JP2008211584A - Radio communication equipment, radio communication system, and radio communication program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a delay time of packet relay and to improve throughput by efficiently transmitting a packet in a radio communication system for relaying a radio packet among radio stations. <P>SOLUTION: This radio communication equipment for relaying a radio packet includes a packet transmitting and receiving part 1 for transmitting and receiving a radio packet to be relayed, a packet relaying part 2 for receiving the packet received by the packet transmitting and receiving part 1 and supplying the packet as a packet to be transmitted to the packet transmitting and receiving part 1, and a synchronization control part 3 for controlling the transmitting timing of the radio packet by the packet transmitting and receiving part 1 so as to synchronize the transmitting timing of the packet transmitting and receiving part about the packet to be transmitted with the transmitting timing of a radio packet to be relayed by another radio communication equipment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a wireless communication apparatus, a wireless communication system, and a wireless communication program that transmit and receive packets wirelessly.

  In wireless communication, because of the influence of noise, transmission power limitation, and the like, the communicable distance is limited. For this reason, in a number of wireless communication systems, a plurality of wireless stations are arranged in a wide range, and the wireless communication lines are relayed by connecting the wireless stations with a wireless communication line in a mesh shape. Some have adopted the extension method. Such a radio station configuration is called a mesh network.

In recent years, adoption of the mesh network configuration has been considered promising for wireless packet communication systems that transmit and receive packets wirelessly. For example, Non-Patent Document 1 introduces a wireless LAN mesh network system that constructs a mesh network using a wireless local area network (LAN), and discloses the standardization status and main configuration technology of the network. ing. The standardization of the wireless LAN mesh network system has been studied by IEEE802.11s, which is a task group of the IEEE (Institute of Electrical and Electronics Engineers) wireless LAN standardization committee. Patent Document 2 discloses an overview of individual items in the IEEE 802.11s standard, the progress of standardization work, and the like.
Shiro Sakata, 2 others, "Ad hoc network and wireless LAN mesh network", IEICE Transactions B, June 2006, Vol. J89-B, No. 6, p.811-823 W. Steven Conner, 3 others, “IEEE 802.11s Tutorial, Overview of the Amendment for Wireless Local Area Mesh Networking”, [online], IEEE (Institute of Electrical and Electronics Engineers), Internet <URL: http://www.ieee802.org/802_tutorials/nov06/802.11s_Tutorial_r5.pdf>

  By the way, in packet relay between radio stations, it is necessary to prevent transmission packets of radio stations from colliding on a radio communication line. This collision occurs at the radio station that receives the transmission packet of each radio station. Each radio station transmits a packet using the same carrier frequency and spreading code, and these packets overlap each other at a slightly shifted timing. It is caused by being received. Therefore, conventionally, transmission packets of radio stations are completely separated by frequency selection, transmission timing time scheduling, spatial isolation or spread code selection, or a combination thereof.

  In a wireless mesh network system (wireless packet communication system adopting a mesh network configuration), a plurality of adjacent wireless stations may relay the same wireless packet having the same carrier frequency and spreading code, and spatial Since transmission packets cannot be separated by selecting isolation or spreading codes, it is necessary to avoid collision of radio packets by scheduling transmission timing times. For this reason, in a wireless mesh network system, it is usual to schedule transmission timing in advance so that packet relay between radio stations is not performed simultaneously with packet relay between other radio stations. It is.

  FIG. 5 is a diagram showing an example of packet relay between wireless stations by such transmission timing scheduling, and shows the state of packet transfer when transmission timing is ideally scheduled for packet relay between wireless stations. Represents. The left side in FIG. 5 shows an outline of the configuration of the wireless mesh network system, and each circle represents a wireless station that relays a wireless packet. The right side in FIG. 5 is a timing chart showing the timing at which the radio stations a to e in the configuration on the left side transmit and receive radio packets.

