JP5680948B2 - Wireless communication system and relay control method - Google Patents

Description

The present invention relates to relay control method in a wireless communication system及beauty with a relay station.

  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 order to cover such a region where radio waves do not reach, a relay station (relay station or repeater) 605 that relays wireless communication between the mobile station 601 and the base station 603 is required as shown in FIG.

  A conventional relay station can not only amplify an RF (Radio Frequency) signal (radio signal) but also improve signal quality (see, for example, Patent Document 1). As a method for improving the signal quality, there are a method of removing unnecessary interference by performing digital signal processing, and a method of demodulating a reception signal at a relay station and reconstructing a transmission signal. However, such a method requires signal buffering and iterative processing. As a result, a delay of several frames to several tens of frames occurs as compared with the case where the base station and the terminal communicate directly.

JP 2010-41685 A

  However, the delay caused by passing through the relay station is not only due to the function of the relay station. As shown in FIG. 7, it is assumed that there are a plurality of mobile stations communicating with the relay destination base station 703. As the number of mobile stations increases, the radio resources of the base station to be used increase and the free radio resources decrease. Therefore, there is a possibility that sufficient radio resources cannot be allocated to the mobile station 701a newly connected to the base station 703 via the relay station 705. A shortage of radio resources causes a decrease in the transmission rate of the mobile station 701a, that is, a delay. The radio resources already allocated to the other mobile stations 701b to 701e can be allocated to the radio resources of the mobile station 701a. In this case, however, the transmission rate of the mobile station having less available radio resources is reduced. .

  Due to this delay, for example, there is a possibility that a HARQ (Hybrid Automatic Repeat reQuest) employed in an LTE (Long Term Evolution) system may not be in time.

Accordingly, an object of the present invention was made in view of the above problems is to provide a relay control method in a wireless communication system及beauty can be relayed to efficiently suppress the occurrence of delay.

In order to solve the various problems described above, the first of inventions,
Is capable of wireless communication with multiple base stations, a radio communication system including a relay station that relays wireless communication between the mobile station and one of said base station,
The base station distributes all the radio resources to the connected mobile stations so that there is no vacancy, and redistributes the radio resources each time the number of connected mobile stations fluctuates,
The relay station monitors the communication status of each base station based on information related to a communication environment transmitted from said plurality of base stations, to connect the new mobile station to the fewest base stations of the connection the mobile station number , That is.

  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 relay control method that implements the first invention of the present invention as a method is as follows:
Ru wireless communication can der a plurality of base station-relay station, a relay control method for relaying radio communication between a mobile station and one of said base station,
The base station distributes all radio resources to the connected mobile stations so as not to be free, and redistributes the radio resources each time the number of connected mobile stations changes;
The relay station monitors the communication status of each base station based on information related to the communication status transmitted from the plurality of base stations, and connects a new mobile station to the base station with the smallest number of connected mobile stations Steps.

According to the onset bright configured as described above, by effectively suppressing the delay generation can relay radio communication between a mobile station and a base station.

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 showing a schematic configuration of the relay station according to one embodiment of the present invention. FIG. 3 is a diagram illustrating a positional relationship among a relay station, a mobile station, and a base station according to an embodiment of the present invention. FIG. 4 is a flowchart showing processing of the relay station according to an embodiment of the present invention. FIG. 5 shows a usage state of radio resources possessed by a base station according to an embodiment of the present invention. FIG. 6 is a schematic diagram of a conventional radio communication system. FIG. 7 is a schematic diagram of a conventional radio communication system.

  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 wireless communication system 11 includes a mobile station 101, a plurality of base stations 103 (103a and 103b), and a relay station 105. The mobile station 101 is a wireless communication terminal such as a mobile phone. The base stations 103a and 103b perform wireless communication with the mobile station 101. For example, in the LTE (Long Term Evolution) system, the base stations 103a and 103b are called eNBs (evolved Node B). The relay station 105 relays wireless communication between the mobile station 101 and the base station 103a or 103b. In FIG. 1, an area 107 indicates a range where radio waves of the mobile station 101 can reach. An area 109a indicates a cell (communication area) of the base station 103a. An area 109b shows a cell of the base station 103b. That is, the relay station 105 in FIG. 1 is located in an area where the mobile station 101 and the base stations 103a and 103b can communicate. The relay station 105 allows the mobile station 101 to wirelessly communicate with the base station 103a or 103b even if the mobile station 101 is located outside the cell range of the base stations 103a and 103b.

  FIG. 2 is a functional block diagram showing a schematic configuration of the relay station according to one embodiment of the present invention.

  The relay station 105 includes a base station side antenna 121, a mobile station side antenna 123, a tilt mechanism unit 125 that constitutes a tilt control unit, a communication unit (RF unit) 127, a baseband unit 129, a control unit 131, It has.

