JP5702246B2 - Wireless communication system and communication control method - Google Patents

Description

  The present invention relates to a radio communication system and a communication control method, and more particularly to a radio communication system and a communication control method using a communication terminal as a relay device.

  In a communication terminal that communicates with a base station while moving, such as a mobile phone, in a place where the communication terminal is away from the communicating base station or where radio waves do not reach such as in a building, the communication terminal Communication quality deteriorates.

  In order to solve such problems, it is conceivable to use a relay device that relays radio waves, but generally the relay device is fixedly installed and configured as a dedicated relay device. Installation is costly.

  On the other hand, in Patent Document 1, in a mobile phone used by a general user, an area where a base station is not sufficiently installed due to a configuration in which a repeater function for relaying communication between another mobile phone and the base station is added. A technology for improving the communication environment in Japan has been proposed.

JP 2007-135154 A

  When a communication terminal is used as a relay device, there may be a plurality of relay devices nearby, but Patent Document 1 does not disclose which relay device is selected in such a case. Further, since the communication terminal is used as a relay device, the relay device may also move. When the relay device moves, the communication quality between the base station and the relay device also changes. Usually, a communication terminal monitors a received radio wave state, and performs handover control for switching a connection by searching for a base station or a relay device having a better radio wave state when the radio wave is weakened. However, when a communication terminal is used as a relay device, even if the radio wave condition between the relay device and the communication terminal is good, the radio wave condition between the base station and the relay device may decrease. The technology cannot cope with it, and the communication quality deteriorates rapidly or the connection is suddenly lost.

  The present invention has been made to solve the above problems, and in a wireless communication system using a communication terminal as a relay device, a communication path with the best communication quality can be selected from a plurality of communication paths. An object of the present invention is to provide a wireless communication system and a communication control method that prevent rapid deterioration of communication quality and sudden disconnection when communication with a base station is performed via a relay device.

In order to solve the above-described problem, a wireless communication system according to the present invention includes a mobile communication terminal, a base station, and a plurality of mobile relay terminals that relay communication between the communication terminal and the base station. The communication terminal includes a radio communication unit that transmits and receives radio signals, and a first connection request message that is transmitted when requesting relay of communication to the relay terminal. A control unit that executes a connection processing sequence with a base station, and each of the relay terminals receives a wireless communication unit that transmits and receives a wireless signal, and at least the first connection request message. A control unit that obtains communication quality at the time of reception as first communication quality information, and creates a second connection request message added to the first connection request message together with identification information of the own device; The base station, when receiving the second connection request message from each of the radio communication unit that transmits and receives radio signals and the relay terminal, acquires the communication quality at the time of reception for each of the second connection request messages Used as relay information from a plurality of the relay terminals based on the second communication quality information and the first communication quality information added to the second connection request message as communication quality information A response message including identification information of the selected relay terminal, and a control unit that executes a connection processing sequence with the communication terminal, the control unit of the base station, the first information of the information of communication quality and the second communication quality, correspondence to all of the plurality of paths that intervention of a plurality of said relay terminals, the most value small communication quality among the plurality of paths That the to section, with all other section corresponding to the section compares the communication quality, using the relay terminal which constitutes the path having the other of the section communication quality indicates the largest value to the relay Choose as.

  One aspect of the wireless communication system according to the present invention is that, when the relay terminal is selected and relays communication between the communication terminal and the base station, a higher-level apparatus than the own apparatus When the communication quality between and becomes less than a predetermined threshold, a relay terminal switching instruction is transmitted to the communication terminal.

  In one aspect of the wireless communication system according to the present invention, when the communication terminal receives an instruction to switch the relay terminal from the relay terminal, the communication terminal creates and transmits the first connection request message to the relay terminal. The relay terminal that relays communication between the communication terminal and the base station discards the first connection request message.

  In one aspect of the wireless communication system according to the present invention, when the communication terminal receives an instruction to switch the relay terminal from the relay terminal, the communication terminal creates and transmits the first connection request message to the relay terminal. The relay terminal that relays communication between the communication terminal and the base station also accepts the first connection request message, acquires the communication quality at the time of reception, and Communication quality information.