  As shown in this figure, a packet generated in the wireless station a indicated by the central black circle is transferred to the surrounding wireless stations by the first relay indicated by the solid arrow and “(1) transmission”. Then, the neighboring wireless stations that have received the wireless packet from the wireless station a transfer the wireless packet at an ideally scheduled transmission timing so that the packet transmissions do not collide with each other, and further relay to the neighboring wireless stations. To do. As a result, packets generated at the wireless station a are sequentially relayed between the wireless stations. As a specific example, in the second relay, the wireless station b and the wireless station c can transmit wireless packets, but if both transmit packets, the wireless packet may collide at the wireless station d. Therefore, in the second relay, only the wireless station b transmits a packet (broken arrow and “(2) transmission”), and the wireless station c waits without transmitting a packet. The wireless station c transmits a wireless packet by the third relay (a dashed-dotted arrow and “(3) transmission”).

  As a result, the wireless station e is to receive the wireless packet delayed by the packet transmission time of the wireless station b, even though the packet has already reached the adjacent wireless station c. That is, while the wireless station b is transmitting a packet, the wireless station c has to wait for packet transmission, resulting in a delay in packet relay. In the usual scheduling performed for packet relay between radio stations, since other radio stations in the vicinity of the radio station that is transmitting packets in this way wait for packet transmission to avoid collision of radio packets, There is a problem that a delay occurs in the packet relay due to the waiting time, and the throughput also decreases.

  The present invention has been made in view of such circumstances, and enables a packet to be efficiently transmitted in a radio communication system that relays radio packets between radio stations, and reduces delay time and throughput of packet relay. It is an object of the present invention to provide a wireless communication device, a wireless communication system, and a wireless communication program that can improve the above.

  In order to achieve the above object, a wireless communication apparatus according to the present invention is a wireless communication apparatus that relays a wireless packet, and is a packet that transmits and receives a wireless packet transmission / reception means and a packet received by the transmission / reception means. The transmission / reception means is configured to synchronize the transmission timing of the wireless packet by the transmission / reception means of the packet to be transmitted to the transmission / reception means and the transmission timing of the wireless packet relayed by another wireless communication device. And a synchronization means for controlling the transmission timing of the wireless packet.

  Here, the synchronization means may use the transmission timing of the wireless packet by the transmission / reception means immediately after completion of reception of the wireless packet by the transmission / reception means or after a lapse of a certain time after completion of reception. In addition, the transmission / reception means transmits / receives a wireless packet through a time slotted wireless communication line, and the synchronization means transmits a time slot immediately after completion of reception of the wireless packet by the transmission / reception means or a time after elapse of a certain time after reception completion The slot may be a transmission timing of the wireless packet by the transmission / reception means. Furthermore, the transmission / reception means may transmit / receive a radio packet by orthogonal frequency division multiplexing.

  A radio communication system according to the present invention is a radio communication system that relays radio packets between radio stations, and a radio communication device that is a radio station that relays radio packets includes: A relay unit that receives a packet received by the transmission / reception unit and supplies the packet to the transmission / reception unit as a packet to be transmitted, a transmission timing of the wireless packet by the transmission / reception unit of the packet to be transmitted, and a wireless packet relayed by another wireless communication device Synchronization means for controlling the transmission timing of the wireless packet by the transmission / reception means so that the transmission timing is synchronized with the transmission timing.

  A wireless communication program according to the present invention is a wireless communication program that relays a wireless packet, receives a packet received by a transmission / reception function that transmits / receives a wireless packet to be relayed, and supplies the packet to the transmission / reception function as a packet to be transmitted; The synchronization for controlling the transmission timing of the wireless packet by the transmission / reception function so that the transmission timing of the wireless packet by the transmission / reception function of the packet to be transmitted is synchronized with the transmission timing of the wireless packet relayed by another wireless communication program A wireless communication program for causing a computer to realize functions.