  The base station antenna 121 communicates with the base station 103 by radio. The base station-side antenna 121 has directivity having a relatively large half-value width (half-value angle). Even when the main axis of directivity (half-width bisector) is directed to a certain base station, It can receive signals from the base station. Therefore, in the present embodiment, the base station side antenna 121 can receive signals from both base stations even if the main axis of directivity of the antenna 121 is in the direction in which either the base station 103a or 103b exists. It should be noted that the base station antenna 121 is not limited to being configured as a transmission / reception integrated antenna, but may be realized by separate transmission antennas and reception antennas.

  The mobile station side antenna 123 communicates wirelessly with the mobile station 101. The mobile station side antenna 123 can have directivity so that radio waves can be radiated to an area that the base station 103 cannot cover. Note that the mobile station side antenna 123 is not limited to having directivity, and the mobile station side antenna 123 can also be realized by a non-directional antenna.

  The tilt mechanism unit 125 directs the principal axis of directivity of the base station side antenna 121 in the direction in which the base station 103a or 103b exists, and is configured by an antenna rotator, for example. In the present embodiment, it is assumed that the direction in which the base stations 103a and 103b exist is known.

  The communication unit 127 down-converts a signal received via the base station side antenna 121 or the mobile station side antenna 123 into an IF (Intermediate Frequency) signal and amplifies it. In addition, the communication unit 127 up-converts and amplifies the signal modulated by the baseband unit 129 to an RF signal in order to transmit a signal via the base station side antenna 121 or the mobile station side antenna 123.

  The signal received by the communication unit 127 via the base station antenna 121 includes, for example, information regarding the communication status of the base station 103. Information on the communication status of the base station 103 includes the number of mobile stations to which the base station 103 is currently connected for communication (number of connected mobile stations) and the usage status of radio resources of the base station 103 (frequency band of the base station 103). Information on the availability of When the radio communication system 11 is an LTE system, information regarding the communication status is transmitted from the base station 103 via PDCCH (Physical Downlink Control CHannel).

  The baseband unit 129 demodulates a signal received via the base station side antenna 121 or the mobile station side antenna 123 and performs digital processing. Then, the baseband unit 129 modulates the digitally processed signal in order to transmit the signal via the mobile station side antenna 123 or the base station side antenna 121. By performing error correction decoding and error detection as digital processing, unnecessary interference can be removed. In addition, the baseband unit 129 extracts information regarding a communication state included in a PDCCH (Physical Downlink Control CHannel) defined by 3GPP (3rd Generation Partnership Project) LTE.

  The control unit 131 controls and manages the entire relay station 105 including each functional block of the relay station 105. Here, the control unit 131 is configured as software executed on an arbitrary 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.

  The control unit 131 will be described in more detail. The control unit 131 monitors the communication status of each base station based on information regarding the communication status transmitted from the plurality of base stations 103a and 103b, and determines the base station with the best communication status as the relay destination. A base station with good communication status is a base station with the smallest number of connected mobile stations when the information about the communication status is related to the number of connected mobile stations. The smaller the number of connected mobile stations, the higher the possibility that the base station has more free radio resources. Therefore, the base station with the smallest number of connected mobile stations can allocate radio resources necessary for realizing a desired transmission rate to a mobile station to be newly connected to the base station. Further, when the information regarding the communication status is related to the usage status of the radio resource, the base station with the best communication status is the base station with the most available radio resource. The base station with the most available radio resources can allocate radio resources necessary for realizing a desired transmission rate to a mobile station to be newly connected to the base station. Hereinafter, in this embodiment, it is assumed that the information regarding the communication status is related to the number of connected mobile stations.

  Next, a method for determining a relay destination base station by the relay station will be described with reference to FIGS. 3, 4, and 5. FIG. 3 is a diagram illustrating a positional relationship among a mobile station, a base station, and a relay station according to an embodiment of the present invention. FIG. 4 is a flowchart showing processing of the relay station according to an embodiment of the present invention. FIG. 5 is a diagram illustrating a usage state of radio resources included in a base station according to an embodiment of the present invention.

  Hereinafter, as shown in FIG. 3, the relay station 105 is located in an area where wireless communication is possible with the mobile station 101 a and the base stations 103 a and 103 b, and the mobile station 101 a is connected to the base stations 103 a and 103 b only via the relay station 105. Is located in a place where wireless communication is possible. Further, it is assumed that the base station 103a wirelessly communicates with the mobile stations 101b to 101e, and the base station 103b wirelessly communicates with the mobile station 101f.

  The communication unit 127 of the relay station 105 receives information on the number of connected mobile stations from each of the base stations 103a and 103b via the base station antenna 121, and monitors the communication status of each base station (step S101). That is, information that the number of connected mobile stations is 4 is received from the base station 103a, and information that the number of connected mobile stations is 1 is received from the base station 103b. For example, the usage status of radio resources by the mobile stations 101b to 101e is FIG. 5A, and the usage status of radio resources by the mobile station 101f is FIG. 5B. The range 141b means a radio resource used by the mobile station 101b. The range 141c means a radio resource used by the mobile station 101c. The range 141d means a radio resource used by the mobile station 101d. A range 141e means a radio resource used by the mobile station 101e. The range 141f means a radio resource used by the mobile station 101f. The range 141aa means radio resources of the base station 103a that can be allocated to the mobile station 101a. The range 141ab means a radio resource of the base station 103b that can be allocated to the mobile station 101a. Thus, the base station with a smaller number of connected mobile stations is more likely to have more radio resources.

