JP5680512B2 - Relay device and communication control method - Google Patents

Description

  The present invention relates to a relay device and a communication control method.

  In order for a mobile station to communicate with a base station, the mobile station needs to be located in a range where radio waves from the base station can reach. However, in urban areas where mountainous areas and high-rise buildings are lined up, there are areas where radio waves are difficult to reach due to many obstacles. In addition, there are many areas where radio waves do not reach from the base stations installed outdoors in the building or underground. In particular, in a high-speed wireless communication method such as WiMAX (Worldwide Interoperability for Microwave Access) (registered trademark) standardized based on the IEEE standard 802.16e, radio waves in a high frequency band of 2.5 GHz or more are used. Such radio waves are highly straight and have a weak property of going around obstacles. For this reason, WiMAX and the like are strongly affected by obstacles. In order to cover such a region where radio waves do not reach, a relay device (repeater) that relays radio waves between the base station and the mobile station is required. The relay device includes a base station side unit (donor unit or MS (Mobile Station) unit) that communicates with a base station, and a mobile station side unit (service unit or BS (Base Station) unit) that communicates with a mobile station. Have.

  In order for the base station and the mobile station to communicate via the relay device, it is necessary to establish synchronization between the base station and the base station side unit and between the mobile station side unit and the mobile station. Here, a conventional synchronization establishment method will be described (see, for example, Patent Document 1). First, the base station side unit periodically receives a radio signal including a synchronization signal (preamble) from the base station. Then, the base station side unit acquires a synchronization signal reception timing and period by detecting a periodic synchronization signal, and establishes synchronization with the base station.

  Subsequently, the base station side unit sends the reception timing to the mobile station side unit. The mobile station side unit generates a synchronization signal transmitted to the mobile station based on the reception timing. Then, the mobile station side unit periodically transmits a radio signal including a synchronization signal to the mobile station. The mobile station detects the synchronization signal and synchronizes the reception timing of the local station with the transmission timing of the mobile station side unit, thereby establishing synchronization between the mobile station side unit and the mobile station. Therefore, synchronization is established between the base station and the base station side unit and between the mobile station side unit and the mobile station.

JP 2010-80991 A

  However, in the conventional relay device, synchronization establishment is not assumed when the base station that is the communication destination of the base station side unit is changed by handover. For example, when the relay device is mounted on a vehicle such as a train, the relay device moves together with the vehicle, so that the communication destination base station may be switched by handover.

  Before the handover is performed, the mobile station has a reception frame 341 and a transmission frame 343 shown in FIG. 9 in order to communicate with the relay apparatus (mobile station side unit). The reception frame indicates a time range in which the mobile station can receive a signal from the relay device. The transmission frame indicates a time range in which the mobile station can transmit a signal to the relay device. In FIG. 9, Tx represents transmission by the mobile station, and Rx represents reception by the mobile station. When the radio signal 345 from the relay apparatus is transmitted at the timing of FIG. 9, the radio signal 345 is contained in the reception frame 341. Therefore, the mobile station can receive the radio signal 345.

  When the base station that is the communication destination of the base station side unit is switched by the handover of the relay device, a radio signal including a synchronization signal is sent to the mobile station from the base station after the handover via the relay device at a new timing. come. However, the mobile station cannot recognize in advance that the base station that is the communication destination of the base station side unit in the relay apparatus has been switched by the handover of the relay apparatus. Therefore, the mobile station tries to receive a radio signal from the base station after the handover with the reception frame 341 at the same timing as before the handover as shown in FIG.

  At this time, the radio signal 347 from the relay apparatus may not be contained in the reception frame 341. In this case, since the mobile station cannot receive the radio signal 347, the mobile station determines that the radio signal 347 is a transient error signal and makes a retransmission request to the base station. However, since the mobile station does not change the timing of the reception frame 341 according to the error signal, there is a high possibility that the retransmitted radio signal cannot be received. Therefore, it is difficult to establish synchronization between the relay apparatus after handover and the mobile station, and communication may be interrupted.

