JP4008870B2 - Wireless packet communication device - Google Patents

Description

  The present invention relates to a wireless packet communication apparatus, and in particular, each wireless station performs carrier sense prior to data transmission and performs wireless packet communication while allowing packet collisions by autonomously determining whether transmission is possible. The present invention relates to a wireless packet communication device.

As a conventional representative wireless packet communication device related to the present invention, for example, a wireless LAN device defined by IEEE 802.11 is assumed. The specifications of IEEE 802.11 are described in detail in Non-Patent Document 1. In the following description, this rule is expressed as the IEEE 802.11 standard.
In the wireless packet communication system composed of a plurality of wireless stations, the operation when packet collision is avoided using the conventional wireless access control of the IEEE 802.11 standard will be described below.

In the IEEE 802.11 standard, CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is defined as an access control method in which a plurality of wireless stations transmit data while performing carrier sensing so that packet collision does not occur.
The collision avoidance operation by this CSMA / CA procedure will be described with reference to FIG. In the example of FIG. 14, it is assumed that data packets are transmitted and received between one radio base station # 201 and three radio terminal stations # 301 to # 303. 14, D1, D2, D3,... Represent data to be transmitted, and A1, A2, A3,... Represent acknowledgment (ACK) frames.

In the example of FIG. 14, first, the wireless terminal station # 301 transmits data D1 to the wireless base station # 201, and after receiving the ACK frame A1 for the data transmission, the wireless terminal station # 301, the wireless terminal station # 302, the wireless terminal Station # 303 waits until the DIFS period (Td) elapses.
At this time, a collision avoidance period (Contention Window: CW), which is a random time, is given to each of the wireless terminal stations # 301, # 302, and # 303. This collision avoidance period is obtained by multiplying the basic unit time (Slot Time) and a random number. In determining the collision avoidance period, as a whole rule among all radio stations including the radio base station, radio base stations and radio terminal stations having data packets to be transmitted have a certain range of integers. Generate randomly distributed random numbers. The obtained random number value is multiplied by the basic unit time (Slot Time) of the collision avoidance period to obtain the collision avoidance period (Tcw).

The wireless base station and each wireless terminal station start transmission after the collision avoidance period elapses unless the wireless medium becomes busy.
In FIG. 14, the collision avoidance period is indicated by a numerical value indicating the number of basic unit times (Slot Time). That is, the collision avoidance period of the wireless terminal station # 301 when transmitting the data D1 is determined to be 2 × (Slot Time), and the collision avoidance period of the wireless terminal station # 302 is determined to be 6 × (Slot Time). The collision avoidance period of the terminal station # 303 is set to 5 × (Slot Time).

In this case, since the collision avoidance period Tcw of the wireless terminal station # 301 is shorter than those of the other wireless terminal stations # 302 and # 303, the wireless terminal station after the collision avoidance period (2 slot time) of the wireless terminal station # 301 has elapsed. Data D1 is transmitted from # 301 to radio base station # 201. At this time, data transmission of the wireless terminal station # 302 and the wireless terminal station # 303 is postponed.
Further, the transmission of the ACK frame A1 to the wireless terminal station # 301 is terminated, and after the DIFS period has elapsed, the Tcw in the back-off of the wireless terminal station # 303 is now the shortest, so that the wireless terminal station # 303 transmits the data. It becomes possible. That is, the random back-off, which is the waiting time after the DIFS has elapsed, is an operation for probabilistically reducing the collision of data packets between wireless stations that intend to start transmission at the same time. The waiting time corresponds to the collision avoidance period.

In other words, the probability that the wireless base station and the wireless terminal station having data to be transmitted simultaneously transmit data by waiting for different collision avoidance periods obtained by random numbers before data transmission is reduced. To do. Thereby, the improvement of the throughput of the whole wireless communication system can be expected.
By the way, in the packet collision avoidance method by random backoff defined in IEEE802.11, the difference in random number generation range greatly affects the collision probability. In other words, since each wireless terminal station and wireless base station autonomously generate random numbers in the back-off control, the probability that the same number will be generated at the same time as the random number generation range is small increases, resulting in packet collisions. Increases the probability of getting up.

In CSMA / CA, when a packet collision occurs, the wireless terminal station and wireless base station that transmitted the packet expand the range in which random numbers can be generated according to the binary exponent backoff procedure, and at the time of the next data transmission Avoid collisions of packets again. The binary exponent back-off procedure here is a procedure for changing the maximum value CW of the random number to be generated according to the number of collisions n. Specifically, the maximum value CW is changed according to the following equation.
CW = 2 ⁿ × (CWmin + 1) −1)
CWmin: Maximum Random Number Generated at New Data Transmission In CSMA / CA control, an operation example for avoiding packet collision when a plurality of wireless stations simultaneously generate the same random value is shown in FIG. ing.

In this example, first, the wireless terminal station # 301 transmits data D1 to the wireless base station # 201, and after receiving the ACK frame A1 for the data transmission, the wireless terminal station # 302 and the wireless terminal station # 303 pass between DIFSs. Wait until. Thereafter, the wireless terminal stations # 302 and # 303 enter back-off control.
In this example, the wireless terminal stations # 302 and # 303 generate random numbers from integers uniformly distributed between 0 and 15, respectively, and generate the same value 3 for both. As a result, the wireless terminal stations # 302 and # 303 simultaneously transmit data packets D2 and D3, and packet collision occurs.

As a result, in the next collision avoidance period (CW), the radio terminal stations # 302 and # 303 double the random number generation range, generate random numbers from integers uniformly distributed between 0 and 31, Get 5,10. As a result, the wireless terminal stations # 302 and # 303 can complete the data transmission without causing a collision at the next data transmission.
That is, in the conventional CSMA / CA, in order to prevent a collision caused by generating the same random number value, the range of random number generation is expanded in the next back-off control, and a plurality of terminals generate the same value. And the collision probability is reduced.

