WO2011089983A1 - 通信システム及び通信方法 - Google Patents
通信システム及び通信方法 Download PDFInfo
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- WO2011089983A1 WO2011089983A1 PCT/JP2011/050565 JP2011050565W WO2011089983A1 WO 2011089983 A1 WO2011089983 A1 WO 2011089983A1 JP 2011050565 W JP2011050565 W JP 2011050565W WO 2011089983 A1 WO2011089983 A1 WO 2011089983A1
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- 238000004891 communication Methods 0.000 title claims abstract description 230
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- 238000010586 diagram Methods 0.000 description 15
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/02—Details
- H04L12/16—Arrangements for providing special services to substations
- H04L12/18—Arrangements for providing special services to substations for broadcast or conference, e.g. multicast
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0808—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA]
- H04W74/0816—Non-scheduled access, e.g. ALOHA using carrier sensing, e.g. carrier sense multiple access [CSMA] with collision avoidance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W74/00—Wireless channel access
- H04W74/08—Non-scheduled access, e.g. ALOHA
- H04W74/0833—Random access procedures, e.g. with 4-step access
- H04W74/0841—Random access procedures, e.g. with 4-step access with collision treatment
- H04W74/085—Random access procedures, e.g. with 4-step access with collision treatment collision avoidance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W84/00—Network topologies
- H04W84/18—Self-organising networks, e.g. ad-hoc networks or sensor networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
- H04W88/02—Terminal devices
- H04W88/04—Terminal devices adapted for relaying to or from another terminal or user
Definitions
- FIG. 7 is a diagram illustrating the operation of each communication device in a conventional communication system.
- the communication device 2 uses the communication device for the surrounding communication devices 1, 3, and 5.
- a route search message for 4 is transmitted.
- the communication device 4 that has received the route search message addressed to itself transmits a route search response message to the transmission source communication device 2.
- the communication devices 1, 3, and 5 that have received the route search message other than those addressed to themselves transfer the received route search message to the surrounding communication devices (communication devices 2 to 4 in the case of the communication device 5).
- the transmission medium A collision of frames (transmission data, message data) is likely to occur on the (wireless communication line), and the route search response message transmitted from the communication device 4 may not be correctly received by the communication device 2 at the destination.
- FIG. 8 is a diagram showing frame transmission timing in a conventional communication apparatus.
- IEEE 802.11e which is a wireless LAN standard
- the transmission timing of various frames varies depending on the type of frame. Further, by providing a random transmission waiting time for each communication device, occurrence of frame collision on the transmission medium is suppressed.
- Frame transmission interval in medium access method in which communication terminals access communication media using CSMA / CA method (Carrier Sense Multiple Access / Collision Avoidance)
- CSMA / CA method Carrier Sense Multiple Access / Collision Avoidance
- IFS frame interval
- wireless communication timing wireless communication timing
- a short frame interval (SIFS) used when transmitting an Ack signal for a certain frame as IFS, and a central control frame used when transmitting a polling frame transmitted from any access point to each terminal Interval (PIFS), frame interval for distributed control (DIFS) used at the time of data frame transmission, and frame transmission interval (AIFS) that can set different frame intervals according to access category (AC) that is the priority of the frame are defined ing.
- SIFS short frame interval
- PIFS terminal Interval
- DIFS distributed control
- AIFS frame transmission interval
- AC access category
- the communication terminals 1 and 3 to 5 that have received the route search message transmitted from the communication device 2 at the same time receive the route search message (forwarding) and the route search response message (next frame) at almost the same time. ) Trying to send.
- the frame (A) of the communication device (A) is transmitted even when the slot time of another communication device (B) is reached. Is not completed yet, the communication device (B) refrains from transmitting the frame (B) to be transmitted. After the transmission of the frame (A) is completed, the communication device (B) receives an allocation of an arbitrary slot time in the next contention window that is newly set after the frame (A).
- the conventional contention window is provided with SIFS, PIFS, and DIFS for the busy media that is the previous transmission frame, and the corresponding contention window is provided with a long transmission standby time. Slot time is provided.
- the iFS with the i-th priority is provided for the previous busy media
- the corresponding contention window is shorter than that for SIFS, PIFS, and DIFS, and less slot time is provided.
- the slot time of the contention window corresponding to SIFS, PIFS, and DIFS and the slot time of the contention window corresponding to AIFS are provided at a partially overlapping timing, and the next frame is actually transmitted.
