JP5763393B2 - Communication system, base station, mobile station, and communication method - Google Patents

Description

  The present invention relates to a communication system, a base station, a mobile station, and a communication method.

  In the wireless communication system, as shown in FIG. 5, when a base station performs carrier sense and receives a request for establishment of a wireless channel from a mobile station that desires communication connection, the base station has a radio with little interference (unused). Assign channels.

  The mobile station to which the radio channel is assigned confirms whether or not the radio channel assigned by carrier sense can be used. When it is determined that the carrier sense of both the base station and the mobile station can be used, communication between the base station and the mobile station is realized.

  On the other hand, a base station in which an adaptive array antenna including a plurality of antennas is mounted is known as a conventional base station (see, for example, Patent Document 1). Use of an AAS (Adaptive Antenna System) function may enable communication on a wireless channel in which strong interference is expected.

  The AAS function is to calculate an antenna weight and perform beam forming or null steering using the calculated antenna weight. Beam forming is a function of concentrating radio waves of a base station on a transmission destination, that is, directing a beam. Null steering is a function of directing a directivity valley (null) in the direction of the interference station so that the radio wave does not fly in the direction in which the interference station exists and does not receive the radio wave from that direction. That is, the base station can communicate with a mobile station desired to communicate by assigning a radio channel used by the interfering station to another mobile station (communication desired mobile station) by directing a null to a certain interfering station. .

  For example, as shown in FIG. 6, a mobile station (interference station) MS1 that emits radio waves using the radio channel CH1 and a mobile station MS2 that desires communication connection are located in the cell C1 of the base station BS1. Suppose that At this time, the base station BS1 directs the beam B (main lobe) toward the mobile station MS2, and directs the null N toward the mobile station MS1. Thereby, the radio wave of mobile station MS1 and the radio wave of mobile station MS2 do not interfere with each other at base station BS1. Therefore, the base station BS1 can communicate with the mobile station MS2 by assigning the radio channel CH1.

JP 2007-318670 A

  However, the AAS function of the base station BS1 is used to make available a radio channel determined to be in use by the carrier sense of the base station BS1, but is in use by the carrier sense of the mobile station MS2. It is not intended to make the wireless channel determined to be usable. For example, the mobile station MS2 is located in a region where the cell C1 of the base station BS1 and the cell C2 of the base station BS2 different from the base station BS1 overlap as shown in FIG. It is assumed that a mobile station MS3 that communicates with the base station BS2 through the radio channel CH1 exists in the cell C2. The base station BS1 can assign the radio channel CH1 used by the mobile station (interference station) MS1 to the mobile station MS2 on the premise of using the AAS function. Then, the mobile station MS2 performs carrier sense, but since the mobile station MS2 can also receive radio waves transmitted from the base station BS2 through the channel CH1, it is determined that the radio channel CH1 is in use. When the assigned radio channel CH1 is used, radio waves from the base station BS1 and radio waves from the base station BS2 interfere with each other at the mobile station MS2. Since the radio channel CH1 cannot be used, the base station BS1 has to reassign another radio channel to the mobile station MS2.

  Accordingly, an object of the present invention made in view of the above problems is to provide a communication system, a base station, a mobile station, and a communication method that efficiently use a radio channel allocated to a mobile station. .

In order to solve the above-described problems, the communication system according to the first aspect is
A communication system comprising a plurality of base stations and a mobile station having a plurality of antennas,
The base station
A base station side communication unit that transmits and receives radio signals to and from the mobile station via the plurality of antennas;
A base station side control unit that performs directivity control including null steering with respect to the antenna,
The mobile station
A mobile station side communication unit for transmitting and receiving radio signals to and from the base station;
When determining that the radio channel allocated from one base station is being used by another base station from the allocation information when receiving the allocation information indicating the allocation status of each radio channel of the base station , When the mobile station side specifies another base station that uses the radio channel and requests the specified base station to send a null to the local station when transmitting a radio signal on the radio channel. It is a communication system provided with the mobile station side control part transmitted to a communication part.

