JP2015211432A - Packet communication method, radio communication system and radio communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the deterioration of a throughput.SOLUTION: A first radio communication device 110 transmits a first packet. A second radio communication device 120 transmits a notification signal which reports collision detection, on detecting a collision between the first packet transmitted by the first radio communication device 110 and a second packet transmitted from a first radio communication device 130. The first radio communication device 110, after receiving the notification signal transmitted by the second radio communication device, retransmits the first packet at timing according to an elapsed time from the transmission completion of the first packet to the reception of the notification signal.

Description

  The present invention relates to a packet communication method, a radio communication system, and a radio communication apparatus.

  Conventionally, an error correction code is added, digitally modulated with a predetermined multi-value number, and transmitted to a wireless network, and a packetized information signal is received and received using an error correction code attached to the received information signal Error correction is performed on the received packetized information signal, and when an uncorrectable error signal is detected, retransmission of the packetized information signal is requested, and the packetized information signal including the error signal is replaced with the retransmitted packetized information signal. The technique of receiving is known (for example, refer to the following Patent Document 1).

Japanese Patent Laid-Open No. 2005-221021

  However, in the above-described conventional technology, for example, when a hidden terminal collides, even if each terminal retransmits a packet, packet collision may occur again, resulting in a problem that throughput is reduced.

  In one aspect, an object of the present invention is to provide a packet communication method, a wireless communication system, and a wireless communication apparatus that can suppress a decrease in throughput.

  In order to solve the above-described problems and achieve the object, according to one aspect of the present invention, a plurality of first wireless communication devices each transmit a packet, and a second wireless communication device transmits the plurality of first wireless communication devices. When a collision of each packet transmitted by the apparatus is detected, a notification signal notifying the detection of the collision is transmitted, and each of the plurality of first wireless communication apparatuses is transmitted by the second wireless communication apparatus A packet communication method, a wireless communication system, and a wireless communication device are proposed in which when the notification signal is received, the packet is retransmitted at a timing corresponding to the elapsed time from the end of transmission of the packet of the own device.

  Further, according to one aspect of the present invention, the plurality of first wireless communication devices each transmit a request signal requesting transmission of a packet, and the second wireless communication device is transmitted by the plurality of first wireless communication devices. When a collision of each request signal is detected, a notification signal for notifying the detection of the collision is transmitted, and the plurality of first wireless communication devices receive the notification signal transmitted by the second wireless communication device In this case, a packet communication method, a wireless communication system, and a wireless communication device are proposed in which the packet is transmitted at a timing corresponding to the elapsed time from the end of transmission of the request signal of the own device.

  According to one aspect of the present invention, a decrease in throughput can be suppressed.

1 is a diagram illustrating an example of a wireless communication system according to a first embodiment; It is a figure which shows an example of the flow of the signal in the radio | wireless communications system shown to FIG. 1A. FIG. 3 is a diagram illustrating an example of a wireless network system according to a second exemplary embodiment. FIG. 3 is a diagram illustrating an example of a wireless communication apparatus according to a second embodiment. It is a figure which shows an example of the flow of the signal in the radio | wireless communication apparatus shown to FIG. 3A. It is a figure which shows an example of the hardware constitutions of a radio | wireless communication apparatus. It is a figure which shows an example of the flow of a signal in the hardware constitutions shown in FIG. 3C. It is a flowchart which shows an example of the reception process by a radio | wireless communication apparatus. It is a flowchart which shows an example of the transmission process by a radio | wireless communication apparatus. It is a figure which shows the process example 1 of a wireless network system. It is a figure which shows the process example 2 of a wireless network system. It is a figure which shows an example of a packet collision. It is a figure which shows the other example of a packet collision. It is a flowchart which shows an example of the detection process of the packet collision by a radio | wireless communication apparatus. It is a figure which shows an example of a packet collision signal. It is a flowchart which shows an example of the transmission process in the case of applying an ALOHA system. It is a flowchart which shows an example of the transmission process in the case of applying a RTS / CTS system. It is a figure which shows an example of reduction of the delay time when a packet collision occurs.

  Exemplary embodiments of a packet communication method, a wireless communication system, and a wireless communication apparatus according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1)
(Radio communication system according to the first embodiment)
FIG. 1A is a diagram illustrating an example of the wireless communication system according to the first embodiment. 1B is a diagram illustrating an example of a signal flow in the wireless communication system illustrated in FIG. 1A. As illustrated in FIGS. 1A and 1B, the wireless communication system 100 according to the first embodiment includes first wireless communication devices 110 and 130 and a second wireless communication device 120.

  The first wireless communication apparatus 110 includes a transmission unit 111 and a reception unit 112. The transmission unit 111 transmits a packet to the second wireless communication apparatus 120 wirelessly.

  The receiving unit 112 receives a notification signal transmitted from the second wireless communication device 120. The notification signal is a notification signal notifying that the second wireless communication device 120 has detected a collision between the packet transmitted by the transmission unit 111 and the packet transmitted from the first wireless communication device 130. The reception unit 112 outputs the notification signal reception result to the transmission unit 111.

  On the other hand, when the notification signal is received by the reception unit 112, the transmission unit 111 retransmits the transmitted packet. At that time, the transmission unit 111 retransmits the packet at a timing corresponding to the elapsed time from the end of the packet transmission to the reception of the notification signal.

  When the first wireless communication device 130 transmits a packet to the second wireless communication device 120 and receives a notification signal transmitted from the second wireless communication device 120, for example, similarly to the first wireless communication device 110, Resend the transmitted packet. At that time, the second wireless communication apparatus 120 retransmits the packet at a timing corresponding to the elapsed time from the end of the packet transmission to the reception of the notification signal.

  The second wireless communication device 120 includes a reception unit 121 and a transmission unit 122. The receiving unit 121 receives the packet transmitted from the first wireless communication device 110 and the packet transmitted from the first wireless communication device 130. The transmission unit 122 monitors the reception unit 121, and when a collision of each packet is detected in the reception unit 121, the transmission unit 122 wirelessly transmits a notification signal that notifies the detection of the collision. The notification signal is not limited to the one that designates the first wireless communication device 110 or 130 as the destination, and may be a signal that notifies the wireless communication devices around the second wireless communication device 120 of the detection of the collision, for example. .

  As described above, according to the first embodiment, the first wireless communication device 110 or 130 transmits a packet from its own device to receive a packet collision notification signal based on the elapsed time. The retransmission timing can be controlled. Thereby, since retransmission can be performed at different timings depending on the transmission timing of the collided packet, collision at the time of retransmission can be suppressed, and a decrease in throughput can be suppressed.

<Example of timing according to elapsed time>
For example, the second wireless communication device 120 may transmit a notification signal when a predetermined time has elapsed from the end of transmission of any of the received packets. In this case, each of the first wireless communication devices 110 and 130, when the elapsed time from the transmission of the packet to the reception of the notification signal does not coincide with the predetermined time, Resend the packet.

  In addition, each of the first wireless communication devices 110 and 130, when the elapsed time from the transmission of the packet to the reception of the notification signal coincides with the predetermined time, resend. The second time is a time different from the first time. Thereby, when the collision which a part of each packet of the 1st radio | wireless communication apparatus 110,130 overlaps temporally occurs, the resending timing of the 1st radio | wireless communication apparatus 110,130 can be shifted.

  In addition, for example, the second wireless communication device 120 may transmit a notification signal when a predetermined time elapses after the later transmission end of each received packet. In this case, for example, the first time can be a predetermined time, and the second time can be longer than the predetermined time.

<Pause packet transmission by other wireless communication device>
In addition, the wireless communication system 100 may include a third wireless communication device that is different from the first wireless communication devices 110 and 130 and the second wireless communication device 120. When the third wireless communication device receives the notification signal from the second wireless communication device 120, the third wireless communication device temporarily stops transmission of the packet from the own device. Thereby, the collision between the transmission packet of the third wireless communication apparatus and the retransmission packet of the first wireless communication apparatuses 110 and 130 can be suppressed.