  Therefore, an object of the present invention made in view of the above problems is to provide a relay apparatus and a communication control method capable of continuing communication between a mobile station and a base station even after the base station is switched by handover in the relay apparatus. Is to provide.

In order to solve the above-mentioned problems, the invention according to the first aspect is
A relay device that relays radio signals transmitted and received between a first communication device that is an upper station and a second communication device that is a lower station,
A first communication unit that wirelessly communicates with the first communication device;
A second communication unit that wirelessly communicates with the second communication device;
A control unit that controls the second communication unit to transmit a radio signal including a synchronization signal at a timing based on the radio signal received by the first communication unit, and the control unit includes:
Via the second communication unit, obtain a reception allowable range between the reception timing of the radio signal in the second communication device and the start timing of the reception frame of the second communication device,
When the upper station is switched to the third communication device by the handover, the difference between the reception timings of the radio signals from the first communication device before the handover and the third communication device after the handover in the relay device is calculated,
When the difference exceeds the allowable reception range, the transmission timing of the radio signal is corrected so that the reception timing of the second communication device is within the reception frame.

  The invention according to a second aspect is characterized in that, in the relay apparatus according to the first aspect, the control unit decreases the correction amount of the transmission timing of the radio signal stepwise. .

  As described above, the solution of the present invention has been described as an apparatus. However, the present invention can be realized as a method, a program, and a storage medium storing the program, which are substantially equivalent thereto, and the scope of the present invention. It should be understood that these are also included.

For example, a communication control method that realizes the first aspect of the present invention as a method includes:
In a communication control method in a relay device that relays radio signals transmitted and received between a first communication device that is an upper station and a second communication device that is a lower station, the relay device includes:
Receiving a radio signal from the first communication device and transmitting a radio signal including a synchronization signal at a timing based on the signal;
Receiving from the second communication device information on an allowable reception range between the reception timing of the radio signal in the second communication device and the start timing of the reception frame of the second communication device;
Calculating a difference in reception timing of radio signals from the first communication device before the handover and the third communication device after the handover in the relay device when the upper station is switched to the third communication device by the handover;
Correcting the transmission timing of the radio signal including the synchronization signal so that the reception timing of the second communication device falls within the reception frame when the difference exceeds the allowable reception range;
And transmitting the wireless signal whose transmission timing is corrected to the second communication device.

  According to the relay apparatus and the communication control method according to the present invention configured as described above, the relay station does not transmit a radio signal at a timing at which the mobile station cannot receive. Communication with the base station can be continued.

FIG. 1 is a schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. FIG. 2 is a functional block diagram illustrating a schematic configuration of the relay device according to the embodiment of the present invention. FIG. 3 is an explanatory diagram showing a reception allowable range of the mobile station according to the embodiment of the present invention. FIG. 4 is an explanatory diagram showing a change of the received frame of the mobile station according to the embodiment of the present invention. FIG. 5 is a flowchart showing processing of the relay device according to the embodiment of the present invention. FIG. 6 is an explanatory diagram showing changes in reception timing of the mobile station according to the embodiment of the present invention. FIG. 7 is an explanatory diagram showing the reception timing of the relay device according to the embodiment of the present invention. FIG. 8 is an explanatory diagram showing changes in reception timing of the mobile station according to the embodiment of the present invention. FIG. 9 is a relationship diagram between a radio signal from a conventional relay device and a received frame of a mobile station. FIG. 10 is a relationship diagram between a radio signal from a conventional relay device and a received frame of a mobile station.

  Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a wireless communication system according to an embodiment of the present invention. The radio communication system 11 includes a base station BS (Base Station) (BS1 and BS2) (first and third communication devices which are higher stations in the claims) and a mobile station MS (Mobile Station) (lower station in the claims). The second communication device) and the relay device 101. When the communication method of the wireless communication system 11 is WiMAX, the wireless communication system 11 employs an orthogonal frequency division multiple access (OFDMA) method and a time division duplex (TDD) method. Is done. The relay apparatus 101 relays data transmitted and received between the base station BS and the mobile station MS in a wireless communication scheme such as WiMAX. The relay device 101 allows the mobile station MS to transmit and receive data to and from the base station BS even if it is located outside the cell (communication area) of the base station BS.

