JP2015133550A - Radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To mitigate communication interference even when a plurality of base stations are arranged not distantly from each other and can mutually cause the communication interference.SOLUTION: A radio communication system for performing radio communication on the basis of the CSMA/CA system comprises: a plurality of base station transmission/reception circuits 11 arranged not distantly from each other and can mutually cause communication interference; a plurality of radio communication networks 21 each of which is formed correspondingly to one base station transmission/reception circuit 11 and includes one or more communication terminals 31 performing radio communication with the base station transmission/reception circuit 11; and a synchronous signal acquisition unit 15 for performing time synchronization between the plurality of base station transmission/reception circuits 11. Respective base station transmission/reception circuits 11 mutually using the same or one by one adjacent frequency channel start transmission approximately at the same time mutually time-synchronized through the synchronous signal acquisition unit 15, in transmitting, by themselves, packet data to a communication terminal 31 in their formed radio communication network 21.

Description

  In a wireless communication system that performs wireless communication based on the CSMA / CA scheme, even when a plurality of base stations are arranged at a distance that can cause communication interference with each other, the communication interference is reduced to prevent deterioration in communication quality. And a preferred wireless communication system.

  Conventionally, standardization of a wireless LAN has been promoted by the Institute of Electrical and Electronics Engineering (IEEE). Particularly in a wireless packet communication system typified by a wireless LAN, contention of wireless resources among a plurality of terminals is regarded as a problem. In order to avoid the competition of radio resources, medium access control (MAC) is necessary. As a MAC protocol in this wireless LAN, a so-called carrier sense is performed in which a terminal detects a carrier wave of another terminal before transmitting a packet, and when the carrier cannot be captured, a CSMA (Carrier Sense Multiple Access) is transmitted. ) Method has been proposed. Also, a CSMA / CA scheme (Carrier Sense Multiple Access with Collision Avoidance) is proposed in which a mechanism for avoiding packet collision is added to the CSMA scheme.

  In this CSMA / CA system, when communication is started and a response of an ACK (Acknowledge) signal is received from the wireless node of the communication partner, it is considered that communication is successful, and when an ACK signal is not received In this system, it is assumed that a communication collision with another wireless node has occurred, and the packet data is retransmitted again with a back-off time.

  In recent wireless communication systems employing the CSMA / CA method, base station transmission / reception circuits 71-1 to 71-n corresponding to base stations are mounted in the same casing 72, as shown in FIG. A system configuration has also been proposed (see, for example, Non-Patent Document 1). This wireless communication system 7 includes a wireless communication network 81-1 formed around a base station transmission / reception circuit 71-1, and a wireless communication network 81-2 formed around a base station transmission / reception circuit 71-2. And a base station transceiver circuit 71-n (n is a positive integer), and further includes a wireless communication network 81-n. In the wireless communication network 81-1, one or more communication terminals 91-1 for performing wireless communication with the base station transmission / reception circuit 71-1 constituting the wireless communication network 81-1 are included in the wireless communication network 81-2. One or more communication terminals 91-2 that perform wireless communication with the base station transmission / reception circuit 71-2 that configures the base station transmission / reception circuit 71-n. One or more communication terminals 91-n that perform wireless communication with each other are provided. That is, in this wireless communication system 7, a plurality of communication terminals 91 are formed for each one base station transmission / reception circuit 71 and each have one or more communication terminals 91 that perform wireless communication with the base station transmission / reception circuit 71. It consists of a wireless communication network 81.

  Hereinafter, in the wireless communication system 7, when attention is paid to the wireless communication network 81-1 and the wireless communication network 81-2, the base station transceiver circuit 71-1 and one or more communication terminals are included in the wireless communication network 81-1. 91-1 communicates packet data with each other, and within the wireless communication network 81-2, the base station transmission / reception circuit 71-2 and one or more communication terminals 91-2 communicate packet data with each other. At this time, these wireless communications are often performed independently without being linked to each other between the wireless communication network 81-1 and the wireless communication network 81-2.

  In such a case, a description will be given below when a frequency channel used for wireless communication in the wireless communication network 81-1 and a frequency channel used for wireless communication in the wireless communication network 81-2 are adjacent to each other. Such communication interference may occur.

  As shown in FIG. 13, in the wireless communication network 81-1, packet data is transmitted from the base station transmission / reception circuit 71-1 to the communication terminal 91-1, so-called downlink is performed, and the wireless communication network is almost at the same time. Consider a case in which packet data is transmitted from the communication terminal 91-2 to the base station transmission / reception circuit 71-2 in 81-2, that is, so-called uplink is performed. In such a case, packet data to be transmitted is generated on the base station transmission / reception circuit 71-1 side and carrier sense is executed, and packet data to be transmitted is also generated on the communication terminal 91-2 side and carrier sense is detected. Run. In each carrier sense, since the frequency channels adjacent to each other are used between the wireless communication network 81-1 and the wireless communication network 81-2, the carriers are not detected. As a result, transmission of packet data from the transmission / reception circuit for base station 71-1 to the communication terminal 91-1 is started, and packet data is transmitted from the communication terminal 91-2 to the transmission / reception circuit for base station 71-2 almost at the same time. Transmission starts.

  At this time, the base station transmission / reception circuit 71-2 that receives the packet data from the communication terminal 91-2 receives leaked radio waves accompanying the transmission of the packet data from the base station transmission / reception circuit 71-1 to the communication terminal 91-1. It will come around. In particular, since the base station transmission / reception circuits 71-1 and 71-2 are mounted in a single casing 72, there is a very high possibility that such leaked radio waves will wrap around. Further, since the frequency channels adjacent to each other are used between the wireless communication network 81-1 and the wireless communication network 81-2, the base station transmission / reception circuit 71-2 includes a communication terminal 91-2 as shown in FIG. In many cases, out-of-band radiation of the frequency channel f1 of the radio wave leaking from the base station transmission / reception circuit 71-1 occurs with respect to the frequency channel f2 received from the base station. Moreover, since the base station transmission / reception circuit 71-2 is arranged at a position closer to the base station transmission / reception circuit 71-1 than the communication terminal 91-2, the frequency received from the communication terminal 91-2. Since the power of the frequency channel f1 of the radio wave leaking from the base station transmission / reception circuit 71-1 is higher than that of the channel f2, there is a higher possibility of causing communication interference. The base station transmission / reception circuit 71-2 generates packet data to be transmitted by itself, starts carrier sense, and performs such communication even if the frequency channel f2 is actually idle (when not used). When interference occurs, it may be erroneously determined that the frequency channel f2 is busy (when in use). When such an error in determining communication interference occurs, it is necessary to wait for the transmission of the frequency channel f2 from the base station transmission / reception circuit 71-2, resulting in a decrease in throughput and a deterioration in communication quality. Will be caused.

