JP2013074501A - Relay device and communication control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a relay device and a communication control method which can efficiently suppress degradation of throughput speed.SOLUTION: A relay device 101 relays wireless signals transmitted and received between a base station and a mobile station. The relay device 101 comprises: a mobile station side communication unit 123 for transmitting/receiving the wireless signals to/from a mobile station; and a control unit 121 which calculates free space loss between the relay device 101 and the mobile station, and releases wireless connection between the mobile station and the mobile station side communication unit 123 on the basis of the free space loss.

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 (service area) 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 (for example, the inside of a building and the basement) where radio waves do not reach from base stations installed outdoors. 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 signals between the base station and the mobile station is required.

  This relay device has the advantage that the service area can be expanded, but has the disadvantage that radio waves emitted by the relay device cause interference with other radio waves. One of the interferences caused by relay devices is between a donor node (MS (Mobile Station) unit) that communicates with a base station and a service node (BS (Base Station) unit) that communicates with a mobile station. Mutual interference (wraparound interference or self-interference) can be mentioned. For example, when the reception period of the donor node and the transmission period of the service node overlap, the transmission wave from the base station interferes with the transmission wave of the service node, and the donor node transmits the transmission wave from the base station with degraded quality. Will be received. Similarly, mutual interference also occurs when the transmission period of the donor node and the reception period of the service node overlap.

  Thus, conventionally, a wireless communication method for suppressing mutual interference has been proposed (see, for example, Patent Document 1). In this method, as shown in FIG. 4, the reception (Rx) period of the donor node and the reception period of the service node are matched within the downlink subframe period (first period) in which the base station transmits the downlink signal. Further, the transmission (Tx) period of the donor node and the transmission period of the service node are combined within the uplink subframe period (second period) in which the base station receives the uplink signal. Thereby, it is possible to suppress the mutual interference as described above. In addition, DL in FIG. 4 means a downlink (Down Link) and UL means an uplink (Up Link).

JP 2010-56711 A

  However, in the conventional method, although mutual interference is suppressed, if the first period and the second period are not equal, a period in which transmission / reception is not performed in the relay apparatus occurs. For example, when the first period is longer than the second period as shown in FIG. 4, the transmission period of the downlink signal of the service node is longer by the third period than the transmission period of the uplink transmission of the donor node. In this third period, the downlink signal is received at the donor node. Therefore, the service node has to stop transmission of downlink signals in order to suppress the occurrence of mutual interference. Therefore, a third period in which transmission / reception is not performed in the service node occurs. That is, in the conventional method, the throughput speed in the communication line between the base station and the mobile station is reduced by passing through the relay device.

  Accordingly, an object of the present invention made in view of the above problems is to provide a relay device and a communication control method capable of efficiently suppressing a decrease in throughput speed.

In order to solve the above-described problems, the invention of the relay device according to the first aspect is as follows:
A relay device that relays radio signals transmitted and received between a base station and a mobile station,
A mobile station side communication unit for transmitting and receiving radio signals to and from the mobile station;
Find the free space loss between the relay device and the mobile station,
The relay apparatus includes a control unit that releases a wireless connection between the mobile station and the mobile station side communication unit based on the free space loss.

  The invention according to a second aspect is the relay apparatus according to the first aspect, wherein the control unit calculates the distance between the relay apparatus and the mobile station using the free space loss, and the distance Is less than the distance threshold, the wireless connection between the mobile station and the mobile station side communication unit is released.

  The invention according to a third aspect is the relay apparatus according to the first aspect, wherein the control unit uses the free space loss and the radio signal from the base station reaches the mobile station directly. The received signal strength at the mobile station is calculated, and when the received signal strength is equal to or higher than the received signal strength threshold, the radio signal between the mobile station and the mobile station side communication unit is released. is there.

  The invention according to a fourth aspect is the relay apparatus according to the first aspect, wherein the control unit uses the free space loss to determine a distance between the relay apparatus and the mobile station, and from the base station. When the radio signal of the mobile station directly arrived at the mobile station and the received signal strength at the mobile station, the distance is less than a distance threshold, and the received signal strength is greater than or equal to the received signal strength threshold, The wireless connection between the mobile station and the mobile station side communication unit is released.

Further, the invention according to a fifth aspect is the relay device according to any one of the first to fourth aspects, wherein the control unit includes:
At the time of relaying a radio signal, the mobile station side communication unit is controlled to transmit an interference signal for interfering with a synchronization signal transmitted from the base station to the mobile station with a predetermined transmission power,
When releasing the wireless connection with the mobile station, the wireless connection between the mobile station and the mobile station side communication unit is released by lowering the transmission power of the interference signal below the predetermined transmission power. It is what.