  In one aspect of the wireless communication system according to the present invention, when the relay terminal receives the second connection request message from a relay terminal lower than the own terminal, the relay terminal acquires the communication quality at the time of reception and As the communication quality information, the second connection request message added to the first connection request message together with its own identification information is created and transmitted to a higher-level device.

  In one aspect of the wireless communication system according to the present invention, the relay terminal is another communication terminal having the same configuration as the communication terminal, and the another communication terminal transmits a relay request to the first connection request message. Is included, it operates as the relay terminal.

The communication control method according to the present invention is a communication in a wireless communication system including a movable communication terminal, a base station, and a plurality of movable relay terminals that relay communication between the communication terminal and the base station. (A) a step of transmitting a first connection request message when requesting relay of communication from the communication terminal to the relay terminal; and (b) each of the relay terminals is at least When the first connection request message is received, the second connection added to the first connection request message together with its own identification information is acquired by obtaining the communication quality at the time of reception. Transmitting a request message; and (c) when the base station receives the second connection request message from each of the relay terminals, obtains communication quality upon reception for each Used for relaying from the plurality of relay terminals based on the second communication quality information and the first communication quality information added to the second connection request message. Selecting one and transmitting a response message including identification information of the selected relay terminal, and (d) when each of the relay terminals receives the response message from the base station, Is not included, the response message is discarded, and if the identification information of its own device is included, the response message is transmitted to the communication terminal, and the step (c) includes: the first information and the information of the second communication quality of the communication quality, the correspondence to all of the plurality of paths that intervention of a plurality of said relay terminals, most value small communication quality among the plurality of paths Show A section, with all other section corresponding to the section compares the communication quality, the relay terminal which constitutes the path having the other of the section communication quality indicates the largest value as using the relay Including a step of selecting.

  According to the wireless communication system of the present invention, communication quality between a plurality of relay terminals is acquired as first communication quality information, and the information is added to the second connection request message. The base station obtains the communication quality between itself and each relay terminal to obtain the second communication quality information, which is added to the second communication quality information and the second connection request message. Based on the first information on the first communication quality, a communication path with the best communication quality can be selected from the plurality of communication paths by selecting one to be used for relay from the plurality of relay terminals.

  According to the communication control method of the present invention, the communication quality between the plurality of relay terminals is obtained as the first communication quality information, and the information is added to the second connection request message. The base station obtains the communication quality between itself and each relay terminal to obtain the second communication quality information, which is added to the second communication quality information and the second connection request message. Based on the first information on the first communication quality, a communication path with the best communication quality can be selected from the plurality of communication paths by selecting one to be used for relay from the plurality of relay terminals.

It is a block diagram which shows the structure of the relay terminal of the radio | wireless communications system which concerns on this invention, and a communication terminal. It is a block diagram which shows the structure of the base station of the radio | wireless communications system which concerns on this invention. It is a figure which shows typically the structural example of the radio | wireless communications system which concerns on this invention. It is a flowchart which shows operation | movement of a communication terminal. It is a flowchart which shows operation | movement of a relay terminal. It is a figure explaining the communication control method in the radio | wireless communications system which concerns on this invention. It is a flowchart which shows operation | movement of a base station. It is a figure explaining the communication control method in the radio | wireless communications system which concerns on this invention. It is a figure explaining the communication control method in the radio | wireless communications system which concerns on this invention. It is a figure explaining the communication control method in the radio | wireless communications system which concerns on this invention. It is a flowchart which shows operation | movement of a relay terminal. It is a figure explaining the communication control method in the radio | wireless communications system which concerns on this invention. It is a flowchart which shows operation | movement of a communication terminal. It is a figure explaining the communication control method in the radio | wireless communications system which concerns on this invention.

<Embodiment>
<Device configuration>
FIG. 1 is a block diagram showing a configuration of a relay terminal RS and a communication terminal MS in a wireless communication system according to the present invention. The configuration of the relay terminal RS corresponds to the configuration of the relay terminals RS1 and RS2 described later.

  As shown in FIG. 1, the relay terminal RS includes a radio reception unit 2, a radio transmission unit 6, a demodulation unit 3, a modulation unit 5, a signal processing unit 4, and a radio wave intensity measurement to which a transmission / reception antenna 1 is connected. Part 7. The signal processing unit 4 and the radio wave intensity measurement unit 7 are included in the control unit 10 that controls the entire relay terminal RS. In FIG. 1, only the configuration according to the invention is shown, and other configurations are omitted.

