JP5758350B2 - Wireless communication system and wireless communication method - Google Patents

Description

  The present invention is a radio in which base stations and terminals of a plurality of wireless communication groups sharing the same channel in a target area perform wireless communication by occupying a wireless space in order using a reservation signal (NAV: Network Allocation Vector). The present invention relates to a communication system and a wireless communication method.

  In autonomous distributed control (DCF), which is an access procedure in the IEEE 802.11 wireless communication standard, each wireless terminal performs carrier sense of a channel before transmission, and when the channel is idle, a contention window ( CSMA / CA (Carrier Sense Multiple Access with Collision) which generates a random number from the range of CW) and transmits a packet after confirming that the channel is idle even after waiting for a period (backoff time) corresponding to the random number. Avoidance) method is used. When the channel becomes busy before the back-off time period elapses, no packet is transmitted, and when the channel becomes idle next time, carrier sensing is performed according to the remaining waiting time.

  On the other hand, the wireless base station that has received the packet normally transmits an ACK signal to notify the wireless terminal that is the transmission source of the fact. Therefore, if the ACK signal is not received within a predetermined time, the wireless terminal that is the transmission source performs retransmission processing by expanding the CW by determining that transmission has failed and expanding the range for generating random numbers. . That is, whenever the number of retransmissions increases, it is determined that the channel is congested, and collision avoidance is performed by expanding the CW.

  However, in wireless communication, a state in which each other's wireless signals do not reach (a radio wave environment in which carrier sense does not function) may occur due to the distance between wireless stations or the influence of obstacles that do not transmit radio waves. In this case, since carrier sense does not function effectively, in the CSMA / CA system, the frequency of frame collision increases, which causes a deterioration in throughput characteristics.

  Therefore, in the IEEE 802.11 standard, a countermeasure function called RTS (Request to Send) / CTS (Clear to Send) is defined in order to cope with a propagation environment in which carrier sense does not function effectively.

FIG. 4 shows an operation procedure of RTS / CTS.
In FIG. 4, before transmitting a data frame, terminal A carries out carrier sense of the backoff time in addition to DIFS, and transmits RTS to the base station that is the destination of the data frame. Since the terminal A and the terminal B are in a propagation environment where carrier sense can be performed, the terminal B also receives the RTS transmitted by the terminal A. The RTS and CTS frames have a duration field in which the scheduled period for using the channel is described, and terminal B prohibits transmission by setting a reservation signal (NAV) only for the period described in the RTS frame. To prevent collisions. However, it is assumed that this RTS does not reach the terminal C.

  The base station that is the destination of the data frame returns a CTS to terminal A after a SIFS time interval after receiving the RTS. Since the CTS transmitted by the base station can also be received by the terminal C, the terminal C sets a reservation signal (NAV) only during the period described in the CTS frame, thereby prohibiting transmission and preventing collision. The terminal A that has received the CTS transmits a data frame after the SIFS time, and the base station that has received the data frame also transmits an ACK signal after the SIFS time and ends the communication. Here, since SIFS and DIFS have a relationship of SIFS <DIFS, by giving priority using SIFS for a short time, once RTS is normally received, the frame is disturbed during the subsequent procedure. The data frame and the ACK signal are exchanged without any change.

  The terminal A that is the transmission source of the data frame and the peripheral radio stations (terminal B and terminal C) other than the base station that is the reception destination use the radio line for the period described in the duration field after receiving the RTS or CTS. The transmission is prohibited only during the period set by the reservation signal (NAV) to prevent collision.

IEEE standard for Local and metropolitan area networks Part 11: Wireless LAN MAC and PHY Specifications, June 2007

  In the conventional technique, a countermeasure function called RTS / CTS is defined to cope with a propagation environment in which carrier sense does not function effectively. During the period described in the duration field of RTS or CTS, the channel is regarded as being used, and collision is prevented by setting a reservation signal (NAV).

