JP2000069522A - Handoff method, base station and communication system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A handoff method for restricting transmission data input to a handoff source base station in synchronization with a handoff, thereby reducing the transfer amount of data waiting to be transmitted to a handoff destination base station. Get. SOLUTION: A step 41 for detecting out-of-synchronism between the base station and the mobile station, a step 44 in which the base station detecting the out-of-synchronization instructs the mobile station to execute a handoff, and the base station restricts input of transmission data. And transmitting the data to be transmitted to the handoff destination base station.
It consists of. Since the base station can know the timing of the handoff, the input of transmission data can be restricted in synchronization with the handoff.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a handoff method in which a mobile station performs a handoff in communication with a base station, the base station, and a communication system. The present invention relates to a handoff method, a base station, and a communication system in which the base station regulates input to the base station.

[0002]

2. Description of the Related Art The following problems have been encountered when the mobile communication that is now widely used is developed and Mobile ATM communication is to be realized in a mobile communication environment and in a geographically continuous, so-called cellular environment. is there. (1) Transmission power: The transmission power of the portable terminal cannot be increased without limit in consideration of the influence on the human body. On the other hand, higher transmission power is required to realize high-speed wireless transmission such as Mobile ATM. After all, when performing wideband transmission with limited transmission power, the zone radius must be reduced. Hereinafter, a qualitative explanation will be given. The transmission power of the mobile terminal is expressed by the following equation as described on page 225 of the basics of mobile communication: edited by the Institute of Electronics, Information and Communication Engineers.

Pt = (ｔmkTBiNfLp) / (GtGr) Γm = long section CNR kTBiNf = noise power of receiver Lp = path loss Gt, Gr = transmission, reception antenna gain

That is, since there is a proportional relationship between the transmission band Bi and the transmission power Pt, if the transmission band Bi is increased without changing the transmission power Pt and the long section CNR, the propagation loss Lp is reduced. Operation within the line of sight is required in order to do so. In other words, operation with a small cell radius is indispensable. In addition, it is indispensable to apply a directional antenna or the like that can expect a high antenna gain. Therefore, in such a high-speed communication system, line-of-sight communication is basically secured, and a wireless line with a low error rate is secured.

On the other hand, when an omnidirectional antenna is used, it may be possible to receive a reflected wave or the like even if the line of sight is blocked, but if a directional antenna is used, the aperture area of the antenna is reduced. If the line of sight is so small that the line of sight is obstructed, the reception level drops significantly and the line quality deteriorates. Therefore, it is considered that the dominant error mainly occurs when the transmission path is interrupted by a person or a moving object. Moreover, it is considered that the error generated in this case is not a random error but a burst-like error. In such a case, the mobile station performs a handoff by switching a communication channel with the base station.

[0006] On the other hand, in the cellular communication system, even when the zone in which the terminal device is located is switched during communication, handoff is performed by switching the communication base station to continue the communication. As the zone radius decreases, the frequency of this handoff increases rapidly.
Particularly in high-speed communication, there are the following problems at the time of handoff. That is, if handoff is performed during communication, instantaneous interruption is unavoidable, resulting in loss of data and deterioration of transmission quality.

[0007] For example, consider the case where ATM cells are transmitted over a high-speed wireless transmission path where the service rate per user exceeds 30 Mbps. If an instantaneous interruption of about one second occurs, an ATM cell loss of about 70,000 or more occurs, which seriously degrades the line quality to the end user. For this reason, it is important to reduce the handoff frequency itself, but at the same time, it is important how to reduce the handoff time from suspending and resuming data communication and how to prevent line quality deterioration.

Various methods have been proposed for shortening the handoff time in order to prevent data loss due to handoff. FIG. 14 is a diagram illustrating a first conventional technique of a handoff method. In FIG. 14, 1a and 2a are base stations,
3 is a mobile station, 4a is a base station controller, 1b, 2b
Is a zone. The operation will be described. For example, FIG.
Consider a case where the mobile station 3 performs handoff from the base station 1a to the base station 2a as shown in FIG.

If the frame timings of the base station 1a and the base station 2a are not synchronized and there is an offset, the mobile station 3 needs to re-synchronize at the time of handoff. Therefore, the time until the synchronization is established depends on the line state and is a statistical amount, so that it is difficult to switch channels without instantaneous interruption. Therefore, a method of measuring the offset value in advance before the handoff and giving the offset value at the switching destination base station 2 at the time of the handoff to eliminate the time required for the resynchronization and establish the handoff at a high speed has been studied.
However, even with this method, the handoff time cannot be reduced to zero, so that it is not enough to prevent data loss at the time of handoff.

In the case of a channel provided with an error recovery function in the upper layer, data loss can be avoided by the error retransmission function. Therefore, when a continuous error occurs in a lower layer such as at the time of a handoff and the error recovery function of an upper layer operates, transmission delay increases. In particular, when the retransmission frequency is high, the transmission delay time caused by the retransmission increases significantly. In multimedia communication represented by B-ISDN (Broadband ISDN), various QoS (Quality of Service
vice), but some applications require a low transmission delay depending on the type of service, and there is a problem with these recovery operations as described above.

