JP5771160B2 - Base station and communication control method - Google Patents

Description

  The present invention relates to a base station and a communication control method.

  In wireless communication systems such as PHS (Personal Handy-phone System) system, XGP (eXtended Global Platform) system, which is a next-generation PHS system, and TD-LTE (Time Division-Long Term Evolution), a base station assigns a channel to a mobile station. Allocation and communication connection is established.

  Here, a conventional channel allocation method will be described (see, for example, Patent Document 1). The base station performs carrier sense, selects a slot and a carrier (frequency band) with the least interference wave, and assigns a combination (channel) of the slot and carrier to the mobile station.

  After the mobile station starts communication with the base station on the assigned channel, the communication quality of the channel may deteriorate due to a change in the communication environment. In this case, the base station senses the carrier of another empty slot and assigns a channel of an empty slot with good communication quality to the mobile station or changes the connection destination of the mobile station by handover.

JP 2009-201074 A

  However, switching from a channel in a certain slot to a channel in another slot or changing a base station due to handover involves temporary interruption of communication, leading to a decrease in throughput. In addition, when there is no vacancy in another slot, or when there is no new connection destination candidate due to handover, the communication quality cannot be improved. When the communication quality is significantly deteriorated, a situation occurs in which the communication connection between the base station and the mobile station cannot be maintained.

  Furthermore, even if an empty channel exists in a slot (same slot) of a channel (used channel) assigned to the mobile station, the base station cannot perform carrier sense in the same slot. Therefore, the base station cannot grasp the communication quality of the empty channel. Therefore, the base station cannot newly allocate a channel with good communication quality to the mobile station in the same slot.

  Accordingly, an object of the present invention made in view of the above problems is to provide a base station and a communication control method capable of performing carrier sense in the same slot.

In order to solve the above-described problems, the invention of the base station according to the first aspect is as follows:
In a base station that adopts a TDD (Time Division Duplex) method in which each radio frame of a continuous radio frame is composed of a downlink frame and an uplink frame, and performs radio communication with a mobile station,
Instructing the mobile station to pause data transmission to the base station in an uplink frame of a predetermined radio frame of the continuous radio frame;
Determining whether data transmission to the mobile station can be paused in a downlink frame of the predetermined radio frame;
When the data transmission to the mobile station can be suspended, the base station includes a control unit that performs carrier sense in the predetermined radio frame.

  The invention according to a second aspect is the base station according to the first aspect, wherein the control unit assigns a channel to be assigned to the mobile station in communication with the base station based on the execution result of the carrier sense. It is characterized by determining.

  Further, the invention according to a third aspect is the base station according to the second aspect, wherein the control unit moves the channel having the best communication quality among the other channels of the allocated channel slot. It is characterized by being assigned to a station.

  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 according to a fourth aspect that realizes the present invention as a method includes:
In a communication control method in a base station that wirelessly communicates with a mobile station by adopting a TDD (Time Division Duplex) method in which each wireless frame of a continuous wireless frame is composed of a downlink frame and an uplink frame, the base station ,
Instructing the mobile station to pause data transmission to the base station in an uplink frame of the predetermined radio frame of the continuous radio frame;
Determining whether data transmission to the mobile station can be suspended in a downlink frame of the predetermined radio frame;
When data transmission to the mobile station can be suspended, the communication control method includes a step of performing carrier sense in the predetermined radio frame.

  According to the base station and the communication control method according to the present invention configured as described above, the base station can perform carrier sense in the slot (same slot) of the channel (used channel) allocated to the mobile 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 base station according to the embodiment of the present invention. FIG. 3 is a flowchart showing processing of the base station according to the embodiment of the present invention. FIG. 4 is an explanatory diagram showing a radio frame according to an embodiment of the present invention.

  Hereinafter, embodiments of 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 100 includes a base station 101 and a mobile station 103. The wireless communication system 100 is a system in which a TDD (Time Division Duplex) method is adopted, and is, for example, an LTE system or an XGP system. In the TDD scheme, continuous radio frames are defined, and each radio frame is composed of a downlink frame and an uplink frame. A downlink frame is a time interval at which the base station 101 can transmit data to the mobile station 103. An uplink frame is a time interval at which the mobile station 103 can transmit data to the base station 101. The downlink frame and the uplink frame do not necessarily have the same length, and can be asymmetric. Each of the downlink frame and the uplink frame is composed of a plurality of slots (time slots). As radio frames continue, downlink frames and uplink frames are alternately repeated. Thereby, the base station 101 and the mobile station 103 repeatedly switch between transmission and reception and perform wireless communication. The mobile station 103 is, for example, a mobile phone terminal or an XGP terminal.