  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 apparatus that relays radio signals transmitted and received between a base station and a mobile station, the relay apparatus includes:
Determining a free space loss between the relay device and the mobile station;
And a step of releasing a wireless connection between the mobile station and the mobile station side communication unit based on the free space loss.

  According to the relay apparatus and the communication control method according to the present invention configured as described above, when it is determined that the relay apparatus is unnecessary based on free space loss, the mobile station and the mobile station side communication unit Since the wireless connection is released, it is possible to prevent a decrease in throughput rate due to the relay device.

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 a flowchart showing processing of the relay device according to the embodiment of the present invention. FIG. 4 is a time chart showing a transmission / reception period of a conventional relay device.

  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), a mobile station MS (Mobile Station), and a relay device 101. When the communication method of the wireless communication system 11 is WiMAX, for example, a time division duplex (TDD) method is adopted for the wireless communication system 11. The relay apparatus 101 relays a radio signal (data) transmitted and received between the base station BS and the mobile station MS in a wireless communication method such as WiMAX. The mobile station MS can transmit and receive radio signals to and from the base station BS via the relay device 101 even if the mobile station MS is located outside the cell (communication area) of the base station BS.

  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 donor node (MS (Mobile Station) unit) 111 that communicates with a base station BS and a service node (BS (Base Station) unit) 113 that communicates with a mobile station MS. The relay device 101 is an integral type, a separation type, or a vehicle type. The integrated relay apparatus 101 includes a donor node 111 and a service node 113 in one housing. In the separation-type or vehicle-type relay device 101, the donor node 111 and the service node 113 can be arranged independently of each other. The separate or vehicle-type donor node 111 and the service node 113 are connected by a signal cable such as a LAN (Local Area Network) cable.

  First, functional blocks of the donor node 111 will be described. The donor node 111 includes a base station side communication unit 117, a storage unit 119, and a control unit 121. The base station side communication unit 117 and the storage unit 119 are connected to the control unit 121.

  The base station side communication unit 117 transmits and receives radio signals to and from the base station BS via an antenna. The base station side communication unit 117 generates a baseband signal by performing amplification and down-conversion with low noise on the received radio signal, and sends the baseband signal to the control unit 121. The base station side communication unit 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 the antenna.

  When the time division duplex method is adopted in the radio communication system 11, the base station side communication unit 117 receives a radio signal from the base station BS in the downlink subframe period (first period) of the base station BS, for example. Then, the radio signal is transmitted to the base station BS in the uplink subframe period (second period) of the base station BS following the first period. And the base station side communication part 117 repeats reception and transmission by repetition of the continuous 1st period and 2nd period.

  The storage unit 119 stores various information such as a distance threshold value and a received signal strength threshold value, and also functions as a work memory.

  The distance threshold is a threshold related to the distance between the relay apparatus 101 and the mobile station MS when the relay apparatus 101 is integrated, and with the service node 113 of the relay apparatus 101 when the relay apparatus 101 is a separation type or a vehicle type. This is a threshold regarding the distance to the mobile station MS. The distance threshold is an index indicating whether the mobile station MS can directly receive a radio signal from the base station BS with stable quality. “Direct” means that the communication between the base station BS and the mobile station MS is not performed via the relay device 101. The stable quality is, for example, a quality capable of demodulating a radio signal from the base station BS or a quality capable of realizing a desired throughput speed. If the distance between the relay device 101 (service node 113) and the mobile station MS is less than the distance threshold, it means that the mobile station MS can directly communicate with the base station BS with stable quality. Further, when the distance between the relay apparatus 101 (service node 113) and the mobile station MS is equal to or greater than the distance threshold, the mobile station MS cannot communicate with the base station BS with stable quality without going through the relay apparatus 101. Means that.

  The received signal strength threshold indicates the received signal strength of the mobile station MS that is necessary so that the mobile station MS can directly receive a radio signal from the base station BS with stable quality, for example, RSSI (Received Signal Strength Indicator). Is the value of The stable quality is, for example, a quality capable of demodulating a radio signal from the base station BS or a quality capable of realizing a desired throughput speed. When the received signal strength of the mobile station MS is equal to or higher than the received signal strength threshold, it means that the mobile station MS can directly receive a radio signal from the base station BS with stable quality. Moreover, when the received signal strength of the mobile station MS is less than the received signal strength threshold, it means that the mobile station MS cannot directly receive a radio signal from the base station BS with stable quality.