Therefore, as a method of preventing data loss due to the handoff as described above, a method of performing data transfer between base stations has been considered. FIG. 15 is a configuration diagram showing a second handoff scheme in the prior art. In FIG. 15, 1a and 2a are base stations, 3 is a mobile station, 4a is a base station controller, and 1b and 2b are base stations 1a and 2a, respectively.
Zones a, 1c, and 2c are downlink communication channels (communication paths from the base station to the mobile station) of the zones 1b and 2b, respectively, and 4c is a transfer data transmission path. Base station 1
a and 2a have a transmission memory and a reception memory (not shown), and the transmission data to the mobile station 3 and the reception data from the mobile station 3 are temporarily stored in these two memories and then output. .

The operation of this configuration is as follows.
It is assumed that the mobile station 3 is handing off to the zone 2b while communicating with the base station 1a in the zone 1b. In this case, for example, data (downlink data) for the mobile station 3 from the base station 1a is provided to the mobile station 3 via the route 1c. Handoff is performed, and the path between the base station controller 4a and the mobile station 3 is switched to the communication path 2c via the base station 2a. The mobile station 3 performs a handoff and switches the downlink communication channel from 1c to 2c. The base station 1a stops transmitting data to the mobile station 3 and transfers the transmission waiting transmission data stored in the memory and not yet transmitted to the mobile station 3 to the transmission network. As for the transfer data, the data in the transmission memory of the base station 1a is transferred to the transmission memory of the base station 2a via the transfer data transfer path 4c.

[0013]

As described above, the lack of data due to handoff is a serious problem particularly in high-speed communication. In addition, a handoff method for transmitting transmission data between base stations occurs particularly in high-speed communication.
This is effective for preventing transmission data from being lost due to handoff. However, ATM cells that have been waiting for transmission in the old zone at the time of handoff need to be transferred between base stations for transmission in the new zone with the handoff. If this is referred to as handoff traffic, when the ATM cells in the transmission waiting state are large, there is a problem that a large overhead is generated due to the large amount of traffic and communication efficiency is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and a first object of the present invention is to provide a handoff method for reducing data loss due to a handoff, and a base station and a communication system thereof. It is a second object of the present invention to obtain a handoff method capable of reducing communication overhead between base stations in data transfer and enabling efficient communication, and to provide the base station and the communication system.

[0015]

According to a first aspect of the present invention, there is provided a handoff method in which a mobile station switches a communication channel, and
A handoff method for performing a handoff from one base station to a second base station, wherein the first base station includes the first base station.
A monitoring step of monitoring a communication state between the base station and the mobile station, and the first base station transmits a signal instructing the mobile station to execute a handoff based on a monitoring result in the monitoring step. A handoff instruction step, and in the first base station, based on a monitoring result in the monitoring step, a regulation step of regulating input of transmission data to the mobile station to the base station, and after the execution of the regulation step, A communication start step of starting communication between a second base station and the mobile station.

[0016] A base station according to a second aspect of the present invention is a base station connected to a network and transmitting data input from the network to a mobile station. A monitoring unit that monitors a communication state; a transmission unit that transmits a signal instructing the mobile station to execute a handoff based on a monitoring result by the monitoring unit; and Regulating means for regulating the input of transmission data to the mobile station.

According to a third aspect of the present invention, in the handoff method, the mobile station switches the communication channel so that the mobile station switches the communication channel from the first base station to the second base station.
A handoff method for performing handoff to a base station of
In the mobile station, an input restriction request signal transmitting step of transmitting an input restriction request signal requesting input control of data transmitted to the mobile station to the first base station; and in the first base station, A receiving step of receiving an input restriction request signal, and the first base station, based on the input restriction request signal in the receiving step, a restriction step of restricting input of transmission data to the mobile station to the base station, A communication start step of starting communication between the second base station and the mobile station after the execution of the regulation step.

A communication system according to a fourth aspect of the present invention is a communication system in which a mobile station switches a communication channel to perform handoff from a first base station to a second base station. An input restriction request signal transmitting means for transmitting an input restriction request signal requesting an input restriction of data to be transmitted to the mobile station to the base station, and performing a handoff by switching a communication channel after transmitting the input restriction request signal Channel switching means, the base station, the receiving means for receiving the input restriction request signal, based on the received input restriction request signal, based on the input restriction request signal, the restriction means for restricting the input of transmission data to the mobile station, , Is characterized by having.

A communication system according to a fifth aspect of the present invention is the communication system according to the fourth aspect, wherein the first base station includes a memory for storing the transmission data, and the second base station transmits the transmission data stored in the memory to the second storage. Having transfer means for transferring to the base station,
The restricting means restricts the transmission data from being stored in the memory.

The base station according to a sixth aspect is the base station according to the second aspect, wherein a memory for storing the transmission data, and the transmission data stored in the memory are transmitted to a base station to which the mobile station is handed off. A transmission unit for transmitting the transmission data to the station, wherein the restriction unit restricts the transmission data from being stored in the memory.

A handoff method according to a seventh aspect of the present invention provides
Alternatively, in the first base station according to the third invention, the first base station includes a storage step of storing the transmission data, and a transfer step of transferring the transmission data stored in the storage step to the second base station. The restricting step restricts the transmission data from being stored in the memory.

