JP2008219446A - Radio communication system, network controller, and terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that efficiency is deteriorated from aspects of a network transfer load, a terminal processing load and radio resource occupation when terminal mobility is attempted to be guaranteed by a soft hand-off system similar to a conventional case of performing communication only by one radio resource when one terminal simultaneously performs the communication using a plurality of radio resources (for example, a plurality of carriers) in a radio communication system such as a CDMA system. <P>SOLUTION: The termination of soft hand-off is determined on the basis of whether or not a data rate obtained by adding all the resources meets a desired rate on the network side based on receiving state notification information from terminals to the respective radio resources and the soft hand-off is forcibly terminated. A hand-off period is shortened by performing this processing, necessary and sufficient receiving intensity is maintained in the terminals, the mobility of the terminal is guaranteed, and on the other hand, the network transfer load, the terminal processing load and the radio resource occupation time are suppressed to the necessary minimum. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication system that supports terminal mobility, such as a mobile phone and a wireless LAN, in particular, a wireless communication system, a terminal, and a base station wireless communication apparatus adopting MC-CDMA (Multi Carrier Code Division Multiple Access). About.

  Conventionally, wireless communication systems such as mobile phones are able to communicate “anytime, anywhere” and can continue communication without interruption during travel (ie, guaranteeing the mobility of terminals). I have been working hard to support you.

  On the other hand, in recent years, the amount of information exchanged by a single user, such as e-mails with pictures and video files attached, and video data of videophones has increased dramatically, and further enhancement of communication capacity has been demanded.

New wireless communication systems, such as wireless LAN and WiMAX, that have low terminal mobility but enable large-capacity communication similar to cable, are rapidly emerging. For future mobile phone systems,
There is an urgent need to examine a method for achieving a good balance between ensuring the mobility of terminals and increasing capacity.

  As a countermeasure for increasing the capacity, a method of increasing the communication capacity by N times by allowing a terminal to communicate with a base station using only one carrier frequency by simultaneously communicating with a plurality of carriers is considered. . For example, there is a 3GPP2 1xEV-DO system (Non-patent Document 1) as a CDMA communication standard using one carrier, but this has been expanded to N carriers to increase the communication capacity per terminal by N times. In this case, efficiency and stability are problems in the conventional soft handoff method. Hereinafter, these problems will be described in detail.

In order to understand the problem, it is necessary to understand the soft handoff method. First, the case of using one carrier will be described from the terminal mobility guarantee method.
In the conventional 1xEV-DO system, the inter-base station software is used so that the communication is not interrupted even if the terminal moves from the communication area of one base station to the communication area of another adjacent base station during communication. Terminal mobility is guaranteed using a method called handoff.

  Soft handoff refers to a system in which two or more base stations with adjacent communication areas cooperate to send a series of downlink transmission data to one terminal alternately. The reception strength of the pilot signal from each base station at the terminal changes one after another due to fading or terminal movement, but by selecting the base station with the best reception state from multiple candidates and sending the data The terminal can move around the communication area while maintaining a good reception state (without interruption of communication). Details of the soft handoff method will be described below with reference to Non-Patent Document 1 and FIG. In FIG. 4, the sequence when the soft handoff is performed is described in order of time.

Sequence (401)
The terminal and the base station manage, as an ActiveSet, a list of neighboring base stations from which the terminal can receive a downlink (base station → terminal) pilot signal with a certain strength or higher. If there is a base station whose reception strength is equal to or higher than the threshold, the terminal transmits a Route Update message and requests to add the terminal to the list of connection terminals managed by the base station.

Sequence (402)
Upon receiving the request (401), the base station (network) side prepares to distribute downlink transmission data addressed to the terminal to the new base station (that is, starts soft handoff), and sets the radio channel necessary for transmission / reception. After performing resource allocation, ActiveSet is updated, and this is notified to the terminal.

Sequence (403)
The terminal selects the base station with the best reception state among the base stations registered in its own ActiveSet, and designates the ID with a signal of DRCCover or DSC included in the uplink (terminal → base station) control channel.
Sequence (404)
The base station designated by DRCCover or DSC starts downlink data transmission toward the terminal after a certain offset time has elapsed.

Sequence (405)
The terminal monitors the reception strength of the pilot signal for each base station included in the ActiveSet, and if there is a base station that has fallen below the threshold for a certain time or longer, the terminal requests the base station to delete it from the list using a RouteUpdate message.