- a high priority frame may be transmitted after a relatively low priority frame transmitted after AIFS.
- the corresponding contention window is shorter than that of the i-th priority AIFS, and an even smaller slot time is provided.
- the slot time of the contention window corresponding to the i-th AIFS with the priority and the slot time of the contention window corresponding to the j-th AIFS with the priority are set at a partially overlapping timing, When actually transmitting the next frame, a frame having a relatively high priority may be transmitted after a frame having a low priority transmitted after the j-th AIFS.
- contention windows with different lengths are set based on the priority of the frames, but because the contention windows provided in the frames with different priorities are provided at a timing that partially overlaps, There is a problem that high priority frames are not always transmitted preferentially.
- the present invention has been made in view of the above, and is provided at a timing in which contention windows provided in frames having different priorities do not overlap each other, so that a high priority frame is always transmitted with priority. It is an object of the present invention to obtain a communication system and a communication method.
- a communication system includes a first communication terminal, a second communication terminal, and a third communication terminal, and the first communication
- the terminal transmits message data destined for the third communication terminal to a plurality of communication terminals
- the second communication terminal receives the message data, confirms the destination of the received message data, and confirms If the destination address is confirmed to be not its own communication terminal, the received message data is transferred to the other communication terminal, and the third communication terminal receives the message data and confirms the destination of the received message data. If it is confirmed that the confirmed destination is its own communication terminal, response data corresponding to the received message data is sent to the first communication terminal that is the transmission source of the received message data.
- the response data is set to have a higher priority for transmission than the message data to be transferred, and the time from when the message data is received until the corresponding response data is transmitted is the message data. Is shorter than the time from when the message is received until the message data is transferred.
- FIG. 1 is a diagram showing frame transmission timing in the communication apparatus of the present invention.
- FIG. 2 is a diagram showing the operation of each communication device in the communication system to which the present invention is applied.
- FIG. 3 is a schematic diagram showing data transmitted by each communication device in the communication system to which the present invention is applied.
- FIG. 4 is a diagram illustrating frame transmission timing in the communication apparatus according to the second embodiment of the present invention.
- FIG. 5 is a diagram illustrating frame transmission timing in the communication apparatus according to the third embodiment of the present invention.
- FIG. 6 is a diagram illustrating frame transmission timing in the communication apparatus according to the fourth embodiment of the present invention.
- FIG. 7 is a diagram illustrating the operation of each communication device in a conventional communication system.
- FIG. 8 is a diagram showing frame transmission timing in a conventional communication apparatus.
- FIG. FIG. 1 is a diagram showing frame transmission timing in the communication apparatus (communication terminal) of the present invention.
- the transmission interval until the next frame (for example, Ack frame) for the busy media (previous frame) is T0, and the next frame such as a route search response message for the busy media is transmitted ( (Transmission time) interval T1, CW1 ⁇ Ts contention window, which is the transmission standby time for the next frame such as a route search response message, etc.
- the contention window that is the transmission waiting time for the next frame such as a route search message is CW2 ⁇ Ts, and the slot times constituting the contention window are each Ts, T0 ⁇ T1 and T1 It is assumed that the condition + Ts ⁇ CW1 ⁇ T2 is satisfied. That is, the priority (priority) is set in the order of the next frame such as the Ack frame, the next frame such as the route search response message, and the next frame such as the route search message.
- the next frame such as the route search response message is preferentially transmitted over the next frame, and the next frame such as the Ack frame is preferentially transmitted over the next frame such as the route search response message.
- FIG. 2 is a diagram showing the operation of each communication device in the communication system to which the present invention is applied.
- the communication devices 1 to 5 access a communication medium (wireless communication) by the CSMA / CA method, and are waiting (usually) to receive a transmission signal transmitted from a certain communication device.
- a communication medium wireless communication
- transmission of the transmission signal scheduled to be transmitted from itself is refrained, and when it is confirmed that transmission of the transmission signal from a certain communication device is completed, the transmission signal of its own is transmitted.
- the communication device 2 transmits a route search message (frame) in order to search for a communication route with the communication device 4.
- the communication devices 1, 3 to 5 receive the route search message.
- the communication devices 1, 3, and 5 confirm the destination of the received route search message, and if it is determined that the route search message is not addressed to itself, the communication device 1, 3, 5 transfers the received route search message to surrounding communication devices.