  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 101 of this embodiment includes a communication unit 111, a storage unit 113, and a control unit 115.

  The communication unit 111 transmits and receives data (radio signal) to and from the mobile station 103 via an antenna. The communication unit 111 generates a baseband signal by performing amplification and down-conversion with low noise on the radio signal received in the uplink frame, and sends the baseband signal to the control unit 115. The communication unit 111 generates a radio signal by performing up-conversion and amplification on the baseband signal, and transmits the radio signal to the mobile station 103 via an antenna in a downlink frame. The data includes user data related to uploading from the mobile station 103 to the base station 101 and downloading from the base station 101 to the mobile station 103, and establishment and maintenance of a communication connection between the base station 101 and the mobile station 103. And control data necessary for the above.

  The storage unit 113 stores various types of information such as a carrier sense threshold value and information on a predetermined radio frame, which will be described later, and also functions as a work memory.

  The control unit 115 controls and manages the entire base station 101 including each functional block of the base station 101. The control unit 115 is configured as software executed on an arbitrary suitable processor such as a CPU (central processing unit) or a dedicated processor (for example, DSP (digital signal processor)) specialized for each process. You can also.

  The control unit 115 performs carrier sense and specifies a channel (a combination of a slot and a carrier) that can be allocated to the mobile station 103. Specifically, the control unit 115 controls the communication unit 111 to transmit a signal in a downstream frame (a slot) using a carrier whose radio wave condition is to be monitored, and the carrier in an upstream frame (a slot). Receive radio waves. Subsequently, the control unit 115 calculates a communication quality value of the received radio wave. The communication quality value is a received signal strength indicator (RSSI), a carrier to noise ratio (CNR), or the like. In this embodiment, it is assumed that the communication quality value is the received electric field strength. Then, the control unit 115 compares the calculated received electric field strength with a predetermined carrier sense threshold value. The carrier sense threshold is an index for determining whether or not channel allocation is possible. When the received electric field strength of the received radio wave is less than the carrier sense threshold, the control unit 115 assigns a channel that is a combination of a slot and a carrier corresponding to the radio wave to the mobile station 103 (assignable channel). ). Then, the control unit 115 allocates a channel that can be allocated to the mobile station 103 to the mobile station 103.

  In order to execute the carrier sense, the base station 101 needs to transmit and receive signals. Therefore, the control unit 115 can perform carrier sense when communication with the mobile station 103 is not performed in a slot to be subjected to carrier sense.

  In addition, the control unit 115 generates a signal instructing to pause data transmission to the base station 101 in an uplink frame of a predetermined radio frame of consecutive radio frames. Then, the control unit 115 controls the communication unit 111 so as to transmit the generated signal to the mobile station 103. The predetermined radio frame is a radio frame of a certain period or a non-periodic radio frame of continuous radio frames. For example, the control unit 115 can instruct the mobile station 103 to pause data transmission at a cycle of once every three uplink frames. The control unit 115 can also determine an uplink frame in which data transmission is paused aperiodically according to the amount of data that the mobile station 103 should transmit to the base station 101. And the control part 115 memorize | stores in the memory | storage part 113 about the information which radio | wireless frame corresponds to a predetermined radio | wireless frame among continuous radio | wireless frames.

  As a result, the mobile station 103 intermittently transmits data (intermittent transmission) to the base station 101 instead of all the upstream frames of the continuous radio frames. Generally, the amount of data in the uplink direction from the mobile station 103 to the base station 101 is smaller than the amount of data in the downlink direction from the base station 101 to the mobile station 103. For this reason, there may be no user data to be transmitted by the mobile station 103 by uploading in the uplink frame. Therefore, even if the mobile station 103 performs intermittent transmission, the throughput does not deteriorate significantly. When data transmission in all uplink frames is enabled, the mobile station 103 transmits control data in order to maintain a connection with the base station 101 even though there is no user data. Battery consumption will be accelerated.