<Packet collision detection method>
For example, the second wireless communication apparatus 120 can measure the received radio wave intensity during reception of a packet whose preamble has been detected, and detect a packet collision based on the measured fluctuation of the received radio wave intensity. Thereby, it is possible to detect a collision in which some of the packets of the first wireless communication apparatuses 110 and 130 overlap in time.

  Further, the second wireless communication apparatus 120 may detect a packet collision using the error detection result of the packet in which the preamble is detected, in addition to the fluctuation of the received radio wave intensity. Thereby, collision of packets can be detected with higher accuracy.

<Modification of Embodiment 1>
A modification of the first embodiment will be described. The transmission unit 111 of the first wireless communication apparatus 110 according to the modified example wirelessly transmits a request signal for requesting transmission (permission) of a packet to the second wireless communication apparatus 120.

  The receiving unit 112 receives a notification signal transmitted from the second wireless communication device 120. The notification signal is a notification signal notifying that the second wireless communication device 120 has detected a collision between the request signal transmitted by the transmission unit 111 and the request signal transmitted from the first wireless communication device 130. The reception unit 112 outputs the notification signal reception result to the transmission unit 111.

  On the other hand, when the notification signal is received by the reception unit 112, the transmission unit 111 transmits a packet related to the transmitted request signal. At that time, the transmission unit 111 transmits the packet at a timing corresponding to the elapsed time from the end of the transmission of the request signal to the reception of the notification signal.

  When the first wireless communication device 130 transmits a request signal to the second wireless communication device 120 and receives a notification signal transmitted from the second wireless communication device 120, for example, similarly to the first wireless communication device 110, Then, a packet related to the transmitted request signal is transmitted. At that time, the second wireless communication apparatus 120 transmits the packet at a timing corresponding to the elapsed time from the end of transmission of the request signal to reception of the notification signal.

  The receiving unit 121 of the second wireless communication device 120 receives the request signal transmitted from the first wireless communication device 110 and the request signal transmitted from the first wireless communication device 130. The second request signal is a request signal for the first wireless communication device 130 to request the second wireless communication device 120 to transmit a packet. The transmission unit 122 monitors the reception unit 121, and when a collision between request signals in the reception unit 121 is detected, the transmission unit 122 wirelessly transmits a notification signal that notifies the detection of the collision.

  Thus, according to the modification, the elapsed time from when the first wireless communication device 110 and the first wireless communication device 130 transmit the request signal from the own device to when the request signal collision notification signal is received. The packet transmission timing can be controlled based on the above. As a result, retransmission can be performed at different timings depending on the transmission timing of the request signals that have collided, so that collisions during packet transmission can be suppressed, and a reduction in throughput can be suppressed.

(Embodiment 2)
(Radio network system according to the second embodiment)
FIG. 2 is a diagram of an example of a wireless network system according to the second embodiment. As illustrated in FIG. 2, the wireless network system 200 according to the second embodiment includes nodes A to J and GW. In FIG. 2, the straight lines between the nodes A to J and GW indicate wireless connection relationships.

  Nodes A to J automatically set communication paths with each other to form an ad hoc network. For example, each of the nodes A to J transmits / receives a control packet such as a Hello packet (Hello message) to / from a node connected in one hop, that is, an adjacent node, so that the route information held by the own node can be obtained. Exchange. The transmission of the Hello packet is performed at regular intervals, for example. In addition, the Hello packet includes, for example, identification information (ID) of a transmission source node, route information indicating a route from the transmission source node to the node GW, and the like.

  Then, the nodes A to J set a route to the node GW using the exchanged route information. Each of the nodes A to J includes a power meter, a sensor, and the like, and transmits data obtained by sensing to the node GW. The node GW is an information collection terminal (gateway) that collects information transmitted from the nodes A to J, for example.

  In the example illustrated in FIG. 2, each of the nodes A, E, F, and G is a node that exists in an area that can directly communicate with the node GW and can directly transmit data to the node GW with one hop. Each of the nodes B and D is a multi-hop node that transmits data to the node GW via the node A. Node C is a multi-hop node that transmits data to node GW via both nodes B and A. The node H is a multi-hop node that transmits data to the node GW via the node G. Each of the nodes I and J is a multi-hop node that transmits data to the node GW via the node F.

  In the wireless network system 200, the nodes A to J and GW communicate autonomously using, for example, a CSMA / CA (Carrier Sense Multiple Access / Collision Avidance) method. For example, each of the nodes A to J and GW performs carrier sense prior to data transmission, and measures the received power level of the carrier frequency.

  Then, each of the nodes A to J and GW determines that the channel is in an idling state if the measured received power level is equal to or less than the threshold value, and executes data transmission. On the other hand, each of the nodes A to J and GW determines that the channel is busy if the measured received power level is greater than the threshold, suppresses data transmission, and performs carrier sense again after a predetermined time. Data transmission.

  At this time, nodes (terminals) that cannot sense each other's carriers transmit signals at the same time, and packet collision may occur. This is called a hidden terminal problem. Each node performs carrier sense again when a packet collision occurs. At this time, the probability of packet collision again is reduced by doubling the value of CW (Contention Window).

  However, for example, when the transmission packet length is long, even if the CW value is doubled, the packet collision probability is high and there is a possibility that a useless packet is transmitted. In addition, as a technique for solving the hidden terminal problem, there is a scheduling method based on RTS / CTS (Request To Send / Clear To Send), but there is a possibility that a packet transmitted by the hidden terminal may collide with the RTS / CTS signal. May cause problems.

  On the other hand, in the second embodiment, when packet collision occurs, the receiving side notifies the packet collision signal to surrounding terminals, the transmitting side autonomously determines the priority of packet transmission, and the priority The packets can be transmitted at different timings depending on the situation. Thereby, packet collision at the time of packet retransmission can be suppressed.

  The first wireless communication device 110, the second wireless communication device 120, and the first wireless communication device 130 illustrated in FIGS. 1A and 1B can be applied to, for example, the nodes A to J and GW. For example, the configurations of the first wireless communication device 110 and the second wireless communication device 120 illustrated in FIGS. 1A and 1B may be provided in each of the nodes A to J and GW. For example, when the node GW does not perform data transmission, the configuration of the second wireless communication device 120 may be provided in the node GW, and the configuration of the first wireless communication device 110 may not be provided.

(Radio communication apparatus according to the second embodiment)
FIG. 3A is a diagram illustrating an example of a wireless communication apparatus according to the second embodiment. 3B is a diagram illustrating an example of a signal flow in the wireless communication apparatus illustrated in FIG. 3A. Each of the nodes A to J and GW illustrated in FIG. 2 can be realized by, for example, the wireless communication device 300 illustrated in FIGS. 3A and 3B.

  The wireless communication apparatus 300 includes a reception unit 311, a preamble / header detection unit 312, a signal demodulation unit 313, a CRC check unit 314, an RSSI fluctuation detection unit 315, a packet collision determination unit 316, and a packet collision signal detection unit 317. In addition, the wireless communication apparatus 300 includes a packet collision signal generation unit 318, a packet transmission control unit 319, a packet retransmission timing determination unit 320, a packet retransmission timing control unit 321, a transmission packet generation unit 322, and a transmission unit 323. .

  The receiving unit 311 receives a signal wirelessly transmitted from another wireless communication device. Then, the reception unit 311 outputs the received signal to the preamble header detection unit 312 and the RSSI fluctuation detection unit 315.

  The preamble header detection unit 312 detects the preamble and header of the signal output from the reception unit 311. Further, the preamble / header detection unit 312 determines whether the signal output from the reception unit 311 is a packet of the radio network system 200 based on the detection result of the preamble and the header. Preamble / header detection unit 312 then outputs a signal determined to be a packet in radio network system 200 to signal demodulation unit 313. The preamble header detection unit 312 outputs the preamble and header detection results to the packet collision determination unit 316.