  In the present embodiment, only the donor node 111 has the storage unit 119, but the present invention is not limited to this configuration. For example, only the service node 113 may have a storage unit, and the storage unit may store various information of the donor node 111 and the service node 113. Moreover, both the donor node 111 and the service node 113 have a storage unit, and each storage unit can store information on each unit associated with the storage unit.

  The control unit 121 controls and manages the entire donor node 111 and service node 113 as well as the functional blocks of the donor node 111 and service node 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 donor node 111 has the control unit 121, but the present invention is not limited to this configuration. For example, only the service node 113 has a control unit, and the control unit can control and manage the donor node 111 and the service node 113 as a whole. Further, both the donor node 111 and the service node 113 have a control unit, and each control unit can control and manage each unit related to the control unit.

  Next, functional blocks of the service node 113 will be described. The service node 113 includes a mobile station side communication unit 123. The mobile station side communication unit 123 is connected to the control unit 121.

  The mobile station side communication unit 123 transmits and receives radio signals to and from the mobile station MS via the antenna. The mobile station side communication unit 123 generates a baseband signal by performing amplification and down-conversion with low noise on the received radio signal, and sends the baseband signal to the control unit 121. Also, the mobile station side communication unit 123 generates a radio signal by performing up-conversion and amplification on the baseband signal, and transmits the radio signal to the mobile station MS via the antenna.

  When the time division duplex method is employed in the wireless communication system 11, the mobile station side communication unit 123 receives, for example, a wireless signal from the mobile station MS within the first period, and transmits the wireless signal to the mobile station MS. Transmit within a second period following the first period. And the mobile station side communication part 123 repeats reception and transmission by repetition of the continuous 1st period and 2nd period. Mutual interference in the relay apparatus 101 is suppressed by the transmission period between the mobile station side communication unit 123 and the base station side communication unit 117 and the reception period between the mobile station side communication unit 123 and the base station side communication unit 117 being aligned. The

Here, the control unit 121 of the donor node 111 will be described in more detail. When the mobile station side communication unit 123 receives a radio signal including information on the transmission output margin (Headroom Margin) of the mobile station MS, the control unit 121 moves with the relay apparatus 101 (service node 113) from the transmission output margin. Calculate the free space loss with the station MS. The transmission output margin of the mobile station MS is the difference between the maximum transmission output of the mobile station MS and the actual transmission output of the mobile station MS. The mobile station MS determines that the communication environment of its own station is worse as the received signal strength of the received radio signal is lower, and increases the transmission output. For this reason, the smaller the transmission output margin, the worse the communication environment of the mobile station MS. There is a one-to-one correspondence between the received signal strength of the mobile station MS and the transmission output, that is, the transmission output margin. Therefore, the control unit 121 can obtain the received signal strength of the mobile station MS by acquiring the transmission output margin. Moreover, since the control part 121 is a self-station | mobile_unit, it can identify the transmission signal strength of the mobile station side communication part 123. FIG. Therefore, the control unit 121 can obtain the free space loss by subtracting the reception signal strength of the mobile station MS from the transmission signal strength of the mobile station side communication unit 123 as in the following formula (1). The free space loss is a value of electric field strength that is lost when radio waves propagate through a space free of obstacles. That is, the free space loss between the relay apparatus 101 (service node 113) and the mobile station MS allows a radio signal from the base station BS to reach the mobile station MS without passing through the relay apparatus 101, thereby realizing stable communication. This is information used to determine whether or not it can be performed.
(Free space loss) = (Transmission signal strength) − (Reception signal strength) (1)

  Note that the method for obtaining the free space loss is not limited to the above solution. For example, when the mobile station MS transmits the transmission signal strength information to the relay apparatus 101, the control unit 121 determines the radio signal from the mobile station MS received by the mobile station side communication unit 123 from the transmission signal strength of the mobile station MS. It is also possible to obtain it by subtracting the received signal strength.

  And the control part 121 can calculate the distance between the relay apparatus 101 (service node 113) and the mobile station MS by solving the following numerical formula (2) about r from the obtained free space loss. . r is the distance between the relay apparatus 101 (service node 113) and the mobile station MS. π is the circumference ratio. λ is a wavelength of a radio signal (radio wave) transmitted by the mobile station side communication unit 123.