  In addition to this, as shown in FIG. 15, the packet data transmission by the base station transceiver circuit 71-1 and the packet data reception by the base station transceiver circuit 71-2 overlap each other in time. In such a case, there was a problem that an error in reception of packet data by the base station transmission / reception circuit 71-2 occurs due to the communication interference described above.

Yozo Soji, Kiyohide Nakauchi, Manabu Ito, Kanerai “Development of virtual network equipment for virtualization for the demonstration of“ Bring Your Own Network (BYON) ”, IEICE Technical Report NS2013-122, November 2013

  Accordingly, the present invention has been devised in view of the above-described problems, and an object of the present invention is a distance that can cause communication interference in a wireless communication system that performs wireless communication based on the CSMA / CA scheme. It is an object of the present invention to provide a wireless communication system capable of preventing communication quality deterioration and suppressing packet data reception errors by reducing communication interference even when a plurality of base stations are arranged.

  In order to solve the above-described problems, the wireless communication system according to claim 1 may interfere with each other in a wireless communication system that performs wireless communication based on a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) scheme. A plurality of base station transceiver circuits arranged at a distance, and one or more communication terminals formed for each of the one base station transceiver circuit and performing wireless communication with the base station transceiver circuit A plurality of radio communication networks each having time synchronization means for synchronizing time between the plurality of base station transmission / reception circuits, and the base station transmission / reception circuits using the same or successive adjacent frequency channels, When transmitting packet data to the communication terminal in the wireless communication network formed by itself, the time synchronization means synchronizes the time with each other. Characterized in that it starts transmitting at approximately the same time that is.

  A plurality of wireless communication systems according to claim 2 are the invention according to claim 1, further comprising longest packet discrimination means for discriminating the longest packet data among the packet data transmitted at the same time from the transmission / reception circuit for each base station. In addition, each of the transmission / reception circuits for each base station describes information on the longest packet data determined by the longest packet determination means in a header of packet data to be transmitted, and other than the packet data having the longest transmission time. The communication terminal that has received the packet data reads information on the longest packet data from the header, and waits for transmission of the packet data to the base station transceiver circuit from the transmission start time until the transmission time ends. It is characterized by.

  A plurality of wireless communication systems according to claim 3 are the wireless communication systems according to claim 1, further comprising: a longest packet discriminating unit that discriminates the longest packet data out of the packet data transmitted from the base station transceiver circuits at the same time. In addition, each of the transmission / reception circuits for each base station transmits itself Null data having a difference length between the longest packet data length determined by the longest packet determination unit and the packet data length transmitted by itself. It is added to packet data.

  In order to solve the above-described problem, the wireless communication system according to claim 4 may interfere with each other in a wireless communication system that performs wireless communication based on a CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance) method. A plurality of base station transceiver circuits arranged at a distance, and one or more communication terminals formed for each of the one base station transceiver circuit and performing wireless communication with the base station transceiver circuit A plurality of wireless communication networks each having a longest packet determination means for determining the longest packet data among the packet data transmitted from the transmission / reception circuits for each base station using the same or successively adjacent frequency channels; Each base station transmission / reception circuit adds the longest parameter to a CTS (clear to send frame) frame located before the packet data to be transmitted. Describes information on the longest packet data determined by the packet determination means, transmits the CTS frame to the communication terminal, the communication terminal reads the transmission time of the longest packet data from the received CTS frame, and The transmission of packet data to the base station transmission / reception circuit is awaited from the transmission start time of the CTS frame until the transmission time ends.

  According to a fifth aspect of the present invention, in the wireless communication system according to any one of the first to fourth aspects, the base station transmitting / receiving circuits using the frequency channels that are the same or adjacent to each other receive the packet data. The carrier sense is performed based on the CSMA / CA method before transmission, and the packet data is transmitted when a predetermined ratio or more in each base station transmission / reception circuit becomes empty. .

  A wireless communication system according to claim 6 is the wireless communication system according to any one of claims 1 to 4, further comprising a base station control unit that controls the transmission / reception circuit for each base station, and is adjacent to each other one after another. The transceiver circuit for each base station using a frequency channel performs carrier sense based on the CSMA / CA method before transmitting the packet data, and periodically transmits the result to the base station controller. The base station control unit receives the result of the carrier sense and issues an instruction to transmit packet data by the base station transceiver circuit.

  According to the present invention having the above-described configuration, in a wireless communication system that performs wireless communication based on the CSMA / CA scheme, the communication interference is reduced even when a plurality of base stations are arranged at a distance that can cause communication interference with each other. Can be made. For this reason, it is possible to improve the throughput and hence the communication quality, and to prevent data reception errors.

It is a figure which shows the structural example of the radio | wireless communications system to which this invention is applied. It is a figure for demonstrating the concept which prevents the communication interference by the radio | wireless communications system to which this invention is applied. It is a time chart which shows the transmission timing of each data in the transmission / reception circuit for base stations. 5 is a flowchart for explaining an operation example of a radio communication system to which the present invention is applied. It is a time chart when the information of the longest packet is described in Duration included in the MAC header. 7 is a flowchart for explaining another operation example of the radio communication system to which the present invention is applied. It is a time chart in the case of adding Null data as an alternative which describes information in Duration of MAC header. It is a flowchart in the case of preventing communication interference by utilizing a CTS frame. It is a time chart in the case of preventing communication interference by utilizing a CTS frame. It is another flowchart in the case of preventing communication interference by utilizing a CTS frame. It is a figure which shows the other structural example of the radio | wireless communications system to which invention is applied. It is a figure which shows the example of a conventional system structure which mounts the transmission / reception circuit for base stations corresponded to a base station in the same housing | casing. It is a figure for demonstrating the problem of a prior art. It is a figure for demonstrating the out-of-band radiation of the frequency channel of the electromagnetic wave leaked from the transmission / reception times for other base stations. It is a figure for demonstrating the communication interference by overlapping in time between the transmission / reception circuits for adjacent base stations.