Sequence (406)
In response to this (405), the base station terminates the soft handoff process, updates the ActiveSet, and notifies the terminal accordingly.

  Next, consider a soft handoff method when expanding to a plurality of carriers in order to increase the capacity. As a first network configuration example, FIG. 1 shows a diagram in the case where one terminal communicates with a base station simultaneously using frequencies for three carriers. Downlink transmission data of carrier frequencies f1 to f3 is transmitted from the PDSN (Packet Data Serving Node) 101 to the base station control node ANC (Access Node Controller) 102, and from the ATTS (Access Node Transmitting System) -A103 to the AT. (Access Terminal) 105. Here, the base station corresponds to ANTS, and the terminal corresponds to AT. An AT (user using) 105 is moving from the call area of ANTS-A 103 to the call area of ANTS-B 104. Since the radio wave has a property of being attenuated depending on the propagation distance, the signal power received from the ANTS-A 103 is gradually weakened. Along with this, the above-mentioned soft handoff process occurs in each carrier, and finally, as shown in FIG. 2, all three carriers transition to a state of communicating with the ANTS-B 104. Soft handoff is performed between the above two states in a transient situation where an AT exists in the communication area of both ANTS.

  The simplest way to transition from the state of FIG. 1 to the state of FIG. 2 is to hand off all carriers at once. However, if all carriers are handed off at the same time, the reception characteristics of the terminal deteriorate, and in the worst case, communication may be interrupted. This is because the propagation path has frequency selectivity when multipath exists. This means that each carrier has a different propagation path. Accordingly, fluctuations in pilot reception strength at the terminal vary from carrier to carrier. (Just because ANTS-B has higher reception strength than ANTS-A at certain frequencies f1 and f2, it does not necessarily mean that ANTS-B is higher at the same timing in other frequencies f3.) In the system, it is assumed that the transmission intensity from the base station is different for each carrier or the frequency repetition pattern in the neighboring base station is different. Therefore, the simultaneous handoff of all carriers may deteriorate the reception characteristics and interrupt communication.

  The question is whether soft handoff processing should be performed independently for each carrier. In the handoff state, radio resources and device resources are consumed by a plurality of radio stations. For example, as shown in FIG. 3, when the carrier is in a handoff state with two base stations with three carriers, the AT 105 requires control processing for a total of six carriers, and the battery duration is shortened due to the large amount of processing. . Also, since a single terminal uses radio channel resources for a total of 6 carriers, if this soft handoff processing time is prolonged, the resource sharing mechanism that should be performed among multiple users will not function effectively, and the entire system will The utilization efficiency of will decrease.

  Next, soft handoff in the second network configuration example will be described with reference to FIG. In this configuration example, an ANC is provided inside each AP, and the APs are connected by CR (Router). Downlink transmission data of carrier frequencies f1 to f3 is transmitted from PDSN (Packet Data Serving Node) 801 via CR-A (Router) 802, and initially transmitted from AP (Access Point) -A803 to AT (Access Terminal) 805. Has been. The AP 803 includes both functions corresponding to the ANC 102 and the ANTS 103 in FIGS. When performing soft handoff in this configuration, the ANC in the AP-A 803 is the main body, and data is transferred to the AP-B 804 via the CR-A 802 and the CR-B 806. In the case of this configuration as well, since the network resources are consumed when the soft handoff state becomes long, it is an important issue to shorten the soft handoff processing time.

  In summary, an object of the present invention is to solve the above-described problems and to provide an efficient terminal mobility guarantee method that has sufficient performance even in MC-CDMA. The present invention is not only MC-CDMA, but a system in which one terminal has a function of communicating with a base station using a plurality of radio resources and has a function of performing soft handoff between a plurality of base stations. The same effect is also exhibited in a wireless communication system using a multiplexing scheme such as OFDMA, OFDM, OFCDMA.