  By the way, the recent wireless communication environment of CSMA / CA is becoming dense with many terminals and base stations in the target area, and data transmission / reception in a favorable wireless communication environment is severe. In addition, when a large number of wireless communication groups exist in the target area, since the same channel is shared, data transmission / reception is in a more severe situation. That is, an algorithm that can occupy a wireless space temporarily is required as one of means for obtaining a favorable wireless communication environment. In addition, an algorithm that can sequentially occupy a wireless space by a plurality of wireless communication groups is required.

  The present invention provides a radio communication system and a radio communication method in which each radio communication group sequentially occupies a radio space using a reservation signal (NAV) and performs radio communication in a target area where a plurality of radio communication groups exist. The purpose is to do.

  In the first invention, there are a plurality of wireless communication groups composed of a base station and subordinate terminals communicating with the base station, and a plurality of common transmission speeds respectively used for communication are prepared in the plurality of wireless communication groups. In the wireless communication system, each base station of the plurality of wireless communication groups transmits a notification signal including network information of the wireless communication group belonging to the area formed by the plurality of wireless communication groups and is registered in advance. A period in which a broadcast signal having network information of a wireless communication group is received, the reception number m (m is an integer of 0 or 1 or more) is counted, and a base station of each wireless communication group reserves a channel in order The base station of the wireless communication group that transmitted the reservation signal, having means for repeatedly receiving the reservation signal designating m once after transmitting it once And the terminal communicates during the period specified in the reservation signal, the base station and the terminal of a radio communication group that has received the reservation signal prohibits the transmission for the period specified in the reservation signal.

  In the wireless communication system of the first invention, the broadcast signal is used to notify a terminal under the base station of a transmission rate used for communication with the base station.

  In the wireless communication system of the first invention, the transmission rate for transmitting the reservation signal is the lowest transmission rate among a plurality of common transmission rates.

  In the radio communication system of the first invention, the period specified by the reservation signal by the base station of each radio communication group is an equal period obtained by dividing a predetermined time (for example, the maximum period that can be specified by the reservation signal) into 1 / (m + 1). Or, it is arbitrarily set within the range of the maximum period that can be designated by the reservation signal for each base station of each wireless communication group.

  The second invention has a plurality of wireless communication groups composed of a base station and subordinate terminals communicating with the base station, and a plurality of common transmission rates respectively used for communication are prepared in the plurality of wireless communication groups. In the wireless communication method, each base station of the plurality of wireless communication groups transmits a notification signal including the network information of the wireless communication group belonging to the area formed by the plurality of wireless communication groups and is registered in advance. A period in which a broadcast signal having network information of a wireless communication group is received, the reception number m (m is an integer of 0 or 1 or more) is counted, and a base station of each wireless communication group reserves a channel in order The base station and the terminal of the wireless communication group that transmitted the reservation signal by repeating the reception of m times after transmitting the reservation signal designating the Communicate the time period specified in the reservation signal, the base station and the terminal of a radio communication group that has received the reservation signal prohibits the transmission for the period specified in the reservation signal.

  In the wireless communication method of the second invention, the broadcast signal is used to notify a terminal under the base station of a transmission rate used for communication with the base station.

  In the wireless communication method of the second invention, the transmission rate for transmitting the reservation signal is the lowest transmission rate among a plurality of common transmission rates.

  In the wireless communication method of the second invention, the period specified by the base station of each wireless communication group with the reservation signal is an equal period obtained by dividing a predetermined time (for example, the maximum period that can be specified with the reservation signal) into 1 / (m + 1). Or, it is arbitrarily set within the range of the maximum period that can be designated by the reservation signal for each base station of each wireless communication group.

  In the present invention, base stations of a plurality of wireless communication groups existing in a target area transmit a broadcast signal including network information (SSID) of wireless communication groups belonging to each other, and network information registered by each base station The number (m + 1) of base stations that transmitted the notification signal including its own station is obtained by counting the number m of receptions of the notification signal having. Then, the (m + 1) base stations sequentially transmit the reservation signal (NAV) once and then receive it m times so that the base station and the terminal of each wireless communication group use the reservation signal. Communication can be performed while sequentially occupying the wireless space.