  The signal demodulator 313 decodes the signal output from the preamble header detector 312. Then, the signal demodulation unit 313 outputs the data packet obtained by decoding to the CRC check unit 314 and the packet collision signal detection unit 317.

  The CRC check unit 314 performs a CRC (Cyclic Redundancy Check) process on the data packet output from the signal demodulation unit 313. Thereby, it is possible to check whether or not the data packet is correctly demodulated in the signal demodulator 313. The CRC check unit 314 outputs the inspection result to the packet collision determination unit 316 and the packet collision signal detection unit 317.

  The RSSI fluctuation detection unit 315 detects the fluctuation of the RSSI (Received Signal Strength Indicator) of the signal output from the reception unit 311. As a result, it is possible to detect that the RSSI has changed due to the reception of another signal while the wireless communication device 300 is receiving a data packet addressed to itself. The RSSI fluctuation detection unit 315 outputs the detection result of the RSSI fluctuation to the packet collision determination unit 316.

  The packet collision determination unit 316 determines whether or not a packet collision has occurred based on the detection results output from the preamble header detection unit 312 and the RSSI fluctuation detection unit 315 and the inspection results output from the CRC check unit 314. Determine whether. For example, the packet collision determination unit 316 determines that a packet collision has occurred when a preamble and header are detected, a CRC error occurs, and an RSSI variation is detected. A packet collision determination method will be described later (see, for example, FIG. 8). The packet collision determination unit 316 outputs the determination result to the packet collision signal generation unit 318.

  The packet collision signal detection unit 317 detects a packet collision signal among the data packets output from the signal demodulation unit 313 based on the inspection result output from the CRC check unit 314. The packet collision signal will be described later (see, for example, FIG. 9). The packet collision signal detection unit 317 outputs the detection result of the packet collision signal to the packet transmission control unit 319 and the packet retransmission timing determination unit 320.

  Based on the determination result output from the packet collision determination unit 316, the packet collision signal generation unit 318 notifies a surrounding wireless communication device that a packet collision has occurred when a packet collision occurs in the own device. A collision signal is generated. Then, the packet collision signal generation unit 318 outputs the generated packet collision signal to the transmission unit 323.

  The packet transmission control unit 319 controls packet transmission by the own device based on the detection result output from the packet collision signal detection unit 317. For example, when a packet collision signal is detected, the packet transmission control unit 319 stops the transmission of the packet by the own device for a predetermined period until the packet retransmission of the other wireless communication device is completed. 322 is controlled.

  The packet transmission control unit 319 stops the packet transmission for a predetermined period T, in which the packet length is L (data), the ACK signal length is L (ACK), and the SIFS (Short Inter Frame Space) time is T (SIFS). ), For example, can be determined by the following equation (1). The SIFS time is set in advance in the wireless network system 200, for example.

  T = 2 × L (data) + 4 × T (SIFS) + 2 × L (ACK) (1)

  In addition, the packet transmission control unit 319 controls the transmission packet generation unit 322 so as to transmit a packet using, for example, a normal packet transmission protocol after a predetermined period has elapsed.

  Based on the detection result output from the packet collision signal detection unit 317, the packet retransmission timing determination unit 320 determines the retransmission timing of the packet of the own device when the packet collision signal is detected after the device transmits the packet. judge. For example, the packet retransmission timing determination unit 320 determines the retransmission timing based on the difference between the transmission completion time when the own device completes packet transmission and the detection time when the own device detects a packet collision signal.

  As an example, the packet retransmission timing determination unit 320 determines that the retransmission priority of the wireless communication device 300 is “low” when the difference between the transmission completion time and the detection time corresponds to the SIFS time. Further, when the difference between the transmission completion time and the detection time is greater than the SIFS time and equal to or less than a predetermined time, the packet retransmission timing determination unit 320 determines that the retransmission priority of the own apparatus is “high”.

  Further, the packet retransmission timing determination unit 320 determines that the retransmission priority of the own apparatus is “0” when a predetermined time or more has elapsed from the transmission completion time. Further, the packet retransmission timing determination unit 320 determines that the retransmission priority of the own device is “−1” when the terminal does not transmit a packet and does not perform packet retransmission. The packet retransmission timing determination unit 320 outputs the determined retransmission priority to the packet retransmission timing control unit 321.

  The packet retransmission timing control unit 321 controls the packet retransmission timing of its own device by controlling the transmission packet generation unit 322 based on the retransmission priority output from the packet retransmission timing determination unit 320.

  For example, when the retransmission priority is “high”, the packet retransmission timing control unit 321 controls to retransmit the packet at the time when SIFS time, that is, T (SIFS) has elapsed after the packet collision signal is detected. To do. Further, when the retransmission priority is “low”, the packet retransmission timing control unit 321 has a time corresponding to 3 × T (SIFS) + L (data) + L (ACK) after the packet collision signal is detected. Control to retransmit the packet at the elapsed time.

  The packet retransmission timing control unit 321 performs normal retransmission processing when the retransmission priority is “0”. For example, when the wireless communication apparatus 300 is a wireless terminal, the packet retransmission timing control unit 321 doubles the CW, randomly selects a backoff length, waits for the selected backoff time, and then transmits a packet. Control to retransmit. Also, the packet retransmission timing control unit 321 performs control so that packet retransmission is not performed when the retransmission priority is “−1”.

  The transmission packet generation unit 322 generates a transmission packet of the own apparatus and outputs the transmission packet to the transmission unit 323 according to control by the packet transmission control unit 319 and the packet retransmission timing control unit 321.

  The transmission unit 323 wirelessly transmits the packet collision signal output from the packet collision signal generation unit 318 and the transmission packet (including the retransmission packet) output from the transmission packet generation unit 322 to another wireless communication apparatus 300. . The transmission packet output from the transmission packet generation unit 322 includes not only the initial packet but also a retransmission packet.

  Although the case where “high”, “low”, “0”, and “−1” are used as retransmission priorities has been described here, the retransmission priorities are not limited to these and can be arbitrarily set.

  1A and 1B can be realized by, for example, a packet retransmission timing determination unit 320, a packet retransmission timing control unit 321, a transmission packet generation unit 322, and a transmission unit 323. The receiver 112 shown in FIGS. 1A and 1B can be realized by the receiver 311, the preamble / header detector 312 and the signal demodulator 313, for example.

  The receiver 121 shown in FIGS. 1A and 1B can be realized by, for example, the receiver 311, the preamble / header detector 312 and the signal demodulator 313. The transmission unit 122 illustrated in FIGS. 1A and 1B can be realized by, for example, the packet collision determination unit 316, the packet collision signal generation unit 318, and the transmission unit 323.

(Hardware configuration of wireless communication device)
FIG. 3C is a diagram illustrating an example of a hardware configuration of the wireless communication device. FIG. 3D is a diagram illustrating an example of a signal flow in the hardware configuration illustrated in FIG. 3C. As illustrated in FIGS. 3C and 3D, the wireless communication apparatus 300 includes, for example, a transmission / reception antenna 351, an amplifier 352, a multiplication unit 353, an analog-digital converter 354, a processor 355, and a memory 356. The wireless communication apparatus 300 includes a digital-analog converter 357, a multiplication unit 358, an amplifier 359, an oscillator 360, and a sensor 361.

  The transmission / reception antenna 351 receives a signal wirelessly transmitted from the surroundings of the own device, and outputs the received signal to the amplifier 352. In addition, the transmission / reception antenna 351 wirelessly transmits the signal output from the amplifier 359 to the surroundings of the own device.

  The amplifier 352 amplifies the signal output from the transmission / reception antenna 351. Then, the amplifier 352 outputs the amplified signal to the multiplication unit 353. The multiplier 353 multiplies the signal output from the amplifier 352 by the clock signal output from the oscillator 360, thereby performing frequency conversion from the high frequency band to the base band. Then, the multiplier 353 outputs the frequency-converted signal to the analog / digital converter 354.