  Hereinafter, embodiments of a wireless communication system to which the present invention is applied will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration example of a wireless communication system 1 to which the present invention is applied. The wireless communication system 1 includes a base station device 2 and a plurality of base station transmission / reception circuits 11-1, 11-2, 11-3, ..., 11-n arranged in the base station device 2. (Where n is a positive integer), antennas 12-1, 12-2, 12-3,..., 12-n provided in each base station transceiver circuit 11, and each base station transceiver circuit 11, a base station accommodating switch 13 connected to the base station 11, a base station control unit 14 connected to each base station transmission / reception circuit 11 and the base station accommodating switch 13, and a synchronization signal acquiring unit 15 connected to the base station control unit 14. And. The base station accommodation switch 13 and the synchronization signal acquisition unit 15 are each connected to the network 3.

  In addition, the wireless communication system 1 includes a wireless communication network 21-1 formed around a base station transmission / reception circuit 11-1 and a wireless communication network 21- formed around a base station transmission / reception circuit 11-2. 2, a wireless communication network 21-3 formed around the base station transmission / reception circuit 11-3, and a wireless communication network 21-n formed around the base station transmission / reception circuit 11-n. .

  Also, in the wireless communication network 21-1, one or more communication terminals 31-1 that perform wireless communication with the base station transceiver circuit 11-1 constituting the wireless communication network 21-1 are included in the wireless communication network 21-2. One or more communication terminals 31-2 that perform wireless communication with the base station transmission / reception circuit 11-2 that constitutes the base station are included in the radio communication network 21-3. One or more communication terminals 31-3 that perform wireless communication with the wireless communication network 21-n include one or more communication terminals 31-n that perform wireless communication with the base station transmission / reception circuit 11-n included in the wireless communication network 21-n. Each communication terminal 31-n exists.

  Each of the base station transmission / reception circuits 11-1, 11-2, 11-3,..., 11-n is disposed at a distance that can cause communication interference with at least another adjacent base station transmission / reception circuit 11. Has been. In the form shown in FIG. 1, an example is shown in which all base station transmission / reception circuits 11-1, 11-2, 11-3,. However, it is not limited to this. That is, even if the base station apparatus 2 is not mounted in a casing, it may be arranged at a distance that can cause communication interference between adjacent base station transmission / reception circuits 11.

  The base station transceiver circuit 11 performs wireless communication with the communication terminal 31 based on the CSMA / CA scheme (Carrier Sense Multiple Access with Collision Avoidance). The base station transmission / reception circuit 11 may perform wireless communication with the communication terminal 31 based on, for example, the IEEE 802.11 MAC standard, or may be based on any other IEEE communication standard. The base station transceiver circuit 11 serves as a so-called central control unit that controls wireless communication performed with the communication terminal 31. As will be described later, the base station transmission / reception circuits 11 perform various controls for avoiding communication interference between the wireless communication networks 21 independently of each other, and cooperate with each other as necessary. In such a case, each base station transceiver circuit 11 performs processing operations under the control of the base station control unit 14.

  The communication terminal 31 includes a personal computer (PC), a mobile communication terminal, a smartphone, a tablet terminal, a wearable terminal, and the like. The communication terminal 31 can perform wireless packet communication with the base station transceiver circuit 11 based on at least the CSMA / CA system.

  The wireless communication network 21 configures a communication terminal 31 based on various network forms such as a star type, a tree type, and a mesh type with the base station transmission / reception circuit 11 as a center. In the wireless communication network 21, when establishing a communication link between the base station transceiver circuit 11 and the communication terminal 31 based on the above-described standard, the packet data transmission side detects the other carrier wave, so-called The carrier sense is executed, and when the carrier cannot be captured, processing for transmitting its own packet is performed. Also, different frequency channels are assigned to the wireless communication networks 21-1 to 21-n. In such a case, frequency channels adjacent to each other may be allocated between the wireless communication networks 21 adjacent to each other.

  The base station accommodation switch 13 is a switch for accommodating the base station transmission / reception circuits 11-1 to 11-n. The base station accommodating switch 13 distributes downlink packet data received from the network 3 to appropriate base station transmission / reception circuits 11-1 to 11-n according to the header information. The base station accommodating switch 13 transfers packet data received from the base station transmission / reception circuits 11-1 to 11-n to the network 3. The base station accommodating switch 13 has a buffer (not shown) for temporarily storing the packet data when transmitting the downlink packet data to the base station transmission / reception circuits 11-1 to 11-n. doing. This buffer (not shown) may be allocated to each of the base station transmission / reception circuits 11-1 to 11-n. The downlink packet data temporarily stored in this buffer is sent to each of the base station transmission / reception circuits 11-1 to 11-n based on a command via a control signal from the base station control unit 14. . At this time, the transmission timing of downlink packet data can also be controlled by a control signal from the base station control unit 14.

  The base station control unit 14 controls each of the base station transmission / reception circuits 11-1 to 11-n. As an example of each control, the base station control unit 14 controls transmission start timing of downlink packet data from the base station transmission / reception circuit 11 to the communication terminal 31. The base station controller 14 also monitors the amount of data stored in a buffer (not shown) allocated to each of the base station transceiver circuits 11-1 to 11-n in the base station accommodating switch 13. In addition, the base station transmission / reception circuits 11-1 to 11-n perform frame generation control when transmission of a control frame such as a CTS (clear to send frame) frame is involved.

  The synchronization signal acquisition unit 15 acquires a synchronization signal necessary for time synchronization between the base station transmission / reception circuits 11-1 to 11-n. The synchronization signal acquisition unit 15 transmits the acquired synchronization signal to the base station control unit 14. The synchronization signal acquisition unit 15 generates or reproduces an accurate time synchronization signal based on a GPS (Global Positioning System) or a reference signal from the network 3. Further, the function as the synchronization signal acquisition unit 15 may be implemented in each of the base station transmission / reception circuits 11-1 to 11-n.