It is a figure which shows the apparatus structural example of the base station of the radio | wireless communications system of this invention. 4 is a flowchart illustrating a processing example of a transmission rate control unit 4. It is a time chart which shows the operation example of the radio | wireless communications system of this invention. It is a time chart which shows the operation | movement procedure of RTS / CTS.

FIG. 1 shows a device configuration example of a base station in a wireless communication system of the present invention.
In FIG. 1, the base station includes a data signal input / output unit 1, a broadcast signal generation unit 2, a reservation signal generation unit 3, a transmission rate control unit 4, a transmission / reception control unit 5, and an antenna 6.

  The data signal input / output unit 1 is connected to the transmission / reception control unit 5 via the transmission rate control unit 4. The notification signal generation unit 2 generates a notification signal that notifies the terminal of the transmission rate used for communication, and outputs the notification signal to the transmission / reception control unit 5 via the transmission rate control unit 4. The reservation signal generation unit 3 generates a reservation signal (NAV) for reserving a channel and outputs the reservation signal (NAV) to the transmission / reception control unit 5 via the transmission rate control unit 4.

  As shown in FIG. 2, the transmission rate control unit 4 controls the transmission rate according to an input data signal, notification signal, or reservation signal. The reservation signal is set to, for example, the lowest transmission rate (1 Mbps) among a plurality of common transmission rates (1 Mbps, 2 Mbps, 5.5 Mbps, 6 Mbps, 11 Mbps, 12 Mbps,...) Prepared in the wireless communication system. The The broadcast signal is set to, for example, the next lowest transmission speed (2 Mbps) other than the transmission speed of the reservation signal, and the transmission speed used for the data signal by the broadcast signal is a transmission speed other than the transmission speed of the reservation signal (for example, 5.5 Mbps). ) Is notified to each terminal. The data signal is set to the transmission rate notified by the notification signal. Thereafter, the transmission rate used for the data signal is set as the notification signal for notifying the transmission rate used for the data signal.

  The transmission / reception control unit 5 transmits a notification signal having network information (SSID) of the wireless communication group at the transmission rate specified by the transmission rate control unit 4. The terminal receives a broadcast signal having network information (SSID) to which the terminal belongs and acquires a transmission rate used for transmitting the data signal. This uses the Suppored Rate defined in the IEEE 802.11 standard, which is a wireless LAN standard. That is, the terminal performs data communication with the base station using the transmission rate negotiated with the base station.

  In addition, there are a plurality of wireless communication groups in the target area, and the notification signal transmitted by the base station of each wireless communication group is received by the base stations of other wireless communication groups together with the subordinate terminals. The transmission / reception control unit 5 of the base station of each wireless communication group receives the notification signal transmitted from the base station of the other wireless communication group and confirms the network information (SSID) of the wireless communication group registered in the list in advance. Then, the number m of received notification signals is counted and notified to the reservation signal generation unit 3. The reservation signal generation unit 2 and the transmission / reception control unit 5 perform a process of transmitting the generated reservation signal once and resting m times, and receiving a reservation signal transmitted from a base station of another wireless communication group during that time.

  For example, the number m of received notification signals including network information (SSID) of wireless communication groups registered in advance is 2, and the reservation signal is transmitted from the base stations of the three wireless communication groups including the own station. In this case, the base station of each wireless communication group repeatedly transmits the reservation signal once and sequentially receives it twice.

FIG. 3 shows an operation example of the wireless communication system of the present invention.
In FIG. 3, the base station 10 of the wireless communication group 1 is connected to the subordinate terminals 11 and 12 and the base station 20 of the wireless communication group 2 is connected to the subordinate terminals 21 and 22 and the base station 30 of the wireless communication group 3. Transmits a notification signal (beacon) for notifying each of the subordinate terminals 31 and 32 of the transmission rate used for the data signal, and sets a transmission rate for transmitting and receiving the data signal to and from the subordinate terminals.