  A radio station to which the CSMA / CA procedure is applied performs carrier sense before data packet transmission, and transmits data packets after confirming that the surrounding radio stations are not transmitting data. For this reason, for example, as shown in FIG. 16, when an obstacle or the like exists between the wireless terminal stations # 301, # 302 and the wireless terminal station # 303 and the wireless terminal station # 303 cannot perform carrier sense, In 303, since it is determined that the wireless channel is free and the data packet is transmitted, a packet collision occurs.

This phenomenon is called a hidden terminal problem and is a big problem in the CSMA / CA procedure. Therefore, in the IEEE 802.11 standard, an RTS / CTS procedure is provided as a method for solving the hidden terminal problem, and the operation when the hidden terminal problem is solved using the RTS / CTS frame is described with reference to FIG. While explaining.
In the example of FIG. 17, as in the case of FIGS. 14 and 15, the wireless terminal station # 301 that intends to transmit a data packet performs carrier sense in the DIFS period, and after the subsequent back-off period ends, Start sending. Here, before data packet transmission, the wireless terminal station # 301 transmits an RTS packet to the wireless base station # 201.

The RTS packet includes information called NAV indicating a period during which other terminals should not transmit data. Therefore, the NAV is set for the wireless terminal station # 302 that has received the RTS packet, and data cannot be transmitted during this period (NAV period).
Thereafter, the wireless base station # 201 that has received the RTS packet from the wireless terminal station # 301 transmits the CTS packet to the wireless terminal station # 301. In this CTS packet, information of a period during which other terminals should not transmit data is stored, and the wireless terminal station # 303 that has not received the RTS packet can also receive the CTS packet. , NAV is set, and a data transmission standby state is entered. The wireless terminal station # 301 transmits a data packet after receiving the CTS.

Note that since the wireless terminal stations # 301 and # 303 are in a hidden terminal relationship, RTS packets may collide with each other. However, since the size of the RTS packet is 20 [Oct], which is sufficiently smaller than the data packet size, even when a collision occurs, the time for occupying the channel unnecessarily is short.
Therefore, in a situation where the hidden terminal problem is considered, each terminal first transmits an RTS packet before transmitting a data packet, confirms that the CTS packet has returned, and then transmits the data packet. Desirably, this allows reliable data communication.
“Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications”, IEEE std 802.11-1999

  As described above, in CSMA / CA defined by IEEE802.11, as shown in FIG. 14, the radio base station and the radio terminal station autonomously perform carrier sense and backoff control, thereby allowing each other to simultaneously transmit data. The probability of transmission is reduced. However, since each wireless terminal station and wireless base station autonomously generate random numbers in backoff control, the same numbers may be generated simultaneously as shown in FIG. 15, resulting in packet collisions. To do. When the number of terminals is small, the probability that a plurality of radio stations generate the same random number is small, but this probability increases as the number of terminals increases. As the number of terminals increases, a plurality of radio stations generate the same random number, and the collision probability of data packets increases, so that a decrease in radio channel throughput becomes a problem.

  On the other hand, the RTS / CTS procedure that can be used to solve the hidden terminal problem is to be applied when the size of a data packet to be transmitted is a certain value (RTSThreshold) or more in the IEEE 802.11 standard. Yes. For this reason, when the size of the data to be transmitted is below a certain value, the RTS / CTS procedure is not applied even if there is a high possibility that the radio channel is crowded and a collision occurs. The collision probability cannot be reduced.

  The present invention can transmit data packets when there are a large number of wireless stations that intend to transmit data packets and there is a large amount of transmission traffic, regardless of the size of the data to be transmitted and the presence of a hidden terminal problem. It is an object of the present invention to provide a wireless packet communication apparatus capable of improving data throughput by transmitting a short packet in advance and minimizing useless channel utilization when packets collide.

The first invention (Claim 1 ) detects the presence or absence of radio waves on the radio channel to be used and the intensity of the received radio waves prior to data transmission, and confirms that there are no radio waves radiated from other radio stations or identifying whether the data transmitted by autonomous control with determination, in a wireless packet communication apparatus for performing radio packet communication by allowing a packet collision, check the presence or absence of radio waves on the wireless channel during a predetermined time T The busy period measuring means for integrating the busy period when the radio channel is busy when a radio wave on the wireless channel is detected, the transmission mode determining timer for managing the time T, and the transmission mode determining timer are referred to and acquires the busy period Tall the previous SL busy period measuring means is measured every time T is compared with a predetermined threshold value T1, busy at M-th point of the control period of time T When the period Tall exceeds the threshold value T1, at the (M + 1) th time point of the control period of time T, a control packet having a size smaller than that of the data packet is transmitted prior to the transmission of the data packet. Data packet transmitting means for transmitting a data packet after receiving a response packet to the packet from another wireless station is provided.

In the first invention, when the busy period Tall is acquired at every time T and the Tall exceeds the threshold value T1, a small control packet is transmitted. Therefore, when the data size of the data packet to be transmitted is small However, when there is a high possibility that a packet collision will occur, as in the case of using the RTS / CTS procedure, it is possible to improve the throughput by reducing the time for occupying the channel wastefully. As the control packet, a packet having the same configuration as the RTS frame and CTS frame in the RTS / CTS procedure may be used.

A second invention (Claim 2 ) is composed of a radio base station connected to a predetermined wired network and at least one radio terminal station that is dependent on the radio base station and performs radio packet communication with the radio base station. The radio base station and all radio terminal stations detect the presence of radio waves on the radio channel to be used and the strength of received radio waves before data transmission, and there are no radio waves emitted from other radio stations. In a wireless packet communication apparatus that performs wireless packet communication by identifying whether data transmission is possible by autonomous control while confirming or determining the packet, and allowing packet collision, the wireless base station receives a packet Obtains the source address and data size of the packet, and if the received packet is addressed to its own station, stores it in a predetermined receive buffer. Packet receiving means, and the packet transmission source address and data size information acquired by the packet receiving means, and the data amount information received within a predetermined time T is distinguished and held for each transmission source address. Based on the received data amount table, and the information held in the received data amount table, the total value Ptbl of the data amount received within the period of time T and the total number Ntbl of wireless stations that transmitted data packets are measured values. The received data amount measuring means to obtain, the transmission mode determining timer for managing the time T, and the transmission mode determining timer are referred to, and the measured value is periodically acquired from the received data amount measuring means at each time T. The measured value Ntbl exceeds N1 and the measured value Ptbl is P at the Mth time point in the control cycle of time T. Is exceeded, at the (M + 1) th time point of the control period of time T, a first control packet having a size smaller than that of the data packet is transmitted prior to the transmission of the data packet. First data packet transmission means for transmitting a data packet after receiving a response packet to the control packet from another wireless station, and the wireless terminal station has a prescribed size of the wireless base station as a communication partner Prior to transmission of the following data packet, when recognizing that the first control packet having a smaller size than the data packet is transmitted, the data packet is transmitted from the radio terminal station to the radio base station. After the second control packet having a small size is transmitted prior to the transmission of the data packet and the response packet for the second control packet is received Characterized in that a second data packet transmitting means for transmitting the Tapaketto.