  The network 3 is a communication network accessible from a PC or a portable information terminal such as the Internet. The base station apparatus 2 acquires necessary information from the network 3 as necessary.

  Next, the operation of the wireless communication system 1 to which the present invention is applied will be described. In the following description of the operation, a case where communication interference between the wireless communication networks 21-1 and 21-2 among the wireless communication networks 21-1 to 21-n is prevented will be described as an example.

  In the wireless communication network 21-1, the base station transceiver circuit 11-1 and one or more communication terminals 31-1 communicate packet data with each other. At this time, as shown in FIG. 2, packet data transmitted from the base station transmission / reception circuit 11-1 to the communication terminal 31-1 is data D1, and the communication terminal 31-1 transmits to the base station transmission / reception circuit 11-1. The packet data transmitted to is assumed to be data U1. Within the wireless communication network 21-2, the base station transceiver circuit 11-2 and one or more communication terminals 31-2 communicate packet data with each other. At this time, the packet data transmitted from the base station transmission / reception circuit 11-2 to the communication terminal 31-2 is data D2, and is transmitted from the communication terminal 31-2 to the base station transmission / reception circuit 11-2. The packet data is assumed to be data U2. Incidentally, in the following example, it is assumed that the frequency channel of data D1 and data U1 and the frequency channel of data D2 and data U2 are adjacent to each other. In addition, the base station transceiver circuit 11-1 and the base station transceiver circuit 11-2 are arranged at a distance that can cause communication interference, and the communication terminal 31-1 and the communication terminal 31-2 do not interfere with each other. It is assumed that they are located apart from each other.

  In such a case, in the present invention, the transmission start time of the data D1 from the base station transmission / reception circuit 11-1 and the transmission start time of the data D2 from the base station transmission / reception circuit 11-2 are set to be substantially the same time. Thereby, the transmission time of the data D1 from the base station transmission / reception circuit 11-1 to the communication terminal 31-1 is different from the transmission time of the data U2 from the communication terminal 31-2 to the base station transmission / reception circuit 11-2. Can be made. Thereby, even when a leaked radio wave accompanying transmission of data D1 from the base station transceiver circuit 11-1 wraps around the base station transceiver circuit 11-2, the base station transceiver circuit 11-2 at that time , Not the phase in which the data U2 is received, but the phase in which the data D2 is transmitted. For this reason, the transmission / reception circuit 11-2 for the base station can avoid the leakage of the radio wave from the data D1 in the time zone for receiving the data U2.

  FIG. 3 is a time chart showing the transmission timing of each data in the base station transceiver circuits 11-1 and 11-2. In the following time chart, Tx indicates downlink data D transmitted from the base station transceiver circuit 11 to the communication terminal 31, and Rx is transmitted from the communication terminal 31 to the base station transceiver circuit 11. The uplink data U to be performed is shown. The horizontal axis is a time axis t.

In this case, when the base station transceiver circuits 11-1 and 11-2 want to transmit data D1 and data D2 to the respective communication terminals 31-1 and 31-2, first, carrier sense (CS ). Next, the base station transceiver circuit 11-1 transmits data D1 to the communication terminal 31-1, and the base station transceiver circuit 11-2 transmits data D2 to the communication terminal 31-2. In such a case, the transmission start times of the data D1 and the data D2 are adjusted so as to be the same time t ₁ .

  When the adjustment at the start of transmission is actually performed, the synchronization signal acquisition unit 15 acquires a reference signal from the GPS or the network 3 and transmits it to the base station control unit 14. Based on the reference signal, the base station control unit 14 performs control so that the data D1 and data D2 to be transmitted from the base station transmission / reception circuits 11-1 and 11-2 are time-synchronized with the transmission start time. . When the function as the synchronization signal acquisition unit 15 is implemented in each of the base station transmission / reception circuits 11-1 and 11-2, the synchronization signal acquisition function implemented in the inside receives the reference signal from the PS or the network 3. Acquired and actual synchronization control is executed through control units (not shown) provided in the base station transmission / reception circuits 11-1 and 11-2, respectively.

In this way, when the data D1 and the data D2 transmitted with the transmission start time set to the same time t ₁ are the same in data length, the transmission ends at the same time t ₂ . In particular, the communication terminal 31-2 that has received the data D2 from the base station transceiver circuit 11-2 may return the data U2 to the base station transceiver circuit 11-2. In such case, the reply start time t ₃ of the data U2 will after time t _2. Therefore, the base station transmission / reception circuit 11-2 receives the data U2 at a timing different from the transmission timing of the data D1 from the base station transmission / reception circuit 11-1. For this reason, the base station transmission / reception circuit 11-2 can prevent transmission of leaked radio waves accompanying transmission of the data D1 from the base station transmission / reception circuit 11-1 when receiving the data U2. As a result, communication interference can be prevented from occurring on the base station transceiver circuit 11-2 side.

  For this reason, the transmission / reception circuit 11-2 for the base station does not cause an error in the determination of communication interference, and can sequentially perform transmission without waiting for transmission of new packet data, thereby improving throughput and eventually improving communication quality. It is possible to improve.

  In addition, since the reception of data U2 by the base station transceiver circuit 11-2 and the transmission of data D1 from the base station transceiver circuit 11-1 do not overlap each other, the above-described communication interference can be prevented. Therefore, it is possible to prevent the reception error of the data U2 by the base station transceiver circuit 11-2.

In the period from time t ₂ to time t ₃ , the leakage power from the data D1 transmitted from the base station transmission / reception circuit 11-1 may wrap around the base station transmission / reception circuit 11-2. However, in the period from the time t ₂ to the time t ₃ , the base station transmission / reception circuit 11-2 is only in the state of transmitting the data D2, and is not in the reception phase of the data U2. There is no communication interference.

Further, in the embodiment described above, the transmission start time of the data D1, and not the transmission start time of the data D2 is necessarily limited if it is the same time t _2, the long substantially identical time, micro There may be a gap in second units.