  Furthermore, the control unit 115 determines whether data transmission to the mobile station 103 can be suspended in a downlink frame of a predetermined radio frame. The suspension of data transmission is determined in terms of whether a desired throughput is achieved. For example, the control unit 115 determines that there is no user data that the base station 101 should transmit to the mobile station 103. Data transmission to the mobile station 103 can be suspended. Further, the control unit 115 has a case where there is little user data to be transmitted in the downlink frame of the predetermined radio frame, and the user data can be transmitted in the next radio frame together with the user data to be transmitted in the next radio frame. In addition, data transmission to the mobile station 103 can be suspended.

  When data transmission is suspended in a downlink frame of a predetermined radio frame, communication between the base station 101 and the mobile station 103 is suspended in both the uplink frame and the downlink frame in the predetermined radio frame. Therefore, the control unit 115 performs carrier sense for other carriers in the slot (same slot) of the channel (used channel) that is already used (allocated) in communication with the mobile station 103 in this predetermined radio frame. Will be able to. Other processes performed by the control unit 115 will be described in detail with reference to FIG.

  Next, a channel allocation method by the base station 101 of this embodiment will be described with reference to FIGS. FIG. 3 is a flowchart showing processing of the base station according to the embodiment of the present invention. FIG. 4 is an explanatory diagram showing a radio frame according to an embodiment of the present invention.

  In FIG. 4, four radio frames 131 to 134 among consecutive radio frames are shown on the time axis. The radio frame 131 is composed of a downlink frame 141 and an uplink frame 142, the radio frame 132 is composed of a downlink frame 143 and an uplink frame 144, and the radio frame 133 is composed of a downlink frame 145 and an uplink frame 146. 134 includes a downstream frame 147 and an upstream frame 148. Then, it is assumed that the base station 101 instructs the mobile station 103 in advance to pause data transmission at a cycle of two uplink frames. Therefore, the mobile station 103 pauses data transmission in the upstream frames 144 and 148. Further, in the downlink frames 141 and 143, it is assumed that there is user data that the base station 101 should transmit to the mobile station 103.

  Further, when the mobile station 103 receives a radio signal from the base station 101 in a downlink frame, the mobile station 103 calculates a reception quality value of the signal. The reception quality value is, for example, a carrier level to interference and noise ratio (CINR) representing the influence of RSSI and interference. Then, the mobile station 103 transmits the reception quality value calculated in the uplink frame to the base station 101. The reception quality value is used by the control unit 115 of the base station 101 to determine whether it is better to allocate a new channel for improving the reception quality of the mobile station 103.

  First, in the downlink frame 141 of the radio frame 131, the control unit 115 of the base station 101 determines whether the radio frame 131 is a radio frame that can pause data transmission (step S101). Since there is user data to be transmitted by the base station 101 in the downlink frame 141 (No in step S101), the control unit 115 is configured to transmit the user data on the use channel already allocated to the mobile station 103. 111 is controlled (step S102).

  When there is an empty slot in the downstream frame 141, the control unit 115 can perform carrier sense for the carrier of the empty slot. Then, the control unit 115 can cause the storage unit 113 to store the carrier sense execution result. Similarly, in the following downstream frames 143, 145, and 147, the control unit 115 can perform carrier sense for carriers in empty slots.

  Then, the control unit 115 determines whether or not the reception quality of the mobile station 103 has deteriorated based on the reception quality value received in the radio frame before the radio frame 131 (step S103). This determination is realized by comparing the reception quality value with a predetermined quality threshold value. The quality threshold is a standard for determining whether or not the mobile station 103 can communicate with the base station 101 with stable quality, and is a value related to RSSI and CINR, for example. The stable quality is, for example, the quality for correctly demodulating the radio signal from the base station 101 or the quality that can realize a desired throughput rate. The control unit 115 can store the quality threshold value in the storage unit 113 in advance.

  If the reception quality value of the mobile station 103 is equal to or higher than the quality threshold value, it is determined that the reception quality of the mobile station 103 has not deteriorated (No in step S103). In this case, the control unit 115 does not assign a new channel to the mobile station 103.

  Subsequently, in the uplink frame 142, the mobile station 103 transmits data to be transmitted to the base station 101. In addition, the mobile station 103 calculates the reception quality value of the radio signal received from the base station 101 received in the downlink frame 141 and transmits the calculated value to the base station 101.

  In the downstream frame 143 of the wireless frame 132 following the upstream frame 142, the control unit 115 of the base station 101 determines whether the wireless frame 132 is a wireless frame that can pause data transmission (step S101). In the downlink frame 143, as with the downlink frame 141, there is user data to be transmitted by the base station 101 (No in Step S101), and therefore the control unit 115 controls the communication unit 111 to transmit user data (Step S101). S102). And the control part 115 determines about the deterioration of the reception quality of the mobile station 103 (step S103).