  Subsequently, the control unit 121 compares the calculated distance with a distance threshold value. When the calculated distance is less than the distance threshold, the mobile station MS can directly communicate with the base station BS with stable quality, and therefore the control unit 121 can determine that the relay apparatus 101 is not necessary. Therefore, the control unit 121 releases the wireless connection between the mobile station MS and the service node 113 (mobile station side communication unit 123). The release of the wireless connection is to disconnect the wireless connection, and can be realized, for example, by invalidating the function of the mobile station side communication unit 123.

  Further, the control unit 121 moves so as to transmit an interference signal with a predetermined transmission power for interfering with a synchronization signal transmitted from the base station BS to the mobile station MS while the relay apparatus 101 relays the radio signal. The station side communication unit 123 may be controlled. When the mobile station MS can receive the synchronization signal from both the relay apparatus 101 and the base station BS, the mobile station MS establishes a wireless connection with the base station BS even though the throughput speed is lower than the wireless connection with the relay apparatus 101. Sometimes. Therefore, the control unit 121 can cause the mobile station-side communication unit 123 to transmit an interference signal that causes interference with the synchronization signal from the base station BS and cannot be detected by the mobile station MS. In this case, the wireless connection can be released by lowering the transmission power of the interference signal below a predetermined transmission power. When the control unit 121 reduces the transmission power of the interference signal, the synchronization signal from the base station BS can easily reach the mobile station MS, and the mobile station MS can establish a wireless connection with the base station BS. Thereby, the wireless connection between the relay apparatus 101 and the mobile station MS is released.

The control unit 121 can also determine release of the wireless connection with the mobile station MS based on the received signal strength of the mobile station MS instead of the distance between the relay apparatus 101 and the mobile station MS. The control unit 121 obtains the received signal strength of the radio signal from the base station BS received by the donor node 111. And, when the radio signal from the base station BS directly reaches the mobile station MS by subtracting the free space loss obtained by the formula (1) from the received signal strength as in the following formula (3) The received signal strength at the mobile station MS can be calculated.
(Received signal strength of mobile station) = (Received signal strength of donor node) − (Free space loss) (3)

  When the calculated received signal strength is equal to or higher than the received signal strength threshold, the mobile station MS can directly receive a radio signal from the base station BS with stable quality, and therefore the control unit 121 does not need the relay device 101. Judge. Therefore, the control unit 121 releases the wireless connection with the mobile station MS.

  Further, the control unit 121, when the distance between the relay apparatus 101 (service node 113) and the mobile station MS is less than the distance threshold and the received signal strength of the mobile station MS is equal to or greater than the received signal strength threshold. The wireless connection with the MS can also be released. Other processes performed by the control unit 121 will be described in detail later with reference to FIG.

  Next, a method for determining the necessity of the relay apparatus 101 will be described with reference to FIG. FIG. 3 is a flowchart showing processing of the relay device according to the embodiment of the present invention.

  First, the control unit 121 acquires the received signal strength of the radio signal from the base station BS received by the base station side communication unit 117 of the donor node 111 (step S101). Here, the control unit 121 uses the acquired received signal strength as a threshold (first threshold) related to the received signal strength of the donor node 111, which is an index indicating whether or not the radio signal from the base station BS reaches the mobile station MS directly. ) Can be compared (step S102). In order for the base station BS and the mobile station MS to communicate without going through the relay apparatus 101, it is necessary for radio waves (radio signals) from the base station BS to reach the mobile station MS directly. Therefore, the value of the received signal strength at the position of the donor node 111 that guarantees that the radio wave from the base station BS reaches the mobile station MS is set as the first threshold value. The value can be obtained in consideration of the attenuation rate of the electric field strength of the radio wave related to the moving distance, the positional relationship between the base station BS, the relay device 101, and the mobile station MS. If the received signal strength of the donor node 111 is less than the first threshold value (No in step S102), it is determined that there is no need to perform the following process because the radio signal from the base station BS does not reach the mobile station MS in the first place. it can. Therefore, it is possible to avoid performing unnecessary processing.