A base station according to an eighth aspect of the present invention is the base station according to the second or sixth aspect.
In the regulating means according to the invention of the present invention, based on the line quality between the base station of the handoff destination of the mobile station and the mobile station,
It is characterized in that either the stop of the input of the transmission data or the restriction is executed.

A communication system according to a ninth aspect of the present invention is the communication device according to the fourth or fifth aspect, wherein the input of the transmission data is performed based on a channel quality between the second base station and the mobile station. Or one of the following restrictions:

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a schematic configuration diagram of a communication system according to an embodiment of the present invention. The figure shows a mechanism for transferring transmission data to a mobile station between base stations when a mobile unit performs a handoff. In the figure, 1a is a base station 1a, 2a is a base station 2a, 3 is a mobile station, 4a is a base station controller,
b, 2b are the serving zones of the base stations 1a, 2a, 1
Reference numerals c and 2c denote downstream communication channels (communication paths from the base station to the mobile stations) of the zone 1b and the zone 2b, respectively, 4c a transfer data transmission path, and 6 a network. The base station controller 4a is on the network side with respect to the base station 1a and the base station 2a.

When the mobile station 3 moves from the zone 1b to the zone 2b during communication with the base station 1a, the mobile station 3 temporarily suspends communication with the base station 1a. Thereafter, the communication channel is switched to perform handoff, and a communication path with the base station 2a is secured to resume communication.

In this case, the base station 1a holds the data to be transmitted to the base station 2a for transmission to the mobile station 3, and transfers the data which has not yet been transmitted and is waiting to be transmitted, using the transfer data transmission path 4c. The data transfer path 4c is configured via the base station controller 4a, and a mobile station in a cell moves to another cell,
It is temporarily reserved only when handoff is performed. still,
Handoff may be performed by switching communication channels in the same base station. In this case,
The transfer of the data waiting for transmission is not executed.

FIG. 3 shows the configuration of the base stations 1a and 2a. 3, reference numeral 30 denotes an antenna, 31 denotes a transmitting unit for transmitting transmission data and the like input from the network to the mobile station 3, 3
Reference numeral 2 denotes a receiving unit that receives received data from the mobile station 3, 33 denotes a baseband processing unit, 35 denotes a transmission memory that stores transmission data to the mobile station 3, and 34 denotes transmission data stored in the transmission memory 35 at a handoff destination. A transfer unit for transferring to a base station,
36 is a reception memory for storing received data from the mobile station 3; 37 is a synchronization monitoring unit for monitoring the state of communication with the mobile station by monitoring the synchronization of the received signal transmitted from the mobile station; 38 is a network side Base station controller 4a
, An input restricting unit that restricts the input of transmission data to the base station 1a, and 48 is a base station out-of-sync notification as an input restriction instruction signal.

The transmission data input from the network is input to and stored in the transmission memory 35 and then transmitted to the transfer unit 3.
The transmission processing is performed by the baseband processing unit 33 via the transmission unit 4 and transmitted to the mobile station 3 in the serving cell via the transmission unit 31. In the transmission processing, transmission data is transmitted at an appropriate timing after adding a demodulation overhead or the like. On the other hand, the received data is received by the antenna 30, passed through the receiving unit 32, received by the baseband processing unit 33, and then sent to the receiving memory 36 via the transfer unit 34. Here, in the receiving process, the receiving timing is captured and maintained, and the data is decomposed according to the format.

The outline of the handoff operation in the present embodiment will be described below. The handoff may be caused by a mobile station-side factor (downlink failure) or may be caused by a base station-side factor (uplink failure). In the present embodiment, a case where handoff is performed in response to an uplink failure will be described. This will be described with reference to FIG. FIG. 4 is a sequence diagram illustrating an outline of the operation of the system for performing handoff according to the present embodiment.

First, the base station 1a monitors the state of communication with the mobile station 3 and detects an out-of-synchronization caused by an uplink failure during a call (step 41). Upon detecting the loss of synchronization, the base station 1a suspends communication with the mobile station 3 and requests input control to the base station control device 4a (step 42). At the same time, the mobile station 3 is instructed to execute handoff (step 43). The mobile station 3 receives the instruction from the base station 1a and executes handoff by switching the communication channel (step 44).

On the other hand, when receiving the input restriction request, the base station controller 4a requests the network 6 to stop the data transfer to the base station 1a, and issues a transfer instruction of the data waiting for transmission to the base station 1a. (Step 45). The base station 1a that has received the transfer instruction transfers the transmission waiting data stored in the transmission memory 35 to the base station 2a (step 46). After the transfer is completed, the base station 2a starts communication with the mobile station 3 (step 47).

Next, the operation of the base station 1a in steps 41 to 43 will be described in detail. The synchronization monitoring unit 37 monitors the synchronization of the received signal transmitted from the mobile station 3 in the serving zone, and detects the loss of synchronization (step 41). It is sufficient for the synchronization monitoring unit 37 to use a commonly used synchronization management method. For example, a method of monitoring the detection / non-detection of a fixed pattern for synchronization included in a received signal and issuing an input restriction instruction when the number of consecutive non-detections exceeds a predetermined number can be considered. For example, the fixed pattern is embedded in the radio overhead part of the radio burst.

