and neighboring cells. It only has to measure the situation. Further, it is possible to reduce the processing for implementing the handover.

  That is, when the handover is performed, the processing of the mobile station UE can be reduced, and the resources of the mobile station UE used for performing the handover can be reduced.

A radio access network can be provided.

  In addition, the mobile station UE according to the first embodiment of the present invention includes a CQI measurement unit 13 that measures radio quality and obtains radio quality data, a reception unit 10 that obtains a measurement command from a radio access network device, and a radio A handover measuring unit 14 that measures the communication status of the link to the base station NodeB, and a transmitting unit 17 that transmits the radio quality data and the measurement result of the communication status to the radio access network device. According to this, by measuring the radio quality from the own cell and transmitting the measurement result to the radio access network, the radio access network does not need to use the measurement result of the communication status in the neighboring cells from the mobile station UE. The communication status in the own cell can be grasped.

  That is, when the handover is performed, the processing of the mobile station UE can be reduced, and the resources of the mobile station UE used for performing the handover can be reduced.

(Mobile communication system according to the second embodiment of the present invention)
A radio access network apparatus according to the second embodiment of the present invention will be described with reference to FIG.

  In the example of FIG. 4, the processes of the demultiplexing unit 222, the CQI processing unit 232, and the comparison unit 242 included in the radio base station NodeB # 1 are mainly different from the radio access network apparatus according to the first embodiment.

  Specifically, the demultiplexer 222 is configured to acquire the CQI from the receiver 212 and transfer it to the transmitter 282.

  The transmission unit 282 is configured to acquire the CQI from the demultiplexing unit 222, calculate transmission power and transmission rate based on the CQI, and transfer them to the radio network controller RNC and the mobile station UE via the transmission / reception antenna 292. Yes.

  The transmission unit 282 is configured to transfer the transmission power and transmission rate information described above to the CQI processing unit 232.

  The CQI processing unit 232 acquires transmission power and transmission rate information from the transmission unit 282, calculates an average value I of transmission power and transmission rate, and transfers the average value I to the comparison unit 242. Here, the average value I does not necessarily need to be an average value of transmission power and transmission rate information, and may be any as long as changes in transmission power and transmission rate information can be smoothed.

  The comparison unit 242 is configured to compare the average value I acquired from the CQI processing unit 232 and the threshold value of the average value I acquired from the reference value database 252.

  As described above, even when the transmission power and the transmission rate are used as the CQI, the mobile station UE does not need to frequently measure the communication status with the own cell and the neighboring cells, and the radio quality data satisfies a predetermined condition. Only in this case, it is only necessary to measure the communication status between the own cell and the neighboring cells. Further, it is possible to reduce the processing for implementing the handover.

  That is, when the handover is performed, the processing of the mobile station UE can be reduced, and the resources of the mobile station UE used for performing the handover can be reduced.

A radio access network can be provided.

(Mobile communication system according to a modification of the embodiment of the present invention)
A radio access network apparatus according to a modification of the embodiment of the present invention will be described with reference to FIGS.

  The example of FIG. 5 is significantly different from the radio access network apparatus according to the embodiment in that the radio access network apparatus can further include a history information unit 263b.

  Specifically, the command generation unit 263a is based on the measurement command generation instruction acquired from the comparison unit 243, and the mobile station UE is the own cell among the plurality of cells in which the mobile station UE is located. A switching command for switching the connection to a different cell is generated, and the switching command is transferred to the multiplexing / combining unit 271.

  The command generation unit 263a is configured to receive history information from the history information unit 263b. Based on the history information, the command generation unit 263a generates a switching command for switching the connection to a cell different from the own cell among the plurality of cells in which the mobile station UE is located, based on the history information. The command is configured to be transferred to the multiple synthesizer 273.

  Specifically, the history information unit 263b describes handover history information of the mobile station UE. The handover history information indicates through which cell the mobile station UE has performed handover.

  Thereby, the command generation part 263a can designate the cell which switches a connection by applying to the mobile station UE with the same handover history.

  Further, history information indicating the CQI ratio of the cell after switching to the cell before switching of the mobile station UE is described in the history information unit 263b.

  Thereby, the command generation unit 261a can designate which cell is designated from the viewpoint of the CQI ratio.

  The multiplexing / combining unit 273 is configured to multiplex-synthesize the switching command acquired from the command generating unit and the transmission data, perform a process for converting the signal into a radio frequency band signal, and transfer the signal to the transmitting unit 283.

  FIG. 6 shows a schematic configuration example of a mobile station UE according to a modification of the present embodiment. As illustrated in FIG. 6, the mobile station UE includes a handover processing unit 37 without including a handover measurement unit and a handover signal generation unit.