3GPP2 C.I. S0024-A_v2.0 (8.7.6.1.6.3, ActiveSet Maintenance)

  A wireless communication system that communicates with a base station using a plurality of wireless resources at the same time in a single terminal, the network control being connected to the first and second base stations and the first and second base stations And when the terminal moves from the communication area of the first base station toward the communication area of the second base station, the terminal transmits pilot signals from both the first base station and the second base station. And a transmission / reception unit for sequentially selecting a base station with a better reception state and notifying to at least one of the first or second base station on an uplink channel, A transmission / reception unit that distributes downlink data to be transmitted to the terminal to a selected base station, wherein the first and second base stations transmit / receive data transmitted from the network control device to the terminal; Part And the network control device transmits the downlink data only from the second base station to the terminal based on the soft handoff execution status in the plurality of radio resources used by the terminal. A wireless communication system, wherein it is determined whether or not a sufficient data rate is receivable, and if it is determined that reception is possible, the first base station is instructed to end soft handoff.

  According to the present invention, it is possible to shorten the soft handoff processing time when one terminal performs communication using a plurality of carriers at the same time, maintain necessary and sufficient reception strength in the terminal, and guarantee the mobility of the terminal. It is possible to minimize the transfer load, terminal processing load, and radio resource occupation time.

  A first embodiment of the present invention will be described with reference to FIG. In the present embodiment, the first network configuration example shown in FIG. 3 will be described as an example. In the present embodiment, the point is to periodically determine the end of soft handoff and avoid a redundant soft handoff state while maintaining stability. Therefore, soft handoff is terminated based on the following sequence.

Sequence (500)
Assume a soft handoff state at three frequencies (f1, f2, f3). The procedure for that is described. These may simultaneously enter a soft handoff state, or may sequentially enter a soft handoff state according to the propagation state. Details coincide with the sequences (401) to (404) described in FIG.

Sequence (501)
In the soft handoff state between a plurality of carriers, the ANC periodically performs a soft handoff end determination which will be described later.

Sequence (502)
If it is determined that the termination is possible, the soft handoff is forcibly terminated from the network side even if the RouteUpdate message from the terminal has not yet been received.

  The end conditions for soft handoff according to the prior art are closed to each carrier, and the end conditions for soft handoff are not defined in view of a plurality of carriers. However, in the embodiment of this patent, the ANC periodically determines the end of soft handoff, and if it meets a specific condition, forcibly performs soft handoff from the network side regardless of the situation of each carrier. It can be terminated and the soft handoff period can be shortened to improve the operational efficiency of radio resources and reduce the battery consumption of the terminal.

  FIG. 6 shows an example of a flowchart for determining soft handoff completion in the ANC in the embodiment. As a precondition, it is assumed that the ANC has information on a rate desired by each terminal or a determination threshold corresponding to a desired rate assumed in advance.

Step 600
A determination regarding the desired rate is made. If the data flow to be determined is a QoS call, the process proceeds to step 603; otherwise, the process proceeds to step 604.

Step 603
If it is determined that the call is a QoS call, the rate should be guaranteed by QoS.

Step 604
If it is not a QoS call, the rate to be guaranteed as the best effort is set to a predetermined minimum guaranteed rate.

Step 601
The ANC can acquire the DRC Cover or DSC notified from the terminal and the accompanying DRCRate (designation of the maximum transmission rate and communication format that can be received by the terminal). DRCCover or DSC is uplink control information that designates a base station with the best reception state among base stations with which the terminal is registered as ActiveSet. Based on these pieces of information, the ANC estimates a receivable rate for all the carriers for the handoff destination base station (ANTS-B). As the estimation method, for example, there is a method of calculating an average estimated rate by holding DRCRate when DRCCover or DSC designates a handoff destination base station (ANTS-B) for a specific time and averaging the time. It is valid. A feature of this patent is to estimate a value obtained by summing up all carriers from the estimated rate, and various methods can be used as long as they meet the purpose, and are within the scope of this patent.

Step 602
As a result of step 601, when the receivable rate obtained by summing up all carriers exceeds the desired rate, it is determined that sufficient reception quality can be obtained even if transmission from the handoff source (ANTS-A) is stopped, Instructs the handoff source to end soft handoff.

  In ANC, a downlink scheduler operates. The scheduler changes the channel allocation method depending on whether the transmission for the terminal guarantees QoS. Therefore, the ANC knows information related to QoS in advance, and uses this information to determine the soft handoff termination condition.