The synchronization monitoring unit 37 sends a signal to the input control unit 38 and the transfer unit 34 only when an out-of-synchronization is detected.
A base station out-of-sync notification is transmitted as the input restriction instruction 48. With this instruction, the input restriction unit 38 is requested to restrict the input of the input traffic (step 41). Input restriction unit 3
8 has a function of monitoring and regulating traffic inflow from the ATM network.

When there is a base station out-of-synchronization notification as the input regulation instruction 48 from the synchronization monitoring section 37,
It requests the base station controller 4a to regulate the acceptance of new input data. That is, the input restricting unit 38 transmits a notification requesting that the reception of new input data be restricted to the network side of the base station 1a. At the same time, the input restricting unit 38 restricts input of transmission data to the base station 1a by stopping or restricting data writing to the transmission memory 35. (Step 42).

The input restriction of transmission data includes both stop and restriction. In the case of restriction, input restriction instruction 4
There is a method of gradually increasing the input limit amount per unit time from zero percent exponentially with respect to the elapsed time until the transfer instruction after the presence of 8. For example, the input speed of the transmission data is reduced exponentially with respect to the elapsed time. At this time, when the input data is stopped, the transmission data to the mobile station 3 is transmitted to the base station 2a, but when the restriction is performed, the transmission data is continuously transmitted to the base station 1a.

When handoff is performed to the base station 2a and communication between the mobile station 3 and the base station 2a is started without fail, the input restricting unit 38 stops writing data to the transmission memory 35. After performing the handoff, the mobile station 3 and the base station 2a
If the channel switching is performed again without starting communication with the base station 1a and communication with the base station 1a may be restarted, data writing to the transmission memory 35 is restricted. In this way, when the communication with the base station 1a is restarted without starting the communication with the base station 2a, that is, when a so-called switching back occurs, the mobile station 3 sent to the base station 2a after the execution of the handoff is performed. It is not necessary to transfer the transmission data to the base station 1a again.

It should be noted that the determination of the stop and the restriction is based on the input restriction instruction 4
8 included. The synchronization monitoring unit 37 determines to stop when the difference in the line quality as the communication state between the cell and the handoff destination cell is equal to or greater than a predetermined value, and determines to limit in the following cases. I do. It is also conceivable to make the determination based only on the line quality of the cell at the handoff destination (step 42). The synchronization monitoring unit 37 provides the mobile station 3 with
A handoff notification for instructing execution of the handoff is transmitted (step 43).

Subsequently, at step 46, the base station 1a
Will be described in detail. FIG. 9 is a configuration diagram illustrating an example of the configuration of the transfer unit 34. 91 is a switching unit, and 92 is an address conversion unit. The switching unit 91 has a function of switching between transmitting data received from the mobile station 3 to the network side during handoff and transferring data from the transmission memory to the network side. The address converter 92 has a function of converting the destination address of the transfer data. The function of the address conversion unit 92 will be described later.

The data stored in the transmission memory 35 is transmitted to the mobile station 3 via the baseband processing unit 33. When the handoff is executed and the mobile station 3 switches the downlink communication channel from 1c to 2c, Only in synchronization with this, the base station stops transmission of the data stored in the transmission memory 35 to the mobile station 3 by switching the switching unit 91,
Switch to transfer to network.

Here, the base station 2a has to know whether it is the transfer data from the base station 1a or the new data. In the case of FIG. 1, the base stations 1a and 2a are under the control of the base station controller 4a. FIG. 2 shows an example in which the base stations to which the mobile station 3 performs handoff are not connected via the same base station controller 4a. This example is also applied to a mobile communication system that does not have an original mobile switching network such as a PHS and depends on an existing network. In FIG. 2, reference numeral 6 denotes a wired network, and other components are the same as those in FIG. The mobile station performs handoff from the base station 1a to the base station 2a as in FIG. 1, but differs in that each base station belongs to a different base station controller 4a, 5a.

In any case, the base station 1a cannot specify to which base station data should be transferred. For this reason, for example, it is necessary for the base station 1a to periodically acquire the base station address of the handoff candidate from the mobile station 3. The mobile station grasps the base station of the handoff destination by periodically monitoring the neighboring cell. This monitoring result is reported to the base station 1a. As a result, the base station 1a can specify the base station to which the data transmission waiting data should be transferred.

The base station 1a generates data for identifying transfer data in the address conversion section 92, adds the data to the transfer data, and transmits the data to the base station controller 4a. For example, when the transfer data is an ATM cell, the processing in the address conversion unit 92 may use a cell header bit, or may add an overhead for each wireless burst.

Referring to FIG. 10, in the address conversion unit 92,
An embodiment of an address added to transfer data will be specifically described. Reference numeral 101 denotes a case where one ATM cell is stored in one radio burst. In this case, a method of using a transfer instruction using a part of the ATM cell header bit as shown in the address transfer instruction A can be considered. The address transfer instruction A includes an address of the mobile station 3 as a transfer source address and an address of the base station 2a as a transfer destination address.