  In addition, although the operation example mentioned above can exhibit an effect when the data length of the data D1 and the data D2 is substantially the same to the last, when the data length of the data D1 and the data D2 is different, the following operation | movement is performed. An example may be executed.

  As shown in the flowchart of FIG. 4, when data D1 to be transmitted from the base station transmission / reception circuit 11-1 to the communication terminal 31-1 is generated in step S11, the data D1 is stored in the base station accommodating switch 13. It is stored in a certain buffer 131. Next, the process proceeds to step S12, where the buffer 131 notifies the base station control unit 14 of the packet data length of the data D1 temporarily stored in the buffer 131.

  Further, when data D2 to be transmitted from the base station transmission / reception circuit 11-2 to the communication terminal 31-2 is generated before and after Steps S11 to S12, the data D2 is stored in the buffer in the base station accommodating switch 13. 132. Next, the process proceeds to step S14, and the packet data length of the data D2 temporarily stored in the buffer 132 is notified from the buffer 132 to the base station control unit 14.

  Next, the process proceeds to step S15, and the base station control unit 14 identifies the packet length of the data D1 and the packet length of the data D2 respectively transmitted from the above-described steps S12 and S14, and the longest packet among these Determine the data length.

  Next, it transfers to step S16 and the base station control part 14 notifies various information with respect to the transmission / reception circuits 11-1 and 11-2 for base stations. In step S16, the base station control unit 14 stores data D1 and data D2, for example, as downlink packet data temporarily in the buffers 131 and 132, and notifies that communication is temporarily suspended. You may do it. In addition, the base station control unit 14 notifies the base station transmission / reception circuits 11-1 and 11-2 of setting values set in an area called Duration given to the headers of the data D1 and data D2. The setting value to be notified may be in accordance with the longest packet data length determined in step S15 in the base station control unit 14. In step S16, the base station control unit 14 may notify the longest packet data length determined in step S15, or whether the packet data is data D1 or data D2.

  Next, the process proceeds to step S17, where carrier sense (CS) is performed on each of the base station transceiver circuits 11-1 and 11-2. As a result of this CS, either idle (when not in use) or busy (when in use) will be transmitted, but the result is notified to the base station control unit 14. It will be. The base station control unit 14 notifies the base station accommodating switch 13 of the packet transmission command in step S18 when the CS result indicates that both the base station transceiver circuits 11-1 and 11-2 are idle.

  In response to the packet transmission command, the base station accommodating switch 13 transfers the data D1 temporarily enabled in the buffer 131 to the base station transmission / reception circuit 11-1. Also, the data D2 stored in the buffer 132 is transferred to the base station transceiver circuit 11-2 (step S19).

  Next, the process proceeds to step S20, and the base station transceiver circuits 11-1 and 11-2 each generate packet data. In step S20, the data D1 and data D2 transferred from the buffers 131 and 132 are converted into packet data. For example, as shown in FIG. 5, the data D1 and data D2 are inserted into the actual data part. . Further, the base station transmission / reception circuits 11-1 and 11-2 describe various information notified in Step S16 in the Duration included in the MAC header. In this Duration, a setting value corresponding to the longest packet data length determined in Step S15 described above may be described. Further, the longest packet data length itself determined in step S15 may be described.

Next, the process proceeds to step S21, and the base station transceiver circuit 11-1 transmits the data D1 converted into packet data to the communication terminal 31-1. Similarly, the base station transceiver circuit 11-2 transmits packetized data D2 to the communication terminal 31-2. In such a case, the transmission start times of the data D1 and the data D2 are adjusted so as to be the same time t ₁ as shown in FIG. The adjustment at the start of transmission is performed under the control of the base station control unit 14 based on the GPS from the synchronization signal acquisition unit 15 or the reference signal from the network 3 as described above.

The communication terminals 31-1 and 32-2 receive data D1 and data D2, respectively. The communication terminal 31-2 receives the data D2 having a shorter data length than the data D1, but at this time reads various information described in the Duration in the MAC header. As a result, the communication terminal 31-2 can determine that the data length received by the communication terminal 31-2 is shorter than the data D1. Further, the communication terminal 31-2 reads the set value according to the longest data D1 or reads the packet data length itself of the longest data D1 if it is described. As a result, the communication terminal 31-2 can grasp the length of the longest data D1, and the time from the transmission start time t ₁ to the transmission end time t ₂ in consideration of the length of the duration. I can grasp it. Actually, the transmission end time t ₂ may include a transmission time of SIFS (Short Interframe Space) or ACK (ACKnowledgement).

Next, it transfers to step S22 and the communication terminal 31-2 performs NAV (Network Allocation Vector) setting. In this NAV setting, transmission of uplink data U2 is prohibited from the communication terminal 31-2 toward the base station transceiver circuit 11-2. As shown in FIG. 5, the set length of the NAV is the time from the transmission start time t ₁ to the transmission end time t ₂ of the longest data D1. Since the time information is known information on the side of the communication terminal 31-2 that has read various information described in Duration, it can be easily set.

In this way, the transmission of the uplink data U2 from the communication terminal 31-2 toward the base station transmission / reception circuit 11-2 is set to be prohibited until the transmission of the data D1 is completed. The Then, the communication terminal 31-2, when returning a data U2 to the base station for transmitting and receiving circuit 11-2, replies the start time t ₃ of the data U2 will after time t _2. Therefore, the base station transmission / reception circuit 11-2 receives the data U2 at a timing different from the transmission timing of the data D1 from the base station transmission / reception circuit 11-1. For this reason, the base station transmission / reception circuit 11-2 can prevent transmission of leaked radio waves accompanying transmission of the data D1 from the base station transmission / reception circuit 11-1 when receiving the data U2. As a result, communication interference can be prevented from occurring on the base station transceiver circuit 11-2 side.

  Even when the data lengths of the data D1 and data D2 to be transmitted from the base station transmission / reception circuits 11-1 and 11-2 are actually different, it is possible to prevent communication interference in the same manner, thereby improving throughput and communication. It becomes possible to improve the quality, and further, it is possible to prevent the reception error of the data U2.