- the communication device 4 confirms the destination of the received route search message and finds that it is a route search message addressed to itself, the communication device 4 sends a route search response message (measurement data or the like) corresponding to the received route search message to the communication terminal. Reply to 2.
- the system of the present invention includes a communication device 1 (10), a communication device 2 (20), a communication device 3 (30), a communication device 4 (40), and a communication device 5 (50).
- the communication device 2 (20) is a transmission source of the route search message, and transmits the route terminal message to the communication terminal 4 (40).
- the communication terminal 1 (10), the communication terminal 3 (30), and the communication terminal 5 (50) receive the route search message transmitted from the communication device 2 (20), the communication terminal 1 (10), the communication terminal 3 (30), and the communication terminal 5 (50) may not be route search messages sent to themselves. Yes, route search message (transfer) is forwarded to surrounding communication devices.
- the communication terminal 4 (40) receives the route search message transmitted from the communication device 2 (20), it is understood that the communication terminal 4 (40) is the route search message sent to itself (destination), and the communication terminal 2 (20: A route search response message is returned to the transmission source.
- the communication device of the present invention finds that it is not a route search message addressed to itself, it will forward the received route search message to surrounding communication devices.
- Each may be provided with an identification number, and when a frame with the same identification number is received again, further forwarding may be avoided. Further, a receivable time (period) may be set for frames having the same identification number. As a result, it is possible to avoid a sudden increase in the number of frames to be transmitted and a wasteful communication line.
- the timing of transfer of the route search message by the communication devices 1, 3, and 5 with respect to the route search message (busy media) transmitted from the communication device 2 is T2 + CW2 ⁇ Ts time after the time T2 has elapsed after receiving the busy media. Timing based on each slot time in the contention window is assigned to each communication device. On the other hand, the transmission timing of the route search response message by the communication device 4 is assigned a timing based on each slot time in the contention window up to T1 + CW1 ⁇ Ts time after the lapse of T1 time after receiving busy media.
- T1 + CW1 ⁇ Ts time is earlier (shorter) than the T2 time that is the transfer timing of the route search message by the communication devices 1, 3, 5; It is always implemented (transmitted) before the transfer of the route search message by 3 and 5.
- the communication device 4 sends a route search response message in response to the received route search message for a predetermined period (T1 to T1 + CW1).
- T1 to T1 + CW1 a predetermined period
- the communication devices 1, 3, and 5 start the route search message at a timing (T2 to T2 + CW2 ⁇ Ts) later than the response timing of the route search response message (T1 to T1 + CW1 ⁇ Ts).
- the communication device 4 When the communication device 4 responds (starts transmission) a route search response message to the communication device 2, the communication devices 1, 3, and 5 detect that the route search response message is being transmitted, and the communication device 4 The transfer of the route search message is suspended until the transmission of the route search response message is completed.
- the present invention can be utilized in a data collection system such as an automatic meter reading system using an ad hoc network.
- a data collection system such as an automatic meter reading system using an ad hoc network.
- the following points are considered. 1.
- There is usually one communication terminal that transmits a route search response message and there is basically no route search response message transmitted from a plurality of communication terminals (almost at the same time). In addition, there is a low possibility that the present communication system and other communication systems compete.
- the route search message arrives at the destination (target) communication terminal, the route search message does not need to be further relayed to another communication terminal. Therefore, it is more necessary to prioritize transmission of the route search response message than to transfer the route search message.
- the high-priority route The search response message can be transmitted reliably (from the communication device 4 to the communication device 2).
- FIG. FIG. 4 is a diagram illustrating frame transmission timing in the communication apparatus according to the second embodiment.
- the transmission interval of the next frame for example, Ack frame
- the transmission interval of the next frame is T0
- the time until transmission of the next frame such as a route search response message for the busy medium is T1
- the contention window is CW1 ⁇ Ts, which is the transmission waiting time for the next frame such as the route search response message
- the (time) interval until the next frame such as the route search message for busy media is transmitted is T2.
- CW2 ⁇ Ts is the contention window that is the transmission waiting time for the next frame such as a route search message
- Ts is the multiple slot times that constitute the contention window.