On the other hand, reference numeral 102 denotes a case where a plurality of ATM cells are mounted. In this case, a method of adding an overhead as indicated by an address transfer instruction B can be considered. The content of the address transfer instruction B is the same as that of the address transfer instruction A. As a result, the transfer data is first transferred from the base station 1a to the base station controller 4a as the transfer data 4c, and is then provided to the base station 2a.

As described above, according to this embodiment,
The base station 1a accurately recognizes the timing at which the mobile station 3 performs the handoff, and within the handoff time from suspending the communication between the mobile station 3 and the base station 1a to resuming the communication with the base station 2a. Since the amount of data flowing into the base station 1a is restricted or stopped, the amount of data transferred to the handoff destination base station 2a can be reduced, unnecessary data transfer can be prevented, and the base station controller 4a And the traffic between base stations and the transfer traffic between base stations via the network can be reduced. This prevents an increase in communication overhead and enables efficient data communication.

Further, the configuration of the base station is configured such that a communication state is monitored by monitoring a transmission signal from a mobile station in the zone, and data inflow to the base station is regulated when synchronization is lost. The data transfer amount can be reduced by using the synchronization information already held by the station. or,
Even when data transfer is not performed between base stations, it is possible to reduce data loss due to handoff by limiting the amount of data flowing into the base station.

As a method of monitoring the communication state between the base station 1a and the mobile station, in addition to detecting deterioration of the line quality such as detection of loss of synchronization, for example, error detection added to the ATM cell header may be performed. A method of diverting a part is also conceivable. That is, the error detector is checked for each ATM cell,
If an error is detected in the ATM cell data portion of consecutive ATM cells, a method of restricting the input can be considered. or,
The data communication method is not limited to ATM cell data. Further, input data transmission restriction to the base station includes a case where input is stopped and a case where input is stopped.

In this embodiment, the base station 1a
Form a base station and a first base station by
Constitutes a second base station, a transfer unit is constituted by the transfer unit 34, a memory is constituted by the transmission memory 35, a monitoring unit is constituted by the synchronization monitoring unit 37, and an input control unit 38
And a synchronizing monitoring unit 37 and a transmitting unit 31.
And the baseband processing unit 33 constitute transmission means. Here, when performing handoff at the same base station, a second base station is configured by the base station 1a.

Further, the monitoring step is constituted by the synchronization monitoring in step 41, and the handoff instruction step is constituted by transmitting the handoff notification in step 43. In step 42, the restriction step is configured by transmitting an input restriction request to the network side, or stopping or restricting data writing to the transmission memory, or both. Further, step 47 constitutes a communication start step, and step 46 constitutes a transfer step. Needless to say, these configurations are examples in this embodiment.

Embodiment 2 In the present embodiment, a handoff is executed in response to a downlink failure in the first embodiment. FIG. 5 is a schematic configuration diagram showing a configuration of base station 1a according to the present embodiment. This is an example of a base station that can cope with a case where handoff occurs due to a mobile station side factor (downlink failure). In the figure, reference numeral 42b denotes an input restriction instruction, which is a mobile station line quality deterioration notification made based on the mobile station line quality deterioration. The other configuration is the same as that of FIG. 4 and the description is omitted.

FIG. 11 is a schematic configuration diagram showing a configuration of the mobile station 3 in the present embodiment. In the figure, 111
, An antenna; 112, a transmission / reception processing unit for transmitting and receiving data; 113, a line quality deterioration detection unit for monitoring the communication state by detecting the deterioration of communication line quality;
Is a communication channel switching unit that executes handoff by switching communication channels. The detection of the deterioration of the line quality is performed, for example, by detecting the loss of synchronization, as in the first embodiment.

FIG. 6 is a sequence diagram for explaining the outline of the operation of the handoff method according to the present embodiment. The operation of handoff and input restriction in the base station 1a will be described with reference to FIG. In the mobile station 3, the line quality deterioration detecting unit 11 detects the line quality deterioration due to a downlink trouble during a call.
When No. 3 is detected, the line quality deterioration detection unit 113 notifies the communication base station 1 of the line quality deterioration and requests input restriction of transmission data (step 61). The base station 1a that has received the notification of the line quality deterioration transmits an input restriction notification to the base station controller 4a to request input restriction (step 62), and performs a handoff notification to the mobile station (step 63). .

Upon receiving the handoff notification, the mobile station 3 switches the communication channel by the communication channel switching unit 114 and executes handoff (step 64). Upon receiving the input restriction notification, the base station control device 4a requests the network 6 to stop the data transfer to the base station 1 (not shown), and further transfers the data waiting for transmission to the base station 1a. Is requested (step 65). The base station 1a that has received the transfer instruction transfers the data waiting for transmission stored in the transmission memory 35 to the base station 2a (step 66). After the transfer is completed, the base station 2a
The communication with the mobile station 3 is started (step 67).

Next, the operation of the base station 1a in steps 62 and 63 will be described in detail. Baseband processing unit 3
3 receives a line quality degradation notification from the mobile station 3 that has detected the downlink failure. Received baseband processing unit 33
Is a mobile station line quality deterioration notification 42 as an input restriction instruction.
b is notified to the input restricting unit 38 and the transfer unit 34, and the input restricting unit 38 is requested to restrict the input of the input traffic.