  In the relay terminal RS, a reception signal received by the transmission / reception antenna 1 is input to the radio reception unit 2, subjected to amplification processing and down-conversion, converted into a baseband signal, and output. The signal received by the transmission / reception antenna 1 is modulated by a BPSK (Binary Phase Shift Keying) modulation method, a QPSK (Quadrature Phase Shift Keying) modulation method, or the like.

  The signal converted into the baseband signal is given to the demodulator 3 to perform error correction processing and the like, and is also given to the radio wave intensity measurement unit 7 to measure the radio wave reception intensity (measurement of communication quality). Is called.

  When the signal demodulated by the demodulating unit 3 includes a first connection request message described later, the signal processing unit 4 analyzes the message and also measures the radio wave measured by the radio wave intensity measuring unit 7. Is added to the first connection request message and sent to the modulation unit 5 to be transmitted to the base station as a second connection request message.

  The modulation unit 5 modulates the signal again using a BPSK modulation method, a QPSK modulation method, or the like, and transmits the signal from the transmission / reception antenna 1 via the wireless transmission unit 6. Note that the wireless reception unit 2 and the wireless transmission unit 6 may be referred to as wireless communication units.

  In the above description, the communication terminal is used as the relay terminal RS. However, when the communication terminal MS is used as the communication terminal MS, the demodulated signal output from the demodulation unit 3 is received by the signal processing unit 4. When it is analyzed that it is an audio signal, it is converted into an audio signal via a speaker or the like (not shown). In addition, when an audio signal is input from an audio input unit such as a microphone (not shown), the modulation unit 5 modulates the signal using a BPSK modulation method, a QPSK modulation method, or the like, and transmits / receives the transmission / reception antenna 1 via the wireless transmission unit 6 Send from.

  FIG. 2 is a block diagram showing the configuration of the base station BS of the wireless communication system according to the present invention. As shown in FIG. 2, the base station BS includes a radio reception unit 12, a radio transmission unit 16, a demodulation unit 13, a modulation unit 15, a signal processing unit 14, and a radio wave intensity measurement to which a transmission / reception antenna 11 is connected. Unit 17, relay terminal selection unit 18, line control unit 19, and line side transmission / reception unit 20. The signal processing unit 14, the radio wave intensity measurement unit 17, the relay terminal selection unit 18, the line control unit 19, and the line side transmission / reception unit 20 are included in a control unit 21 that controls the entire base station BS. In FIG. 2, only the configuration according to the invention is shown, and other configurations are omitted.

  In the base station BS, a reception signal received by the transmission / reception antenna 11 is input to the radio reception unit 12, subjected to amplification processing and down-conversion, converted into a baseband signal, and output. The signal received by the transmission / reception antenna 11 is modulated by a BPSK (Binary Phase Shift Keying) modulation method, a QPSK (Quadrature Phase Shift Keying) modulation method, or the like.

  The signal converted into the baseband signal is supplied to the demodulator 13 to perform error correction processing and the like, and is also supplied to the radio wave intensity measurement unit 17 to measure the radio wave reception intensity (measurement of communication quality). Is called.

  When the signal demodulated by the demodulating unit 13 includes the second connection request message, the signal processing unit 14 decodes the message, and receives the radio wave reception intensity measured by the radio wave intensity measuring unit 17 and the first signal. The identification information of the relay terminal selected by the relay terminal selection unit 18 is added to the response message based on the reception strength information (communication quality information) at the relay terminal RS sent in addition to the connection request message 2 Then, the signal is sent to the modulation unit 15 to be transmitted to each relay terminal. The modulation unit 15 modulates the signal again using a BPSK modulation method, a QPSK modulation method, or the like, and transmits the signal from the transmission / reception antenna 11 via the wireless transmission unit 16. Note that the wireless reception unit 12 and the wireless transmission unit 16 may be referred to as wireless communication units.