  In the uplink frame 144, the mobile station 103 is instructed to pause data transmission, so the mobile station 103 does not transmit data to the base station 101.

  In the downlink frame 145 of the radio frame 133, since there is no user data to be transmitted from the base station 101 to the mobile station 103, the control unit 115 determines that data transmission to the mobile station 103 can be suspended (Yes in step S101). . Then, the control unit 115 determines whether the radio frame 133 is a radio frame including an uplink frame that instructs the mobile station 103 to pause data transmission (step S104). That is, the control unit 115 reads information on the predetermined radio frame in the storage unit 113 and determines whether the radio frame 133 is a predetermined radio frame. Since the radio frame 133 is not a predetermined radio frame (No in step S104), the control unit 115 does not suspend data transmission to the mobile station 103 and controls data for maintaining a communication connection with the mobile station 103. The communication unit 111 is controlled to transmit (step S102).

  In the uplink frame 146, the mobile station 103 transmits data to be transmitted to the base station 101.

  In the downlink frame 147 of the radio frame 134, since there is no user data to be transmitted from the base station 101 to the mobile station 103, the control unit 115 determines that data transmission to the mobile station 103 can be paused as in the downlink frame 145. (Yes in step S101). Subsequently, the control unit 115 determines whether the wireless frame 134 is a predetermined wireless frame (step S104). Since the control unit 115 instructs the mobile station 103 to pause data transmission in the upstream frame 148 of the radio frame 134 (Yes in step S104), the control unit 115 transmits the data to the mobile station 103 in the downstream frame 147. Pause data transmission.

  Then, the control unit 115 performs carrier sense in the radio frame 134 (step 105). In the radio frame 134, since data transmission / reception between the base station 101 and the mobile station 103 is suspended, the control unit 115 performs carrier sense on the carrier in the slot (same slot) of the used channel. be able to. Then, the control unit 115 causes the storage unit 113 to store the carrier sense execution result.

  Here, it is assumed that the reception quality value of the mobile station 103 is less than the quality threshold value (Yes in step S103). Then, the control unit 115 determines a channel (allocation channel) to be allocated to the mobile station 103 communicating with the base station 101 based on the carrier sense execution result (step S106). For example, the control unit 115 identifies the channel having the best communication quality among the other channels in the same slot from the carrier sense execution result. In this embodiment, the channel with the best communication quality is the channel with the lowest received electric field strength. Then, the control unit 115 newly allocates a channel with the best communication quality to the mobile station 103. That is, the control unit 115 controls the communication unit 111 so as to transmit information on the channel with the best communication quality to the mobile station 103. Since the channel is changed within the same slot, the mobile station 103 can switch the channel without interrupting communication with the base station 101.

  When there is no channel (assignable channel) less than the carrier sense threshold in the same slot, the control unit 115 can identify the channel with the best communication quality in the empty slot and assign it to the mobile station 103.

  Further, when there is no assignable channel even in the empty slot, the control unit 115 can instruct the mobile station 103 to execute the handover.

  As described above, in the present embodiment, the control unit 115 of the base station 101 performs carrier sense in the predetermined radio frame 134 including the downlink frame 147 that can pause data transmission to the mobile station 103. Since data transmission / reception between the base station 101 and the mobile station 103 is suspended in the predetermined radio frame 134, the control unit 115 may perform carrier sense on the carrier in the slot (same slot) of the used channel. it can. As a result, the control unit 115 can grasp the communication quality of the channel in the same slot, so that a channel having a good communication quality in the same slot can be newly assigned to the mobile station 103.

  Further, when the mobile station 103 is performing intermittent packet communication with the base station 101, carrier sense in the same slot by the control unit 115 is effective. In intermittent packet communication, the mobile station 103 does not always perform data communication while establishing a communication connection with the base station 101. Therefore, the base station 101 always assigns a channel to the mobile station 103. There is no need. Therefore, it is conceivable that the base station 101 assigns a channel only when the mobile station 103 transmits / receives data, and assigns a channel of the same slot to another mobile station when the mobile station 103 does not transmit / receive data. The control unit 115 needs to execute carrier sense after communication with the mobile station 103 by performing carrier sense for the carrier in the same slot while establishing a communication connection with the mobile station 103. There is no. Therefore, the control unit 115 can quickly assign a channel with good communication quality in the same slot to another mobile station.