  According to the present invention, the wireless communication device that relays the wireless packet synchronizes the transmission timing of the wireless packet by the transmission / reception unit of the transmitted packet with the transmission timing of the wireless packet that is relayed by the other wireless communication device. Even if the same wireless packet is transmitted from a plurality of wireless communication devices on the receiving side that is the relay destination of the wireless packet, they are all transmitted at the same transmission timing. Therefore, if the transmission path lengths between the wireless communication apparatuses are exactly the same, the reception timing is completely equal, and packet collision does not occur. As a result, the same wireless packet can be transmitted simultaneously by a plurality of wireless communication devices, and other wireless communication devices in the vicinity need to wait for the transmission of the same wireless packet while transmitting a wireless packet of a certain wireless communication device. Will disappear. As a result, it is possible to efficiently transmit a packet in relaying a wireless packet, and it is possible to realize a reduction in packet relay delay time and an improvement in throughput.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a wireless communication apparatus according to an embodiment of the present invention. The wireless communication apparatus constitutes a wireless station that relays wireless packets in a wireless packet communication system. In the block diagram of FIG. 1, the main part of the wireless communication apparatus, which is the main configuration of the wireless station, is illustrated. Is shown. As shown in FIG. 1, the wireless communication apparatus includes a packet transmission / reception unit 1, a packet relay unit 2, and a synchronization control unit 3 as shown in the figure. A wireless mesh network system is configured in which each wireless station is connected in a mesh form with a wireless communication line and relays wireless packets to extend the communication distance.

  The packet transmitting / receiving unit 1 is a means for transmitting and receiving a wireless packet by an OFDM (Orthogonal Frequency Division Multiplexing) system, and has a modulator, a demodulator, and the like for performing the transmission and reception. Antennas 1a such as omni antennas for transmitting and receiving radio signals to and from the other radio stations (other radio stations each constituted by the radio communication apparatus). When receiving the wireless packet, the packet transmitting / receiving unit 1 supplies the received packet obtained by demodulating the wireless packet to the packet relay unit 2 and outputs packet reception information notifying the reception of the wireless packet to the synchronization control unit 3.

  The packet relay unit 2 is means for temporarily storing radio packets received from other radio stations and further relaying them to other radio stations, and is configured by a predetermined storage device or the like that temporarily stores packet data. The The packet relay unit 2 temporarily stores the received packet supplied from the packet transmitting / receiving unit 1 and transfers the received packet data by supplying the stored received packet as a transmission packet to the packet transmitting / receiving unit 1. Relay wireless packets.

  The synchronization control unit 3 is a means for controlling the wireless packet transmission timing of the local station so that the transmission timing of the wireless packet between the other wireless station and the local station (the wireless station) is synchronized. Based on the packet reception information and the like, packet transmission timing information for instructing the transmission timing of the relayed wireless packet is supplied to the packet transmitting / receiving unit 1. Thereby, the packet transmission / reception unit 1 transmits a wireless packet obtained by modulating the transmission packet from the packet relay unit 2 at the transmission timing indicated by the packet transmission timing information.

  The synchronization control unit 3 determines the transmission timing of the wireless packet, and indicates the determined transmission timing with the packet transmission timing information, thereby synchronizing the packet transmission timing of each wireless station. As a form of the synchronization control by the determination and instruction of the transmission timing performed by the synchronization control unit 3, for example, the following can be cited.

First synchronization control mode The synchronization control unit 3 determines the transmission timing of the wireless packet immediately after the completion of reception of the wireless packet to be relayed or after a lapse of a certain time after the reception is completed, and uses the packet transmission timing information as the transmission timing. The transmitter / receiver 1 is instructed. As a result, the time until the wireless packet is transmitted for relay after the wireless packet is received by each wireless station is unified, and the transmission timing of the relay packet between the wireless stations is synchronized.

  Here, when the transmission timing is immediately after the completion of reception of the wireless packet, the time required to receive each wireless packet (the time from the reception start time of one wireless packet to the reception completion time) is known in advance. The transmission timing may be the time when the time has elapsed since the reception of the packet reception information. The transmission timing after the elapse of a certain time after completion of reception is a case where there is a difference in the timing of receiving the same radio packet between the own station and other peripheral radio stations. For example, there is a possibility that both the local station and other peripheral wireless stations receive the same wireless packet, but the route length (distance between wireless stations) from the wireless station that transmitted the wireless packet is This is a case where there is a difference in the reception completion time at each wireless station. In such a case, for example, the wireless station with the latest reception completion time is set as the transmission timing immediately after the reception completion, and for the other wireless stations, the latest reception completion time and the reception completion time at the other wireless station. The time corresponding to the difference between the two times may be set as the predetermined time, and the time after the completion of reception may be set as the transmission timing. Note that the difference between the reception completion times mentioned here can be known in advance based on the difference in the path length, etc. The transmission timing can be determined in advance immediately after completion of reception or after a lapse of a certain time after completion of reception.