  In the above description, the case where the base station BS selects the relay terminal RS has been described. However, when the base station BS performs a normal operation, the demodulated signal output from the demodulation unit 13 is When the signal processing unit 14 analyzes that the signal is to be given to another base station via the network line, the signal is given to the line side control unit 19 and is sent to the network line (not shown) via the line side transmission / reception unit 20. Given. Further, when a signal to be transmitted from the network line to the communication terminal is given, it is given to the line side control unit 19 via the line side transmission / reception unit 20, and is given from the line side control unit 19 to the signal processing unit 14. Identification information of a communication terminal to be transmitted is added in the signal processing unit 14 and given to the modulation unit 15. The modulation unit 15 modulates the signal again using a BPSK modulation method, a QPSK modulation method, or the like, and transmits the signal from the transmission / reception antenna 11 via the wireless transmission unit 16.

<Device operation>
Next, the operation of the wireless communication system according to the present invention will be described with reference to FIGS. FIG. 3 is a diagram schematically showing an example of the configuration of a wireless communication system according to the present invention, in which relay terminals RS1 and RS2 exist for a communication terminal MS that requests connection with a base station BS. Show. Note that the communication terminal MS and the relay terminals RS1 and RS2 described above correspond to mobile electronic devices such as mobile phone terminals and PDAs (Personal Digital Assistants) having a wireless communication function.

  The communication terminal MS is outside the communication area A of the base station BS and cannot communicate directly with the base station BS, but is in a position where the relay terminals RS1 and RS2 can be used as relay terminals. In such a situation, the communication terminal MS transmits a first connection request message to start communication with the base station BS. The first connection request message is conventionally used. When the communication terminal MS is outside the communication area A of the base station BS, the relay information is added to the communication terminal MS and transmitted.

  The relay information here includes a message for requesting the relay terminal to relay to the base station. For example, any bit of the first connection request message composed of a plurality of bits is set as a relay request flag. If it is “1”, it is assumed that there is a relay request, and if it is “0”, there is no relay request.

  The operation of the communication terminal MS described above will be further described using the flowchart shown in FIG. As shown in FIG. 4, when the communication terminal MS starts the connection sequence process with the base station BS, the communication terminal MS determines whether or not the current position is outside the communication area of the base station BS (step S1). . This determination is made, for example, by measuring the reception strength of a pilot signal periodically transmitted from the base station BS, and when the reception strength of the pilot signal is equal to or less than a predetermined value, It is determined that it is located outside the communication area. This determination and connection sequence processing are executed in the control unit 10 (FIG. 1) of the communication terminal MS.

  If it is determined in step S1 that it is within the communication area of the base station BS, the communication terminal MS transmits a first connection request message (step S4). This first connection request message is conventionally used and does not include relay information. After transmitting the first connection request message, the connection sequence process with the base station BS is continued (step S3), and the connection with the base station BS is established by completing the connection sequence process.

  On the other hand, if it is determined in step S1 that it is outside the communication area of the base station BS, the communication terminal MS transmits a first connection request message including relay information (step S2). After transmitting the first connection request message, the connection sequence process with the base station BS via the relay terminal is continued (step S3), and the connection with the base station BS is established by completing the connection sequence process. To do.

  Returning to the description of FIG. 3, the first connection request message does not reach the base station BS, but reaches the relay terminals RS1 and RS2 in the communication area A of the base station BS and receives them. When the relay information is added, each of the relay terminals RS1 and RS2 measures the received radio wave intensity when the connection request message is received. Then, each of relay terminals RS1 and RS2 adds its own identification information and the measured reception strength value to the relay information of the first connection request message and transmits the relay information to base station BS.

  The operation of the relay terminals RS1 and RS2 described above will be further described using the flowchart shown in FIG. As shown in FIG. 5, the relay terminals RS1 and RS2 normally function as communication terminals, and the function as the relay terminal is in a standby state.

  When the radio receiving units 2 (FIG. 1) of the relay terminals RS1 and RS2 in the standby state receive the first connection request message from the communication terminal MS (step S11), they are demodulated by the demodulating unit 3 (FIG. 1). The signal processing unit 4 analyzes and determines whether or not relay information (relay request) is included in the first connection request message (step S12). If the relay information (relay request) is not included in the first connection request message, the first connection request message is discarded because there is no need to operate as a relay terminal (step S17), and the standby state is entered. Return.