  When the received signal strength of the donor node 111 is equal to or higher than the first threshold (Yes in step S102), the control unit 121 performs communication on the mobile station side so as to receive a radio signal including information on the transmission output margin from the mobile station MS. The unit 123 is controlled to acquire the transmission output margin (step S103). Here, the control unit 121 uses the acquired transmission output margin as an index indicating whether or not the mobile station MS is receiving a radio signal from the relay apparatus 101 in a good communication environment. It can be compared with a threshold (second threshold) relating to the margin (step S104). In order for the base station BS and the mobile station MS to communicate without going through the relay apparatus 101, the communication environment of the mobile station MS needs to be good. A good communication environment is, for example, an environment in which a radio signal received by the mobile station MS has a sufficient electric field strength and can be correctly demodulated. As the communication environment is better and the electric field strength of the received signal is larger, the mobile station MS transmits a radio signal with smaller transmission power. Therefore, the transmission output margin increases. Therefore, a value of the transmission output margin that guarantees that the communication environment of the mobile station MS is good is set as the second threshold value. When the transmission output margin is less than the second threshold (No in step S104), even if the radio signal from the base station BS reaches the mobile station MS, it is not received correctly. Therefore, it can be determined that there is no need to perform the following processing. Therefore, it is possible to avoid performing unnecessary processing.

  When the transmission output margin is greater than or equal to the second threshold (Yes in step S104), the control unit 121 calculates free space loss from the above equation (1) (step S105). Then, the control unit 121 determines the distance between the relay apparatus 101 (service node 113) and the mobile station MS from the free space loss, and the received signal strength when the radio signal from the base station BS directly reaches the mobile station MS. Both or either one is calculated, and the necessity of the relay apparatus 101 is determined (step S106). Hereinafter, in step S106, it is assumed that the distance between the relay apparatus 101 (service node 113) and the mobile station MS is calculated.

  When the calculated distance is equal to or greater than the distance threshold stored in the storage unit 119, the control unit 121 determines that the relay device 101 is necessary (Yes in step S106), and determines that the service node 113, the mobile station MS, The wireless connection is maintained (step S107). When the calculated distance is less than the distance threshold, the control unit 121 determines that the relay apparatus 101 is not necessary (No in step S106), and releases the wireless connection between the service node 113 and the mobile station MS. (Step S108).

  Thus, in the present embodiment, the control unit 121 of the relay apparatus 101 obtains a free space loss between the relay apparatus 101 (service node 113) and the mobile station MS, and moves with the mobile station MS based on the free space loss. The wireless connection with the station side communication unit 123 is released. The free space loss between the relay apparatus 101 and the mobile station MS determines whether or not a radio signal from the base station BS reaches the mobile station MS without passing through the relay apparatus 101 and stable communication can be realized. Information used above, for example, the distance between the relay device 101 (service node 113) and the mobile station MS, or a mobile station when a radio signal from the base station BS reaches the mobile station MS directly from the loss of free space It is possible to obtain the received signal strength at the MS. Therefore, the control unit 121 can determine the necessity of the relay device 101 from the value obtained using the free space loss. When the relay device 101 is not necessary, the mobile station MS and the mobile station side communication unit 123 releases the wireless connection. As a result, it is possible to prevent a decrease in throughput speed and self-interference caused by the relay apparatus 101.

  In the present embodiment, the control unit 121 calculates the distance between the relay device 101 (service node 113) and the mobile station MS using free space loss, and when the distance is less than the distance threshold, the mobile station The wireless connection between the MS and the mobile station side communication unit 123 can be released. The distance threshold is an index indicating whether or not the mobile station MS can directly receive a radio signal from the base station BS with stable quality. Therefore, the control unit 121 determines that the calculated distance is less than the distance threshold. Therefore, it can be determined that the relay apparatus 101 is unnecessary. Therefore, the control unit 121 can release the wireless connection between the mobile station MS and the mobile station side communication unit 123 while maintaining communication between the base station BS and the mobile station MS.

  In the present embodiment, the control unit 121 calculates the received signal strength at the mobile station MS when the radio signal from the base station BS directly reaches the mobile station MS using the free space loss, and receives the received signal. When the signal strength is equal to or greater than the received signal strength threshold, the radio signal between the mobile station MS and the mobile station side communication unit 123 can be released. Since the received signal strength threshold is a value of the received signal strength of the mobile station MS that is necessary for the mobile station MS to directly receive a radio signal from the base station BS with stable quality, the control unit 121 calculates When the received signal strength is equal to or higher than the received signal strength threshold, it can be determined that the relay apparatus 101 is unnecessary. Therefore, the control unit 121 can release the wireless connection between the mobile station MS and the mobile station side communication unit 123 while maintaining communication between the base station BS and the mobile station MS.