  In the above, the rate guaranteed in the best effort may be changed according to the wireless status and the priority of the terminal. For example, the guaranteed rate may be changed depending on the device resources of the base station. When there is a margin in device resources, a high user rate can be secured for the terminal by increasing the guaranteed rate, so that the serviceability of the system is improved. Further, the guaranteed rate may be changed based on the interference power information measured by the base station. When the interference power is large, the tightness of radio resources can be predicted. In such a case, the guaranteed rate is lowered and the system is changed so that more terminals can be connected. In addition, if the terminal should be prioritized, the guaranteed rate can be set higher. By doing in this way, serviceability according to a fee system, for example, can be provided.

  FIG. 9 shows a flowchart when the first embodiment is applied to the second network configuration example described above. In the present embodiment, as in the first embodiment, it is important to periodically determine the end of the soft handoff and avoid a redundant soft handoff state while maintaining stability. Therefore, soft handoff is terminated based on the following sequence.

Sequence (900)
Assume a soft handoff state at three frequencies (f1, f2, f3). The procedure for that is described. These may simultaneously enter a soft handoff state, or may sequentially enter a soft handoff state according to the propagation state. Details are equivalent to the sequences (401) to (404) described in FIG. The difference is that the ANC in FIG. 4 is divided into multiple parts, so the PCF / PDSN always sends f1 data to the soft handoff source ANC-A, and the terminal requests data transmission to the soft handoff destination ANC-B. In this case, it is necessary to transfer data from ANC-A to ANC-B.

Sequence (902)
The ANC-A 901 inside the AP-A mainly determines whether the soft handoff can be finished.

Sequence (904)
A hand-off request is notified to ANC-B 903 inside AP-B.

Sequence (906)
When ACK 905 is returned from ANC-B, the end of handoff of the remaining carrier is instructed.

  A third embodiment of the present invention will be described with reference to FIG. In the present embodiment, the soft handoff end determination similar to that in the first embodiment is performed in response to the reception of a RouteUpdate message for soft handoff end from a terminal for one of a plurality of carriers (701). In this case as well, by shortening the soft handoff period, it is possible to improve the operational efficiency of radio resources and reduce the battery consumption of the terminal.

  FIG. 10 shows a flowchart when the third embodiment is applied to the second network configuration example described above. As in FIG. 9, the ANC-A 1001 of the AP-A determines whether or not the soft handoff can be ended (1002), and notifies the ANC-1003 in the AP-B of the handoff request (1004). When ACK 1005 is returned from ANC-B, the end of handoff of the remaining carrier is instructed (1006).

  In the first embodiment, the end of the soft handoff is described in order to avoid the soft handoff using a plurality of carriers. However, even if the soft handoff is ended once, the terminal immediately starts a new one due to the reception strength. A RouteUpdate message is raised, and it is conceivable that the soft handoff state is restored again by a plurality of carriers, and the effect of this patent is expected to be drastically reduced. Therefore, it is necessary to devise the portion indicated by 500 in FIG. The following two methods are the fifth embodiment of this patent.

  The first is suppression of the RouteUpdate message. When the terminal enters the soft handover state, the threshold for transmitting the RouteUpdate message on the new carrier is changed according to the number of carriers to be connected. For example, if the pilot reception power of a new base station exceeds the threshold value 1 in the first carrier when not currently in the soft handoff state, soft handoff on the first carrier is started. Next, when the pilot reception power of the new base station exceeds the threshold value 2 on the second carrier, soft handoff on the second carrier is started. Next, when the pilot reception power of the new base station exceeds the threshold 3 on the third carrier, soft handoff on the third carrier is started. At this time, the threshold relationship is set such that threshold 1 <threshold 2 <threshold 3. Since only a terminal cannot estimate an appropriate value as a threshold, a message instructing the above threshold 1, threshold 2, and threshold 3 is broadcast from the base station. This makes it possible to control the probability of soft handoff in a plurality of carriers at the same time by the threshold operation. Thus, the problem is solved.

  In the present embodiment, it is also a category to change the above threshold value by QoS or best effort. The best effort threshold is set to threshold 1 << threshold 2 << threshold 3 (the difference between the thresholds is large) to guarantee the lowest rate. For QoS calls, threshold 1 <threshold 2 <threshold 3 (each threshold By reducing the difference between the two, the system can easily guarantee QoS.

  The second method is to reject (reject) the RouteUpdate message. In this embodiment, a RouteUpdate message is frequently raised from the terminal, but the handoff destination ANTS rejects it. The ANTS stores the ID of the terminal that has performed soft handoff for a limited time, and rejects the connection to the terminal that requests re-soft handoff within a certain time. Thereby, soft handoff with hysteresis can be realized, and the problem can be solved by, for example, combination with the first embodiment.