  On the other hand, when relay information (relay request) is included in the first connection request message, the received power (RSSI: Receive Signal Strength) measured by the radio field strength measuring unit 7 (FIG. 1) when the connection request message is received. A value such as “Indication” is set as the received radio wave intensity, and the value is added as relay information to the first connection request message in the signal processing unit 4 (FIG. 1), and the wireless transmission unit 6 (FIG. 1) ) To the base station BS (step S13). Therefore, the relay information here includes information on the received radio wave intensity between the communication terminal MS and the own device. In addition, identification information of the own machine that is the transmission source is also included.

  The relay terminals RS1 and RS2 that have transmitted the second connection request message wait for reception of a connection response message from the base station BS (step S14).

  Here, returning to the description of FIG. 3, the base station BS that has received the second connection request message from the relay terminals RS1 and RS2 measures the received radio wave strength with each relay terminal when the connection request message is received. . Then, based on the received radio wave intensity at each relay terminal added as relay information and the received radio wave intensity between each relay terminal measured by the base station BS, the relay terminal to be used is selected.

  The selection method here is, for example, to compare the received radio field strengths in all the routes for the section showing the lowest received radio wave intensity between the communication terminal and the relay terminal and between the relay terminal and the base station. The route having the section showing the largest value is selected.

  For example, in FIG. 3, when the received radio wave intensity between the relay terminal RS1 and the base station BS is the lowest, a route through the relay terminal RS2 is used, for example, between the relay terminal RS1 and the communication terminal MS. Even if the radio field intensity at is highest, the route via the relay terminal RS1 is not used, that is, the relay terminal RS1 is not selected.

  The base station BS that has selected the relay terminal to use transmits a connection response message as shown in FIG. The connection response message is conventionally used. In this case, the identification information of the selected relay terminal is added and transmitted.

  The operation of the base station BS described above will be further described using the flowchart shown in FIG. As shown in FIG. 7, when the radio receiver 12 (FIG. 2) of the base station BS receives the first or second connection request message from the relay terminals RS1 and RS2 or the communication terminal MS (step S21), the demodulator 13 (FIG. 2), after being demodulated by the signal processing unit 14 (FIG. 2), whether or not the connection request message includes relay information (information on received radio wave intensity and relay terminal identification information). Is determined (step S22). If the connection request message does not include relay information (information on received radio wave intensity or relay terminal identification information), the connection request message is determined to be a direct first connection request message from the communication terminal MS, The sequence process is continued (step S24).

  On the other hand, if relay information (information on received radio wave intensity or identification information of the relay terminal) is included, the second connection request message is given to the relay terminal selection unit 18 as having been received.

  The relay terminal selection unit 18 receives the values of the received power (RSSI) between the relay terminals RS1 and RS2 measured by the radio wave intensity measurement unit 17 (FIG. 2) when receiving the connection request message. The received radio field strength is used together with the received radio field strength information between the relay terminals RS1 and RS2 with the communication terminal MS (step S23). An example of the selection method is as described above.

  The selection result in the relay terminal selection unit 18 is given to the signal processing unit 14 (FIG. 2), and the signal processing unit 14 supplies the identification information of the selected relay terminal (relay terminal RS2 in the example of FIG. 6) to the connection response message. And transmitted via the wireless transmission unit 16 (FIG. 2) to continue the connection sequence process (step S24). When the series of connection sequence processes is completed, the connection is completed between the communication terminal MS and the base station BS (step S25).

  Here, returning to the description of FIG. 6, each of the relay terminals RS1 and RS2 that have received the connection response message confirms whether or not its own device is selected as the relay terminal based on the identification information of the connection response message. . In this case, since relay terminal RS2 is selected, relay terminal RS2 relays the connection response message to communication terminal MS.

  The operation of the relay terminals RS1 and RS2 described above will be further described using the flowchart shown in FIG. As shown in step S14 of FIG. 5, the relay terminals RS1 and RS2 that have transmitted the second connection request message are waiting to receive a connection response message from the base station BS. It is confirmed whether or not the identification information of the own device is included in (step S15). If the identification information of the own device is not included, it is determined that the own device has not been selected, the connection response message is discarded (step S18), and the process returns to the standby state. In this case, all subsequent messages are discarded.

  On the other hand, if the identification information of the own device is included in the connection response message, the connection response message is relayed to the communication terminal MS, and the connection sequence process is continued (step S16).

  Thereafter, the connection sequence is relayed by the relay terminal RS2, and communication is started when the connection between the communication terminal MS and the base station BS is completed.