- the route search message (frame) is relayed (transferred to surrounding communication devices) by a plurality of communication devices, contention (of various frames) is likely to occur during the relay. That is, since the route search message received by each communication terminal is to be transmitted to another communication terminal at substantially the same time, there is a possibility of contention (collision) of route search messages transmitted from each communication terminal. Increases very much. Therefore, it is desirable to increase the number of slots in the contention window (CW2). By setting the contention window slot number CW2 to be large (large), the possibility of collision of the route search message is suppressed, and it becomes easy to reliably transmit the route search message to the target communication device.
- the route search response message is transmitted from one communication device that is the destination of the route search message, the probability of contention is low. Therefore, a decrease in the throughput of the route search response message can be suppressed by setting the number of slots CW1 in the contention window of the route search response message to be small (less).
- the start of the contention window of the route search message is delayed from the end of the contention window of the route search response message, and the slot number CW2 of the contention window of the route search message is set to the contention window of the route search response message.
- the route search message can be transmitted more reliably without reducing the throughput of the route search response message.
- FIG. 5 is a diagram illustrating frame transmission timing in the communication apparatus according to the third embodiment. As shown in FIG. 5, the transmission interval from the busy media (previous frame) to the next frame (for example, an Ack frame) is T0, and a unicast frame is transmitted in one (direction) to the busy media.
- the transmission interval from the busy media (previous frame) to the next frame for example, an Ack frame
- the interval is T3
- the contention window that is the transmission waiting time for unicast frames is CW3 ⁇ Ts
- the transmission interval of broadcast frames that transmit frames in multiple (directions) to busy media is T4
- the transmission waiting time for broadcast frames When a certain contention window is CW4 ⁇ Ts and a plurality of slot times constituting the contention window are Ts, T0 ⁇ T3 and T3 + Ts ⁇ CW3 ⁇ T4.
- a route search message related to the communication device 4 is broadcast to the communication devices around the communication device 2. Then, the communication devices 1, 3, 5 that have received the route search message that is not addressed further forward (broadcast) the received route search message to surrounding communication devices, and have received the route search message addressed to itself. The communication device 4 transmits a route search response message to the communication device 2 by unicast.
- a route search response message with a high priority is communicated with a unicast frame
- a route search message with a low priority is communicated with a broadcast frame
- the beginning of the contention window for the broadcast frame (low priority) is By delaying from the end of the contention window for the (high priority) unicast frame, a route search response message with a high priority can be transmitted reliably.
- FIG. 6 is a diagram illustrating frame transmission timing in the communication apparatus according to the fourth embodiment. As shown in FIG. 6, the transmission interval until the next frame (for example, Ack frame) with respect to the busy medium (previous frame) is T0, and the transmission of the unicast frame is transmitted in one (direction) with respect to the busy medium.
- the next frame for example, Ack frame
- T0 the transmission interval until the next frame (for example, Ack frame) with respect to the busy medium (previous frame)
- the transmission of the unicast frame is transmitted in one (direction) with respect to the busy medium.
- the interval is T3, the contention window that is the transmission waiting time for unicast frames is CW3 ⁇ Ts, the transmission interval of broadcast frames that transmit frames in multiple (directions) to busy media is T4, and the transmission waiting time for broadcast frames
- T3 the contention window that is the transmission waiting time for unicast frames
- T4 the transmission interval of broadcast frames that transmit frames in multiple (directions) to busy media
- T4 the transmission waiting time for broadcast frames
- a broadcast frame is used when (frame) is transmitted to many communication apparatuses.
- This communication system is used for transmission of a route search message for network management. In the transmission of the route search message, a relatively long delay is allowed.
- Unicast frames make it easy to confirm the arrival of a message to the destination communication device using an Ack signal or the like. If it is detected that the message has not reached the destination communication device, the message is resent. By doing so, it is possible to improve the message arrival rate to the destination communication device.
- the unicast frame is used when (frame) is transmitted to a specific communication device.
- This communication system is used for transmission of a route search response message for network management and transmission / reception of automatic meter reading data.
- the route search response message and the automatic meter reading data in this communication system be transmitted with as little delay as possible. Further, when collecting automatic meter reading data (between the transmission source and other communication terminals), the possibility that a unicast frame is simultaneously transmitted from each communication terminal is not so high.
- the number of slots in the contention window of the unicast frame is set to be small (small)
- the frame transmission interval of the unicast frame can be shortened, and the throughput of the unicast frame can be improved.