  When the synchronization control unit 3 obtains the packet reception information, the wireless packet is determined to be the transmission timing of the wireless packet after a predetermined time has elapsed since the reception of the wireless packet in this way, and the transmission timing is instructed to the packet transmission / reception unit 1 . As a result, the time until each wireless station transmits the wireless packet after the wireless packet is received at each wireless station (after the reception at the wireless station with the slowest reception is completed) is unified. The transmission timing of radio packets relayed between stations can be synchronized. According to this first synchronization control mode, it is possible to synchronize the packet transmission timing of each wireless station (each wireless communication device) with relatively simple control.

Second Synchronization Control Mode In a wireless packet communication system, since a wireless communication line is often time-slotted at regular time intervals, the packet transmitting / receiving unit 1 uses the time-slotted wireless communication line. In many cases, wireless packets are transmitted and received. In this case, the synchronization control unit 3 can synchronize the transmission timing of the radio packet by determining the transmission timing so that the time slots for transmitting the radio packet are aligned in each radio station. That is, the time slot immediately after the completion of reception of the wireless packet to be relayed or the time slot after the elapse of a certain time after the completion of reception is determined as the transmission timing of the wireless packet, and the transmission timing is transmitted to the packet transmitting / receiving unit 1 using the packet transmission timing information. Instruct. As a result, after receiving the wireless packet at each wireless station, the time slot for transmitting the wireless packet for relaying is unified, and the transmission timing of the relay packet between the wireless stations is synchronized.

  Here, in order to synchronize the time slots, for example, the synchronization control unit 3 of each wireless station acquires high-accuracy time information by means such as GPS (Global Positioning System (Global Positioning System)). In determining the transmission timing, the synchronization control unit 3 of each wireless station may establish time slot synchronization of the wireless communication line by sharing a time slot based on common time information. In the case of using GPS, for example, a GPS receiver may be mounted on each radio station to acquire time information of a GPS clock, or time information may be supplied from a GPS receiver at another location.

  When the transmission timing is the time slot immediately after reception of a wireless packet is completed, the time required to receive each wireless packet is known in advance, so the time immediately after that time has elapsed since the packet reception information was received. A slot may be used as a transmission timing. The time slot after the elapse of a certain time after completion of reception is set as the transmission timing in the same manner as in the case where the elapse of the certain time after completion of reception is set as the transmission timing in the first synchronization control mode. This is a case where a difference occurs in the timing of receiving the same radio packet with the radio station. In such a case, for example, in the wireless station with the latest reception completion time of the wireless packet, the time slot immediately after the reception completion is set as the transmission timing, and for the other wireless stations, the latest reception completion time point and the other The time corresponding to the difference between the reception completion points of the wireless packet at the wireless station is set as the predetermined time, and the time slot after the elapse of the predetermined time after the reception is completed may be set as the transmission timing. Note that the difference between the reception completion points mentioned here can be grasped in advance based on the difference in the path length between the radio stations in the same manner as the difference between the reception completion points in the first synchronization control mode. The transmission timing at the station can be set in advance to a time slot immediately after the completion of reception or a time slot after the elapse of a fixed time after completion of reception.

  When the synchronization control unit 3 obtains the packet reception information, the time slot after the elapse of a predetermined time after receiving the wireless packet is determined as the transmission timing of the wireless packet, and the transmission timing is determined as the packet transmission / reception unit 1. To instruct. As a result, the time slots for transmitting the wireless packets received by the wireless stations for relaying are unified, and the transmission timing of the wireless packets relayed between the wireless stations can be synchronized. According to the second synchronization control mode, the time slot can be synchronized with highly accurate time information such as GPS, so that the packet transmission timing of each wireless station (each wireless communication device) is synchronized with relatively high accuracy. Can be made.