  At this time, as shown in FIG. 8, the communication quality is good between the communication terminal MS and the relay terminal RS2 and between the relay terminal RS2 and the base station BS.

  Here, as shown in FIG. 9, when the relay terminal RS2 moves and approaches the outer edge of the communication area A of the base station BS, the communication quality between the relay terminal RS2 and the base station BS decreases, but the communication terminal The communication quality between the MS and the relay terminal RS2 remains good. In this case, when the relay terminal RS2 detects that the radio field strength with the base station BS is low, the relay terminal RS2 transmits a relay switching instruction message instructing switching of the relay terminal to the communication terminal MS as shown in FIG. To do.

  The operation of the relay terminal RS2 described above will be further described using the flowchart shown in FIG. The relay terminal RS2 that relays communication between the communication terminal MS and the base station BS measures the received radio wave intensity by periodically measuring the received power (RSSI) or the like in the radio wave intensity measuring unit 7 (FIG. 1). If the received radio wave intensity is less than a predetermined threshold value (step S31), the signal processing unit 4 (FIG. 1) that receives the information creates a relay switching instruction message and performs communication. It transmits to the terminal MS (step S32).

  Receiving the relay switching instruction message, the communication terminal MS again transmits the first connection request message including the relay information as shown in FIG.

  The operation of the communication terminal MS will be further described with reference to the flowchart shown in FIG. In FIG. 13, the communication terminal MS is currently communicating with the base station BS via the relay terminal RS2. In this state, when receiving the relay switching instruction message from the relay terminal RS2 (step S41), the communication terminal MS determines whether or not the current position is outside the communication area of the base station BS (step S42).

  If it is determined in step S42 that it is within the communication area of the base station BS, the communication terminal MS transmits a first connection request message (step S46). This first connection request message is conventionally used and does not include relay information. After transmitting the first connection request message, the connection sequence process with the base station BS is continued (step S44), and the communication connection currently being performed with the base station BS via the relay terminal RS2 is established. Processing for cutting is executed (step S45). Thereafter, direct communication is performed with the base station BS.

  On the other hand, if it is determined in step S42 that the communication terminal MS is out of the communication area of the base station BS, the communication terminal MS transmits a first connection request message including relay information (step S43).

  Here, returning to the description of FIG. 12, the first connection request message reaches the relay terminals RS1 and RS2, but since the relay terminal RS2 is already in communication, the first connection request message is received even if the first connection request message is received. Discard. As a result, the relay terminal RS2 that has transmitted the relay switching instruction message is not selected again as a relay terminal, and the time spent for selecting a communication path can be reduced.

  On the other hand, the relay terminal RS1 that has received the first connection request message, when relay information is added, measures the received radio wave intensity at the time of receiving the first connection request message, and measures its own identification information and measurement. The received reception strength value is added to the relay information of the first connection request message, and is transmitted to the base station BS as the second connection request message.

  The relay terminal RS1 operation in this case is the same as the operations in steps S11 to S13 described with reference to FIG.

  The relay terminal RS1 that has transmitted the second connection request message waits for reception of a connection response message from the base station BS (step S14).

  Here, returning to the description of FIG. 12, the base station BS that has received the second connection request message from the relay terminal RS1 measures the received radio wave intensity with the relay terminal RS1 when the connection request message is received. Then, based on the received radio wave intensity at the relay terminal RS1 added as the relay information and the received radio wave intensity between the relay terminal RS1 measured at the base station BS, the relay terminal to be used is selected. This operation is the same as the operations in steps S21 to S24 described with reference to FIG.

  As described above, the selection method here is to compare the radio field strength between the communication terminal and the relay terminal and between the relay terminal and the base station over all paths, and select the relay terminal that constitutes the path with the smallest value. Make a selection to exclude. However, in the example shown in FIG. 14, there is no target route only through the relay terminal RS1, so the radio field strength between the communication terminal MS and the relay terminal RS1 and between the relay terminal RS1 and the base station BS is If both are larger than the predetermined value, the route is used, that is, RS1 between relay terminals is selected.