- the communication device 2 searches for a communication route to the communication device 4, if a route search message related to the communication device 4 is broadcasted to communication devices around the communication device 2, The communication device 4 that has received the route search message transmits the route search response message to the communication device 2 by unicast, and the communication devices 1, 3, and 5 that have received the route search message that is not addressed to itself receive the route search message. Is broadcast and transferred to surrounding communication devices.
- the start end of the contention window of the unicast frame is delayed from the end of the contention window of the broadcast frame, and the slot number CW2 of the contention window of the broadcast frame is set to the number of slots of the contention window of the unicast frame.
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Abstract
Description
従来の経路探索方法では、アドホックネットワークにおいて、ある通信装置2から他の通信装置4に対して通信経路を探す場合、通信装置2は、周辺の通信装置1、3、5に対して当該通信装置4に対する経路探索メッセージを送信する。自身宛の経路探索メッセージを受信した通信装置4は、送信元の通信装置2に対して経路探索応答メッセージを送信する。また、自身宛以外の経路探索メッセージを受信した通信装置1、3、5は、受信した経路探索メッセージを周辺の通信装置(通信装置5の場合は通信装置2~4)に対して転送する。
無線LANの標準規格であるIEEE 802.11eでは、フレームの種別により、各種フレームの送信タイミングに差異を持たせている。また、通信装置毎にランダムな送信待ち時間を設けることにより、伝送媒体上でのフレームの衝突の発生を抑えている。
IEEE 802.11eでは、IFSとして、あるフレームに対するAck信号の送信時に用いられる短フレーム間隔(SIFS)、任意のアクセスポイントから各端末に対して送信されるポーリング用のフレーム送信時に用いられる集中制御用フレーム間隔(PIFS)、データフレームの送信時に用いられる分散制御用フレーム間隔(DIFS)、及び、フレームの優先度であるアクセスカテゴリ(AC)によって異なるフレーム間隔が設定できるフレーム送信間隔(AIFS)が定義されている。
このように、フレームの種別によって、フレームの送信間隔に差異が設けられ、フレームの優先度が高いものほど早いタイミングで送信されることにより、送信するフレームの種別によって優先制御が行われている。
先のビジーメディアに対して優先度がi番目のAIFSを設けると、対応するコンテンションウインドウは、SIFS、PIFS、DIFSの時よりも短く、より少ないスロットタイムを設ける。しかし、SIFS、PIFS、DIFSに対応するコンテンションウインドウのスロットタイムと、AIFSに対応するコンテンションウインドウのスロットタイムとは、一部重複するタイミングで設けられており、実際に次のフレームを送信する際には、優先度の高いフレームが、AIFSの後に送信する優先度の比較的低いフレームよりも後に送信されることが起こり得る。
図1は、この発明の通信装置(通信端末)におけるフレーム送信タイミングを示す図である。
図1に示すように、ビジーメディア(先のフレーム)に対する次のフレーム(例えば、Ackフレーム等)までの送信間隔をT0、ビジーメディアに対する経路探索応答メッセージ等の次のフレームを送信するまでの(送信時間)間隔をT1、経路探索応答メッセージ等の次のフレームに関する送信待機時間であるコンテンションウインドウをCW1×Ts、ビジーメディアに対する経路探索メッセージ等の次のフレームを送信するまでの(送信時間)間隔をT2、経路探索メッセージ等の次のフレームに関する送信待機時間であるコンテンションウインドウをCW2×Ts、コンテンションウインドウを構成する複数のスロットタイムをそれぞれTsとした場合、T0<T1、且つ、T1+Ts×CW1<T2、の条件が成り立つものとする。