  Further, the base stations 10, 20, and 30 of each wireless communication group receive the notification signals to be transmitted from each other, thereby determining that there are three wireless communication groups in the target area and transmitting the reservation signal. Control to adjust the order. Here, for example, the order of the base stations 10, 20, and 30 is set in advance according to the value of the network information (SSID) of the wireless communication group to which each base station belongs.

  The base station 10 of the wireless communication group 1 transmits a reservation signal (NAV) designating a channel reservation period at a predetermined transmission rate (1 Mbps in the above example). This reservation signal is also received by the base station 20 and the terminals 21 and 22 of the wireless communication group 2 and the base station 30 and the terminals 31 and 32 of the wireless communication group 3, and the base stations 20 and 30 and the terminals 21, 22, 31 32, a transmission prohibition period by the reservation signal (NAV) is set.

  On the other hand, the terminals 11 and 12 under the base station 10 of the wireless communication group 1 ignore the reservation signal transmitted by the base station 10. That is, the transmission prohibition period by the reservation signal is set in the base station 20 and the terminals 21 and 22 of the other radio communication groups 2 and 3, and the base station 30 and the terminals 31 and 32, and the base station 10 of the radio communication group 1 is set. And the terminals 11 and 12 can transmit and receive data signals with priority.

  Next, when the transmission prohibition period set by the base station 10 ends, the base station 20 of the wireless communication group 2 transmits a reservation signal (NAV). This reservation signal is also received by the base station 10 and the terminals 11 and 12 of the wireless communication group 1 and the base station 30 and the terminals 31 and 32 of the wireless communication group 3, and the base station 10 and 30 and the terminals 11, 12, 31 32, a transmission prohibition period by the reservation signal (NAV) is set.

  On the other hand, the terminals 21 and 22 under the base station 20 of the wireless communication group 2 ignore the reservation signal transmitted by the base station 20. That is, the transmission prohibition period by the reservation signal is set in the base station 10 and the terminals 11 and 12 of the other radio communication groups 1 and 3, and the base station 30 and the terminals 31 and 32, and the base station 20 of the radio communication group 2 And terminals 21 and 22 can transmit and receive data signals with priority.

  Next, when the transmission prohibition period set by the base station 20 ends, the base station 30 of the wireless communication group 3 transmits a reservation signal (NAV). The reservation signal is also received by the base station 10 and the terminals 11 and 12 of the wireless communication group 1 and the base station 20 and the terminals 21 and 22 of the wireless communication group 2, and the base station 10 and 20 and the terminals 11, 12, 21 , 22 sets a transmission prohibition period by the reservation signal (NAV).

  On the other hand, the terminals 31 and 32 under the base station 30 of the wireless communication group 3 ignore the reservation signal transmitted by the base station 30. That is, the transmission prohibition period by the reservation signal is set in the base station 10 and the terminals 11 and 12 of the other radio communication groups 1 and 2 and the base station 20 and the terminals 21 and 22, and the base station 30 of the radio communication group 3 And the terminals 31 and 32 can transmit and receive data signals with priority.

  Similarly, reservation signals (NAV) are transmitted in the order of the base stations 10, 20, and 30. Thus, the timing at which each base station 10, 20, 30 transmits the reservation signal is repeated with a pause of two times while shifting at a rate of once every three times.

  In the above description, the reservation signal is transmitted in the order of the base stations 10, 20, and 30. However, the number (m + 1) of wireless communication groups that share the transmission of the reservation signal is determined from the number m of reception of the notification signal. After grasping, it is determined that the base station of each wireless communication group transmits once and receives m times, and the order can be determined as follows. First, (m + 1) base stations wait for a time generated from a predetermined random number in order to transmit a reservation signal, and the base station that first transmitted the reservation signal is numbered first. The first base station repeatedly transmits a reservation signal once and receives m times. The other base station receives a reservation signal (NAV) from the first base station, sets a transmission prohibition period, and after that period, similarly waits for a time generated from a predetermined random number, and makes a reservation first. The base station that transmitted the signal is number 2. The second base station repeats transmitting the reservation signal once and receiving it m times. Similarly, the process is repeated until the m-th base station, and the last (m + 1) -th base station is determined.