  In FIG. 1, it is assumed that the relay device 101 is mounted on a vehicle 103 and moves in a direction 105 together with the vehicle 103. The handover is executed when the vehicle 103 moves to the position 107, and the communication destination of the relay apparatus 101 is changed from the base station BS1 (base station before handover) (first communication apparatus) to the base station BS2 (base station after handover). Switch to (third communication device). Note that the present invention is not limited to the relay device 101 being for a moving vehicle, and the relay device 101 can be integrated or separated as long as the base station is switched by handover.

  FIG. 2 is a functional block diagram illustrating a schematic configuration of the relay device according to the embodiment of the present invention.

  The relay apparatus 101 includes a base station side unit 111 that communicates with the base station BS and a mobile station side unit 113 that communicates with the mobile station MS. The base station side unit 111 is arranged outside the vehicle 103, the mobile station side unit 113 is arranged inside the vehicle 103, and the base station side unit 111 and the mobile station side unit 113 are signal cables such as LAN cables. 115 is connected.

  First, functional blocks of the base station side unit 111 will be described. The base station side unit 111 includes a base station side transmission / reception unit 117 (a first communication unit in claims), a storage unit 119, and a control unit 121.

  The base station side transmission / reception unit 117 performs radio communication with the base station BS via an antenna. The base station side transmitting / receiving unit 117 generates a baseband signal by performing amplification and down-conversion with low noise on the received radio signal, and transmits the baseband signal to the control unit 121. In addition, the base station side transceiver 117 generates a radio signal by performing up-conversion and amplification on the baseband signal, and transmits the radio signal to the base station BS via an antenna.

  The storage unit 119 stores various information and also functions as a work memory. In the present embodiment, only the base station side unit 111 has a storage unit, but the present invention is not limited to this configuration. For example, only the mobile station side unit 113 has a storage unit, and the storage unit can receive and store various information of the base station side unit 111 via the signal cable 115. Moreover, both the base station side unit 111 and the mobile station side unit 113 have a memory | storage part, and each memory | storage part can memorize | store the information of each unit.

  The control unit 121 controls and manages the base station unit 111 and the mobile station unit 113 as a whole, including the functional blocks of the base station unit 111 and the mobile station unit 113. Here, the control unit 121 is configured as software executed on any suitable processor such as a CPU (Central Processing Unit), or a dedicated processor specialized for each process (for example, DSP (Digital Signal Processor)). Can also be configured. In the present embodiment, only the base station side unit 111 has a control unit, but the present invention is not limited to this configuration. For example, only the mobile station side unit 113 has a control unit, and the control unit can control and manage the entire base station side unit 111 via the signal cable 115. Moreover, both the base station side unit 111 and the mobile station side unit 113 have a control part, and each control part can also control and manage each unit.

  The control unit 121 will be described in more detail. The control unit 121 detects a synchronization signal (preamble) included in a radio signal from the base station BS received by the base station side transmitting / receiving unit 117. The detection of the synchronization signal is realized by performing AD conversion and fast Fourier transform (FFT) on the baseband signal transmitted from the base station side transmission / reception unit 117. Since the synchronization signal is periodically transmitted from the base station BS, the control unit 121 obtains the reception timing and the cycle at which the relay apparatus 101 receives the synchronization signal by converting the number of clock pulses in the counter of the control unit 121. To do.

  And the control part 121 produces | generates the synchronizing signal for transmitting to mobile station MS based on the radio signal received by the base station side transmission / reception part 117. FIG. That is, the control unit 121 generates a synchronization signal to be transmitted to the mobile station MS at the same timing as the reception timing of the relay apparatus 101 from the acquired reception timing and period. The control unit 121 generates a radio signal by adding a synchronization signal to the head of the data, and controls a mobile station side transmission / reception unit 123 described later so as to transmit the radio signal.