In the second invention, as in the first invention, the total amount Ptbl of data received every predetermined time T and the total number Ntbl of wireless stations that transmitted data packets are obtained, and Ntbl exceeds the threshold value N1, and When Ptbl exceeds the threshold value P1, the first control packet having a small size is transmitted. Therefore, even when the data size of the data packet to be transmitted is small, there is a high possibility that a packet collision will occur. In this case, as in the case of using the RTS / CTS procedure, it is possible to improve the throughput by reducing the time for occupying the channel wastefully.

The first control packet may be a packet having the same configuration as the RTS frame and CTS frame in the RTS / CTS procedure. In the second invention, when the radio base station transmits the first control packet, the radio terminal station under the radio base station also transmits the second control packet. The operation of the terminal station can be controlled on the radio base station side.

A third invention (Claim 3 ) is composed of a radio base station connected to a predetermined wired network and at least one radio terminal station that is dependent on the radio base station and performs radio packet communication with the radio base station. The radio base station and all radio terminal stations detect the presence of radio waves on the radio channel to be used and the strength of received radio waves before data transmission, and there are no radio waves emitted from other radio stations. the identifying whether the data sent by check or discrimination while autonomous control, in a wireless packet communication apparatus for performing radio packet communication by allowing a packet collision, wherein the radio base station, during a predetermined time T the presence or absence of radio waves on the wireless channel check, a busy period measurement means for integrating a busy period radio channel is busy when it detects a radio wave on the wireless channel, A transmission mode determination timer that manages the time T, by referring to the transmission mode determination timer acquires the busy period Tall the previous SL busy period measuring means is measured every time T is compared with a predetermined threshold value T1 When the busy period Tall exceeds the threshold value T1 at the Mth time point of the control period of time T, the data packet is transmitted prior to the transmission of the data packet at the (M + 1) th time point of the control period of time T. A first data packet transmitting means for transmitting a data packet after transmitting a first control packet smaller than the first control packet and receiving a response packet to the first control packet from another wireless station; The wireless terminal station includes a first control parameter having a size smaller than that of the data packet prior to transmission of a data packet having a size equal to or less than a predetermined size by the wireless base station as a communication partner. Before transmitting the data packet, the second control packet having a size smaller than the data packet is transmitted from the wireless terminal station to the wireless base station. A second data packet transmission means is provided for transmitting a data packet after receiving a response packet to the second control packet.

In the third invention, as in the first invention, the busy period Tall is acquired every time T, and when Tall exceeds the threshold value T1, a small control packet is transmitted. Even if the data size of the data packet is small, if there is a high possibility of packet collision, the throughput will be improved by reducing the time it takes to occupy the channel as in the case of using the RTS / CTS procedure. can do.

As the control packet, a packet having the same configuration as the RTS frame and CTS frame in the RTS / CTS procedure may be used. In the third invention, when the radio base station transmits the first control packet, the subordinate radio terminal station also transmits the second control packet. The operation of the terminal station can be controlled on the radio base station side.

According to a fourth aspect of the present invention (invention 4 ), in the wireless packet communication apparatus of claim 2 or claim 3 , the first data packet transmitting means is required to transmit a second control packet. When it is necessary to notify the wireless terminal station, the presence or absence of a data packet on the transmission buffer is confirmed. If the data packet to be transmitted does not exist in the transmission buffer, the first control packet is designated as a data packet. Is characterized by being transmitted independently regardless.

In the fourth aspect of the invention, even if no data packet exists on the transmission buffer of the radio base station, the first control packet is transmitted alone, so that it waits for the data packet to appear on the transmission buffer. Therefore, it is possible to notify the radio terminal station that the second control packet needs to be transmitted from the radio base station, and control delays can be suppressed.

In the first invention, each wireless station calculates the sum total of the periods when the channels are busy within a certain time, determines whether the channels are congested based on the information of the sum total of the pizy periods, If it is determined that the data is busy, a control packet is transmitted prior to data packet transmission. For this reason, when it is thought that many collisions between packets occur, efficient data transfer can be performed.

In the second invention, only the radio base station executes the same control as in the first invention, and the subordinate radio terminal station has detected that the radio base station is transmitting a control packet prior to data packet transmission. In response to this, a control packet with a small size is transmitted in the same manner as the radio base station. That is, the base station determines whether or not to transmit the control packet prior to the transmission of the data packet. When each wireless terminal station autonomously determines whether or not transmission of a control packet is necessary, there is a high possibility of erroneous calculation and determination in a situation where a hidden terminal problem occurs as shown in FIG. Such malfunction is eliminated by the second invention. Therefore, the data transfer efficiency of the entire system can be improved.

In the third invention, only the radio base station executes the same control as in the first invention, and the subordinate radio terminal station has detected that the radio base station is transmitting a control packet prior to data packet transmission. In response to this, a control packet with a small size is transmitted in the same manner as the radio base station. That is, the base station determines whether or not to transmit the control packet prior to the transmission of the data packet. When each wireless terminal station autonomously determines whether or not transmission of a control packet is necessary, there is a high possibility of erroneous calculation and determination in a situation where a hidden terminal problem occurs as shown in FIG. Such malfunction is eliminated by the third invention. Therefore, the data transfer efficiency of the entire system can be improved.