つまり、Ackフレーム等の次のフレーム、経路探索応答メッセージ等の次のフレーム、経路探索メッセージ等の次のフレーム、の順に優先度(優先順位)が高く設定されており、経路探索メッセージ等の次のフレームよりも経路探索応答メッセージ等の次のフレームが優先的に送信され、この経路探索応答メッセージ等の次のフレームよりもAckフレーム等の次のフレームが優先的に送信されるものである。
通信装置1~5は、CSMA/CA方式により通信媒体(無線通信)にアクセスするものであり、ある通信装置から送信された送信信号を受信すべく(通常は)待機しており、ある通信装置から送信された送信信号を受信すると自身から送信する予定の送信信号の送信を控え、ある通信装置からの送信信号の送信が終了したことを確認すると、自身の送信信号を送信するものである。
仮に、通信装置2は、通信装置4との間の通信経路を探すため、経路探索メッセージ(フレーム)を送信するものとする。
本発明のシステムは、通信装置1(10)と通信装置2(20)と通信装置3(30)と通信装置4(40)と通信装置5(50)とから構成される。この時、通信装置2(20)が経路探索メッセージの送信元となっており、通信端末4(40)に対して経路端末メッセージを送信している。通信端末1(10)、通信端末3(30)及び通信端末5(50)は、通信装置2(20)から送信された経路探索メッセージを受信すると、自身に送付された経路探索メッセージでないことが分かり、周りの通信装置に対して経路探索メッセージ(転送)を転送する。一方、通信端末4(40)は、通信装置2(20)から送信された経路探索メッセージを受信すると、自身(宛先)に送付された経路探索メッセージであることが分かり、通信端末2(20:送信元)に対して経路探索応答メッセージを応答する。
1.経路探索応答メッセージを送信する通信端末は通常1台であり、複数の通信端末から(ほぼ同時期に)経路探索応答メッセージが送信されることは基本的に無い。また、本通信システムと他の通信システムとが競合する可能性は低い。
2.経路探索メッセージが宛先(目的)の通信端末に届いた場合、この経路探索メッセージは(中継されて)更に他の通信端末に転送される必要は無い。そのため、経路探索メッセージを転送することよりも、経路探索応答メッセージの送信を優先する必要性の方が高い。そして、この経路探索応答メッセージを送信する際には、他の通信端末から送信される経路探索メッセージと競合(衝突)しないように制御する。
そのため、各通信端末からは、同時にフレームが送信されて、複数のフレームが衝突しないように、フレーム間隔(T1,T2)やコンテンションウインドウ(CW1×Ts,CW2×Ts)を設定しなければならない。
図4は、実施形態2の通信装置におけるフレーム送信タイミングを示す図である。
図4に示すように、ビジーメディア(先のフレーム)に対する次のフレーム(例えば、Ackフレーム)の送信間隔をT0、ビジーメディアに対する経路探索応答メッセージ等の次のフレームを送信するまでの(時間)間隔をT1、経路探索応答メッセージ等の次のフレームに関する送信待機時間であるコンテンションウインドウをCW1×Ts、ビジーメディアに対する経路探索メッセージ等の次のフレームを送信するまでの(時間)間隔をT2、経路探索メッセージ等の次のフレームに関する送信待機時間であるコンテンションウインドウをCW2×Ts、コンテンションウインドウを構成する複数のスロットタイムをそれぞれTsとした場合、T0<T1、T1+Ts×CW1<T2、且つ、CW1<CW2、の条件が成り立つものとする。
つまり、各通信端末が受信した経路探索メッセージは、ほぼ同時期に他の通信端末に対して送信しようとされるため、各通信端末から送信される経路探索メッセージの競合(衝突)の可能性が非常に高まる。そのため、コンテンションウインドウ(CW2)のスロット数は大きくすることが望ましい。
コンテンションウインドウのスロット数CW2を大きく(多く)設定することにより、経路探索メッセージの衝突の可能性が抑制され、経路探索メッセージを目的の通信装置まで確実に伝達することが容易となる。
従って、経路探索応答メッセージのコンテンションウインドウのスロット数CW1を小さく(少なく)設定することにより、経路探索応答メッセージのスループットの低下を抑制することができる。
図5は、実施形態3の通信装置におけるフレーム送信タイミングを示す図である。
図5に示すように、ビジーメディア(先のフレーム)に対する次のフレーム(例えば、Ackフレーム)までの送信間隔をT0、ビジーメディアに対して一(方向)にフレームを送信するユニキャストフレームの送信間隔をT3、ユニキャストフレームに関する送信待機時間であるコンテンションウインドウをCW3×Ts、ビジーメディアに対して複数(方向)にフレームを送信するブロードキャストフレームの送信間隔をT4、ブロードキャストフレームに関する送信待機時間であるコンテンションウインドウをCW4×Ts、コンテンションウインドウを構成する複数のスロットタイムをTsとした場合、T0<T3、且つ、T3+Ts×CW3<T4、とする。
図6は、実施形態4の通信装置におけるフレーム送信タイミングを示す図である。