  In addition, when the communication with the one base station is completed, the mobile station side control unit sends a message to the other base station to request cancellation of directing null to the mobile station side communication unit. It is desirable to send to.

In order to solve the above-described problems, the mobile station according to the third aspect is
Communicates unit that sends and receives a plurality of base stations and a radio signal,
When determining that the radio channel allocated from one base station is being used by another base station from the allocation information when receiving the allocation information indicating the allocation status of each radio channel of the base station , wherein identifying the other base stations using a radio channel, wherein to the specified base station, before Symbol communications a message requesting to direct a null to the own station when transmitting a radio signal in the radio channel a mobile station and a Ru control section is transmitted to the part.

In order to solve the above-described problems, the communication method according to the fourth aspect is
A communication method in a communication system including a plurality of base stations and mobile stations, each having a plurality of antennas and capable of directivity control including null steering, wherein the mobile station is:
Upon receiving the allocation information indicating allocation status of the base station of each radio channel, from the assignment information, and determining whether the radio channel assigned from a base station being used by other base stations ,
When it is determined that the radio channel is being used by another base station, another base station that uses the radio channel is identified, and a radio signal is transmitted to the identified base station using the radio channel. Includes a step of transmitting a message requesting to direct null to the own station.

  According to the communication system, the base station, the mobile station, and the communication method according to the present invention configured as described above, when a radio channel assigned from one base station is used by another base station, the other To the base station, a message requesting that the mobile station direct null toward the mobile station is transmitted. This prevents the mobile station from receiving radio waves of the same radio channel from a plurality of base stations. Accordingly, since the radio channel used by another base station can be used, the utilization efficiency of the radio channel is improved.

FIG. 1 is a schematic configuration diagram of a communication system according to an embodiment of the present invention. FIG. 2 is a functional block diagram showing a schematic configuration of the base station according to the embodiment of the present invention. FIG. 3 is a functional block diagram showing a schematic configuration of the mobile station according to the embodiment of the present invention. FIG. 4 is a sequence diagram showing processing between a mobile station and a base station according to an embodiment of the present invention. FIG. 5 is a sequence diagram showing processing between a conventional mobile station and a base station. FIG. 6 is a schematic diagram of a conventional communication system. FIG. 7 is a schematic diagram of a conventional communication system.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a communication system according to an embodiment of the present invention. The communication system 11 includes a mobile station 101 (101a and 101b) and a base station 103 (103a and 103b) having a plurality of antennas. The mobile station 101 is a wireless communication terminal in LTE (Long Term Evolution) or XGP (eXtended Global Platform). The base station 103 performs radio communication with the mobile station 101. For example, the base station 103 is referred to as an evolved Node B (eNB) in the LTE system and a BS (Base Station) in the XGP system. In FIG. 1, a region 105a indicates a cell (communication area) of the base station 103a. A region 105b indicates a cell of the base station 103b. It is assumed that the mobile station 101b is communicating with the base station 103b through a radio channel (frequency band) 107, and the mobile station 101a desires communication with the base station 103a.

  FIG. 2 is a functional block diagram showing a schematic configuration of the base station according to the embodiment of the present invention. The base station 103 includes an array antenna ANT, a base station side communication unit 111, a base station side storage unit 113, and a base station side control unit 115.

  The array antenna ANT is composed of a plurality of antennas and can realize directivity control including beam forming and null steering. For example, the array antenna ANT is an adaptive array antenna.

  The base station side communication unit 111 transmits and receives a radio frequency (RF) signal (radio signal) to and from the mobile station 101 via the array antenna ANT. The wireless signal includes various communication messages and information.

  The base station side storage unit 113 stores various information such as antenna weight (including transmission weight and reception weight) values and carrier sense threshold values, and also functions as a work memory. The antenna weight is a weight for controlling the phase and amplitude of each of a plurality of antennas constituting the array antenna ANT. The antenna weight is set corresponding to each of the plurality of antennas, and by combining the antenna weights, beam forming for directing a beam only in a certain direction and null steering for directing a null in a certain direction are possible. What determines the directivity upon transmission is the transmission weight, and what determines the directivity upon reception is the reception weight.