  The analog / digital converter 354 (A / D) is an ADC (Analog / Digital Converter) that converts the signal output from the multiplier 353 from an analog signal to a digital signal. The analog-digital converter 354 outputs the signal converted into the digital signal to the processor 355.

  The processor 355 governs overall control of the wireless communication apparatus 300. The processor 355 can be realized by, for example, a CPU (Central Processing Unit) or a DSP (Digital Signal Processor). The processor 355 performs reception processing on the signal output from the analog-digital converter 354. Further, the processor 355 performs a transmission process of generating a signal to be transmitted by the own device and outputting the generated signal to the digital / analog converter 357.

  In addition, the processor 355 performs processing based on the physical quantity information output from the sensor 361. Further, the processor 355 may perform a process of controlling the transmission power of the own apparatus by controlling the amplifier 359 based on the signal output from the analog-digital converter 354, for example.

  The memory 356 includes, for example, a main memory and an auxiliary memory. The main memory is, for example, a RAM (Random Access Memory). The main memory is used as a work area for the processor 355. The auxiliary memory is a non-volatile memory such as a magnetic disk or a flash memory. Various programs for operating the processor 355 are stored in the auxiliary memory. The program stored in the auxiliary memory is loaded into the main memory and executed by the processor 355. Further, for example, various predetermined threshold values are stored in the auxiliary memory.

  The digital-analog converter 357 is a DAC (Digital / Analog Converter) that converts the signal output from the processor 355 from a digital signal to an analog signal. The digital / analog converter 357 outputs the signal converted into the analog signal to the multiplication unit 358.

  The multiplier 358 multiplies the signal output from the digital-analog converter 357 by the clock signal output from the oscillator 360, thereby performing frequency conversion from the baseband to the high-frequency band. Then, the multiplier 358 outputs the frequency-converted signal to the amplifier 359. The amplifier 359 amplifies the signal output from the digital / analog converter 357. Then, the amplifier 359 outputs the amplified signal to the transmission / reception antenna 351.

  The oscillator 360 oscillates a clock signal (continuous wave AC signal) having a predetermined frequency. Then, the oscillator 360 outputs the oscillated clock signal to the multipliers 353 and 358. The sensor 361 measures various physical quantities and outputs baseband physical quantity information indicating the measured physical quantities to the processor 355. Examples of physical quantities measured by the sensor 361 include temperature, humidity, acceleration, illuminance, wind direction, wind speed, earthquake motion, rainfall, loudness, water level, power consumption, water usage, and gas usage. Such as quantity.

  The receiving unit 311 illustrated in FIGS. 3A and 3B can be realized by, for example, the transmission / reception antenna 351, the amplifier 352, the multiplication unit 353, the analog-digital converter 354, and the oscillator 360. The transmission unit 323 illustrated in FIGS. 3A and 3B can be realized by, for example, the transmission / reception antenna 351, the digital / analog converter 357, the multiplication unit 358, the amplifier 359, and the oscillator 360.

  The preamble header detection unit 312, the signal demodulation unit 313, the CRC check unit 314, the RSSI fluctuation detection unit 315, the packet collision determination unit 316, and the packet collision signal detection unit 317 illustrated in FIGS. 3A and 3B are realized by the processor 355, for example. can do. The packet collision signal generation unit 318, the packet transmission control unit 319, the packet retransmission timing determination unit 320, the packet retransmission timing control unit 321 and the transmission packet generation unit 322 illustrated in FIGS. 3A and 3B can be realized by the processor 355, for example. it can.

(Reception processing by wireless communication device)
FIG. 4 is a flowchart illustrating an example of reception processing by the wireless communication device. For example, the wireless communication device 300 repeatedly performs the steps illustrated in FIG. 4 as the reception process. First, the wireless communication device 300 determines whether or not a packet from another wireless communication device 300 has been received (step S401). The determination in step S401 can be made, for example, based on whether or not the preamble of the own system has been detected.

  In step S401, when no packet is received (step S401: No), the wireless communication device 300 ends a series of reception processing. When the packet is received (step S401: Yes), the wireless communication device 300 determines whether a CRC error is detected from the decoding result of the received packet (step S402).

  In step S402, when a CRC error is detected (step S402: Yes), the wireless communication apparatus 300 determines whether a packet collision with respect to the received packet is detected (step S403). This makes it possible to determine whether the CRC error is due to packet collision. The packet collision detection process will be described later (for example, see FIG. 8). When packet collision is not detected (step S403: No), the wireless communication device 300 ends a series of reception processes.

  When packet collision is detected in step S403 (step S403: Yes), the wireless communication device 300 determines whether or not packet transmission by the own device is possible by carrier sense (step S404). When packet transmission is not possible (step S404: No), the wireless communication apparatus 300 waits for time ΔT (step S405) and returns to step S404.

  In step S404, when packet transmission is possible (step S404: Yes), the wireless communication apparatus 300 waits for SIFS time (step S406). SIFS is a predetermined time defined in, for example, IEEE (The Institute of Electrical and Electronics Engineers) 802.11. Next, the wireless communication apparatus 300 transmits a packet collision signal notifying that a packet collision has occurred to the surroundings (step S407), and ends a series of reception processes.

  If no CRC error is detected in step S402 (step S402: No), the wireless communication device 300 determines whether the received packet is addressed to itself (step S408). If the received packet is addressed to the own device (step S408: Yes), the wireless communication device 300 waits for SIFS time (step S409). Next, the wireless communication apparatus 300 transmits an ACK (Acknowledgement) for the received packet (step S410), and ends a series of reception processes.

  In step S408, when the received packet is not addressed to the own device (step S408: No), the wireless communication device 300 determines whether the received packet is a packet collision signal from another wireless communication device (step S411). ). If the received packet is not a packet collision signal (step S411: No), the wireless communication device 300 ends a series of reception processes.

  In step S411, when the received packet is a packet collision signal (step S411: Yes), the wireless communication apparatus 300 performs a process of stopping the transmission process in which the own apparatus transmits the packet for a predetermined time (step S412). A series of reception processing ends.

  Thereby, it is possible to stop the transmission process by the own device until retransmission in the other wireless communication device is completed, and to suppress the collision. The transmission process of the own device will be described later (see, for example, FIG. 5). The predetermined time for stopping the transmission process in step S412 is, for example, a time of 4 × SIFS time + 2 × packet length + 2 × ACK length or more after receiving the packet collision signal (see, for example, FIGS. 6A and 6B).

(Transmission processing by wireless communication device)
FIG. 5 is a flowchart illustrating an example of transmission processing by the wireless communication device. For example, the wireless communication apparatus 300 repeatedly executes the steps shown in FIG. 5 as the transmission process. The transmission process by the wireless communication device 300 is executed in parallel with the reception process shown in FIG. 4, for example. Further, the transmission processing by the wireless communication apparatus 300 is stopped for a predetermined time in step S412 shown in FIG.

  First, the wireless communication device 300 determines whether or not a packet to be transmitted from the device itself has occurred (step S501). When the packet which should be transmitted has not generate | occur | produced (step S501: No), the radio | wireless communication apparatus 300 complete | finishes a series of transmission processes. When a packet to be transmitted is generated (step S501: Yes), the wireless communication apparatus 300 initializes “number of transmissions” (number of transmissions = 0) (step S502). “Number of transmissions” is information indicating the number of times the wireless communication apparatus 300 has transmitted a packet by backoff processing.

  Next, the wireless communication device 300 performs a back-off process (step S503). Next, the wireless communication apparatus 300 transmits the packet generated in step S501 to the destination (step S504). Next, the wireless communication apparatus 300 waits for SIFS time (step S505).

  Next, wireless communication apparatus 300 determines whether or not an ACK has been received for the packet transmitted in step S504 (step S506). When the ACK is received (step S506: Yes), the wireless communication device 300 ends a series of transmission processes. When ACK is not received (step S506: No), the wireless communication apparatus 300 determines whether a packet collision signal is received (step S507).