  In the present embodiment, the control unit 121 uses the free space loss to determine the distance between the relay apparatus 101 and the mobile station MS and the mobile station when the radio signal from the base station BS reaches the mobile station MS directly. The received signal strength at the MS is calculated, and when the distance is less than the distance threshold and the received signal strength is greater than or equal to the received signal strength threshold, the wireless connection between the mobile station MS and the mobile station side communication unit 123 is released. be able to. The control unit 121 can more reliably determine the necessity of the relay apparatus 101 by using both the distance and the received signal strength as a reference for releasing the radio signal between the mobile station MS and the mobile station side communication unit 123. Can do.

  Further, in the present embodiment, the control unit 121 transmits the interference signal for interfering with the synchronization signal transmitted from the base station BS to the mobile station MS at a predetermined transmission power when the radio signal is relayed. When controlling the communication unit 123 and releasing the wireless connection with the mobile station MS, the wireless connection between the mobile station MS and the mobile station side communication unit 123 is achieved by lowering the transmission power of the interference signal below a predetermined transmission power. Can be released. The control unit 121 can also release the wireless connection by disabling the function of the mobile station side communication unit 123, but if the function of the mobile station side communication unit 123 is disabled, the mobile station communicating with the relay apparatus 101 is When there are a plurality of mobile stations, wireless connections with all mobile stations are released. For this reason, the radio signal from the relay apparatus 101 arrives, but the communication between the mobile station and the base station BS that are located where the radio signal from the base station BS does not reach is disconnected. On the other hand, when the transmission power of the interference signal is lowered, the mobile station located near the relay apparatus 101 and capable of receiving the radio signal from the base station BS with stable quality receives the synchronization signal from the base station BS, and Start direct communication with the station BS. A mobile station that is located far from the relay apparatus 101 and cannot receive a radio signal from the base station BS continues to communicate with the base station BS via the relay apparatus 101 because the mobile station side communication unit 123 functions. it can.

  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 description of the embodiment of the present invention described above, for example, the meaning of the technical idea of the expression such as the threshold “more than” or the threshold “less than” is not necessarily a strict meaning, and depending on the specifications of the relay device, The meaning of including or not including the reference value is included. For example, the threshold “above” may imply not only the case where the value to be compared with the threshold reaches the threshold but also the case where the threshold is exceeded. Further, for example, “less than the threshold value” can imply not only when the value to be compared with the threshold value is below the threshold value but also when the threshold value is reached, that is, when the threshold value is below the threshold value.

DESCRIPTION OF SYMBOLS 11 Wireless communication system 101 Relay apparatus 111 Donor node 113 Service node 117 Base station side communication part 119 Storage part 121 Control part 123 Mobile station side communication part BS Base station MS Mobile station

Claims (6)

A relay device that relays radio signals transmitted and received between a base station and a mobile station,
A mobile station side communication unit for transmitting and receiving radio signals to and from the mobile station;
Find the free space loss between the relay device and the mobile station,
A relay apparatus comprising: a control unit that releases a wireless connection between the mobile station and the mobile station side communication unit based on the free space loss. The relay device according to claim 1, wherein the control unit includes:
The distance between the relay device and the mobile station is calculated using the free space loss, and when the distance is less than a distance threshold, the wireless connection between the mobile station and the mobile station side communication unit is released. A relay device characterized by The relay device according to claim 1, wherein the control unit includes:
Using the free space loss, calculating the received signal strength at the mobile station when the radio signal from the base station directly reaches the mobile station, if the received signal strength is equal to or greater than the received signal strength threshold, A relay apparatus that releases radio signals between the mobile station and the mobile station side communication unit. The relay device according to claim 1, wherein the control unit includes:
Using the free space loss, calculate the distance between the relay device and the mobile station, and the received signal strength at the mobile station when a radio signal from the base station reaches the mobile station directly, A relay apparatus that releases a wireless connection between the mobile station and the mobile station side communication unit when a distance is less than a distance threshold and the received signal strength is greater than or equal to a received signal strength threshold. 5. The relay device according to claim 1, wherein the control unit includes:
At the time of relaying a radio signal, the mobile station side communication unit is controlled to transmit an interference signal for interfering with a synchronization signal transmitted from the base station to the mobile station with a predetermined transmission power,
When releasing the wireless connection with the mobile station, the wireless connection between the mobile station and the mobile station side communication unit is released by lowering the transmission power of the interference signal below the predetermined transmission power. A relay device. In a communication control method in a relay apparatus that relays radio signals transmitted and received between a base station and a mobile station, the relay apparatus includes:
Determining a free space loss between the relay device and the mobile station;
And a step of releasing a wireless connection between the mobile station and the mobile station side communication unit based on the free space loss.

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