図6に示すように、ビジーメディア(先のフレーム)に対する次のフレーム(例えば、Ackフレーム)までの送信間隔をT0、ビジーメディアに対して一(方向)にフレームを送信するユニキャストフレームの送信間隔をT3、ユニキャストフレームに関する送信待機時間であるコンテンションウインドウをCW3×Ts、ビジーメディアに対して複数(方向)にフレームを送信するブロードキャストフレームの送信間隔をT4、ブロードキャストフレームに関する送信待機時間であるコンテンションウインドウをCW4×Ts、コンテンションウインドウを構成する複数のスロットタイムをTsとした場合、T0<T3、T3+Ts×CW3<T4、且つ、CW3<CW4、の条件が成り立つものとする。
また、ユニキャストフレームのコンテンションウインドウのスロット数を小さく(少なく)設定することにより、ユニキャストフレームのフレーム送信間隔を短縮することが可能となり、ユニキャストフレームのスループットを向上させることが可能となる。
Claims (5)
- 第一の通信端末と、第二の通信端末と、第三の通信端末とを有し、
前記第一の通信端末は、前記第三の通信端末を宛先としたメッセージデータを複数の通信端末に対して送信し、
前記第二の通信端末は、前記メッセージデータを受信し、この受信したメッセージデータの宛先を確認し、確認した宛先が自身の通信端末ではないことを確認すると、前記受信したメッセージデータを、他の通信端末に転送し、
前記第三の通信端末は、前記メッセージデータを受信し、この受信したメッセージデータの宛先を確認し、確認した宛先が自身の通信端末であることを確認すると、前記受信したメッセージデータに対応する応答データを、前記受信したメッセージデータの送信元である前記第一の通信端末に対して送信し、
前記応答データは、転送されるメッセージデータよりも送信のための優先順位が高く設定されており、
メッセージデータが受信されてから対応する応答データが送信されるまでの時間は、メッセージデータが受信されてから当該メッセージデータを転送するまでの時間よりも短い
ことを特徴とする通信システム。 - ある通信端末でメッセージデータが受信されてから対応する応答データが送信されるまでの時間は、送信間隔(T1)を経てコンテンションウインドウ(CW1×Ts)が設けられており、
他の通信端末でメッセージデータが受信されてから当該メッセージデータを転送するまでの時間は、送信間隔(T2)を経てコンテンションウインドウ(CW2×Ts)が設けられており、
前記応答データのコンテンションウインドウ(CW1×Ts)の終端のタイミングは、前記メッセージデータを転送する際のコンテンションウインドウ(CW2×Ts)の始端のタイミングよりも早い
ことを特徴とする請求項1に記載の通信システム。 - コンテンションウインドウ(CW*×Ts)は、所定の時間間隔(スロットタイム(Ts))をスロット数(CW*)分だけ設けるものであり、
前記応答データのコンテンションウインドウ(CW1×Ts)のスロット数(CW1)は、前記メッセージデータを転送する際のコンテンションウインドウ(CW2×Ts)のスロット数(CW2)よりも少ない
ことを特徴とする請求項2に記載の通信システム。 - メッセージデータの送信には、複数の通信端末に送信可能なブロードキャストフレームを用い、
メッセージデータに対応する応答データの送信には、一の通信端末に送信するユニキャストフレームを用いる
ことを特徴とする請求項1に記載の通信システム。 - 第一の通信端末は、第三の通信端末を宛先としたメッセージデータを複数の通信端末に対して送信し、
第二の通信端末は、前記メッセージデータを受信して、この受信したメッセージデータの宛先を確認して、確認した宛先が自身の通信端末ではないことを確認すると、前記受信したメッセージデータを、他の通信端末に転送し、
第三の通信端末は、前記メッセージデータを受信して、この受信したメッセージデータの宛先を確認して、確認した宛先が自身の通信端末であることを確認すると、前記受信したメッセージデータに対応する応答データを、前記受信したメッセージデータの送信元である前記第一の通信端末に対して送信し、
前記応答データは、転送されるメッセージデータよりも優先順位が高く設定され、
メッセージデータが受信されてから対応する応答データを送信するまでの時間は、メッセージデータが受信されてから当該メッセージデータを転送するまでの時間よりも短い
ことを特徴とする通信システムにおける通信方法。
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JP2000224088A (ja) * | 1999-02-03 | 2000-08-11 | Matsushita Electric Ind Co Ltd | 無線通信システム |
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JP2007300573A (ja) * | 2006-05-08 | 2007-11-15 | Kddi Corp | 無線マルチホップネットワークの中継通信方法、宛先無線局、中継通信システム及びプログラム |
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