  In addition, the control unit 121 obtains the communication quality value of the radio signal received by the base station side transmitting / receiving unit 117. Communication quality values are, for example, SNR (Signal to Noise Ratio), CNR (Carrier to Noise Ratio), SINR (Signal to Interference and Noise Ratio), CINR (Carrier to Interference and Noise Ratio) and the like, the larger the communication quality value, the better the communication state of the base station BS which is the communication destination of the relay apparatus 101. Then, when the obtained communication quality value is less than the threshold value stored in advance in storage unit 119, control unit 121 performs handover and switches the communication destination base station. In the present invention, the criterion for performing handover is not limited to the communication quality value being less than the threshold value, and the control unit 121 may perform handover when the communication quality value is equal to or less than the threshold value. it can. Other processes performed by the control unit 121 will be described in detail later with reference to FIG.

  Next, functional blocks of the mobile station side unit 113 will be described. The mobile station side unit 113 includes a mobile station side transmission / reception unit 123 (second communication unit in claims).

  The mobile station side transmission / reception unit 123 performs radio communication with the mobile station MS via an antenna, and, like the base station side transmission / reception unit 117, generates a baseband signal from a radio signal and generates a radio signal from a baseband signal. Do. For example, the mobile station side transmitting / receiving unit 123 transmits a radio signal including a synchronization signal to the mobile station MS, or receives a radio signal including information on the allowable reception range from the mobile station MS. Here, the allowable reception range of the mobile station MS will be described with reference to FIG. The mobile station MS sets the reception frame 133 from the synchronization signal included in the received radio signal 131. The reception frame 133 indicates a time range in which the mobile station MS can receive a signal from the relay apparatus 101 (mobile station side unit 113). The mobile station MS can receive the radio signal when the radio signal arrives in the reception frame 133. The reception allowable range is a time interval d1 between the start timing t1 of the reception frame 133 and the reception timing t2 of the radio signal 131. Even if the wireless signal arrives earlier than the reception timing t2 due to a change in the communication environment or the like, the mobile station MS can receive the wireless signal if the arrival timing is within the allowable reception range.

  In addition, the mobile station MS can shift the reception frame every time a radio signal is received so that the reception allowable range of the reception frame becomes a predetermined value α. The predetermined value α indicates the timing of receiving a radio signal from the base station BS via the relay device 101 when the mobile station MS can establish synchronization with the base station BS. Hereinafter, in the present embodiment, the predetermined value α is assumed to be d1. As shown in FIG. 4, it is assumed that the mobile station MS receives the radio signal 135 at the reception timing t3 in the same reception frame 133 as in FIG. At this time, it is assumed that the allowable reception range is d2 (d2 <d1). The mobile station MS can set the new reception frame 137 at the start timing t4 by advancing the start timing t1 of the reception frame 133 by (d1-d2) in order to set the allowable reception range to d1. Thereby, after the mobile station MS shifts the reception frame 133, if the radio signal 138 arrives at the mobile station MS at the same timing as the radio signal 135, the reception allowable range becomes d1. Along with the movement of the reception frame, the transmission frame 139 indicating the time range in which the mobile station MS can transmit a signal to the relay apparatus 101 can be changed to the transmission frame 140.

  Next, a synchronization signal transmission method of the relay apparatus 101 will be described with reference to FIGS. 5, 6, 7, and 8. FIG. 5 is a flowchart showing processing of the relay device according to the embodiment of the present invention. 6 and 8 are explanatory diagrams showing changes in reception timing of the mobile station according to the embodiment of the present invention. FIG. 7 is an explanatory diagram showing the reception timing of the relay device according to the embodiment of the present invention.

  First, the mobile station MS establishes synchronization with the base station BS1 via the relay apparatus 101, and periodically sets the reception frame 141 and the transmission frame 143 shown in FIG. The mobile station MS communicates with the base station BS1 via the relay device 101. The start timing of the reception frame 141 is t11, and the mobile station MS receives the radio signal 145 at the reception timing t12 at which the allowable reception range is d1.