  Incidentally, the NAV period set on the communication terminal 31-2 side described above is performed for all other communication terminals 31-2 included in the same wireless communication network 21-2. As a result, transmission of data U2 from any other communication terminal 31-2 to the base station transceiver circuit 11-2 can be suppressed, and communication interference can be prevented more firmly.

Further, in the above-described example, the processing operation for the communication terminal 31-2 that has received packet data (data D2) other than the packet data (data D1) having the longest transmission time has been mainly described. However, it is also possible to carry out the same processing operations also communication terminal 31-1 receives the data D1, but since the end time t ₂ of the end time and NAV period of the data D1 are the same, the data U1 The transmission disclosure time does not change after all.

  Note that the present invention is not limited to the flowchart of FIG. 4 described above, and may be operated based on a flow as shown in FIG. 6, for example. In the flowchart of FIG. 6, the same steps as those in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted.

  In FIG. 6, after the notification of various information in step S16 is completed, the process proceeds to step S19 ′. In step S19 ′, the base station accommodating switch 13 transfers the data D1 temporarily stored in the buffer 131 to the base station transmission / reception circuit 11-1. In addition, the data D2 stored in the buffer 132 is transferred to the base station transceiver circuit 11-2.

  Thereafter, the process proceeds to step S20, where the base station transceiver circuits 11-1 and 11-2 convert the data D1 and data D2 transferred from the buffers 131 and 132, respectively, into packet data. By performing this step S20 prior to CS in step S17, the generation of packet data is completed first. In step S20 as well, of course, in the Duration, a set value or the like corresponding to the longest packet data length determined in step S15 is described.

  After step S20 is completed, the process proceeds to step S17 to perform CS. After this CS is completed, the process proceeds to step S18 ′, and a packet transmission command is transmitted directly from the base station control unit 4 to the base station transceiver circuits 11-1 and 11-2. The base station transmission / reception circuits 11-1 and 11-2 receive the packet transmission command and transmit the already generated packet data to the base station transmission / reception circuits 11-1 and 11-2. The processing operations after step S21 are the same as those in FIG. 4 and the case.

  In this way, after receiving information such as the setting value of Duration at the base station transmission / reception circuit 11 side in step S16, packet data is immediately generated, then CS is performed, and a packet transmission command from the base station control unit 14 is generated. Even if the packet data is transferred to the communication terminal 31 after directly receiving the message, communication interference can be similarly prevented.

  In the present invention, Null data that is empty data may be added to FIG. 7 as an alternative to describing information in the Duration of the MAC header described above.

  The processing operation flow in this case is the same as the flowcharts of FIGS. However, in step S16, the base station control unit 14 notifies the longest packet data length itself determined in step S15, instead of transmitting information to be described in the Duration area.

Further, in the packet generation step in step S20, the base station transmission / reception circuits 11-1 and 11-2 generate Null data consisting of the difference between the longest packet data length and the packet data length to be transmitted by itself. It is added to the packet data D to be transmitted. For example, the base station transmission / reception circuit 11-2 adds Null data corresponding to the difference in length between the data D2 to be transmitted by itself and the data D1 which is the longest packet data to the rear end of the data D2. As a result, the total frame length of the data D2 and Null data to be transmitted by the base station transceiver circuit 11-2 is substantially the same as the frame length of the data D1, which is the longest packet data. On the other hand, the base station transmission / reception circuit 11-1 does not perform the above-described process particularly because the packet data D1 to be transmitted by itself is the longest. The length of the Null data may be such that this transmission end time t ₂ includes SIFS and ACK transmission time.

The communication terminals 31-1 and 32-2 receive data D1 and data D2, respectively. The communication terminal 31-2 receives data D2 having a shorter data length than the data D1, but since there is subsequent Null data, data reception is continuously performed during that time. Then, until a time t ₂ the Null data is completed, the communication terminal 31-2 can not perform the transmission of data U2 uplink to the base station for transmitting and receiving circuit 11-2.

In this way, the transmission of the uplink data U2 from the communication terminal 31-2 toward the base station transmission / reception circuit 11-2 is set to be prohibited until the transmission of the data D1 is completed. The Then, the communication terminal 31-2, when returning a data U2 to the base station for transmitting and receiving circuit 11-2, replies the start time t ₃ of the data U2 will after time t _2. Therefore, the base station transmission / reception circuit 11-2 receives the data U2 at a timing different from the transmission timing of the data D1 from the base station transmission / reception circuit 11-1. For this reason, the base station transmission / reception circuit 11-2 can prevent transmission of leaked radio waves accompanying transmission of the data D1 from the base station transmission / reception circuit 11-1 when receiving the data U2. As a result, communication interference can be prevented from occurring on the base station transceiver circuit 11-2 side. For this reason, it is possible to improve the throughput of the entire system, and hence to improve the communication quality, and to prevent the reception error of the data U2.

  In the present invention, information may be described in a CTS (clear to send frame) frame positioned before the CTS packet data D as an alternative to describing information in the Duration of the MAC header.

  FIG. 8 shows a processing operation flow when such a CTS frame is utilized. The same processing operations as those in the flowchart of FIG. 4 described above are denoted by the same reference numerals, and the following description is omitted.

  After the storage of the data D1 in the buffer 131 in step S11 and the notification of the packet data length of the data D1 in step S12 are completed, the process proceeds to step S31.

  In step S31, the presence or absence of data D2 to be transmitted from the base station transceiver circuit 11-2 to the communication terminal 31-2 is determined on the buffer 132 side. As a result, if the presence of the data D2 cannot be confirmed over a certain period, the process proceeds to step S32. In step S <b> 32, a timeout notification is sent from the buffer 132 to the base station control unit 14.

  In step S31, the frame length of the data D2 is shorter than the predetermined time except when there is no data D2 to be transmitted from the base station transceiver circuit 11-2 to the communication terminal 31-2 on the buffer 132 side. In this case as well, it may be determined that there is no data D2, and the process may proceed to step S32. After step S32 is completed, the process proceeds to step S15.

  In step S15, the base station control unit 14 identifies the packet length of the data D1 sent from step S12 described above, and determines the longest packet data length among these. In this case, since the packet length is notified only for the data D1, the packet data length of the data D1 is determined.