  The carrier sense threshold is an index for determining a radio channel used within a range in which the base station 103 can receive radio waves. For example, a received signal strength indicator (RSSI) is set. It is determined that the radio channel for which the received electric field intensity equal to or higher than the carrier sense threshold is already used. Further, the radio channel for which the received electric field strength less than the carrier sense threshold is measured is determined to be a radio channel that can be allocated for new communication.

  The base station side control unit 115 controls and manages the entire base station 103 including each functional block of the base station 103. The base station side control unit 115 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. The processing performed by the base station side control unit 115 will be described in detail with reference to FIG.

  Next, functional blocks showing a schematic configuration of the mobile station 101 will be described with reference to FIG. FIG. 3 is a functional block diagram showing a schematic configuration of the mobile station according to the embodiment of the present invention. The mobile station 101 includes a mobile station side communication unit 121, a mobile station side storage unit 123, and a mobile station side control unit 125.

  The mobile station side communication unit 121 transmits and receives an RF signal (radio signal) to and from the base station 103 via an antenna.

  The mobile station side storage unit 123 stores various information such as a carrier sense threshold value, and also functions as a work memory.

  The mobile station side control unit 125 controls and manages the entire mobile station 101 including each functional block of the mobile station 101. The mobile station side control unit 125 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. The processing performed by the mobile station side control unit 125 will be described in detail with reference to FIG.

  Next, a method in which the base station 103a and the mobile station 101a shown in FIG. 1 communicate via the radio channel 107 will be described with reference to FIG. FIG. 4 is a sequence diagram showing processing between a mobile station and a base station according to an embodiment of the present invention. In addition, as a reference code regarding each functional block shown in the base station 103 of FIG. 2, the reference symbol of the functional block related to the base station 103a is a, and the reference symbol of the functional block related to the base station 103b is b To do. In addition, as reference numerals relating to the functional blocks shown in the mobile station 101 of FIG. 3, the reference numerals of the functional blocks relating to the mobile station 101a will be described by adding a.

  The base station side control unit 115a of the base station 103a performs carrier sense using the carrier sense threshold stored in the base station side storage unit 113a, for example, in an empty slot, and can be used in the cell of the base station 103a. Know the channel (1 in FIG. 4). The base station side control unit 115a of the base station 103a can store information on usable radio channels in the base station side storage unit 113a.

  The mobile station side control unit 125a of the mobile station 101a that desires a communication connection with the base station 103a controls the mobile station side communication unit 121a to transmit a radio channel establishment request message to the base station 103a (FIG. 4). 2).

  When the base station side communication unit 111a receives the wireless channel establishment request message, the base station side control unit 115a assigns one of the available radio channels stored in the base station side storage unit 113a to the mobile station 101a. (3 in FIG. 4). That is, the base station side communication unit 111a transmits information on the radio channel to the mobile station 101a.

  When the mobile station side communication unit 121a receives the wireless channel information, the mobile station side control unit 125a performs carrier sense using the carrier sense threshold value stored in the mobile station side storage unit 123a (4 in FIG. 4). ). That is, the mobile station side control unit 125a uses the assigned radio channel (allocation channel) based on the received electric field strength of the signal received by the mobile station side communication unit 121a (reception result by the mobile station side communication unit 121a). Determine whether it is possible.

  When the allocated channel is usable, a synchronization burst signal is transmitted and received between the base station 103a and the mobile station 101a, and after aligning the signal transmission and reception timing, the mobile station 101a communicates with the base station 103a through the allocated channel. Can start.

  When it is determined that the allocation channel is not usable, there is a base station using the allocation channel. When the allocation channel is the radio channel 107, since the base station 103b uses the radio channel 107, it is determined that the allocation channel cannot be used. Hereinafter, the allocation channel is assumed to be the radio channel 107.