  The mobile station side transmission / reception unit 123 receives a radio signal including the information (d1) of the allowable reception range from the mobile station MS (step S101), and sends it to the control unit 121.

  The control unit 121 acquires information on the allowable reception range from the radio signal. Then, information on the permissible reception range is stored in the storage unit 119 (step S102).

  In addition, the control unit 121 acquires the reception timing of the radio signal from the synchronization signal included in the radio signal from the base station BS1, and stores it in the storage unit 119 (step S103).

  Further, the control unit 121 obtains the communication quality value of the radio signal from the base station BS1 and compares it with the threshold value stored in the storage unit 119. When the vehicle 103 on which the relay device 101 is mounted moves to the position 107, the communication quality value becomes less than the threshold value, and the control unit 121 executes a handover (step S104). As a result of the handover, the communication destination of the relay apparatus 101 is switched from the base station BS1 (base station before the handover) to the base station BS2 (base station after the handover).

  The base station side transmitting / receiving unit 117 of the relay apparatus 101 receives a radio signal including a synchronization signal from the base station BS2 (step S105). The control unit 121 acquires the reception timing and period of the synchronization signal from the radio signal received by the base station side transmission / reception unit 117 (step S106). And the control part 121 produces | generates the synchronizing signal for transmitting to the mobile station MS based on the received radio signal.

  Next, the control unit 121 calculates a difference between the reception timing of the radio signal from the base station BS1 before the handover and the reception timing of the radio signal from the base station BS2 after the handover (step S107). That is, as shown in FIG. 7, when relay apparatus 101 receives radio signal 145 from base station BS1 before handover and receives radio signal 147 from base station BS2 after handover, control unit 121 Calculates the difference d3 in the reception timing.

  The control unit 121 compares the calculated reception timing difference d3 with the allowable reception range of the mobile station MS stored in the storage unit 119 (step S108). When the difference d3 is equal to or smaller than the allowable reception range d1 (d3 ≦ d1) (Yes in step S108), the control unit 121 causes the mobile station side transmitting / receiving unit 123 to transmit the radio signal 147 having the generated synchronization signal at the head. (Step S109). Since the difference d3 is less than or equal to the allowable reception range d1, the radio signal 147 reaches the reception frame 141 of the mobile station MS as shown in FIG. Therefore, the mobile station MS can receive the radio signal 147.

  Next, a case where the difference d3 exceeds the allowable reception range d1 (d3> d1) (No in step S108) will be described. When the relay apparatus 101 transmits the radio signal 147 to the mobile station MS based on the generated synchronization signal, the radio signal 147 arrives earlier than the start timing t11 of the reception frame 141 of the mobile station MS as shown in FIG. End up. That is, the mobile station MS cannot receive the radio signal 147. Therefore, the control unit 121 corrects the transmission timing t14 of the radio signal 147 (step S110).

  Specifically, the control unit 121 delays the transmission timing t14 of the radio signal 147 by (d3-d1) or more. By doing so, the reception timing of the radio signal 147 at the mobile station MS falls within the reception frame 141. When the transmission timing t14 of the wireless signal 147 is delayed more than d3, the control unit 121 needs to shift the transmission timing t14 of the wireless signal 147 so that the end timing t13 of the wireless signal 147 does not fall outside the reception frame 141. There is. Hereinafter, in the present embodiment, the control unit 121 shifts the transmission timing so that the transmission timing of the radio signal 147 overlaps the start timing of the reception frame of the mobile station MS.

  Therefore, the control unit 121 delays the transmission timing t14 of the radio signal 147 by (d3-d1). Then, the control unit 121 transmits the radio signal 147 to the mobile station side transmission / reception unit 123 at the corrected transmission timing (step S111). Hereinafter, the wireless signal 147 transmitted by the first transmission timing correction is referred to as a wireless signal 147-1.