  The synchronization control unit 3 synchronizes the transmission timing of the radio packet to be relayed with the transmission timing of the radio packet at another radio station by the synchronization control such as the first synchronization control mode and the second synchronization control mode. The information is supplied to the packet transmitting / receiving unit 1, and the packet transmitting / receiving unit 1 transmits the radio packet at the same timing as other peripheral radio stations based on the packet transmission timing information obtained from the synchronization control unit 3. At this time, since the packet transmitting / receiving unit 1 transmits a wireless packet by the OFDM method, the relayed wireless packet is G. I. (Guard Interval, the same applies hereinafter) is transmitted by the inserted OFDM symbol.

  FIG. 2 is a diagram showing the relationship between a relayed wireless packet and an OFDM symbol, where (a) is a wireless packet to be relayed, (b) is the OFDM symbol transmission timing of a wireless station (1), (c) Represents the OFDM symbol transmission timing of the other radio station (2). The wireless station (1) and the wireless station (2) here are adjacent wireless stations that may relay the same wireless packet in the wireless mesh network system, but are assumed for convenience of explanation of the OFDM symbol. However, it is not a radio station by this radio communication apparatus (the transmission timing is not synchronized). (b) and (c) show the OFDM symbol transmission timing when the radio station (1) and the radio station (2) both relay the same radio packet of (a) with the horizontal direction as a common time axis. ing. Therefore, in (b) and (c), the transmission data is exactly the same, and all the data including the header of the radio packet in (a) is transmission data based on the OFDM symbol.

  As shown in FIG. 2, when the OFDM method is used, a wireless packet to be transmitted is transmitted after being divided into a plurality of OFDM symbols. I. Is added. These G.M. I. In the OFDM symbol to which is added, the transmission timings of the wireless station (1) and the wireless station (2) are as shown in FIG. I. Even if they deviate within the range, the interference does not interfere with each other, and the OFDM symbol from the wireless station (1) and the OFDM symbol from the wireless station (2) are G. I. Even if the signal is deviated within the above range, it can be demodulated and received normally. This is the same even if the data to be transmitted is one OFDM symbol.

  However, in order to exhibit such characteristics, the radio signals transmitted by the radio station (1) and the radio station (2) must be exactly the same (the signal itself is merely shifted in the range of GI). Must be exactly the same.) Here, since the transmission data of the wireless station (1) and the wireless station (2) are the same including the header, the carrier frequency of the wireless packet (OFDM symbol) is also the same, the frequency synchronization is the same, and the signal information is If there are other headers to be sent, the same contents can be used (this is possible), and normal reception can be performed with the above characteristics.

  The packet transmitting / receiving unit 1 in this wireless communication apparatus transmits a wireless packet using the OFDM symbol having the above characteristics. Then, in the wireless mesh network system configured by arranging a plurality of wireless stations by this wireless communication apparatus, this wireless packet is transmitted at the same transmission timing of each wireless station by the synchronization control of the synchronization control unit 3 described above. The wireless packet is relayed between the wireless stations.

  FIG. 3 is a diagram illustrating an example of relaying a wireless packet between the wireless stations, and is a wireless mesh network system (corresponding to a wireless communication system according to an embodiment of the present invention) configured by a wireless station by the wireless communication apparatus. Hereinafter, a state of a packet transfer example when a wireless packet is relayed by "this wireless mesh network system") is shown. The left side in FIG. 3 shows an outline of a configuration example of the wireless mesh network system, and each circle represents a wireless station by the wireless communication apparatus. A plurality of quadrangles arranged in a mesh form represent a mesh network constructed by connecting each wireless station with a wireless communication line in a mesh form. The right side in FIG. 3 is a timing chart showing the timings at which the wireless stations A to E in the configuration example respectively transmit and receive wireless packets.

  As shown in FIG. 3, the packet generated in the wireless station A indicated by the central black circle is transferred between the surrounding wireless stations concentrically by an antenna 1a such as an omni antenna, and is indicated by a solid line arrow and “(1) transmission”. It is relayed to neighboring wireless stations by the first relay. Then, all the peripheral wireless stations that have received the wireless packet from the wireless station A transmit the wireless packet at the same transmission timing by the synchronization control of the respective synchronization control units 3, and further wirelessly transmit to other peripheral wireless stations. Forward the packet.