In the fourth aspect of the invention, since the control packet can be transmitted even when there is no data to be transmitted to the radio base station, it is necessary to transmit the control packet prior to the data packet transmission. It is possible to promptly notify the subordinate radio terminal station from the station.

(First embodiment : Reference example )
One embodiment of a wireless packet communication apparatus of the present invention will be described with reference to FIGS . This form is a reference example.
FIG. 1 is a flowchart showing the main operation (1) of the radio station used in this embodiment. FIG. 2 is a flowchart showing the main operation (2) of the radio station used in this embodiment. FIG. 3 is a block diagram showing a configuration example of a radio station used in this embodiment. FIG. 4 is a time chart showing an example of data transmission operation between wireless stations of this form. In FIG. 3, solid arrows indicate the flow of received signals and transmission signals, and dotted arrows indicate the flow of control signals.

In this embodiment, by using a radio station configured as shown in FIG. 3, it is assumed that transmitting and receiving data packets over a wireless link with a plurality of radio stations.

  Referring to FIG. 3, the radio station includes a radio transmission / reception processing unit 110, an access control unit 120, an upper layer transmission / reception unit 130, and an antenna 140. Further, the access control unit 120 includes a packet reception unit 121, a reception buffer 122, a reception data amount measurement unit 123, a transmission mode determination timer 124, a reception data amount table 125, a data packet transmission unit 126, an ACK transmission unit 127, and a transmission buffer. 128 is provided. The main operation of the present invention is controlled by the access control unit 120.

In the block diagram shown in FIG. 3 , only one antenna 140 and wireless transmission / reception processing unit 110 are described. However, a plurality of antennas are provided and wireless communication is performed using a plurality of wireless channels. Wireless communication may be performed by space-division multiplexing a plurality of signals on one wireless channel.
The data packets to be transmitted by the radio station are sequentially input from the upper layer transmitting / receiving unit 130 to the access control unit 120, temporarily held on the transmission buffer 128, and then transmitted according to the control of the data packet transmitting unit 126. The data is read from 128, subjected to processing such as modulation by the wireless transmission / reception processing unit 110, and transmitted as a wireless signal via the antenna 140.

  In addition, a signal such as a data packet transmitted as a radio signal from another radio station is received by the antenna 140 and subjected to processing such as demodulation by the radio transmission / reception processing unit 110, and the demodulated signal is received by the access control unit 120. Input to the unit 121. The packet receiving unit 121 examines the contents of the received packet and grasps the packet type, the packet data size, the destination identification information, the transmission source identification information, and the like.

  When this radio station receives a data packet addressed to itself, the data packet is output from the packet receiving unit 121, temporarily stored in the reception buffer 122, and output to the upper layer transmitting / receiving unit 130. In addition, when the data packet addressed to the own station is normally received, the ACK transmission unit 127 transmits the ACK packet to the transmission source of the data packet. This ACK packet is also subjected to processing such as modulation by the radio transmission / reception processing unit 110 and is transmitted as a radio signal from the antenna 140.

  The reception data amount measurement unit 123 measures the total reception data amount within a certain time and the number of terminals that have transmitted data. The transmission mode determination timer 124 manages the time of the control period T for determining the transmission mode. The received data amount table 125 stores information on the amount of data received by the packet receiving unit 121 within a certain period of time, for each packet transmission source terminal. The content of the received data amount table 125 is updated every control cycle T.

  The data packet transmission unit 126 identifies whether or not a predetermined condition described later is satisfied based on the content of the received data amount table 125. If the condition is satisfied, a predetermined control packet is transmitted prior to transmission of the data packet. (Short packet) is transmitted. This control packet is sufficiently smaller than the data packet and includes information for determining a data transmission prohibition period (NAV). This control packet is output from the transmission buffer 128 prior to transmission of the data packet, subjected to processing such as modulation by the wireless transmission / reception processing unit 110, and then transmitted as a wireless signal from the antenna 140.

The radio station shown in FIG. 3 performs the operations shown in FIGS. 1 and 2 under the control of the access control unit 120. The operation shown in FIGS. 1 and 2 will be described below.
In step S001, the count value of the transmission mode determination timer 124 (TM1) is cleared to 0, and then the count of this timer is started. In the next step S003, carrier sense is started. That is, the presence / absence of radio waves transmitted from other radio stations on the radio channel to be used is monitored.

In step S004, it is identified from the carrier sense result whether the channel is busy. If the channel is busy, the process proceeds from step S004 to step S005 in FIG. 2, and if the channel is idle, the process proceeds to step S015.
In step S005, it is identified whether or not a packet has been received. If a packet is received, the process proceeds from step S005 to step S006, and if no packet is received, the process proceeds to step S010.

  In step S006, the information contained in the received packet is checked, and the transmission source address Xn and data size Ln of this packet are acquired. In the next step S007, the same address as the transmission source address Xn acquired in step S006 is stored in the received data amount table 125 (TBL) with the terminal No. In step S008, the process proceeds to step S008. If it does not exist, the process proceeds to step S009.

In step S008, the same terminal No. as Xn on the received data amount table 125 (TBL). The data size Ln acquired this time is added to the received data amount associated with. In step S009, the transmission source address Xn acquired this time and the data size Ln corresponding thereto are added as new items on the reception data amount table 125 (TBL).
In step S010, it is identified whether or not the transmission mode determination timer 124 (TM1) has timed out. If timed out, the process proceeds to step S011, and if not timed out, the process returns to step S003.