  Next, it transfers to step S16 and the base station control part 14 notifies various information with respect to the transmission / reception circuits 11-1 and 11-2 for base stations. In step S16, the base station control unit 14 may temporarily store data D1 as downlink packet data in the buffer 131, and may notify that communication is temporarily suspended. . In step S16, the base station controller 14 notifies the length of the longest packet data (data D1) determined in step S15. After step S16 is completed, steps S17 to S19 are executed.

  After completing the data transfer in step S19, the process proceeds to step S33. In step S33, the base station transceiver circuits 11-1 and 11-2 each generate a CTS frame. Various information notified in step S16 is described in this CTS frame. Specifically, information regarding the data D1, which is the longest packet data, may be described in the CTS frame, for example, the data length of the data D1 may be described.

  Next, the process proceeds to step S34, where the CTS frame is transmitted from the base station transceiver circuit 11-1 to the communication terminal 31-1. Similarly, the base station transceiver circuit 11-2 transmits a CTS frame to the communication terminal 31-2. FIG. 9 shows a time chart when this processing operation is performed. It can be seen from the base station transceiver circuits 11-1 and 11-2 that the CTS frame is located after the CS is performed. Incidentally, the transmission start times of the CTS frames transmitted from the base station transceiver circuits 11-1 and 11-2 do not have to be the same.

The communication terminals 31-1 and 31-2 read information related to the data D1, which is the longest packet data, described in the CTS frame. Thus, each communication terminal 31-1, 31-2 it is possible to determine a transmission end time t ₂ of the data D1. Note that this CTS frame, that transmission start time of the data D1 also have been written together, each communication terminal 31-1, 31-2 more easily determine a transmission end time t ₂ of the data D1 It becomes possible to do.

Next, the process proceeds to step S35, and the communication terminal 31-2 performs NAV setting. In this NAV setting, transmission of uplink data U2 is prohibited from the communication terminal 31-2 toward the base station transceiver circuit 11-2. As shown in FIG. 9, the set length of this NAV is the time until the transmission end time t ₂ of the longest data D1. This transmission end time t ₂ may include SIFS and ACK transmission time. These pieces of time information are known information on the side of the communication terminal 31-2 that has read various information described in the CTS frame, and can be easily set.

  Next, proceeding to step S20, the base station transceiver circuit 11-1 converts the data D1 transferred from the buffer 131 into packet data. After completing Step S20, the process proceeds to Step S21, and data D1 is transmitted from the base station transceiver circuit 11-1 to the communication terminal 31-1.

In this way, the transmission of the uplink data U2 from the communication terminal 31-2 toward the base station transmission / reception circuit 11-2 is set to be prohibited until the transmission of the data D1 is completed. The Then, the communication terminal 31-2, when returning a data U2 to the base station for transmitting and receiving circuit 11-2, replies the start time t ₃ of the data U2 will after time t _2. Therefore, the base station transmission / reception circuit 11-2 receives the data U2 at a timing different from the transmission timing of the data D1 from the base station transmission / reception circuit 11-1. For this reason, the base station transmission / reception circuit 11-2 can prevent transmission of leaked radio waves accompanying transmission of the data D1 from the base station transmission / reception circuit 11-1 when receiving the data U2. As a result, communication interference can be prevented from occurring on the base station transceiver circuit 11-2 side.

  Note that the present invention is not limited to the flowchart of FIG. 8 described above, and may be operated based on a flow as shown in FIG. In the flowchart of FIG. 10, the same steps as those in FIG. 8 are denoted by the same reference numerals, and the description thereof will be omitted.

  In FIG. 10, after the notification of various information in step S16 is completed, the process proceeds to step S19 ′. In step S19 ′, the base station accommodating switch 13 transfers the data D1 temporarily stored in the buffer 131 to the base station transmission / reception circuit 11-1. After that, the process proceeds to step S33 to generate a CTS frame, and then to step S20, the base station transceiver circuit 11-1 converts the data D1 transferred from the buffer 131 into packet data. By performing this step S20 prior to CS in step S17, the generation of packet data is completed first. In step S33 as well, the setting value corresponding to the longest packet data length determined in step S15 is described in the CTS frame.

  After step S20 is completed, the process proceeds to step S17 to perform CS. After this CS is completed, the process proceeds to step S18 ′, and a packet transmission command is directly transmitted from the base station control unit 4 to the base station transceiver circuit 11-1. In response to the packet transmission command, the base station transmission / reception circuit 11-1 transmits the already generated packet data to the base station transmission / reception circuit 11-1. The processing operations after step S18 ′ are the same as those in FIG. 8 and the case.

  Even in the processing operation flow shown in FIG. 10, communication interference can be similarly prevented.

  In the above-described embodiment, the case where all the components including the base station transmission / reception circuit 11 are installed in the base station apparatus 2 has been described as an example. However, the present invention is not limited to this. is not

  FIG. 11 shows an example in which the concept of the base station device 2 is eliminated, and each component is arranged in the network 3 and others. In the network 3, a synchronization signal acquisition unit 15, a base station control unit 14, and a base station accommodation switch 13 are arranged, and the base station transmission / reception circuits 11-1 to 11-n are connected to the base station accommodation switch 13. Wireless or wired communication is possible. The base station transmission / reception circuits 11-1 to 11-n are also connected to the base station control unit 14 and can communicate with each other. Although the base station transmission / reception circuits 11-1 to 11-n are not mounted in the same casing, at least the distance between adjacent base station transmission / reception circuits 11-1 to 11-n can cause communication interference. It shall be arranged in. The radio communication system 1 to which the present invention is applied may adopt the configuration shown in FIG.

  In the above-described embodiment, the case where the frequency channels adjacent to each other between the adjacent base station transmission / reception circuits 11 are used has been described as an example. However, the present invention is not limited to this. For example, it goes without saying that the same effect can be obtained between frequency channels adjacent to each other, and also between frequency channels adjacent to each other.

  In the above-described embodiment, the description has been made focusing on the two base station transmission / reception circuits 11-1 and 11-2 that are adjacent to each other. However, the present invention is not limited to this, and there are three or more base stations. Even when there is a possibility that communication interference occurs between the transmission / reception circuits 11, the communication interference can be similarly suppressed based on the processing operation.