  The mobile station side control unit 125a sends a message (null steering request message) requesting the base station 103b to direct null to the mobile station 101a when transmitting a radio signal through the radio channel 107. 121a is transmitted (5 in FIG. 4). The null steering request message includes allocation channel information and the like. Note that the mobile station side control unit 125a can also transmit the allocated channel information to the mobile station side communication unit 121a after the null steering request message, independently of the null steering request message.

  The base station 103b that has received the null steering request message determines whether the own station is using the same radio channel as the assigned channel. Then, the base station using the same radio channel 107 as the assigned channel directs null to the mobile station 101a (6 in FIG. 4). That is, in this embodiment, the base station side control unit 115b of the base station 103b controls the base station side communication unit 111b so as to direct null toward the mobile station 101a. The transmission weight for directing null toward the mobile station 101a can be obtained from the reception weight at the time of receiving the null steering request message, or can be obtained based on the estimated arrival direction of the message. Direction of arrival estimation includes beam former method, Capon method based on linear prediction method and maximum entropy method, multiple signal separation method based on eigenvalue expansion of correlation matrix of array input signal and ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) It can be performed by a known method such as a method. When the base station 103b is communicating with a mobile station (not shown) other than the mobile station 101b, the base station 103b directs a null to the mobile station 101a only when communicating with the mobile station 101b. be able to.

  After transmitting the null steering request message, the mobile station 101a transmits / receives a synchronization burst signal to / from the base station 103a (7 in FIG. 4). After aligning the signal transmission / reception timing, the mobile station 101a transmits the assigned radio channel 107. To start communication with the base station 103a (8 in FIG. 4). Note that the base station 103b can continue to direct the null toward the mobile station 101a following the movement of the mobile station 101a by continuously receiving the radio wave emitted by the mobile station 101a during the reception period.

  When the communication between the base station 103a and the mobile station 101a is completed, the mobile station-side control unit 125a transmits a message (null steering cancellation request message) requesting cancellation of directing null to the base station 103a. The side communication unit 121a is controlled (9 in FIG. 4). When the base station side communication unit 111b receives the null steering cancellation request message, the base station side control unit 115b changes the transmission weight and stops null steering.

  As described above, in this embodiment, the mobile station side control unit 125a of the mobile station 101a uses the radio channel 107 allocated from the base station 103a by the base station 103b based on the reception result by the mobile station side communication unit 121a. When transmitting a radio signal on the radio channel 107, the base station 103b is caused to transmit a message requesting that the mobile station 101a be directed to null to the mobile station side communication unit 121a. As a result, the base station 103b directs null toward the mobile station 101a by directivity control of the array antenna ANTb. Therefore, radio waves emitted from the base station 103b using the radio channel 107 do not reach the mobile station 101a. Therefore, even if the base station 103a and the mobile station 101a communicate using the radio channel 107, radio waves from the base station 103b do not cause interference. The mobile station 101a can use the assigned radio channel 107 regardless of the result of carrier sense. Since the wireless channel 107 that is being used can also be used according to the carrier sense result, the utilization efficiency of the wireless channel is improved.

  Further, in this embodiment, when the communication with the base station 103a is completed, the mobile station side control unit 125a sends a message requesting the base station 103b to cancel the directing of null toward the mobile station 101a. It can be transmitted to the unit 121a. Thereby, the base station 103b can grasp | ascertain the timing which stops null steering, and can suppress the process which performs the null steering of the base station 103b to the required minimum.

  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-described embodiment, the mobile station 101a has been described as performing carrier sense to determine whether a radio channel allocated from a certain base station is being used by another base station. It is not limited to. For example, the base station side control unit 115b of the base station 103b can control the base station side communication unit 111b so as to periodically transmit allocation information indicating the allocation status of the radio channel in the own station 103b. That is, the mobile station 101a can determine which base station is using which radio channel from the allocation information received by the mobile station side communication unit 121a (the reception result by the mobile station side communication unit 121a). . That is, the mobile station side control unit 125a can determine from the allocation information whether a radio channel allocated from a certain base station is used by another base station. The determination based on the allocation information allows the mobile station to specify a base station that uses the allocated radio channel (allocation channel) unlike carrier sense. Therefore, the mobile station 101a can transmit a null steering request message only to the base station 103b that uses the assigned channel. Since the reception of the null steering request message means that the received base station uses the allocation channel, after receiving the message, it is determined whether the allocation channel is used as in the above embodiment. do not have to. Therefore, since the base station 103b can perform null steering execution processing immediately after receiving the null steering request message, even if the mobile station 101a starts communication on the assigned channel immediately after transmitting the null steering request message, interference is not caused. Effectively suppressed.