In step S011, the information held in the reception data amount table 125 (TBL) is referred to, and the total number Ntbl (3 in the example of FIG. 3) of the address (terminal No.) and the total amount Ptbl of reception data (FIG. 3). In the example, Pa + Pb + Pc) is acquired, and Ntbl and Ptbl are respectively compared with predetermined thresholds N1 and P1.
If both the conditions (Ntbl ≧ N1) and (Ptbl ≧ P1) are satisfied, the process proceeds from step S010 to S013. Otherwise, the process proceeds to step S012. In step S013, “1” is set to the short packet transmission trigger St, and in step S012, “0” is set to the short packet transmission trigger St. The value of the short packet transmission trigger St is used to determine whether or not to transmit a control packet (short packet) having a smaller size prior to transmission of the data packet. In the next step S014, all the information recorded in the received data amount table 125 (TBL) is deleted. After this, the process returns to step S001.

  On the other hand, if it is detected in step S004 that the channel is empty based on the result of carrier sense, the process proceeds from step S004 to S015 to check whether the carrier sense end time has come. If the carrier sense end time has not been reached, the process returns to step S004. If the carrier sense end time has been reached, the process proceeds to step S016 to start backoff.

If the channel is busy after starting the backoff, the process proceeds from step S017 to S005. If the channel is idle until the backoff end time, the process proceeds to the data transmission procedure from step S018 to S019. .
In step S019, it is identified whether or not there is a data packet to be transmitted on the transmission buffer 128. If there is no data packet on the transmission buffer 128, the process proceeds to step S031, and if there is a data packet, the process proceeds to step S020. In step S031, it is identified whether the channel is busy. If the channel is busy, the process proceeds to step S005. If the channel is idle, the process returns to step S019.

In step S020, it is identified whether or not the value of the short packet transmission trigger St described above is “0”. When the value of St is “0”, the process proceeds to step S021, and when the value of St is “1”, the process proceeds to step S026.
In step S026, an RTS packet is transmitted. The RTS packet is a control packet having a size smaller than that of the data packet, and includes information on the data transmission prohibition period (NAV). In the next step S027, counting of the CTS timer (TM3) is started. The CTS timer is used to manage the time until receiving the CTS packet.

  In step S028, it is identified whether or not the CTS packet from the transmission destination of the RTS packet transmitted in step S026 has been received. The CTS packet is a control packet having a size smaller than that of the data packet, and includes information on the data transmission prohibition period (NAV). If a CTS packet has been received, the process proceeds to step S021, and if no CTS packet has been received, the process proceeds to step S029 to identify whether the CTS timer (TM3) has timed out.

If the CTS packet is received before the CTS timer (TM3) times out, the data packet is transmitted in step S021. After transmitting this data packet, the process proceeds to step S022, and the received data amount corresponding to the own station in the received data amount table 125 is updated by the size of the transmitted data packet.
In the next step S023, the ACK timer (TM2) is started. In step S024, it is identified whether or not an ACK packet has been received from the destination terminal of the data packet transmitted in S021. If an ACK packet is received, the process proceeds to step S030. If not received, the process proceeds to S025 to check whether the ACK timer (TM2) has timed out.

  If an ACK packet is received from the destination terminal before the ACK timer (TM2) times out, the ACK timer (TM2) and CTS timer (TM3) are reset in step S030, and the process proceeds to step S010. If the CTS timer (TM3) times out in step S029 or if the ACK timer (TM2) times out in step S024, the process proceeds to step S030, and the ACK timer (TM2) and CTS timer (TM3) are reset. To do.

An example of an operation when data is transmitted between wireless stations in a system configured using four wireless stations shown in FIG. 3 will be described with reference to FIG. In FIG. 4, D1, D2, D3, and D4 represent data packets, A1, A2, A3, and A4 represent ACK packets, R4 represents an RTS packet, and C4 represents a CTS packet.
The control in each radio station is repeated periodically every time (T) managed by the transmission mode determination timer 124.

  In the example of FIG. 4, in the M-th control cycle, the radio stations # 101 to # 104 perform back-off control after performing carrier sense for a predetermined time Td according to the CSMA / CA procedure, respectively. . That is, it waits for the back-off period Tb determined by the random number. By this back-off control, the radio station having the smallest random number value transmits the data packet.

  In the example of FIG. 4, the data packets D1, D2, D3 of the Mth control cycle are transmitted by the same procedure as in the conventional CSMA / CA. Then, each of the wireless stations # 101 to # 104 received within the period (T) of the Mth control cycle including the data packet whose destination is other than the own station when the Mth control cycle ends. The amount of data (Ptbl) is calculated. At the same time, the number (Ntbl) of wireless stations that have transmitted data within the period (T) of the Mth control cycle is calculated.

If the received data amount (Ptbl) exceeds the threshold value P1 bit and the number of wireless stations (Ntbl) exceeds the threshold value N1, the data packet is transmitted at the next M + 1 control cycle. RTS packet is transmitted prior to transmission of.
That is, in the example of FIG. 4, in the calculation in the M-th cycle, the radio stations # 101 to # 104 respectively determine that the RTS packet needs to be transmitted in the next cycle, and the first in the M + 1-th cycle. Radio station # 104 that transmits data transmits RTS packet R4 to an arbitrary address (radio station # 103 in the case of FIG. 4) prior to transmission of data packet D4, and receives the CTS packet from radio station # 103. If received, the data packet D4 is transmitted.

  Therefore, even when the data size of the data packet to be transmitted is small, if there is a high possibility of packet collision as in the case of heavy traffic, the RTS packet is transmitted prior to the transmission of the data packet. The CTS packet is transmitted in response to the RTS packet. As a result, a data transmission prohibition period (NAV) can be allocated, and the influence of a decrease in channel utilization efficiency due to packet collision can be minimized.

(Second Embodiment)
One embodiment of the wireless packet communication device of the present invention will be described with reference to FIGS. This form corresponds to a specific example of claim 1 .
FIG. 5 is a block diagram showing a configuration example of a radio station used in this embodiment. FIG. 6 is a flowchart showing the main operation (1) of the radio station used in this embodiment. FIG. 7 is a flowchart showing the main operation (2) of the radio station used in this embodiment. FIG. 8 is a time chart showing an example of data transmission operation between wireless stations of this form. In FIG. 5, solid arrows indicate the flow of reception signals and transmission signals, and dotted arrows indicate the flow of control signals.