  In the fifth embodiment, the same wireless system has been described for ease of description. In recent years, multi-mode terminals for connecting a plurality of wireless systems have been researched and developed. It is clear that the effect of this patent is the same when replacing multiple carriers with multiple wireless systems. For example, even if there are vacant radio resources even between completely different systems such as EVDO and WLAN, an intersystem soft handoff state in which both systems are connected at the same time is possible. Also in this case, a handoff method similar to that described in Examples 1 to 5 (FIGS. 1 to 10) can be performed.

  Furthermore, at this time, if the connection state to a plurality of systems can be controlled by threshold operation at a terminal as in the fifth embodiment, for example, throughput control as the entire system can be easily performed. In the threshold operation, a simple procedure for performing connection control between a plurality of wireless systems can be provided on the same basis of comparison between the pilot power measurement result and the threshold. The threshold broadcast may be performed using a wireless system with a wide service area, or may be broadcast in all wireless systems. The former reduces the overhead, but the terminal connected to a specific system cannot update the threshold. Therefore, the latter is more suitable when the system threshold is dynamically changed according to traffic. As for the number of lines to be connected at the same time, if the resources are available, it is more serviceable to connect multiple lines. The soft handoff status between multiple systems can be controlled by adaptively changing the threshold value according to the availability of resources (frequency and hardware resources) of each wireless system. As a result, it is possible to provide a system with high convenience and high frequency utilization efficiency by controlling the trade-off between convenience and frequency effective utilization efficiency that changes under various conditions.

  In the fifth embodiment, thresholds are not distinguished between carriers. However, in the case of inter-system soft handoff, a terminal is connected by setting a soft handoff threshold to a specific system low. Easy systems can be purposely created and priorities can be set between systems. For example, when there is a cellular system that covers a wide area and a wireless system that covers a relatively narrow area such as WiMAX, the threshold for determining the soft handoff start to the cellular system is set high, and the soft handoff start to the WiMAX system is determined. By lowering the threshold value, handoff to WiMAX can be easily generated. As a result, cellular resources are less likely to be deprived and connections to systems such as WiMAX can be easily maintained.

  Further, the above only defines a threshold value for changing from a single system to a multi-system, but a threshold value for updating from a multi-system to a single system may be defined. This makes it easier to control the priority between the above systems. For example, in the above-mentioned cellular and WiMAX talk, when a multi-system is established, the threshold for separating the cellular side is set higher and the threshold for separating the WiMAX side is set lower, so that the cellular side is separated earlier. Thus, valuable cellular frequency resources can be used effectively. The threshold value defined here can also be statistically processed between the systems in accordance with the situation at that time by changing the threshold timely by broadcast from the base station side.

  This concept can also be applied to a single wireless system having multiple bands. For example, if there is a wireless system that provides services in the 800 MHz band and the 2 GHz band, a multiband connection that gives priority to a specific band (for example, 2 GHz) is possible from the handoff threshold operation. In general, the higher the frequency of radio waves, the longer the propagation distance and the smaller the cell radius. Therefore, it is considered that there are many cases where handoff from a 2 GHz system to an 800 MHz system occurs when both threshold values are the same. However, due to the effect of this patent, a connection giving priority to 2 GHz becomes possible. As a result, for example, when traffic in the 2 GHz band increases instantaneously, switching from 2 GHz to 800 MHz by lowering the threshold of 2 GHz band ⇒ 800 MHz band and increasing the threshold of 800 MHz band ⇒ 2 GHz band by operating the threshold value Can be distributed so that resource allocation is even. Therefore, the utilization efficiency as the whole system can be raised.

The figure which shows the structure of the communication at the time of performing soft handoff, performing simultaneous communication by 3 carriers in a 1st network configuration example. The figure which shows the structure in the case of handoffing all the carriers simultaneously at the time of performing soft handoff while simultaneously communicating with 3 carriers in a 1st network structural example. The figure which shows the mechanism of the communication at the time of carrying out a soft handoff compulsorily from the network side according to this invention, when performing a soft handoff while simultaneously communicating with 3 carriers in a 1st network structural example. Soft handoff flow diagram in a conventional one-carrier system. The flowchart which shows the process order of 1st Example by this invention in a 1st network structural example. The flowchart which shows the processing order of the soft handoff completion determination in the method of 1st Example by this invention. The flowchart which shows the process order of the 3rd Example by this invention in a 1st network structure example. The figure which shows the structure of the communication at the time of performing soft handoff while performing simultaneous communication by 3 carriers in the second network configuration example. The flowchart which shows the process order of the 2nd Example by this invention in a 2nd network structure example. The flowchart which shows the process order of the 4th Example by this invention in a 2nd network structure example.