  At this time, all the wireless packets transmitted by the wireless stations are the same wireless packet transmitted by the wireless station A in the first relay, and therefore the transmission data of each wireless station is the same including the header. (In a wireless mesh network, since the same packet is relayed to a plurality of wireless stations in this way, the contents of transmission data when those wireless stations further relay are all the same). Each wireless station uses a carrier wave of the same frequency as a carrier wave for transmitting the wireless packet, and if there are other headers for sending signal information to the wireless packet, all of them are the same. That is, each wireless station that has received a wireless packet from wireless station A transmits the wireless packet at the same transmission timing with the same wireless signal.

  As a result, the wireless packet received by each wireless station from the wireless station A is transferred to another wireless station (a wireless station further away from the wireless station A), and is indicated by a broken-line arrow and “(2) transmission”. The second relay is performed. In the second relay, for example, in the wireless station D, since the wireless station B and the wireless station C transmit the wireless packet at the same time, the wireless signal of the wireless packet is transmitted from both the wireless station B and the wireless station C. To come.

  Here, if the distance “C-D” between the wireless station C and the wireless station D is longer than the distance “BD” between the wireless station B and the wireless station D, the wireless station D As a result, the same two radio signals with slightly different timings are received, and an effect such as inter-symbol interference due to so-called multipath may occur. However, in this wireless communication apparatus, since transmission / reception of wireless packets is performed by the OFDM method, the wireless station B and the wireless station C respectively perform “(2) as shown in the second relay on the right side in FIG. ) Transmission ”causes a shift in the reception timing at the wireless station D. I. If it is within the range, it is possible to normally demodulate the radio signal arriving at the radio station D and receive the radio packet due to the characteristics of OFDM such as the above characteristics.

  On the other hand, the distance “BD” and the distance “CD” are both distances between adjacent wireless stations in the mesh network, and the packet transmission timings of the wireless station B and the wireless station C are exactly the same. . Therefore, as shown in FIG. I. The wireless station D can receive the wireless packet normally.

  As described above, the wireless communication device constituting each wireless station synchronizes the transmission timing of the wireless packet to be relayed by the function of the synchronization control unit 3 and further reduces the influence of the multipath by the OFDM method. Since it is transmitting and receiving, there is no need to wait for packet transmission to avoid collision of wireless packets, and the wireless packet is transferred immediately after the reception at each wireless station is completed in each relay, and the next relay is performed. It can be carried out. Thereby, the delay of the packet relay due to the waiting time of packet transmission is eliminated, the packet can be transmitted efficiently, and the delay time of the packet relay can be reduced and the throughput can be improved.

  FIG. 4 shows calculated values of the improvement effect of the channel throughput and the average delay time (average transmission delay time) according to the packet relay example of FIG. 3 as an example of the reduction of the delay time and the improvement of the throughput of the packet relay. It is a figure. The horizontal axis in FIG. 4 indicates the relay distance of radio packets normalized by the distance between nodes (distance between adjacent radio stations), and the vertical axis indicates the channel throughput in the packet relay example of FIG. 6 shows the channel throughput in the packet relay example of FIG. 3 normalized by FIG. 3, and the average delay time in the packet relay example of FIG. 3 normalized by the average delay time in the packet relay example of FIG. According to the calculated value of the improvement effect, the packet relay example of FIG. 3 improves the channel throughput by about 50% as shown by the solid line graph, and the average delay time as shown by the one-dot chain line graph. It turns out that it improves about 12%.

  In the packet relay example of FIG. 3, in the wireless station A, the wireless packet transmitted by the local station in the first relay is received from the wireless station B or the like in the second relay. Station A is not supposed to transfer. In this wireless mesh network system, processing for avoiding duplicate transfer of the same wireless packet as described above may be introduced as appropriate, and processing for preventing the state of an infinite loop where the transfer of the same wireless packet is repeated forever. Etc. are introduced as appropriate. The process for preventing the endless loop state from occurring can be considered as a process related to routing defined in a higher layer, and therefore, various processes may be used in combination as appropriate. For example, a sequence number (SN (Sequence Number)) is assigned to the header part of each wireless packet, and processing that does not retransmit even if a wireless packet transferred in the past is received again by referring to it is adopted. May be.