This form is a modification of the first embodiment. In each figure, elements and steps corresponding to those in the first embodiment are denoted by the same reference numerals.
In this embodiment, the busy period measuring means, the transmission mode determining timer, and the data packet transmitting means of claim 1 correspond to the busy period measuring section 223, the transmission mode determining timer 124, and the data packet transmitting section 126B, respectively.

In this embodiment, it is assumed that data packets are transmitted and received between a plurality of radio stations via a radio channel using a radio station having the configuration shown in FIG.
Referring to FIG. 5, the radio station includes a radio transmission / reception processing unit 110, an access control unit 120B, an upper layer transmission / reception unit 130, and an antenna 140. The access controller 120B includes a packet receiver 121, a reception buffer 122, a transmission mode determination timer 124, a data packet transmission unit 126B, an ACK transmission unit 127, a transmission buffer 128, a busy period measurement unit 223, a carrier detection unit 225, and A busy period measuring timer 226 is provided. The main operation of the present invention is controlled by the access control unit 120B.

In the block diagram shown in FIG. 5, only one antenna 140 and one wireless transmission / reception processing unit 110 are described. However, a plurality of antennas are provided and wireless communication is performed using a plurality of wireless channels. Wireless communication may be performed by space-division multiplexing a plurality of signals on one wireless channel.
The busy period measuring unit 223 is provided for measuring a period during which a wireless channel to be used is busy. The carrier detection unit 225 monitors the presence / absence of a received radio wave (carrier) on the radio channel scheduled to be used, and identifies whether the channel is busy. Based on the measurement result of the busy period measurement unit 223, the data packet transmission unit 126B determines whether to transmit a control packet having a smaller size prior to the transmission of the data packet.

  In this embodiment, a small control packet (short packet) is transmitted as in the first embodiment, but the method is different from that in the first embodiment until it is determined whether or not to transmit this control packet. ing. The procedure for transmitting a data packet after this determination is the same as in the first embodiment. That is, the procedures in steps S015 to S030 in FIGS. 6 and 7 are almost the same as those in the first embodiment. The following description is omitted about the same part.

  The radio station shown in FIG. 5 starts processing from step S001B in FIG. In step S001B, the value (T) of the transmission mode determination timer 124 is reset to 0, the value (Tbusy) of the busy period measurement timer 226 is reset to 0, and the accumulated value (Tall) of the busy period is reset to 0. The transmission mode determination timer 124 (TM1) is started. The busy period integrated value (Tall) is used to hold the integrated value of the busy period within a certain period (T).

  As in the first embodiment, carrier sense is started in step S003, and whether or not the channel is busy is identified in the next step S004. If it is determined in step S004 that the channel is busy, the busy period measurement timer 226 (TM4) is started in step S105 in FIG. 7, and the processes in steps S105 and S106 are repeated until the channel becomes idle. That is, the time Tbusy until the channel changes to idle is measured by the busy period measuring timer 226.

When the channel changes to idle, the process proceeds from step S106 to S107, the busy period measuring timer 226 (TM4) is stopped, and the time Tbusy is acquired. In the next step S108, the time Tbusy acquired this time is added to the integrated value (Tall) of the busy period, and the time Tbusy is reset to zero.
In step S010, it is determined whether or not the transmission mode determination timer 124 (TM1) has timed out. If timed out, the process proceeds to the next step S011B. If not timed out, the process returns to step S003. In step S011B, the integrated value (Tall) of the busy period is compared with a predetermined threshold value T1. If the condition of (Tall ≧ T1) is satisfied, the process proceeds to step S013. Otherwise, the process proceeds to step S012.

That is, when the condition of (Tall ≧ T1) is satisfied, the short packet transmission trigger St is set to “1”, and when the condition is not satisfied, St is set to “0”.
An example of operation when data is transmitted between wireless stations in a system configured using four wireless stations shown in FIG. 5 will be described with reference to FIG. In FIG. 8, D1, D2, D3, and D4 represent data packets, A1, A2, A3, and A4 represent ACK packets, R4 represents an RTS packet, and C4 represents a CTS packet. Tx1, Tx2, and Tx3 indicate periods during which the channel is busy.

The control in each radio station is repeated periodically every time (T) managed by the transmission mode determination timer 124. Each wireless station measures the times Tx1, Tx2, and Tx3 when the channel is busy, including the transmission time of the data packet transmitted by itself every fixed period.
In the example of FIG. 8, the result of calculating the sum of the busy periods Tx1, Tx2, and Tx3 in the Mth control cycle exceeds the threshold value T1, and therefore, in the M + 1th control cycle, the radio stations # 101 to # 104 Transmits an RTS packet prior to the transmission of the data packet.

That is, when the wireless station # 104 transmits the RTS packet R4 to an arbitrary address (wireless station # 103 in the example of FIG. 8) and receives the CTS packet from the wireless station # 103 prior to transmission of the data packet D4. Data packet D4 is transmitted.
(Third embodiment)
One embodiment of the wireless packet communication device of the present invention will be described with reference to FIGS. This form corresponds to a specific example of claims 2 to 4 .
FIG. 9 is a block diagram showing a configuration example of a wireless terminal station used in this embodiment. FIG. 10 is a flowchart showing the main operation (1) of the wireless terminal station used in this embodiment. FIG. 11 is a flowchart showing the main operation (2) of the wireless terminal station used in this embodiment. FIG. 12 is a time chart showing a data transmission operation example (1) between wireless stations of this embodiment. FIG. 13 is a time chart showing a data transmission operation example (2) between wireless stations of this embodiment. In FIG. 9, solid arrows indicate the flow of reception signals and transmission signals, and dotted arrows indicate the flow of control signals.

In this embodiment, the packet receiving means of claim 2, received data volume table, the reception data amount measuring means, the transmission mode decision timer, the first data packet transmitting means and the second data packet transmission means, each packet receiver 121, a received data amount table 125, a received data amount measuring unit 123, a transmission mode determining timer 124, a data packet transmitting unit 126, and a data packet transmitting unit 126C. Also, busy period measuring means according to claim 3, transmission mode determination timer, the first data packet transmitting means and the second data packet transmission means, busy period measuring unit 223, respectively, the transmission mode decision timer 124, the data packet It corresponds to the transmission unit 126B and the data packet transmission unit 126C.