  In step S507, when the packet collision signal has not been received (step S507: No), the wireless communication device 300 determines whether a predetermined time has elapsed (step S508). The determination in step S508 is, for example, a determination as to whether or not a predetermined time has elapsed since the time of transition from step S506 to step S507. This predetermined time T (wait) can be determined by the following equation (2), for example. In the following equation (2), L (packet) is the packet length, and N is the number of terminals of packet collision to be detected.

  T (wait) = (N−1) × L (packet) (2)

  In step S508, when the predetermined time has not elapsed (step S508: No), the wireless communication device 300 waits for time ΔT (step S509) and returns to step S507. As a result, reception of a packet collision signal is waited for a predetermined time. When the predetermined time has elapsed (step S508: Yes), the wireless communication apparatus 300 increments “number of transmissions” (number of transmissions + 1) (step S510).

  Next, the wireless communication apparatus 300 determines whether or not the “number of transmissions” exceeds a predetermined maximum number of retransmissions (step S511). If the “number of transmissions” does not exceed the maximum number of retransmissions (step S511: No), the wireless communication apparatus 300 returns to step S503. When the “number of transmissions” exceeds the maximum number of retransmissions (step S511: Yes), the wireless communication apparatus 300 ends a series of transmission processes.

  In step S507, when the packet collision signal is received (step S507: Yes), the wireless communication device 300 determines whether T2-T1 corresponds to the SIFS time (step S512). T1 is the packet transmission completion time in step S504. T2 is the reception time of the packet collision signal in step S507.

  That is, T2-T1 is an elapsed time from when the device transmits a packet until it receives a packet collision signal. When it is determined in step S512 that T2-T1 corresponds to the SIFS time (step S512: Yes), it can be determined that the retransmission priority of the wireless communication apparatus 300 is “low”. In this case, radio communication apparatus 300 waits for time T3 (step S513), and proceeds to step S515. T3 is, for example, a time corresponding to 3 × SIFS time + packet length + ACK length.

  If it is determined in step S512 that T2-T1 does not correspond to the SIFS time (step S512: No), it can be determined that the retransmission priority of the wireless communication apparatus 300 is “high”. In this case, the wireless communication apparatus 300 waits for SIFS time (step S514). Next, the wireless communication apparatus 300 retransmits the packet transmitted in step S504 (step S515). Next, the wireless communication apparatus 300 waits for SIFS time (step S516).

  Next, wireless communication apparatus 300 determines whether or not an ACK has been received for the packet retransmitted in step S515 (step S517). When ACK is not received (step S517: No), the wireless communication apparatus 300 moves to step S510. As a result, when the ACK cannot be received after the packet is retransmitted, the packet retransmission process by the normal back-off process is performed by incrementing the number of transmissions.

  In step S517, when ACK is received for the retransmitted packet (step S517: Yes), the wireless communication device 300 ends a series of transmission processes.

(Example of wireless network system processing)
FIG. 6A is a diagram illustrating a processing example 1 of the wireless network system. In FIG. 6A, the horizontal axis indicates time. In the example shown in FIG. 6A, it is assumed that nodes A and C are in a hidden terminal relationship with each other. For this reason, the nodes A and C cannot detect each other by carrier sense. First, it is assumed that the nodes A and C transmit packets 611 and 612 to the node B, respectively, and a packet collision 613 in which the packets 611 and 612 collide at the node B occurs.

  The node B detects the packet collision 613, and transmits a packet collision signal 621 for notifying the occurrence of the packet collision 613 when the SIFS time has elapsed since the transmission of the later packet 612 of the collided packets 611 and 612 is completed.

  Since the node A does not receive the ACK before the SIFS time elapses after the terminal 601 transmits the packet 611 and receives the packet collision signal 621 within a predetermined time, the retransmission priority of the terminal A is “high”. Judge. Therefore, the node A transmits the retransmission packet 631 when the SIFS time has elapsed after receiving the packet collision signal 621. The retransmission packet 631 is a retransmission packet having the same content as the packet 611.

  In the example shown in FIG. 6A, it is assumed that the retransmission packet 631 does not collide with other packets and is normally received by the Node B. Therefore, the Node B transmits an ACK 632 for the retransmission packet 631 when the SIFS time has elapsed.

  Since the node C receives the packet collision signal 621 when the SIFS time elapses after the terminal 601 transmits the packet 612, the node C determines that the retransmission priority of the terminal itself is “low”. For this reason, the node C transmits a retransmission packet 641 when a predetermined time has elapsed after receiving the packet collision signal 621. The retransmission packet 641 is a retransmission packet having the same content as the packet 612. This predetermined time is, for example, 3 × SIFS time + packet length + ACK length.

  In the example illustrated in FIG. 6A, it is assumed that the retransmission packet 641 does not collide with other packets and is normally received by the Node B. For this reason, the Node B transmits an ACK 642 for the retransmission packet 641 when the SIFS time has elapsed.

  In addition, each of the other wireless communication devices around the node B also receives the packet collision signal 621 (for example, step S411 in FIG. 4). For this reason, these wireless communication apparatuses determine that other wireless communication apparatuses perform packet retransmission, and stop transmission processing for a period of time until each retransmission of nodes A and C shown in FIG. 6A ends, for example. (For example, step S412 in FIG. 4). As a result, the retransmission packets 631 and 641 by the nodes A and C can reach the node B without colliding with packets from other wireless communication apparatuses.

  Here, if the difference between the transmission completion time and the detection time is equivalent to the SIFS time, it is determined that the retransmission priority is “low”, and the difference between the transmission completion time and the detection time is larger than the SIFS time for a predetermined time. The case where it is determined that the retransmission priority is “high” in the following cases has been described. On the other hand, for example, if the difference between the transmission completion time and the detection time corresponds to the SIFS time, it is determined that the retransmission priority is “high”, and the difference between the transmission completion time and the detection time is larger than the SIFS time. May be determined to be “low”.

  In this case, in the example shown in FIG. 6A, it is determined that the retransmission priority of the terminal itself is “low”. Therefore, the node A transmits the retransmission packet 631 when a predetermined time has elapsed after receiving the packet collision signal 621. This predetermined time is, for example, 3 × SIFS time + packet length + ACK length.

  Node C determines that its own retransmission priority is “high”. For this reason, the node C transmits a retransmission packet 641 when the SIFS time has elapsed after receiving the packet collision signal 621. The retransmission packet 641 is a retransmission packet having the same content as the packet 612.

  In this way, the packet may be transmitted at a different timing depending on whether or not the difference between the transmission completion time and the detection time corresponds to the SIFS time. Thereby, the retransmission timing of the packet from each node can be shifted and the collision at the time of retransmission can be suppressed.

  FIG. 6B is a diagram illustrating a processing example 2 of the wireless network system. In FIG. 6B, the horizontal axis indicates time. In the example illustrated in FIG. 6B, it is assumed that the nodes A, E, and G are in a hidden terminal relationship. For this reason, the nodes A, E, and G cannot detect each other by carrier sense. First, assume that nodes A, E, and G transmit packets 651 to 653 to the node GW, respectively, and a packet collision 654 occurs in which the packets 651 to 653 collide at the node GW.

  The node GW detects the packet collision 654, and transmits a packet collision signal 661 when the SIFS time has elapsed since the transmission of the latest packet 653 among the collided packets 651 to 653 has been completed.

  Node A has received a packet collision signal 661 within a predetermined time period after the SI terminal transmits a packet 651 and does not receive an ACK before the SIFS time elapses, so that its retransmission priority is “high”. Judge. Therefore, the node A transmits the retransmission packet 671 when the SIFS time has elapsed after receiving the packet collision signal 661. The retransmission packet 671 is a retransmission packet having the same content as the packet 651.