  As described above, the wireless communication apparatus and the wireless mesh network system simultaneously transmit relay packets as wireless packets using the OFDM scheme by utilizing the characteristics of OFDM that do not cause interference even if the same OFDM symbol is transmitted simultaneously. As a result, it is possible to reduce the delay time of the packet relay by enabling a plurality of wireless stations constituting the wireless mesh network to simultaneously receive a wireless packet composed of the same data relayed through the wireless mesh network, and throughput. Can be improved.

  In other words, the wireless communication device and the wireless mesh network system employ the OFDM method, establish synchronization of packet transmission timing between the wireless communication devices, and simultaneously transmit the same OFDM symbol from a plurality of wireless communication devices. By doing so, wireless packets can be transmitted efficiently, and wireless packets can be relayed efficiently. As a result, the transmission delay of the wireless packet can be shortened, the average delay time can be reduced, and the throughput can be improved. Furthermore, the advantage of the present wireless communication apparatus and the present wireless mesh network system is that the complicated scheduling control between the wireless stations, which is necessary for avoiding the collision of the wireless packets as in the usual scheduling described above, is unnecessary. Can be mentioned.

  However, the configuration employing the OFDM scheme is a means for reducing the influence of multipath, and is not essential in the case where it can be said that there is no such influence. In other words, the effect of adopting the OFDM method is that in the so-called multipath state in which there is a shift in the reception timing of radio packets from each radio station as in the case of radio packet reception at radio station D described above, and the influence of multipath occurs. Even in such a case, the wireless packet can be normally received. On the other hand, for example, when the reception timing of a wireless packet received by a certain wireless station from each of a plurality of other wireless stations is exactly the same, these wireless packets are exactly the same wireless signal (contents of transmission data and As long as the signals are transmitted by radio signals having the same carrier frequency or the like, a multipath state does not occur, so that radio packets can be received without depending on the OFDM scheme.

  Here, it is possible in the wireless mesh network system that each wireless station transmits the same wireless packet with exactly the same wireless signal as described in the packet relay example of FIG. And, in the wireless mesh network system, each wireless station is connected in a mesh form with a wireless communication line. Therefore, if there is a premise that the packet transmission timing in each wireless station is synchronized as described above, each wireless station Thus, it is possible to arrange each wireless station in advance so that the reception timings of the wireless packets from the surrounding wireless stations are the same. That is, if the configuration is such that the packet transmission timing of each radio station is synchronized, the mesh network is configured in advance so that the reception timing of radio packets from other peripheral radio stations at the radio station is exactly the same. Even if the OFDM system is not adopted, a wireless communication apparatus or a wireless mesh network that can reduce the delay time of packet relay and improve the throughput as described above can be configured.

  The wireless communication apparatus and the wireless mesh network can adopt a form that does not employ the OFDM scheme due to the configuration in which the packet transmission timings of the wireless stations are synchronized as described above. In the packet relay based on the usual scheduling as shown in FIG. 5 above, each radio station transmits the same radio packet with the same radio signal, and when a multipath state occurs, the radio packet collides and the radio on the receiving side The station cannot receive normally. Therefore, the wireless station a in FIG. 5 is shown as if it receives a wireless packet in the second relay, but in reality, the distance between the wireless stations does not exactly match, Since the packet transmission timings of the wireless stations do not match, the wireless packet from the wireless station b and the wireless packet from the wireless station at the symmetrical position of the wireless station b collide, and normal reception cannot be performed (wireless packet). May be received by coincidence by chance, but it may be received very rarely and hardly received.) On the other hand, in the wireless communication apparatus and the wireless mesh network, the packet transmission timing of each wireless station is actively synchronized. For example, the wireless station A in FIG. Similarly, a wireless packet can be received by the second relay. In the wireless communication device and the wireless mesh network, the wireless packet can be normally received even if the wireless packet once transferred in this way is simultaneously transferred again from a plurality of wireless stations. By referring to the contents of the transmission data, etc., it is determined whether or not it is the same as the wireless packet that the local station has transferred in the past, so that the same wireless packet is not duplicated and the above-mentioned infinite loop state is avoided. Can also be realized.