  In this mode, a communication system is configured using one radio base station and a plurality of radio terminal stations connected to a predetermined wired communication network, and data packets are transmitted between the radio base station and the radio terminal stations. It is assumed that this is done. As the radio base station, the radio station as described in the first embodiment or the radio station as described in the second embodiment is used. Further, the wireless terminal station is configured as shown in FIG. 9, and a wireless station that performs control as shown in FIGS. 10 and 11 is used. 9 to 11, elements and steps corresponding to those in the first embodiment or the second embodiment are denoted by the same reference numerals.

  Referring to FIG. 9, the wireless terminal station includes a wireless transmission / reception processing unit 110, an access control unit 120C, an upper layer transmission / reception unit 130, and an antenna 140. Further, the access control unit 120C is provided with a packet reception unit 121, a reception buffer 122, a data packet transmission unit 126C, an ACK transmission unit 127, and a transmission buffer 128. Main operations in the wireless terminal station of the present invention are controlled by the access control unit 120C.

In the block diagram shown in FIG. 9, only one antenna 140 and one wireless transmission / reception processing unit 110 are described. However, a plurality of antennas are provided and wireless communication is performed using a plurality of wireless channels. Wireless communication may be performed by space-division multiplexing a plurality of signals on a wireless channel.
The data packet transmission unit 126C determines whether or not the wireless terminal station transmits a small control packet prior to transmission of the data packet, but the data packet transmission unit 126C does not perform autonomous control and Operates according to instructions from the station. That is, when the data packet transmission unit 126C detects that a control packet having a size smaller than that of the data packet is transmitted prior to transmission of the data packet having a predetermined size or less, the local station also transmits the control packet. Consider it necessary.

Next, the operation of the wireless terminal station will be described with reference to FIGS. Note that steps S015 to S031 in FIGS. 10 and 11 are the same as those in the first embodiment except that a part of them is omitted. Different parts from the first embodiment will be described below.
The wireless terminal station in FIG. 9 starts carrier sense in step S003, and identifies whether the channel is busy in step S004. If the channel is busy, the process proceeds from step S004 to step S005 in FIG. 11 to identify whether or not a packet from another wireless station has been received. If the packet cannot be received, the process returns to step S003. If the packet has been received, the process proceeds to step S204.

  In step S204, the contents of the received packet are examined to acquire the packet source address Xn. In the next step S205, it is checked whether or not the transmission source address Xn acquired in S204 matches the address assigned to the radio base station. If the transmission source of the received packet is a radio base station, the process proceeds to step S206. If not, the process returns to step S003.

  In step S206, the contents of the received packet are examined to identify whether the type is an RTS packet. If an RTS packet is received, the process proceeds to step S207. If any other packet is received, the process proceeds to step S209. In step S207, it is determined whether or not the size of the data packet following the RTS packet is equal to or smaller than a threshold value (RTSThreshold). If it is equal to or smaller, “1” is set to the short packet transmission trigger St in step S208. If it exceeds, the process proceeds to step S209 and "0" is set to the short packet transmission trigger St.

Therefore, this wireless terminal station only when it detects that the wireless base station is transmitting a control packet having a size smaller than the data packet prior to transmission of the data packet having a specified size (RTSThreshold) or less. The own station also transmits a small RTS packet for control according to the short packet transmission trigger St.
FIG. 12 shows an operation example when communication is performed between the radio base station # 201 configured by the radio stations of the first embodiment or the second embodiment and the three radio terminal stations # 301 to # 303. Will be described with reference to FIG.

In the example of FIG. 12, the radio base station # 201 receives the data packet D1 from the subordinate radio terminal station # 301 in the M-th cycle, and RTS / CTS at the time of data packet transmission in the M + 1-th cycle from this reception result Determines whether the procedure should be applied.
When the radio station of the first embodiment is adopted as the radio base station # 201, the radio base station # 201 has a number Ntbl of terminals that transmitted data packets in the M-th cycle of N1 or more, In addition, only when the transmission data amount Ptbl from the subordinate radio terminal stations # 301 to # 303 is P1 or more, the RTS / CTS procedure is applied at the time of data packet transmission in the M + 1th cycle.

In addition, when the radio station of the second embodiment is adopted as the radio base station # 201, the radio base station # 201 has a sum total Tall of times when the channel becomes pid in the M-th cycle exceeds T1. Only in the case, the RTS / CTS procedure is applied at the time of data packet transmission in the (M + 1) th cycle.
In the example of FIG. 12, in the (M + 1) th cycle, the radio base station # 201 transmits the RTS packet R2 prior to the data packet D2, and the size Td2 of the data packet D2 is equal to or less than “RTSThreshold”. For this reason, each of the radio terminal stations # 301 to # 303 detects the RTS packet R2 transmitted from the radio base station # 201 in the M + 1th cycle, and recognizes that the RTS packet should be transmitted from the own station.

For this reason, when the wireless terminal station # 302 transmits the data packet D3 in the (M + 1) th cycle, the RTS packet R3 is transmitted to the wireless base station # 201 prior to the transmission of the data packet D3. In this case, the radio base station # 201 transmits a CTS packet to the radio terminal station # 302. The wireless terminal station # 302 transmits the data packet D3 after receiving the CTS packet C3.
Next, an operation example shown in FIG. 13 will be described. This operation example is a modification of FIG. In the operation example of FIG. 12, since it is assumed that the RTS packet is transmitted earlier than the transmission timing based on the transmission timing of the data packet, the data packet to be transmitted does not exist in the transmission buffer of the own station. In some cases, no RTS packet is transmitted. However, since the wireless terminal station does not perform autonomous control in this form, when the wireless base station detects that the wireless terminal station should transmit the RTS packet, this is performed as soon as possible. It is desirable to notify.