In the embodiment described above, packet data can be transmitted after CS is performed. However, if, for example, eight base station transceiver circuits 11-1, 11-2,... 11-8 are using adjacent ch1, ch2, ch3,..., Ch6, ch7, ch8, all channels Cause the problem that the probability of vacant becomes very small at the same time and the throughput does not come out (I'm sorry, but I don't understand why), so please tell me.
If the probability that ch1 is vacant is 50% (= 1/2), the probability that all 8 channels are vacant is (1/2) ⁸ = 1/256, which is less than 1%. End up. When the channels are adjacent to each other, the probability that all the channels are free is the probability that transmission is possible, and this will dominate the throughput performance, but if it becomes 1% or less, the throughput performance will be considerably reduced. It will end up.
In such a case, the packet transmission command in step S18 after the CS is not when all the channels are vacant, but more than 1/2 of the number of channels (8 in the above example) requiring synchronous transmission, 1/4 As described above, it may be performed when a predetermined ratio or more such as 1/8 or more becomes empty. As a result, as described above, data can be transmitted to the destination with a probability of at least 1/2 or 1/4 or more compared to the throughput performance of 1% or less, and the throughput is improved accordingly. I can expect.

Further, as an example of determining whether each base station transmission / reception circuit 11-1 to 11-n is busy or idle through CS, when each base station transmission / reception circuit 11-1 to 11-n is busy, base station control is performed. You may make it notify to the part 14 that it is busy regularly. Further, when each of the base station transmission / reception circuits 11-1 to 11-n is idle, the base station control unit 14 may be periodically notified that it is idle.
That is, as a means for the base station control unit 14 to grasp whether the detection result is idle or busy while each base station transceiver circuit 11-1 to 11-n is executing CS, each base station The transmission / reception circuits 11-1 to 11-n periodically notify that they are idle during 1) idle, or 2) periodically notify that they are busy during busy. Further, 3) When the state transitions from idle to busy, a notification to that effect is made, and when the state changes from busy to idle, the fact is notified. Since it is desirable that the number of messages that need to be notified is small, 2) is preferable for a system with a relatively long busy state, and 1) is preferable for a system with a relatively long idle state. The most efficient method is 3), but it is susceptible to non-delivery of notification messages and reception errors. For this reason, which one of the methods 1) to 3) is selected may be set freely on the user side or the system administrator side.

DESCRIPTION OF SYMBOLS 1 Wireless communication system 2 Base station apparatus 3 Network 4 Base station control part 11 Base station transmission / reception circuit 12 Antenna 13 Base station accommodation switch 14 Base station control part 15 Synchronization signal acquisition part 21 Wireless communication network 31 Communication terminals 131 and 132 Buffer

Claims (6)

In a wireless communication system that performs wireless communication based on CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance),
A plurality of transmission / reception circuits for base stations arranged at a distance that can cause communication interference with each other;
A plurality of wireless communication networks formed for each of the one base station transmission / reception circuit, each having one or more communication terminals for performing wireless communication with the base station transmission / reception circuit;
Time synchronization means for synchronizing the time between the plurality of base station transceiver circuits,
When transmitting and receiving packet data to the communication terminals in the wireless communication network formed by the base station transmission / reception circuits that use the same or the next adjacent frequency channels, the base station transmission / reception circuits communicate with each other through the time synchronization means. A wireless communication system, wherein transmission is started at approximately the same time that is synchronized. A longest packet discriminating means for discriminating the longest packet data among the packet data transmitted at the same time from the plurality of base station transceiver circuits;
Each of the transmission / reception circuits for each base station describes information on the longest packet data determined by the longest packet determination means in the header of packet data to be transmitted,
The communication terminal that has received packet data other than the packet data having the longest transmission time reads information on the longest packet data from the header, and transmits / receives the base station from the transmission start time until the transmission time ends. The wireless communication system according to claim 1, wherein the wireless communication system waits for transmission of packet data to the circuit. A longest packet discriminating means for discriminating the longest packet data among the packet data transmitted at the same time from the plurality of base station transceiver circuits;
Each of the transmission / reception circuits for each base station converts Null data consisting of the difference between the longest packet data length determined by the longest packet determination means and the packet data length transmitted by itself into the packet data transmitted by itself. The wireless communication system according to claim 1, further comprising: In a wireless communication system that performs wireless communication based on CSMA (Carrier Sense Multiple Access) / CA (Collision Avoidance),
A plurality of transmission / reception circuits for base stations arranged at a distance that can cause communication interference with each other;
A plurality of wireless communication networks formed for each of the one base station transmission / reception circuit, each having one or more communication terminals for performing wireless communication with the base station transmission / reception circuit;
A longest packet discriminating means for discriminating the longest packet data among the packet data transmitted from the transceiver circuits for each base station using the same or successively adjacent frequency channels;
Each of the transmission / reception circuits for the base station describes information on the longest packet data determined by the longest packet determination means in a CTS (clear to send frame) frame located before the packet data to be transmitted. Send the frame to the communication terminal,
The communication terminal reads the transmission time of the longest packet data from the received CTS frame and waits for transmission of packet data to the base station transceiver circuit from the transmission start time of the CTS frame until the transmission time ends. A wireless communication system. Each of the base station transmission / reception circuits that use the same or adjacent frequency channels performs carrier sensing based on the CSMA / CA scheme before transmitting the packet data, and the base station transmission / reception circuit performs predetermined sensing. The wireless communication system according to any one of claims 1 to 4, wherein the packet data is transmitted when a ratio equal to or greater than the ratio becomes empty. A base station control unit for controlling the base station transceiver circuit;
The transmission / reception circuits for the base stations that use the same or successively adjacent frequency channels perform carrier sense based on the CSMA / CA scheme before transmitting the packet data, and periodically send the result to the base station Sent to the control unit,
5. The base station control unit according to claim 1, wherein the base station control unit receives a result of the carrier sense and issues an instruction to transmit packet data by each of the base station transmission / reception circuits. Wireless communication system.

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