  Since the node E does not receive the ACK until the SIFS time elapses after the terminal 65 transmits the packet 652 and receives the packet collision signal 661 within a predetermined time, the retransmission priority of the terminal E is “high”. Judge. Therefore, the node E transmits a retransmission packet 672 when the SIFS time has elapsed after receiving the packet collision signal 661. The retransmission packet 672 is a retransmission packet having the same content as the packet 652.

  For this reason, in the example shown in FIG. 6B, retransmission packets 671 and 672 from the nodes A and E are simultaneously transmitted, and a packet collision 673 in which the retransmission packets 671 and 672 collide occurs. On the other hand, since the node GW cannot normally receive the retransmission packets 671 and 672 and cannot detect the packet collision 673, the packet collision signal for the packet collision 673 is not transmitted.

  Since the node G receives the packet collision signal 661 when the SIFS time elapses after the terminal transmits the packet 653, the node G determines that the retransmission priority of the terminal is “low”. For this reason, the node G transmits a retransmission packet 681 when a predetermined time has elapsed after receiving the packet collision signal 661. The retransmission packet 681 is a retransmission packet having the same content as the packet 653. This predetermined time is, for example, 3 × SIFS time + packet length + ACK length.

  In the example illustrated in FIG. 6B, it is assumed that the retransmission packet 681 does not collide with other packets and is normally received by the node GW. For this reason, the node GW transmits an ACK 682 for the retransmission packet 681 when the SIFS time has elapsed.

  Since the nodes A and E do not receive the ACK for the retransmission packets 671 and 672 and do not receive the packet collision signal after the retransmission packets 671 and 672 are transmitted, they wait until the packet retransmission of the node G is completed, Resend. At this time, for example, even if the retransmission packets of the nodes A and E collide, if the two packets collide, retransmission can be performed at different timings by the same processing as in FIG. 6A.

(Packet collision)
FIG. 7A is a diagram illustrating an example of packet collision. Packets 710 and 720 illustrated in FIG. 7A are packets transmitted from different wireless communication apparatuses 300, respectively. As an example, the packets 710 and 720 are packets transmitted from the nodes A and C to the node B, respectively. Packets 710 and 720 include preamble header portions 711 and 721 (Preamble + header) and data portions 712 and 722 (data), respectively.

  In the example shown in FIG. 7A, the packets 710 and 720 collide with each other when the packet 720 does not overlap the preamble header portion 711 of the packet 710 and the packet 720 overlaps the data portion 712 of the packet 710. For this reason, for example, since the RSSI changes in the middle of the data portion 712 of the packet 710 and a CRC error occurs, the Node B can detect the collision between the packets 710 and 720.

  FIG. 7B is a diagram illustrating another example of packet collision. In FIG. 7B, the same parts as those shown in FIG. 7A are denoted by the same reference numerals and description thereof is omitted. In the example shown in FIG. 7B, the packets 710 and 720 collide with each other when the packet 720 overlaps the preamble header portion 711 of the packet 710. For this reason, the Node B cannot detect the preamble header portion 711 of the packet 710 and cannot detect a collision between the packets 710 and 720. However, since the ratios of the preamble header parts 711 and 721 in the packets 710 and 720 are small, the probability that the packet collision shown in FIG. 7B will occur is low.

(Detection process of packet collision by wireless communication device)
FIG. 8 is a flowchart illustrating an example of packet collision detection processing by the wireless communication apparatus. For example, the wireless communication device 300 performs the steps shown in FIG. 8 as packet collision detection processing. First, the wireless communication device 300 determines whether a preamble and header of a predetermined packet defined in the wireless network system 200 have been detected (step S801).

  If the preamble and header are not detected in step S801 (step S801: No), the wireless communication device 300 ends a series of detection processes. When the preamble and header are detected (step S801: Yes), the wireless communication apparatus 300 measures RSSI in a packet (received packet) including the detected preamble and header (step S802).

  Next, the wireless communication apparatus 300 determines whether a CRC error has been detected as a result of decoding the received packet (step S803). When no CRC error is detected (step S803: No), the wireless communication device 300 ends a series of detection processes.

  If a CRC error is detected in step S803 (step S803: Yes), the wireless communication apparatus 300 determines whether the maximum RSSI change amount exceeds a predetermined threshold based on the RSSI measurement result in step S802. (Step S804). The maximum RSSI change amount is, for example, the maximum moving average value among a plurality of RSSI moving average values calculated for received packets.

  In step S804, when the maximum RSSI change amount does not exceed the threshold (step S804: No), the wireless communication device 300 ends a series of detection processes. When the maximum RSSI change amount exceeds the threshold (step S804: Yes), the wireless communication device 300 determines that there is a packet collision (step S805), and ends a series of detection processes.

  Through the steps shown in FIG. 8, when a preamble and header are detected, a CRC error occurs, and an RSSI variation is detected, it can be determined that a packet collision has occurred.

(Packet collision signal)
FIG. 9 is a diagram illustrating an example of a packet collision signal. For example, a packet collision signal 900 shown in FIG. 9 can be used as a packet collision signal for notifying the surroundings that there has been a packet collision. The packet collision signal 900 includes a preamble 901, a transmission terminal ID 902, a packet type 903, and a CRC 904.

  The preamble 901 is a predetermined pattern provided at the head of the packet collision signal 900 in order to receive the packet collision signal 900. The transmission terminal ID 902 is identification information of the wireless communication device 300 that is the transmission source of the packet collision signal 900.

  The packet type 903 is information indicating that the packet collision signal 900 is a packet collision signal for notifying the surroundings that a packet collision has occurred. CRC 904 is a CRC code for performing CRC decoding of the packet collision signal 900.

(Application to ALOHA method)
Although the case where the CSMA / CA scheme is applied to the radio network system 200 has been described, the ALOHA scheme, which is one of multiple random access schemes, can also be applied to the radio network system 200. The difference between the case of applying the ALOHA method and the case of applying the CSMA / CA method will be described.

(Transmission processing when the ALOHA method is applied)
FIG. 10 is a flowchart showing an example of transmission processing when the ALOHA method is applied. When the ALOHA method is applied to the wireless network system 200, the wireless communication apparatus 300 executes, for example, each step shown in FIG. 10 as a reception process. The transmission process shown in FIG. 10 is executed in parallel with the reception process shown in FIG. 4, for example. Further, the transmission process shown in FIG. 10 is stopped for a predetermined time in step S412 shown in FIG.

  First, step S1001 shown in FIG. 10 is the same as step S501 shown in FIG. After step S1001, the wireless communication apparatus 300 determines a signal transmission standby time (step S1002).

  Next, the wireless communication apparatus 300 determines whether or not the standby time determined in step S1002 has elapsed (step S1003). If the standby time has not elapsed (step S1003: No), radio communication apparatus 300 waits for time ΔT (step S1004) and returns to step S1003. When the standby time has elapsed (step S1003: Yes), the wireless communication device 300 proceeds to step S1005.

  Steps S1005 to S1010 are the same as steps S504 to S509 shown in FIG. However, if the predetermined time has elapsed in step S1009 (step S1009: Yes), the wireless communication device 300 returns to step S1002. Steps S1011 to S1016 are the same as steps S512 to S517 shown in FIG.

(Application to RTS / CTS method)
Although the case where the CSMA / CA method or the ALOHA method is applied to the wireless network system 200 has been described, the RTS / CTS method can also be applied to the wireless network system 200. In the case of applying the RTS / CTS method, a different part from the case of applying the CSMA / CA method will be described.

(Transmission processing when applying the RTS / CTS method)
FIG. 11 is a flowchart illustrating an example of transmission processing when the RTS / CTS scheme is applied. When the RTS / CTS method is applied to the wireless network system 200, the wireless communication apparatus 300 executes, for example, each step shown in FIG. 11 as the reception process. The transmission process shown in FIG. 11 is executed in parallel with the reception process shown in FIG. 4, for example. Further, the transmission process shown in FIG. 11 is stopped for a predetermined time in step S412 shown in FIG.