  The base station BS that has selected the relay terminal to use transmits a connection response message to which the identification information of the selected relay terminal is added, and each of the relay terminals RS1 and RS2 that has received the connection response message identifies the connection response message. Based on the information, it is confirmed whether or not the own device is selected as a relay terminal. In this case, since the relay terminal RS1 is selected, the relay terminal RS1 relays the connection response message to the communication terminal MS, and continues the connection sequence process. Thereafter, the connection sequence is relayed by the relay terminal RS1, and communication is started when the connection between the communication terminal MS and the base station BS is completed.

  The relay terminal RS2 operation in this case is the same as the operations in steps S14 to S16 and step S18 described with reference to FIG.

  By performing communication via the relay terminal RS1 selected in such a manner, as shown in FIG. 14, good communication quality is obtained between the communication terminal MS and the relay terminal RS1, and between the relay terminal RS1 and the base station BS. Can be obtained.

  As described above, in a wireless communication system using a communication terminal as a relay device, when there are a plurality of relay terminals that can be relayed, the received radio wave intensity between each relay terminal and the communication terminal is measured, and the information is 2 is added to the connection request message and given to the base station. The base station measures the received radio wave strength between itself and each relay terminal, and is added to the measured received radio wave strength and the second connection request message. Based on the received radio wave intensity between each relay terminal and the communication terminal, the relay terminal used for relay is determined. For this reason, the communication path with the best communication quality can be selected from a plurality of paths.

  In addition, the relay terminal that is relaying monitors the received radio wave strength with the base station, and when the received radio wave strength decreases, the communication terminal is instructed to switch the relay terminal. , Can prevent sudden disconnection.

<Modification>
In the above description, when the relay terminal RS2 receives the connection request message transmitted from the communication terminal MS after receiving the relay switching instruction message from the relay terminal RS2, the relay terminal RS2 is already communicating, and therefore receives the connection request message. The connection request message is discarded as described above. However, even during communication, the reception radio wave intensity at the time of receiving the first connection request message is measured again, and the identification information of the own device and the value of the measured reception intensity are measured. May be added to the relay information of the second connection request message and transmitted to the base station BS.

  That is, the relay terminal RS2 transmits the relay switching instruction message because the received signal strength with the base station BS is reduced, but the relay terminal RS2 further moves to receive signals with the base station BS. There is also a possibility that strength will be restored. In this case, since the relay terminal RS2 can be used again as a relay terminal, the number of communication path candidates can be increased by performing the above-described operation.

  In the above description, after receiving the relay switching instruction message from the relay terminal RS2, the communication terminal MS transmits the connection request message to switch the relay terminal RS to which the communication terminal MS is connected. . However, in the communication terminal MS, for example, the user who uses it determines that the current communication speed is not good and operates the operation unit (not shown) to instruct to switch the relay terminal RS connected to the communication terminal MS, When communication quality or throughput does not satisfy a predetermined standard, the control unit of the communication terminal MS detects that the instruction or the standard is not satisfied, and transmits a connection request message to control the communication terminal MS. What is necessary is just to comprise so that the relay terminal RS which MS connects may be switched.

  Furthermore, in the above description, the case where there are two relay terminals is illustrated, but it goes without saying that the present invention can be applied to even more cases, and a plurality of relay terminals are connected in series. The present invention can also be applied when communicating with each other.

  In this case, also in the relay terminal that has received the second connection request message transmitted from the relay terminal, the same processing as the flow shown in FIG. 5 is performed, and the received signal strength of its own device is added to the second connection request message. What is necessary is just to comprise so that information and identification information may be added and transmitted.

  In the base station, the second connection request messages obtained via one relay terminal and the second connection request messages obtained via a plurality of relay terminals are accumulated and based on the information provided by them. It is possible to select a communication path with the best communication quality. In addition, the base station can instruct the relay terminal included in the route to relay data by transmitting the identification information of each relay terminal included in the selected communication route in the connection response message. Become. By adopting such a configuration, even when there is a communication terminal in a place that cannot be relayed by one relay terminal, it is possible to communicate with the base station by relaying in a relay manner.

  In the above description, the communication terminal is used as a relay terminal, and the relay terminal has the same configuration as the communication terminal. Thus, by using the communication terminal for general purposes, the communication environment in an area where the base station is not sufficiently installed can be improved without providing a dedicated relay device. However, the present invention is also effective for a system in which a plurality of dedicated relay apparatuses are provided to expand the communication area of the base station.