  Then, the radio signal 147-1 arrives at the start timing t11 of the reception frame 141 of the mobile station MS. Therefore, the mobile station MS can receive the radio signal 147-1. The mobile station MS receives the radio signal 147-1 and advances the reception frame 141 (and the transmission frame 143) by α in order to maintain the allowable reception range at a predetermined value α (= d1). That is, the mobile station MS sets a new reception frame 149 (and transmission frame 151). Then, the mobile station MS can include the information of the start timing t15 of the received frame 149 after the change in the radio signal and transmit it to the relay apparatus 101.

  The mobile station side transmitting / receiving unit 123 receives the information of the changed start timing t15 (step S112), and the control unit 121 compares the start timing t15 with the transmission timing t14 before correction of the radio signal 147 (step S113). ). When the transmission timing t14 before correction is less than the start timing t15, that is, when the transmission timing t14 before correction is earlier than the start timing t15 (t14 <t15) (Yes in step S113), the control unit 121 transmits the transmission timing of the radio signal 147. t14 is delayed by (d3-d1 × 2) (step S110). Then, the control unit 121 causes the mobile station side transmission / reception unit 123 to transmit the radio signal 147 at the corrected transmission timing (step S111). Hereinafter, the wireless signal 147 transmitted by the second transmission timing correction is referred to as a wireless signal 147-2.

  The radio signal 147-2 arrives at the start timing t15 of the reception frame 149 of the mobile station MS. Therefore, the mobile station MS can receive the radio signal 147-2. The mobile station MS receives the radio signal 147-2 and advances the reception frame 149 (and the transmission frame 151) by α in order to maintain the allowable reception range at the predetermined value α. That is, the mobile station MS sets a new reception frame 153 (and transmission frame 155). The mobile station MS can include the information of the start timing t16 of the received frame 153 after the change in the radio signal and transmit it to the relay apparatus 101.

  The mobile station side transmission / reception unit 123 receives the information of the changed start timing t16 (step S112), and the control unit 121 compares the start timing t16 with the transmission timing t14 before correction of the radio signal 147 (step S113). ). As shown in FIG. 8, when the transmission timing t14 before the correction is equal to or greater than the start timing t16 (t14 ≧ t16) (No in step S113) due to the correction of the transmission timing twice, the control unit 121 transmits the radio signal. The radio signal 147 is transmitted to the mobile station side transmitting / receiving unit 123 without correcting the transmission timing t14 of 147 (step S109).

  The radio signal 147 reaches the reception frame 153 of the mobile station MS, and the mobile station MS can receive the radio signal 147. The mobile station MS further advances the reception frame 153 (and transmission frame 155) and sets a new reception frame 157 (and transmission frame 159) so that the allowable reception range becomes the predetermined value α. Therefore, the mobile station MS can receive a signal from the base station BS2 after the handover at a reception timing at which the reception allowable range becomes the predetermined value α. Thereby, the synchronization between the base station BS2 and the mobile station MS is established.

  The correction amount of the transmission timing of the radio signal 147 is (d3-d1) for the first time, and (d3-d1 × 2) for the second time. That is, the control unit 121 can set the reception frame 157 in which the allowable reception range is the predetermined value α by gradually reducing the transmission timing correction amount.

  As described above, in this embodiment, the control unit 121 of the relay apparatus 101 receives the reception timing t12 of the radio signal 145 at the mobile station MS and the start timing t11 of the reception frame 141 of the mobile station MS via the mobile station side transmission / reception unit 123. The reception allowable range d1 between the two is acquired. Then, when the communication destination base station is switched by the handover, the control unit 121 calculates a difference d3 in reception timing of radio signals from the base station BS1 before the handover and the base station BS2 after the handover in the relay apparatus 101. Subsequently, when the difference d3 exceeds the allowable reception range d1, the control unit 121 corrects the transmission timing of the radio signal 147 so that the reception timing of the mobile station MS is within the reception frame 141. That is, when the communication destination base station is switched by handover, the control unit 121 determines whether the mobile station MS can receive a radio signal based on a synchronization signal from the base station after the handover. When it is determined that the mobile station MS cannot be received, the control unit 121 transmits the radio signal while shifting the transmission timing so that the mobile station MS can receive it. Thereby, even if the communication destination base station changes after the handover, the mobile station MS can receive the radio signal and can continue communication with the base station BS2.