  The wireless communication device and the wireless communication system (wireless mesh network system) according to the embodiment of the present invention have been described above. The wireless communication device or the wireless communication system described above is a wireless communication that relays wireless packets between a plurality of wireless stations. It can be applied to general systems. For example, the above-described wireless communication apparatus can also be applied to MP (Mesh Point), MAP (Mesh Access Point), MPP (Mesh Portal), etc. in a wireless LAN mesh network. It can also be implemented as a mesh network or the like.

  Further, the functions of the wireless communication apparatus or the wireless communication system as described above may be realized by a computer by a program that defines the content of the processing or operation. For example, for the packet transmission / reception unit 1, the packet relay unit 2, and the synchronization control unit 3 to the wireless mesh network of FIG. You may make a computer implement | achieve a wireless mesh network.

It is the block diagram which showed the structure of the radio | wireless communication apparatus by one Embodiment of this invention. It is a figure showing the relationship between the radio | wireless packet and OFDM symbol which are relayed. It is the figure which showed the example of relay of the radio | wireless packet between the radio stations by the radio | wireless communication apparatus. FIG. 4 is a diagram illustrating calculated values of an improvement effect of channel throughput and average delay time according to the packet relay example of FIG. 3. It is the figure which showed the example of a packet relay between the radio stations by the scheduling of usual transmission timing.

Explanation of symbols

1 packet transmitter / receiver,
2 packet relay part,
3 synchronization control unit,
A to E radio stations.

Claims (6)

A wireless communication device that relays wireless packets,
Means for transmitting and receiving wireless packets to be relayed;
A relay unit that receives the packet received by the transmission / reception unit and supplies the packet to the transmission / reception unit as a packet to be transmitted;
Synchronization means for controlling the transmission timing of the wireless packet by the transmission / reception means so that the transmission timing of the wireless packet by the transmission / reception means of the packet to be transmitted and the transmission timing of the wireless packet relayed by another wireless communication apparatus are synchronized When,
A wireless communication apparatus comprising: The wireless communication device according to claim 1,
The synchronization means sets the transmission timing of the wireless packet by the transmission / reception means immediately after completion of reception of the wireless packet by the transmission / reception means or after a lapse of a certain time after completion of reception.
A wireless communication apparatus. The wireless communication device according to claim 1,
The transmission / reception means transmits / receives a wireless packet in a time-slotted wireless communication line,
The synchronization means uses a time slot immediately after completion of reception of the wireless packet by the transmission / reception means or a time slot after elapse of a certain time after completion of reception as the transmission timing of the wireless packet by the transmission / reception means,
A wireless communication apparatus. In the radio | wireless communication apparatus in any one of Claim 1 to 3,
The transmission / reception means transmits and receives radio packets by orthogonal frequency division multiplexing.
A wireless communication apparatus. A wireless communication system that relays wireless packets between wireless stations,
Wireless communication devices that are wireless stations that relay wireless packets
Means for transmitting and receiving wireless packets to be relayed;
A relay unit that receives the packet received by the transmission / reception unit and supplies the packet to the transmission / reception unit as a packet to be transmitted;
Synchronization means for controlling the transmission timing of the wireless packet by the transmission / reception means so that the transmission timing of the wireless packet by the transmission / reception means of the packet to be transmitted and the transmission timing of the wireless packet relayed by another wireless communication device are synchronized Including and
A wireless communication system. A wireless communication program for relaying wireless packets,
A relay function that receives a packet received by a transmission / reception function that transmits / receives a wireless packet to be relayed and supplies the packet to the transmission / reception function as a packet to be transmitted;
A synchronization function for controlling the transmission timing of the wireless packet by the transmission / reception function so that the transmission timing of the wireless packet by the transmission / reception function of the packet to be transmitted is synchronized with the transmission timing of the wireless packet relayed by another wireless communication program When,
A wireless communication program for realizing the above on a computer.

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