MS communication terminal RS1, RS2 relay terminal BS base station

Claims (7)

A wireless communication system comprising a plurality of movable communication terminals, a base station, and a plurality of movable relay terminals that relay communication between the communication terminal and the base station,
The communication terminal is
A wireless communication unit for transmitting and receiving wireless signals;
A first connection request message to be transmitted when requesting relay of communication to the relay terminal, and a control unit for executing a connection processing sequence with the base station,
Each of the relay terminals is
A wireless communication unit for transmitting and receiving wireless signals;
When at least the first connection request message is received, the communication quality at the time of reception is acquired and used as the first communication quality information, and the second information added to the first connection request message together with the identification information of the own device. A control unit for creating a connection request message of
The base station
A wireless communication unit for transmitting and receiving wireless signals;
When the second connection request message is received from each of the relay terminals, the communication quality at the time of reception is acquired for each of the relay terminals and used as second communication quality information, and the second communication quality information and the first Based on the information of the first communication quality added to the connection request message of No. 2, the one used for relay is selected from the plurality of relay terminals, and a response message including identification information of the selected relay terminal is created And a control unit that executes a connection processing sequence with the communication terminal,
The control unit of the base station is
The first information of the information of communication quality and the second communication quality, correspondence to all of the plurality of paths that intervention of a plurality of said relay terminals, the most value small communication quality among the plurality of paths those using the section indicated, the relay terminal with all other section corresponding to the section compares the communication quality, which constitutes a path having the other of the section communication quality indicates the largest value to the relay Select as a wireless communication system. The relay terminal is
When the own device is selected and the communication between the communication terminal and the base station is relayed, the communication quality with the higher-level device is lower than a predetermined threshold value. The wireless communication system according to claim 1, wherein a relay terminal switching instruction is transmitted to the communication terminal. The communication terminal is
If the relay terminal switching instruction is received from the relay terminal, the first connection request message is created and transmitted to the relay terminal,
3. The wireless communication system according to claim 2, wherein among the relay terminals, those that relay communication between the communication terminal and the base station discard the first connection request message. The communication terminal is
If the relay terminal switching instruction is received from the relay terminal, the first connection request message is created and transmitted to the relay terminal,
Among the relay terminals, those relaying communication between the communication terminal and the base station also accept the first connection request message, acquire the communication quality at the time of reception, and The wireless communication system according to claim 2, wherein the communication quality information is used. The relay terminal is
When the second connection request message is received from a relay terminal lower than the own device, the communication quality at the time of reception is acquired as first communication quality information, and the first connection information together with the identification information of the own device The wireless communication system according to claim 1, wherein the second connection request message added to the request message is generated and transmitted to an upper apparatus. The relay terminal is another communication terminal having the same configuration as the communication terminal,
The another communication terminal is:
The wireless communication system according to claim 1, wherein the wireless communication system operates as the relay terminal when a relay request is included in the first connection request message. A communication control method in a wireless communication system comprising a plurality of movable communication terminals, a base station, and a plurality of movable relay terminals that relay communication between the communication terminal and the base station,
(a) transmitting a first connection request message from the communication terminal when requesting relay of communication to the relay terminal;
(b) When each of the relay terminals receives at least the first connection request message, the relay terminal acquires the communication quality at the time of reception and uses it as the first communication quality information, together with its own identification information. Transmitting a second connection request message added to the one connection request message;
(c) When the base station receives the second connection request message from each of the relay terminals, the base station acquires the communication quality at the time of reception for each, and uses the second communication quality information as the second communication quality information. Based on the communication quality information and the first communication quality information added to the second connection request message, a plurality of relay terminals to be used for relaying are selected, and the selected relay terminal Sending a response message including identification information;
(d) When each of the relay terminals receives the response message from the base station, if the identification information of the own device is not included, the response message is discarded and the identification information of the own device is included. If there is, the step of transmitting the response message to the communication terminal,
The step (c)
The first information of the information of communication quality and the second communication quality, correspondence to all of the plurality of paths that intervention of a plurality of said relay terminals, the most value small communication quality among the plurality of paths those using the section indicated, the relay terminal with all other section corresponding to the section compares the communication quality, which constitutes a path having the other of the section communication quality indicates the largest value to the relay A communication control method including the step of selecting as.

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