  And the control part 131 of the relay station 105 specifies the base station with the fewest number of connected mobile stations from the information regarding the number of connected mobile stations (step S102). In the present embodiment, the base station 103b is specified.

  Subsequently, the control unit 131 determines whether there is a mobile station that needs to be relayed based on a signal received via the base station side antenna 121 or the mobile station side antenna 123 (step S103). If there is no mobile station that needs to be relayed (No in step S103), the processes in steps S101 and S102 are repeated, and the base station with the smallest number of connected mobile stations is updated.

  In the present embodiment, since there is a mobile station 101a that needs to be relayed (Yes in step S103), the control unit 131 uses a tilt mechanism to relay wireless communication between the mobile station 101a and the base station 103b. The main axis of directivity of the base station antenna 121 is directed to the direction in which the base station 103b exists through the unit 125 (step S104). The control unit 131 starts relaying between the mobile station 101a and the base station 103b specified in step S102 (step S105). That is, the relay station 105 transmits the signal received from the mobile station 101a to the base station 103b, and transmits the signal received from the base station 103b to the mobile station 101a. If relay station 105 has already relayed mobile station 101a to a base station other than base station 103b, relay station 105 disconnects the relay and connects mobile station 101a to base station 103b.

  As described above, in the present embodiment, the control unit 131 of the relay station 105 monitors the communication status of each base station based on the information on the number of connected mobile stations transmitted from the plurality of base stations 103a and 103b, and connects mobile stations. The base station with the smallest number is determined as the relay destination. This means that a base station with a smaller number of connected mobile stations is more likely to have more available radio resources. Therefore, the relay station 105 can effectively use the free radio resources by connecting the new mobile station 101a to the base station having the smallest number of connected mobile stations. The more radio resources are available, the more radio resources necessary to realize a desired transmission rate can be allocated to the new mobile station 101a. Therefore, the delay is efficiently suppressed, and the mobile station 101a and the base station 103b. Wireless communication with

  Further, in the present embodiment, the tilt mechanism unit 125, when relaying wireless communication between the mobile station 101a and the base station 103b determined as the relay destination, moves the base station side antenna in the direction in which the base station 103b exists. 121 directivity principal axes can be directed. Since the strongest radio wave is emitted in the direction of the main axis of directivity, the relay station 105 can perform stable wireless communication with the base station 103b that is the relay destination.

  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, the base station side antenna 121 has been described assuming a directional antenna. However, the base station side antenna 121 may be realized by an omnidirectional antenna or an adaptive array antenna. it can. When the base station antenna 121 is an adaptive array antenna composed of a plurality of antennas, the tilt control unit adjusts the direction of the main axis of directivity of the adaptive array antenna and the phase of the radio wave transmitted from each antenna. It may be determined by.

  In the description of the embodiment of the present invention described above, it is assumed that the radio resources of the base station are not used by all connected mobile stations. However, the base station connects all radio resources to the connected mobile station. Can be redistributed every time the number of connected mobile stations fluctuates. In this case, the number of connected mobile stations does not directly indicate the availability of radio resources, but the smaller the number of connected mobile stations, the more radio resources are distributed to each mobile station, so the number of connected mobile stations is the smallest. This means that a base station can allocate many radio resources to a newly connected mobile station. Therefore, the relay station connects a new mobile station to the base station with the smallest number of connected mobile stations, so that the new mobile station can use more radio resources than when connected to another base station. , Can communicate at high transmission speed. As a result, delay can be suppressed.

11 wireless communication system 101, 101a to 101f mobile station 103a, 103b base station 105 relay station 107, 109a, 109b area 121 base station side antenna 123 mobile station side antenna 125 tilt mechanism part 127 communication part 129 baseband part 131 control part 141aa 141ab, 141b, 141c, 141d, 141e, 141f

Claims (2)

A wireless communication system comprising a relay station capable of wireless communication with a plurality of base stations and relaying wireless communication between one of the base stations and a mobile station,
The base station distributes all the radio resources to the connected mobile stations so that there is no vacancy, and redistributes the radio resources each time the number of connected mobile stations fluctuates,
The relay station monitors the communication status of each base station based on information related to the communication status transmitted from the plurality of base stations, and connects a new mobile station to the base station with the smallest number of connected mobile stations. Wireless communication system. Ru wireless communication can der a plurality of base station-relay station, a relay control method for relaying radio communication between a mobile station and one of said base station,
The base station distributes all radio resources to the connected mobile stations so as not to be free, and redistributes the radio resources each time the number of connected mobile stations changes;
The relay station monitors the communication status of each base station based on information related to the communication status transmitted from the plurality of base stations, and connects a new mobile station to the base station with the smallest number of connected mobile stations A relay control method including steps.

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