  Note that the allocation information can be transmitted through a free area of an existing control channel or a new control channel for transmitting allocation information. The existing control channel is, for example, BCCH (Broadcasting Control CHannel: broadcast channel), SCCH (Signaling Control CHannel: common bidirectional control channel), or PCH (Paging CHannel: paging channel). Since SCCH and PCH are channels for realizing a call, there are many free areas during idle. It is possible to transmit allocation information by effectively using the free area of such an existing channel.

  In the above description of the embodiment of the present invention, the base station 103b that has received the null steering request message has been described as directing null to the mobile station 101a when using the radio channel 107. It is also possible to stop using the radio channel 107 and allocate another channel to communicate with the mobile station 101b. In this case, 101a can communicate with the base station 103a using the allocated channel 107.

  Further, in the description of the embodiment of the present invention described above, for example, the meaning of the technical idea of expression such as “carrier sense threshold“ above ”or“ carrier sense threshold “less than” ”is not necessarily a strict meaning. Depending on the specifications, the meanings when the reference value is included or not included are included. For example, the carrier sense threshold “above” may imply not only when the carrier sense result reaches the carrier sense threshold but also when the carrier sense threshold is exceeded. In addition, for example, the carrier sense threshold “less than” may imply not only when the carrier sense result falls below the carrier sense threshold, but also when the carrier sense threshold is reached, that is, when the carrier sense threshold falls below the carrier sense threshold. To do.

  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.

11 Communication system 101, 101a, 101b Mobile station 103, 103a, 103b Base station 105a, 105b Area (cell)
107 radio channel 111 base station side communication unit 113 base station side storage unit 115 base station side control unit 121 mobile station side communication unit 123 mobile station side storage unit 125 mobile station side control unit ANT array antenna

Claims (4)

A communication system comprising a plurality of base stations and a mobile station having a plurality of antennas,
The base station
A base station side communication unit that transmits and receives radio signals to and from the mobile station via the plurality of antennas;
A base station side control unit that performs directivity control including null steering with respect to the antenna,
The mobile station
A mobile station side communication unit for transmitting and receiving radio signals to and from the base station;
When determining that the radio channel allocated from one base station is being used by another base station from the allocation information when receiving the allocation information indicating the allocation status of each radio channel of the base station , When the mobile station side specifies another base station that uses the radio channel and requests the specified base station to send a null to the local station when transmitting a radio signal on the radio channel. A communication system comprising a mobile station side control unit to be transmitted to a communication unit. The communication system according to claim 1 ,
When the communication with the one base station is completed, the mobile station side control unit transmits a message requesting cancellation of directing a null to the other base station to the mobile station side communication unit. A communication system. Communicates unit that sends and receives a plurality of base stations and a radio signal,
When determining that the radio channel allocated from one base station is being used by another base station from the allocation information when receiving the allocation information indicating the allocation status of each radio channel of the base station , wherein identifying the other base stations using a radio channel, wherein to the specified base station, before Symbol communications a message requesting to direct a null to the own station when transmitting a radio signal in the radio channel a mobile station and a Ru control section is sent to the department. A communication method in a communication system including a plurality of base stations and mobile stations, each having a plurality of antennas and capable of directivity control including null steering, wherein the mobile station is:
Upon receiving the allocation information indicating allocation status of the base station of each radio channel, from the assignment information, and determining whether the radio channel assigned from a base station being used by other base stations ,
When it is determined that the radio channel is being used by another base station, another base station that uses the radio channel is identified, and a radio signal is transmitted to the identified base station using the radio channel. Transmitting a message requesting to direct null to the local station.

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