  Further, even when the mobile station 103 communicates with the base station 101 using a plurality of slots using slot diversity, and all the slots of the radio frame are used by the plurality of mobile stations, the control unit 115 is also used. Carrier sense in the same slot by is valid. When a new mobile station desires a communication connection with the base station 101, the base station 101 assigns one of a plurality of slots assigned to the mobile station 103 to the new mobile station. Although the number of slots used by the mobile station 103 decreases and the communication quality related to the mobile station 103 decreases, the mobile station 103 can continue to communicate with the base station 101 because at least one slot can still be used. By performing carrier sense in the same slot regarding the mobile station 103, it is possible to grasp the communication quality of a plurality of slots allocated to the mobile station 103. Therefore, the control unit 115 of the base station 101 assigns the slot having the best (or bad) communication quality among the plurality of slots to the new mobile station according to the importance of the mobile station 103 and the new mobile station. Can do.

  Further, when the base station 101 and the mobile station 103 are performing communication disconnection processing, a new mobile station wishes to establish a communication connection with the base station 101. Carrier sense is effective. By performing carrier sense in the same slot during communication connection with the mobile station 103, the control unit 115 promptly selects a channel with good communication quality in the same slot after disconnecting the communication connection with the mobile station 103. It can be assigned to a new mobile station.

  Further, in the present embodiment, the control unit 115 assigns the channel having the lowest received electric field strength (the best communication quality) among the other channels of the channel (used channel) assigned to the mobile station 103 to the mobile station. 103. Thereby, since the channel is changed in the same slot, the mobile station 103 can switch the channel without interrupting the communication with the base station 101.

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

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

  In the above description of the embodiment of the present invention, it has been described that the control unit 115 newly assigns a channel to the mobile station 103 when the reception quality value of the mobile station 103 becomes less than the quality threshold value. It is not limited to this aspect. When the reception quality value of the mobile station is less than the quality threshold value, there is a possibility that a signal for assigning a new channel may not reach the mobile station correctly from the base station. Therefore, the control unit can assign the channel with the best communication quality to the mobile station every time carrier sense is executed, regardless of the reception quality value of the mobile station. As a result, the control unit can continue to assign to the mobile station a channel that reliably improves the reception quality of the mobile station. Further, as long as the control unit continues to assign other channels of the used channel slot to the mobile station, communication between the base station and the mobile station is not interrupted, so that no problem occurs even if the channels are frequently assigned. When the channel with the best communication quality is the channel used, even if the channel is assigned to the mobile station by the control unit, the channel is not switched in the mobile station.

  Further, 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 “greater than” or the threshold “less than” is not necessarily a strict meaning, and depends on the specifications of the base station. In addition, the meaning when the reference value is included or not included 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 100 Wireless communication system 101 Base station 103 Mobile station 111 Communication part 113 Storage part 115 Control part 131-134 Radio | wireless frame 141,143,145,147 Down frame 142,144,146,148 Up frame

Claims (4)

In a base station that adopts a TDD (Time Division Duplex) method in which each radio frame of a continuous radio frame is composed of a downlink frame and an uplink frame, and performs radio communication with a mobile station,
Instructing the mobile station to pause data transmission to the base station in an uplink frame of a predetermined radio frame of the continuous radio frame;
Determining whether data transmission to the mobile station can be paused in a downlink frame of the predetermined radio frame;
A base station comprising a control unit that performs carrier sense in the predetermined radio frame when data transmission to the mobile station can be suspended.   The base station according to claim 1, wherein the control unit determines a channel to be allocated to the mobile station in communication with the base station based on the execution result of the carrier sense.   3. The base station according to claim 2, wherein the control unit allocates a channel having the best communication quality among the other channels of the allocated channel slot to the mobile station. In a communication control method in a base station that wirelessly communicates with a mobile station by adopting a TDD (Time Division Duplex) method in which each wireless frame of a continuous wireless frame is composed of a downlink frame and an uplink frame, the base station ,
Instructing the mobile station to pause data transmission to the base station in an uplink frame of the predetermined radio frame of the continuous radio frame;
Determining whether data transmission to the mobile station can be suspended in a downlink frame of the predetermined radio frame;
A step of performing carrier sense in the predetermined radio frame when data transmission to the mobile station can be suspended.

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