  Moreover, in this embodiment, the control part 121 can make small the correction amount of the transmission timing of the radio | wireless signal 147 based on the synchronizing signal from base station BS2 after a hand-over. In other words, by reducing the amount by which the transmission timing of the radio signal 147 is delayed, the start timing of the reception frame of the mobile station MS is advanced, and the radio signal 147 can be transmitted within the reception frame without shifting the transmission timing of the radio signal 147. Will fit in. Thereby, the reception allowable range of the reception frame of the mobile station MS can be brought close to a predetermined value, and synchronization between the mobile station MS and the base station BS2 can be established.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention.

  For example, functions included in each member, each means, each step, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, steps, etc. can be combined or divided into one. Is possible.

  In the above description of the embodiment of the present invention, it has been described that the communication destination of the relay apparatus 101 switched by handover is a base station, but the present invention is not limited to this mode. For example, when communication between a base station and a mobile station is relayed by a plurality of relay devices, the communication destination of the relay device that is switched by handover can be the relay device. Also, for example, a relay device whose mobile station side unit is another relay device as a communication destination acquires information on the allowable reception range from the other relay device, and corrects the transmission timing of the radio signal as described above. You can also.

DESCRIPTION OF SYMBOLS 11 Wireless communication system 101 Relay apparatus 103 Vehicle 105 Direction 107 Position 111 Base station side unit 113 Mobile station side unit 115 Signal cable 117 Base station side transmission / reception part 119 Storage part 121 Control part 123 Mobile station side transmission / reception part 131,135,138, 145, 147, 147-1, 147-2 Radio signal 133, 137, 141, 149, 153, 157 Received frame 139, 140, 143, 151, 155, 159 Transmitted frame BS1, BS2 Base station MS Mobile station d1, d2 Acceptable reception range d3 Difference t1, t4, t11, t15, t16 Start timing t2, t3, t12 Reception timing t13 End timing t14 Transmission timing α Predetermined value

Claims (3)

A relay device that relays radio signals transmitted and received between a first communication device that is an upper station and a second communication device that is a lower station,
A first communication unit that wirelessly communicates with the first communication device;
A second communication unit that wirelessly communicates with the second communication device;
A control unit that controls the second communication unit to transmit a radio signal including a synchronization signal at a timing based on the radio signal received by the first communication unit, and the control unit includes:
Via the second communication unit, obtain a reception allowable range between the reception timing of the radio signal in the second communication device and the start timing of the reception frame of the second communication device,
When the upper station is switched to the third communication device by the handover, the difference between the reception timings of the radio signals from the first communication device before the handover and the third communication device after the handover in the relay device is calculated,
A relay device that corrects the transmission timing of a radio signal so that the reception timing of the second communication device is within the reception frame when the difference exceeds the allowable reception range. The relay device according to claim 1, wherein the control unit includes:
A relay apparatus that reduces the correction amount of the transmission timing of the radio signal in a stepwise manner. In a communication control method in a relay device that relays radio signals transmitted and received between a first communication device that is an upper station and a second communication device that is a lower station, the relay device includes:
Receiving a radio signal from the first communication device and transmitting a radio signal including a synchronization signal at a timing based on the signal;
Receiving from the second communication device information on an allowable reception range between the reception timing of the radio signal in the second communication device and the start timing of the reception frame of the second communication device;
Calculating a difference in reception timing of radio signals from the first communication device before the handover and the third communication device after the handover in the relay device when the upper station is switched to the third communication device by the handover;
Correcting the transmission timing of the radio signal including the synchronization signal so that the reception timing of the second communication device is within the reception frame when the difference exceeds the allowable reception range;
Transmitting the wireless signal with corrected transmission timing to the second communication device.

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