The input restricting unit 38 has a function of monitoring traffic inflow from the ATM network. That is, the synchronization monitoring unit 3
7, the base station monitoring device 4a requests the base station monitoring device 4a to stop accepting new input data, and at the same time, stops or restricts data writing to the transmission memory 35 to the base station 1a. (Step 62). The synchronization monitoring unit 37 sends a handoff notification to the mobile station 3 to instruct execution of a handoff (step 63). In step 66,
The operation of transmitting the transmission data by the base station 1a is the same as in the first embodiment, and the description is omitted.

As described above, according to this embodiment,
In addition to the effects of the first embodiment, the configuration of the base station is such that data inflow to the base station is restricted based on the channel quality deterioration information from the mobile station. In addition, it is possible to regulate the data inflow to the base station in response to the degradation of the downlink quality. Note that the line quality deterioration detecting unit 113 and the transmitting / receiving unit 112 constitute an input restriction request signal transmitting unit, and the communication channel switching unit constitutes a communication channel switching unit. The transmission of the line quality deterioration notification in step 61 constitutes an input restriction request signal transmission step. Needless to say, these configurations are examples in this embodiment.

Embodiment 3 The present embodiment relates to a method in which base station 1a performs a handoff notification to mobile station 3 and restricts input of input data in Embodiment 1, and particularly relates to a method of restricting input quality and handoff when deteriorating channel quality. Error retransmission technology (ARQ: Auto R
epeat Request) is used. The ARQ retransmission delay will be described. First, the operation of the ARQ will be described with reference to FIG. In ARQ, the transmitting side attaches a continuous sequence number to transmission data and transmits the data. On the receiving side, the data is rearranged according to the sequence number attached to the received data. The receiving side determines that an error has occurred when the sequence numbers are not consecutive, and requests the transmitting side to retransmit.

In FIG. 12, the base station transmits data to the mobile station.
Is transmitted, but since the data of data [2] was not transmitted correctly, the mobile station requests retransmission, the base station receives the retransmission request, and retransmits data [2] after transmitting data [4]. are doing. Next, the delay time characteristic of the ARQ retransmission delay will be described with reference to FIG. Here, the delay time is, for example, a time d from the transmission of data [2] by the base station to the final reception of data [2] by the mobile station in FIG.
It is equivalent to ata [2] delay time. FIG. 13 is a diagram illustrating the relationship between the delay time and the channel quality. As can be seen from the figure, the delay time increases when the line quality deteriorates.
From this, by measuring the delay time of data,
You can know the line quality.

FIG. 7 shows base station 1 according to the present embodiment.
It is a schematic block diagram which shows the structure of a. In the figure, reference numeral 71 denotes an ARQ retransmission delay monitoring unit 71 for monitoring the communication state by measuring the transmission delay time of each received signal. The other configuration is the same as that of FIG. 4 and the description is omitted. In the present invention, an output signal from the ARQ retransmission delay monitoring unit 61 is used as an input to the input control unit 38.

FIG. 8 is a sequence diagram for explaining the outline of the operation of the handoff method in the present embodiment. The operation of handoff and input restriction in the base station 1a will be described with reference to FIG. First, the base station 1a reports that the transmission delay time has exceeded a predetermined value due to an uplink failure during a call.
Detected by the ARQ retransmission delay monitoring unit 71 (step 8
1). When detecting the transmission delay, the base station 1a requests input control to the base station controller 4a (step 83), and at the same time, instructs the mobile station 3 to execute handoff (step 82).

The mobile station 3 executes a handoff in response to the instruction from the base station 1a (step 85). On the other hand, when the base station control device 4a receives the notification of the input restriction request,
It requests the network side to stop data transfer to the base station 1 (not shown), and issues a transfer instruction to the base station 1a (step 84). The base station 1a that has received the transfer instruction transfers the data waiting for transmission stored in the transmission memory 35 to the base station 2a (step 86). Base station 2a
Starts communication with the mobile station 3 after the transfer is completed (step 87).

Next, the operation of the base station 1a in steps 81 to 83 will be described in detail. ARQ retransmission delay monitor 7
1 measures the transmission delay time of the received signal transmitted from the mobile station 3 in the visited zone, and detects that the transmission delay time exceeds a predetermined value (step 81). The ARQ retransmission delay monitoring unit 71 instructs the input control unit 38 and the transfer unit 34 to input control 73 only when the transmission delay time exceeds a predetermined value. This requests the input restricting unit 38 to restrict the input of the input traffic.

The input restriction unit 38 has a function of monitoring and restricting the inflow of traffic from the ATM network. When there is an input restriction instruction 73 from the ARQ retransmission delay monitoring unit 71, the network side is requested to stop accepting new input data, and at the same time, input is restricted by stopping or restricting data writing to the transmission memory. (Step 83).
The ARQ retransmission delay monitoring unit 71 transmits a handoff notification to the mobile station 3 (Step 82).