  According to the radio access network device according to the modification of the present embodiment, the demultiplexing unit 31 acquires the switching command via the receiving unit 30 and transfers the switching command to the handover processing unit 37.

  The handover processing unit 37 can perform a handover by receiving a switching command from the demultiplexing unit 31.

  According to such a mobile station UE, it is not necessary to measure the communication status between the own cell and the neighboring cells.

  That is, when the handover is performed, the processing of the mobile station UE can be reduced, and the resources of the mobile station UE used for performing the handover can be reduced.

(Handover control method according to the first embodiment of the present invention)
Hereinafter, the handover control method according to the present embodiment will be described with reference to FIG. Specifically, a case where the mobile station UE performs handover by the handover control method according to the present embodiment will be described.

  The handover control method according to the embodiment of the present invention may be changed depending on conditions as well as the above-described case.

  As shown in FIG. 7, in step S1001, radio quality data indicating radio quality in a communication link between the mobile station UE and the radio base station NodeB is acquired.

  In step S1002, the mobile station UE transmits radio quality data to the radio base station NodeB.

  In step S1003, when the radio quality data satisfies a predetermined condition, the radio base station NodeB generates a measurement command that causes the mobile station UE to start measuring the communication status in the neighboring cells of the mobile station UE.

  In step S1004, the radio access network apparatus transmits a measurement start command to the mobile station UE.

  In step S1005, the mobile station UE measures the communication status in the neighboring cells of the mobile station UE and obtains a measurement result.

  In step S1006, the mobile station UE transmits the measurement result of the communication status in the neighboring cell to the radio base station NodeB.

  In step S1007, the radio access network apparatus determines a measurement result and generates a handover command for causing the mobile station UE to perform a handover.

  In step S1008, the radio access network apparatus transmits a handover command to the mobile station UE.

  In step S1009, the mobile station UE performs handover by using a handover command.

(Operations and effects of the handover control method according to the first embodiment of the present invention)
As described above, according to the handover control method according to the present invention, the mobile station UE does not need to frequently measure the communication status with the own cell and neighboring cells, and the radio quality data satisfies a predetermined condition. Only in this case, it is only necessary to measure the communication status between the own cell and the neighboring cells. Further, it is possible to reduce the processing for implementing the handover.

  That is, it is possible to provide a handover control method capable of reducing the processing of the mobile station UE and reducing the resources of the mobile station UE used for performing the handover when performing the handover.

211 ... receiving unit 221 ... demultiplexing unit 231 ... CQI processing unit 241 ... comparing unit 251 ... reference value database 261 ... command generating unit 271 ... multiple combining unit 281 ... transmitting unit 291 ... transmitting / receiving antenna

Claims (5)

A receiver that acquires radio quality data indicating radio quality in a communication link between the mobile station and the base station from the mobile station;
When the wireless quality data satisfies a predetermined condition, a command generation unit that generates a measurement command for starting measurement of a communication state in a neighboring cell of the mobile station;
A radio access network apparatus comprising: a transmission unit that transmits the measurement command to the mobile station. A receiver that acquires radio quality data indicating radio quality in a communication link between the mobile station and the base station from the mobile station;
When the wireless quality data satisfies a predetermined condition, the mobile station generates a switching command for handing over the mobile station from the first cell to which the mobile station is currently connected to a second cell different from the first cell. A command generator to
A radio access network apparatus comprising: a transmission unit that transmits the switching command to the mobile station. The mobile station handover history is provided in the history information section,
The radio access network apparatus according to claim 2, wherein the switching command generation unit specifies the second cell based on the handover history. A radio quality measurement unit that measures radio quality in a communication link with a base station and obtains radio quality data indicating the radio quality;
A receiving unit for acquiring a measurement command for starting measurement of communication status in a neighboring cell from a radio access network device;
After obtaining the measurement command, a measurement unit that measures the communication status in the neighboring cells;
A mobile station, comprising: a transmission unit that transmits the wireless quality data and the measurement result of the communication status to the wireless access network device. A mobile station obtaining radio quality data indicating radio quality in a communication link between the mobile station and a base station;
A radio access network device acquiring radio quality data from the mobile station;
When the radio quality data satisfies a predetermined condition, the radio access network device generates a measurement command for causing the mobile station to start measurement of a communication status in a neighboring cell of the mobile station; and
The radio access network device transmitting the measurement command to the mobile station;
A handover control method, comprising: a step of measuring a communication state in a neighboring cell of the mobile station.