  The period designated by the reservation signal by each base station may be an equal period obtained by dividing a predetermined time (for example, the maximum period that can be designated by the reservation signal) into 1 / (m + 1). In this case, each base station always has one opportunity to transmit a data signal at the predetermined time, but the time is shortened according to the number of base stations (m + 1). On the other hand, the period designated by the reservation signal by each base station may be arbitrarily set within the range of the maximum period that can be designated by the reservation signal. In this case, by transmitting a reservation signal designating a period according to the traffic between the radio communication groups, the transmission prohibition period of each radio communication group is minimized and the transmission efficiency of the entire radio communication system is increased. Can do.

DESCRIPTION OF SYMBOLS 1 Data signal input / output part 2 Information signal generation part 3 Reservation signal generation part 4 Transmission rate control part 5 Transmission / reception part 6 Antenna 10, 20, 30 Base station 11, 12, 21, 22, 31, 32 Terminal

Claims (8)

In a wireless communication system in which there are a plurality of wireless communication groups composed of a base station and subordinate terminals communicating with the base station, and a plurality of common transmission speeds used for communication are prepared in each of the plurality of wireless communication groups ,
Each base station of the plurality of wireless communication groups transmits a notification signal including network information of the wireless communication group belonging to the area formed by the plurality of wireless communication groups, and is registered in advance. Reservation in which a broadcast signal having group network information is received, the number m of reception is counted (m is an integer of 0 or 1 or more), and the base station of each wireless communication group sequentially designates a period for reserving a channel Means for repeating the reception of m times after transmitting a signal once;
The base station and terminal of the wireless communication group that transmitted the reservation signal communicate during the period specified by the reservation signal, and the base station and terminal of the wireless communication group that received the reservation signal are specified by the reservation signal. A wireless communication system characterized in that transmission is prohibited only during a specified period. The wireless communication system according to claim 1, wherein
The wireless communication system, wherein the notification signal is used to notify a terminal under the base station of a transmission rate used for communication with the base station. The wireless communication system according to claim 1, wherein
A wireless communication system, wherein a transmission rate for transmitting the reservation signal is the lowest transmission rate among the plurality of common transmission rates. The wireless communication system according to claim 1, wherein
The period specified by the reservation signal by the base station of each wireless communication group is an equal period obtained by dividing a predetermined time by 1 / (m + 1), or specified by the reservation signal for each base station of each wireless communication group A wireless communication system characterized in that it is arbitrarily set within the range of the maximum possible period. In a wireless communication method in which there are a plurality of wireless communication groups composed of a base station and subordinate terminals communicating with the base station, and a plurality of common transmission speeds respectively used for communication are prepared in the plurality of wireless communication groups ,
Each base station of the plurality of wireless communication groups transmits a notification signal including network information of the wireless communication group belonging to the area formed by the plurality of wireless communication groups, and is registered in advance. Reservation in which a broadcast signal having group network information is received, the number m of reception is counted (m is an integer of 0 or 1 or more), and the base station of each wireless communication group sequentially designates a period for reserving a channel Repeat sending the signal once and receiving it m times,
The base station and terminal of the wireless communication group that transmitted the reservation signal communicate during the period specified by the reservation signal, and the base station and terminal of the wireless communication group that received the reservation signal are specified by the reservation signal. A wireless communication method characterized by prohibiting transmission only during a specified period. The wireless communication method according to claim 5, wherein
The wireless communication method, wherein the notification signal is used to notify a terminal under the base station of a transmission rate used for communication with the base station. The wireless communication method according to claim 5, wherein
The wireless communication method, wherein a transmission rate for transmitting the reservation signal is a lowest transmission rate among the plurality of common transmission rates. The wireless communication method according to claim 5, wherein
The period specified by the reservation signal by the base station of each wireless communication group is an equal period obtained by dividing a predetermined time by 1 / (m + 1), or specified by the reservation signal for each base station of each wireless communication group A wireless communication method characterized in that it is arbitrarily set within the range of the maximum possible period.

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