Explanation of symbols

101 ... PDSN (Packet Data Serving Node)
102 ... ANC (Access Node Controller)
103 ... ANTS (Access Node Transmitting System) -A
104 ... ANTS (Access Node Transmitting System) -B
105 ... AT (Access Terminal).

Claims (6)

A wireless communication system that communicates with a base station using a plurality of wireless resources simultaneously in one terminal,
A network controller connected to the first and second base stations and the first and second base stations,
When the terminal moves from the communication area of the first base station toward the communication area of the second base station, the terminal receives pilot signals from both the first base station and the second base station, A transmission / reception unit that sequentially selects a base station having a better reception state and notifies it to at least one of the first and second base stations via an uplink channel; A transmitter / receiver for distributing downlink data to be transmitted to the terminal to the station, and the first and second base stations have a transmitter / receiver for transmitting data received from the network control device to the terminal. ,
Even if the network control apparatus transmits the downlink data to the terminal only from the second base station based on the soft handoff implementation status in the plurality of radio resources used by the terminal, the network control apparatus has sufficient data A wireless communication system, characterized by determining whether or not a rate is receivable, and instructing the first base station to end soft handoff when it is determined that reception is possible. The wireless communication system according to claim 1,
Even when the network control apparatus transmits the downlink data only from the second base station to the terminal, it is notified on the uplink channel when determining whether or not the terminal can receive a sufficient data rate. The first information about the selected base station and the second information about the maximum transmission rate and transmission format that can be received from the selected base station are referenced for each radio resource, and reception is possible for all resources used by the terminal. The total maximum transmission rate is compared with the transmission rate desired by the terminal, and if the maximum receivable transmission rate exceeds the transmission rate desired by the terminal, soft handoff to the first base station is performed. A wireless communication system characterized by instructing termination. The wireless communication system according to claim 2,
The transmission rate desired by the terminal is the minimum transmission rate guaranteed by the QoS communication when the terminal is performing communication requesting a certain quality of service (QoS), and the terminal performs the best effort communication. A wireless communication system characterized by a minimum transmission rate guaranteed by the best effort communication. The wireless communication system according to claim 1,
Independent of the network control apparatus, the terminal determines whether or not to terminate soft handoff for each radio resource based on the reception status of pilot signals from each base station and the selection frequency, and should terminate the soft handoff. A soft handoff termination request for the radio resource determined to be transmitted to at least one of the first or second base station via an uplink channel, and the network control apparatus sends one of the radio resources from the terminal. Even if the downlink data is transmitted to the terminal only from the second base station upon receiving a soft handoff termination request, the terminal determines whether or not a sufficient data rate can be received. A wireless communication system. A terminal that communicates with a base station using a plurality of radio resources at the same time, and a network controller connected to the first and second base stations,
When the terminal moves from the communication area of the first base station toward the communication area of the second base station, the terminal that has the better reception state among the first base station and the second base station A base station that receives base station selection information to be sequentially selected and notified on an uplink channel, and has a transmission / reception unit that distributes downlink data to be transmitted to the terminal to the selected base station,
Whether or not a sufficient data rate can be received by the terminal even if the downlink data is transmitted to the terminal only from the second base station based on the soft handoff execution status in the plurality of radio resources used by the terminal A network control device that instructs the first base station to end a soft handoff when it is determined that reception is possible. A terminal connected to the first and second base stations and capable of communicating with the first and second base stations using a plurality of radio resources at the same time;
When the terminal moves from the communication area of the first base station toward the communication area of the second base station, the terminal that has the better reception state among the first base station and the second base station Select the station sequentially and notify to the uplink channel,
In addition, for each radio resource, it is determined whether or not soft handoff should be terminated based on the reception status of pilot signals from each base station and the selection frequency, and soft handoff is terminated for the radio resource that is determined to be terminated. A terminal that notifies a request to at least one of the first and second base stations through an uplink channel.