  Steps S1101 to S1103 shown in FIG. 11 are the same as steps S501 to S503 shown in FIG. Following step S1103, the wireless communication apparatus 300 transmits an RTS (transmission request) signal before transmission of the packet generated in step S1101 (step S1104). The RTS signal is a packet for requesting packet transmission (permission). Next, the wireless communication apparatus 300 waits for SIFS time (step S1105).

  Next, wireless communication apparatus 300 determines whether or not a CTS (transmission enabled) signal for the RTS signal transmitted in step S1104 has been received (step S1106). When the CTS signal is received (step S1106: Yes), the wireless communication device 300 transmits the packet generated in step S1101 (step S1107), and ends a series of transmission processes.

  In step S1106, when the CTS signal is not received (step S1106: No), the wireless communication apparatus 300 proceeds to step S1108. Steps S1108 to S1118 are the same as steps S507 to S517 shown in FIG.

  The predetermined time T (wait) in step S1109 can be determined by the following equation (3), for example. In the following equation (3), L (RTS) is the RTS signal length, and N is the number of terminals of packet collision to be detected.

  T (wait) = (N−1) × L (RTS) (3)

  If it is determined in step S1113 that T2-T1 does not correspond to the SIFS time (step S1113: No), the wireless communication apparatus 300 waits for the SIFS time (step S1115) and transmits a packet (step S1116). . This is because the wireless communication apparatus 300 can determine that the handshake with the receiving side has been made by receiving the packet collision signal even if the CTS signal is not received.

(Reduction of delay time when packet collision occurs)
FIG. 12 is a diagram illustrating an example of a reduction in delay time when packet collision occurs. In FIG. 12, the horizontal axis represents the normalized delay time. The normalized delay time is a delay time obtained by dividing the delay time by the packet length. The vertical axis represents CDF (Cumulative Distribution Function).

  The delay time distribution 1201 shows the delay time distribution when packet collisions occur between the two wireless communication apparatuses 300 in the second embodiment. The delay time distribution 1202 shows the delay time distribution when a packet collision occurs between two wireless communication devices in the conventional retransmission processing as a reference.

  In the example shown in FIG. 12, in the PHY / MAC layer of IEEE 802.11b, the packet length (data size) is 1 [ms], CWmin is 31, and the two wireless communication apparatuses 300 are hidden terminals. Shows the case. In the example shown in FIG. 12, for example, when the delay time distributions 1201 and 1202 are compared at CDF = 90%, according to the second embodiment, the delay time can be reduced to about 1 / 4.54 compared to the conventional method. I understand.

  Thus, according to the second embodiment, the retransmission timing of the packet is based on the elapsed time from when the wireless communication device 300 on the transmission side transmits the packet from its own device until it receives the packet collision signal. Can be controlled. Thereby, since retransmission can be performed at different timings depending on the transmission timing of the collided packet, collision at the time of retransmission can be suppressed, and a decrease in throughput can be suppressed.

  Alternatively, according to the second embodiment, the packet related to the RTS signal is based on the elapsed time from when the wireless communication device 300 on the transmission side transmits the RTS signal from the own device until the packet collision signal is received. Can be controlled (see, for example, FIG. 11). Thereby, since packet transmission can be performed at different timings depending on the transmission timing of the request signals that have collided, collision of packet transmissions can be suppressed and a decrease in throughput can be suppressed.

  As described above, according to the packet communication method, the wireless communication system, and the wireless communication apparatus, it is possible to suppress a decrease in throughput.

  For example, a conventional protocol that causes packet collision is ALOHA. ALOHA is a protocol in which each terminal transmits a packet at an arbitrary timing. In these methods, packet collisions frequently occur.

  In addition, IEEE 802.11 and IEEE 802.15.4, which have been spreading explosively in recent years, employ the CSMA / CA method as an access method. In this CSMA / CA system, carrier sense is first performed, and when a signal transmission of another terminal is detected, a signal is not transmitted, and when a signal transmission of another terminal is not detected, a signal is transmitted.

  At this time, the terminal waits for a time defined by a system called DIFS (Distributed Inter-Frame Space), and confirms that there is no signal such as ACK during that time. After the DIFS time elapses, each terminal transmits a signal after waiting for the backoff time. This back-off time can be calculated by slot time × random number.

  The maximum value of this random number is called CW. As a result, the terminal that has acquired the smallest back-off time among the terminals that are trying to communicate comes to communicate first, and the probability that a terminal collides simultaneously and packet collision occurs is reduced.

  If a packet collision occurs and communication fails, the terminal increases the CW value, performs carrier sense processing again, and retransmits the packet. There is a binary exponential backoff algorithm for increasing CW. This is a method of doubling the CW value at the time of retransmission and returning it to the initial value if transmission is successful.

  Further, as a method for avoiding packet collision, there is an RTS / CTS method in which scheduling is performed in advance by transmitting and receiving an RTS signal and a CTS signal before packet transmission.

  However, in the binary exponential backoff algorithm, when the collision occurs, the value of CW gradually increases. Therefore, if the packet length is large, the packet is wasted until the packet collision probability decreases. This leads to a decrease in system throughput.

  In addition, there is a problem that the delay time per link required for the system cannot be satisfied. Further, when the RTS / CTS method is used, the RTS signal and the CTS signal give extra interference, and the system throughput is lowered. In addition, when the RTS signal and the CTS signal collide, backoff control is performed using the above-described binary exponential backoff algorithm or the like, so that the system throughput also decreases when the RTS signal collides.

  On the other hand, according to each embodiment described above, when a packet collision is detected on the receiving side, a packet collision signal is transmitted to the surroundings. On the other hand, the terminal that caused the packet collision autonomously determines the priority of packet retransmission, and retransmits the packet at a predetermined timing according to the priority. Thereby, since packet collision at the time of retransmission can be suppressed, throughput can be improved.

  In each of the above-described embodiments, the case where the wireless communication system 100 is applied to the wireless network system 200 has been described. However, the application destination of the wireless communication system 100 is not limited to an ad hoc network such as the wireless network system 200. For example, the wireless communication system 100 can be applied to various wireless communication systems in which packet collision occurs. The wireless communication system 100 is not limited to the CSMA / CA method, the ALOHA method, the RTS / CTS method, and the like, and can be applied to various methods of wireless communication systems in which packet collision occurs.

  The following additional notes are disclosed with respect to the above-described embodiments.

(Appendix 1) Each of the plurality of first wireless communication devices transmits a packet,
When the second wireless communication device detects a collision of each packet transmitted by the plurality of first wireless communication devices, it transmits a notification signal notifying the detection of the collision,
When each of the plurality of first wireless communication devices receives the notification signal transmitted by the second wireless communication device, the packet is transmitted at a timing corresponding to an elapsed time from the end of transmission of the packet of the own device. Resend the
And a packet communication method.

(Appendix 2) The second wireless communication device transmits the notification signal when a predetermined time has elapsed from the end of transmission of any of the packets,
Each of the plurality of first wireless communication devices retransmits the packet when the first time elapses after receiving the notification signal when the elapsed time does not match the predetermined time, and the elapsed time is the predetermined time The packet is retransmitted when a second time that is different from the first time elapses after receiving the notification signal,
The packet communication method according to supplementary note 1, wherein:

(Supplementary Note 3) The second wireless communication device transmits the notification signal when the predetermined time has elapsed since the later transmission end of the packets.
The first time is the predetermined time,
The second time is longer than the predetermined time.
The packet communication method according to appendix 2, wherein:

(Supplementary note 4) The packet communication according to any one of supplementary notes 1 to 3, wherein when the third wireless communication device receives the notification signal, the transmission of the packet from the own device is temporarily stopped. Method.

(Additional remark 5) Said 2nd radio | wireless communication apparatus detects the said collision based on the fluctuation | variation of the received radio wave intensity during reception of the packet which detected the preamble, Any one of Additional remark 1-4 characterized by the above-mentioned. Packet communication method.