A wireless communication system in which voice and data coexist includes applications that require low transmission delay characteristics. For example, in ATM communication, QoS (Quality of
A service) management item defines a maximum delay. For such a service, the transmission delay time is included in the line quality. In such a case, by measuring the transmission delay time after AQR as shown in this embodiment, the degradation of the line quality can be grasped from the viewpoint of the increase of the transmission delay, so that the input at an appropriate timing can be performed. It is possible to execute a regulation instruction and a handoff.

As described above, according to this embodiment,
Since the configuration of the base station equipped with the error retransmission procedure is configured to monitor the delay time that occurs in the data transmission time due to the error retransmission and regulate the data inflow to the base station, the effects of the first and second embodiments are achieved. In addition, the data transfer amount at the time of handoff can be reduced even for an application whose data transmission delay time is strict.

In this embodiment, the base station measures the transmission delay time, but the mobile station 3 may measure it. In this case, input control of transmission data to the base station 1a is performed by notification from the mobile station 3 as in the second embodiment. In this embodiment, the monitoring means is constituted by the ARQ retransmission delay monitoring unit 71. This configuration,
Needless to say, this is an example in the present embodiment.

[0067]

According to a first aspect of the present invention, there is provided a handoff method in which a mobile station switches a communication channel to perform a handoff from a first base station to a second base station. A monitoring step of monitoring a communication state between the first base station and the mobile station at the station;
In the base station, based on the monitoring result in the monitoring step, a signal for instructing the mobile station to execute handoff, a handoff instruction step, and in the first base station, the monitoring result in the monitoring step A restricting step of restricting input of transmission data to the mobile station to the base station, and a communication start step of starting communication between the second base station and the mobile station after performing the restricting step Therefore, it is possible to reduce data loss due to handoff.

A base station according to a second aspect of the present invention is a base station connected to a network and transmitting data input from the network to a mobile station, wherein the base station is located between the base station and the mobile station. A monitoring unit that monitors a communication state; a transmission unit that transmits a signal instructing the mobile station to execute a handoff based on a monitoring result by the monitoring unit; and And a restricting means for restricting the input of transmission data to the mobile station. Therefore, it is possible to reduce data loss due to handoff.

[0069] In the handoff method according to the third aspect of the present invention, the mobile station switches the communication channel, and the second base station switches the communication channel from the first base station.
A handoff method for performing handoff to a base station of
In the mobile station, an input restriction request signal transmitting step of transmitting an input restriction request signal requesting input control of data transmitted to the mobile station to the first base station; and in the first base station, A receiving step of receiving an input restriction request signal, and the first base station, based on the input restriction request signal in the receiving step, a restriction step of restricting input of transmission data to the mobile station to the base station, A communication start step of starting communication between the second base station and the mobile station after the execution of the restricting step, thereby reducing data loss due to handoff. It becomes possible.

A communication system according to a fourth aspect of the present invention is a communication system in which a mobile station switches a communication channel and performs handoff from a first base station to a second base station. An input restriction request signal transmitting means for transmitting an input restriction request signal requesting an input restriction of data to be transmitted to the mobile station to the base station, and performing a handoff by switching a communication channel after transmitting the input restriction request signal Channel switching means, the base station, the receiving means for receiving the input restriction request signal, based on the received input restriction request signal, based on the input restriction request signal, the restriction means for restricting the input of transmission data to the mobile station, , It is possible to reduce data loss due to handoff.

A communication system according to a fifth aspect of the present invention is the communication system according to the fourth aspect, wherein the first base station includes a memory for storing the transmission data, and the second base station transmits the transmission data stored in the memory to the second base station. Having transfer means for transferring to the base station,
Since the restricting means restricts the transmission data from being stored in the memory, in particular, it reduces overhead associated with data transfer between base stations at the time of handoff, and improves the efficiency. Communication is possible.

A base station according to a sixth aspect of the present invention is the base station according to the second aspect, wherein a memory for storing the transmission data, and the transmission data stored in the memory are transmitted to a base station at a handoff destination of the mobile station. A transfer unit for transferring the data to a station, wherein the restricting unit restricts the transmission data from being stored in the memory. The overhead associated with transfer is reduced, and efficient communication is enabled.

The handoff method according to the seventh invention is characterized in that
Alternatively, in the first base station according to the third invention, the first base station includes a storage step of storing the transmission data, and a transfer step of transferring the transmission data stored in the storage step to the second base station. Since the restricting step is characterized by restricting the transmission data from being stored in the memory, in particular, the overhead involved in data transfer between base stations during handoff is reduced, and the efficiency is reduced. Communication is possible.

The base station according to the eighth invention is the base station according to the second or sixth aspect.
In the regulating means according to the invention of the present invention, based on the line quality between the base station of the handoff destination of the mobile station and the mobile station,
When the transmission data input is stopped or restricted, the handoff destination circuit quality is particularly poor, and the original base station and mobile station start communication again. In addition, transmission data to the mobile station can be prevented from being transmitted to the handoff destination base station, and efficient communication can be performed.

In a communication system according to a ninth aspect of the present invention, in the control means according to the fourth or fifth aspect, the input of the transmission data is performed based on a channel quality between the second base station and the mobile station. In particular, when the first base station and the mobile station start communication again because the state of the line quality with the second base station is poor. Furthermore, transmission data to the mobile station can be prevented from being transmitted to the second base station, and efficient communication can be performed.