(Additional remark 6) The said 2nd radio | wireless communication apparatus detects the said collision based on the said fluctuation | variation and the error detection result of the packet which detected the said preamble, The packet communication method of Additional remark 5 characterized by the above-mentioned.

(Supplementary note 7) A plurality of first wireless communication devices each transmitting a packet;
A second wireless communication device that transmits a notification signal notifying the detection of the collision when a collision of each packet transmitted by the plurality of first wireless communication devices is detected;
Including
Each of the plurality of first wireless communication devices receives the notification signal transmitted by the second wireless communication device, and receives the packet at a timing corresponding to an elapsed time from the end of transmission of the packet of the own device. Resend the
A wireless communication system.

(Supplementary note 8) a transmission unit that transmits a packet to another wireless communication device;
A receiving unit that receives from the other wireless communication device a notification signal notifying that a collision between the packet transmitted by the transmitting unit and a packet transmitted from a wireless communication device different from the own device is detected; ,
With
The transmitter retransmits the packet at a timing according to an elapsed time from the end of transmission of the packet of the own device when the notification signal is received by the receiver;
A wireless communication apparatus.

(Supplementary Note 9) A receiving unit that receives each packet transmitted by a plurality of wireless communication devices;
A transmission unit that transmits a notification signal notifying the detection of the collision when the collision of each packet in the reception unit is detected;
With
The receiving unit receives the packet to be retransmitted at a timing according to an elapsed time from the end of transmission of the packet of the own device when each of the plurality of wireless communication devices receives the notification signal;
A wireless communication apparatus.

(Supplementary Note 10) Each of the plurality of first wireless communication devices transmits a request signal requesting transmission of a packet,
When the second wireless communication device detects a collision of the request signals transmitted by the plurality of first wireless communication devices, it transmits a notification signal notifying the detection of the collision,
When the plurality of first wireless communication devices receive the notification signal transmitted by the second wireless communication device, the packet is transmitted at a timing according to an elapsed time from the end of transmission of the request signal of the own device. Send,
And a packet communication method.

(Supplementary Note 11) A plurality of first wireless communication devices that transmit request signals each requesting transmission of a packet;
A second wireless communication device that transmits a notification signal notifying the detection of the collision when a collision of the request signals transmitted by the plurality of first wireless communication devices is detected;
Including
When the plurality of first wireless communication devices receive the notification signal transmitted by the second wireless communication device, the plurality of first wireless communication devices receive the packet at a timing according to an elapsed time from the end of transmission of the request signal of the own device. Send,
A wireless communication system.

(Supplementary Note 12) A transmission unit that transmits a request signal for requesting transmission of a packet to another wireless communication device;
Reception receiving from the other wireless communication device a notification signal notifying that a collision between the request signal transmitted by the transmission unit and a request signal transmitted from a wireless communication device different from the own device is detected. And
With
The transmission unit transmits the packet at a timing according to an elapsed time from the end of transmission of the request signal of the own device when the notification signal is received by the reception unit;
A wireless communication apparatus.

(Additional remark 13) The receiving part which receives each request signal which requests | requires transmission of the packet transmitted by the some 1st radio | wireless communication apparatus,
A transmission unit for transmitting a notification signal notifying the detection of the collision when a collision of the request signals in the reception unit is detected;
With
When each of the plurality of first wireless communication devices receives the notification signal, the reception unit receives the packet to be transmitted at a timing according to an elapsed time from the end of transmission of the request signal of the own device. To
A wireless communication apparatus.

DESCRIPTION OF SYMBOLS 100 Wireless communication system 110,130 1st wireless communication apparatus 111,122,323 Transmission part 112,121,311 Reception part 120 2nd wireless communication apparatus 200 Wireless network system 300 Wireless communication apparatus 312 Preamble header detection part 313 Signal demodulation part 314 CRC check unit 315 RSSI fluctuation detection unit 316 Packet collision determination unit 317 Packet collision signal detection unit 318 Packet collision signal generation unit 319 Packet transmission control unit 320 Packet retransmission timing determination unit 321 Packet retransmission timing control unit 322 Transmission packet generation unit 351 Transmission / reception Antenna 352, 359 Amplifier 353, 358 Multiplier 354 Analog to digital converter 355 Processor 356 Memory 357 Digital to analog converter 360 Oscillator 361 Capacitors 611,612,651～653,710,720 packet 613,654,673 packet collisions 621,661,900 packet collision signal 631,641,671,672,681 retransmission packet 632,642,682 ACK
711, 721 Preamble header portion 712, 722 Data portion 901 Preamble 902 Sending terminal ID
903 Packet type 904 CRC
1201, 1202 Delay time distribution

Claims (8)

A plurality of first wireless communication devices each transmit a packet,
When the second wireless communication device detects a collision of each packet transmitted by the plurality of first wireless communication devices, it transmits a notification signal notifying the detection of the collision,
When each of the plurality of first wireless communication devices receives the notification signal transmitted by the second wireless communication device, the packet is transmitted at a timing corresponding to an elapsed time from the end of transmission of the packet of the own device. Resend the
And a packet communication method. The second wireless communication device transmits the notification signal when a predetermined time has elapsed from the end of transmission of any of the packets,
Each of the plurality of first wireless communication devices retransmits the packet when the first time elapses after receiving the notification signal when the elapsed time does not match the predetermined time, and the elapsed time is the predetermined time The packet is retransmitted when a second time that is different from the first time elapses after receiving the notification signal,
The packet communication method according to claim 1.   3. The packet communication method according to claim 1, wherein when the third wireless communication apparatus receives the notification signal, the third wireless communication apparatus temporarily stops transmission of a packet from the own apparatus. A plurality of first wireless communication devices each transmitting a packet;
A second wireless communication device that transmits a notification signal notifying the detection of the collision when a collision of each packet transmitted by the plurality of first wireless communication devices is detected;
Including
Each of the plurality of first wireless communication devices receives the notification signal transmitted by the second wireless communication device, and receives the packet at a timing corresponding to an elapsed time from the end of transmission of the packet of the own device. Resend the
A wireless communication system. A transmitter for transmitting packets to other wireless communication devices;
A receiving unit that receives from the other wireless communication device a notification signal notifying that a collision between the packet transmitted by the transmitting unit and a packet transmitted from a wireless communication device different from the own device is detected; ,
With
The transmitter retransmits the packet at a timing according to an elapsed time from the end of transmission of the packet of the own device when the notification signal is received by the receiver;
A wireless communication apparatus. A plurality of first wireless communication devices each transmitting a request signal requesting transmission of a packet;
When the second wireless communication device detects a collision of the request signals transmitted by the plurality of first wireless communication devices, it transmits a notification signal notifying the detection of the collision,
When the plurality of first wireless communication devices receive the notification signal transmitted by the second wireless communication device, the packet is transmitted at a timing according to an elapsed time from the end of transmission of the request signal of the own device. Send,
And a packet communication method. A plurality of first wireless communication devices each transmitting a request signal for requesting transmission of a packet;
A second wireless communication device that transmits a notification signal notifying the detection of the collision when a collision of the request signals transmitted by the plurality of first wireless communication devices is detected;
Including
When the plurality of first wireless communication devices receive the notification signal transmitted by the second wireless communication device, the plurality of first wireless communication devices receive the packet at a timing according to an elapsed time from the end of transmission of the request signal of the own device. Send,
A wireless communication system. A transmission unit that transmits a request signal for requesting transmission of a packet to another wireless communication device;
Reception receiving from the other wireless communication device a notification signal notifying that a collision between the request signal transmitted by the transmission unit and a request signal transmitted from a wireless communication device different from the own device is detected. And
With
The transmission unit transmits the packet at a timing according to an elapsed time from the end of transmission of the request signal of the own device when the notification signal is received by the reception unit;
A wireless communication apparatus.

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