[0076]

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a communication system according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a communication system according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of a base station according to Embodiment 1 of the present invention.

FIG. 4 is a sequence diagram according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of a base station according to Embodiment 2 of the present invention.

FIG. 6 is a sequence diagram according to the second embodiment of the present invention.

FIG. 7 is a configuration diagram of a base station according to Embodiment 3 of the present invention.

FIG. 8 is a sequence diagram according to the third embodiment of the present invention.

9 is a configuration diagram of a transfer unit 34. FIG.

FIG. 10 is a diagram illustrating address transfer instruction information.

FIG. 11 is a schematic configuration diagram of a mobile station according to Embodiment 2.

FIG. 12 is a diagram illustrating the operation of ARQ.

FIG. 13 is another diagram illustrating the relationship between the round trip error rate and the transmission delay time.

FIG. 14 is a diagram illustrating a first example of a conventional handoff method.

FIG. 15 is a diagram illustrating a second example of a conventional handoff method.

[Explanation of symbols]

1a, 2a base station, 1b, 2b service area, 1c,
2c downlink, 3 mobile station, 4a, 5a base station controller, 4c transfer data transmission path, 5c transfer data, 6
Wired network, 6c transfer data, 30 antennas, 31 transmitting section, 32 receiving section, 33 baseband processing section, 34 transferring section, 35 transmitting memory, 36 receiving memory, 37 synchronization monitoring section, 38 input regulating section, 3
8, 42b, 73 Input restriction instruction, 71 ARQ retransmission delay monitoring unit, 91 switching unit, 92 address conversion unit 20

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Noriyuki Fukui 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Mitsui Electric Co., Ltd. F-term (reference) 5K030 GA12 HA10 HC09 HD05 JL01 JT09 5K067 AA04 AA11 AA23 BB02 BB21 DD25 EE02 EE10 EE24 GG01 GG11 HH01 HH07 HH12 HH17 HH23 JJ01 JJ12 JJ35 JJ39 LL01 LL05

Claims (9)

[Claims] 1. A handoff method in which a mobile station switches a communication channel to perform a handoff from a first base station to a second base station, wherein the first base station and the first base station communicate with each other. A monitoring step of monitoring a communication state with the mobile station; and a handoff instruction step of, in the first base station, transmitting a signal instructing the mobile station to perform a handoff based on a monitoring result in the monitoring step. The first base station, based on the monitoring result in the monitoring step, restricting input of transmission data to the mobile station to the base station; and, after executing the restricting step, the second base station. A communication start step for starting communication between a station and the mobile station. 2. A base station connected to a network and transmitting data input from the network to a mobile station, comprising: monitoring means for monitoring a communication state between the base station and the mobile station; Transmitting means for transmitting a signal instructing the mobile station to execute handoff based on the monitoring result by the monitoring means; and transmitting data to the mobile station from the network based on the monitoring result by the monitoring means. A base station, comprising: a control unit that controls input. 3. A handoff method in which a mobile station switches a communication channel to perform handoff from a first base station to a second base station, wherein the mobile station is provided with the mobile station by the first base station. An input restriction request signal transmitting step of transmitting an input restriction request signal requesting an input restriction of data to be transmitted to the first base station; and a receiving step of receiving the input restriction request signal in the first base station; In the base station, based on the input restriction request signal in the receiving step, a restriction step of restricting input of transmission data to the mobile station to the base station, and after performing the restriction step, the second base station and the A communication start step of starting communication with a mobile station. 4. In a communication system in which a mobile station switches a communication channel to perform handoff from a first base station to a second base station, the mobile station transmits the mobile station to the first base station. An input restriction request signal transmitting unit that transmits an input restriction request signal that requests input restriction of data to be transmitted to, and a channel switching unit that switches communication channels and performs handoff after transmitting the input restriction request signal. The base station comprises: a receiving unit that receives the input restriction request signal; and a restriction unit that restricts input of transmission data to the mobile station based on the received input restriction request signal. Communications system. 5. The first base station comprises: a memory for storing the transmission data; and a transfer unit for transferring the transmission data stored in the memory to the second base station; The communication system according to claim 4, wherein the communication restricts the transmission data from being stored in the memory. 6. The base station, comprising: a memory for storing the transmission data; and a transfer unit for transferring the transmission data stored in the memory to a base station to which the mobile station is to be handed off. 3. The base station according to claim 2, wherein the means restricts the transmission data from being stored in the memory. 7. The first base station, comprising: a storage step of storing the transmission data; and a transfer step of transferring the transmission data stored in the storage step to the second base station, 4. The method according to claim 1, wherein the restricting step restricts the transmission data from being stored in the memory.
The handoff method according to the above. 8. The method according to claim 1, wherein the restricting unit is configured to perform a handoff of the mobile station based on a line quality between the base station and the mobile station.
The base station according to claim 2, wherein one of stop and restriction of the transmission data is executed. 9. The method according to claim 8, wherein the restricting unit executes one of a stop and a limit of the input of the transmission data based on a channel quality between the second base station and the mobile station. The communication system according to claim 4.