  Therefore, in the operation example of FIG. 13, when the radio base station determines that the RTS packet should be transmitted, if the data packet to be transmitted does not exist in the transmission buffer of the radio base station, Irrelevantly transmits the RTS packet R1 alone. Thereby, the radio base station can promptly notify the subordinate radio terminal station that it is necessary to transmit the RTS packet before transmitting the data packet.

  In the RTS packet to be transmitted, the time until the return CTS packet is transmitted is described as the value of NAV, and after the wireless terminal station # 301 transmits the CTS packet to the wireless base station # 201, The NAV set for all the wireless terminal stations is canceled, and the wireless terminal stations # 301 to # 303 apply the RTS / CTS procedure at the subsequent data packet transmission in the M + 1th cycle.

  In the operation example of FIG. 13, if the data packet to be transmitted does not exist in the buffer, the radio base station only exchanges the RTS / CTS frame and does not perform subsequent data packet transmission. After transmitting and receiving the CTS frame, a new short packet having no data information may be generated and transmitted to the destination of the RTS frame. The above “short packet without data information” is a data packet called a data type “Null Function” defined by the IEEE 802.11 standard. By using this “Null Function” data, the IEEE 802.11 standard is used. Without changing, the radio base station can notify the subordinate radio terminal that RTS packet transmission is required before data packet transmission.

It is a flowchart which shows the main operation | movement (1) of the radio station used by 1st Embodiment. It is a flowchart which shows the main operation | movement (2) of the radio station used by 1st Embodiment. It is a block diagram which shows the structural example of the radio station used by 1st Embodiment. It is a time chart which shows the data transmission operation example between the radio stations of 1st Embodiment. It is a block diagram which shows the structural example of the radio station used by 2nd Embodiment. It is a flowchart which shows the main operation | movement (1) of the radio station used by 2nd Embodiment. It is a flowchart which shows the main operation | movement (2) of the radio station used by 2nd Embodiment. It is a time chart which shows the data transmission operation example between the radio stations of 2nd Embodiment. It is a block diagram which shows the structural example of the radio | wireless terminal station used by 3rd Embodiment. It is a flowchart which shows main operation | movement (1) of the radio | wireless terminal station used by 3rd Embodiment. It is a flowchart which shows main operation | movement (2) of the radio | wireless terminal station used by 3rd Embodiment. It is a time chart which shows the data transmission operation example (1) between the radio stations of 3rd Embodiment. It is a time chart which shows the data transmission operation example (2) between the radio stations of 3rd Embodiment. It is a time chart which shows the example of the collision avoidance operation | movement by a CSMA / CA procedure. It is a time chart which shows the example of the collision avoidance operation | movement by a binary exponential backoff procedure. It is a block diagram which shows the structural example of the system which a hidden terminal problem arises. It is a time chart which shows the conventional control using an RTS / CTS frame.

Explanation of symbols

DESCRIPTION OF SYMBOLS 110 Radio | wireless transmission / reception processing part 120,120B Access control part 121 Packet receiving part 122 Reception buffer 123 Received data amount measuring part 124 Transmission mode determination timer 125 Received data amount table 126 Data packet transmitting part 127 ACK transmitting part 128 Transmission buffer 130 Upper layer Transmission / reception unit 140 Antenna 223 Busy period measurement unit 225 Carrier detection unit 226 Busy period measurement timer

Claims (4)

Prior to data transmission, the presence or absence of radio waves on the wireless channel to be used and the strength of received radio waves are detected, and data transmission by autonomous control is performed while confirming or determining that there are no radio waves emitted from other radio stations. In a wireless packet communication device that performs wireless packet communication by identifying whether or not to allow packet collision,
The presence or absence of radio waves on the wireless channel during a predetermined time T Check, a busy period measurement means for integrating a busy period radio channel is busy when it detects a radio wave on the wireless channel,
A transmission mode determination timer for managing the time T;
Referring to the transmission mode determination timer acquires the busy period Tall measured previous SL busy period measuring means every time T is compared with a predetermined threshold value T1, busy at the time of the M-th control period of time T When the period Tall exceeds the threshold value T1, at the (M + 1) th time point of the control period of time T, a control packet having a size smaller than that of the data packet is transmitted prior to the transmission of the data packet. A wireless packet communication apparatus, comprising: a data packet transmission unit configured to transmit a data packet after receiving a response packet to the packet from another wireless station. A radio base station connected to a predetermined wired network and at least one radio terminal station that is dependent on the radio base station and performs radio packet communication with the radio base station, the radio base station and all radio terminals Prior to data transmission, the station detects the presence of radio waves on the wireless channel to be used and the intensity of received radio waves, and performs autonomous control while confirming or determining that there are no radio waves emitted from other radio stations. In a wireless packet communication device that identifies whether data transmission is possible and performs wireless packet communication by allowing packet collision,
The radio base station includes
When receiving a packet, obtain the source address and data size of the packet, and if the received packet is addressed to its own station, packet receiving means for storing it in a predetermined reception buffer;
A received data amount table for managing information on the transmission source address and data size of the packet acquired by the packet receiving means, and distinguishing and holding information on the amount of data received within a predetermined time period T;
Based on information held in the received data amount table, a received data amount measurement that obtains, as measured values, a total amount Ptbl of data amounts received during the period of time T and a total number Ntbl of wireless stations that transmitted data packets. Means,
A transmission mode determination timer for managing the time T;
Referring to the transmission mode determining timer, the measured value is periodically acquired from the received data amount measuring means every time T and compared with predetermined threshold values N1 and P1, and the Mth time point of the control cycle of time T In the case where the measured value Ntbl exceeds N1 and the measured value Ptbl exceeds P1, at the (M + 1) th time point of the control period of time T, before the data packet is transmitted, A first data packet transmitting means for transmitting a data packet after transmitting a first control packet having a small size and receiving a response packet for the first control packet from another wireless station, Wireless terminal stations
When the wireless base station of the communication partner recognizes that the first control packet having a size smaller than the data packet is transmitted prior to the transmission of the data packet having a predetermined size or less, the wireless terminal station The second control packet having a size smaller than that of the data packet is transmitted to the radio base station prior to the transmission of the data packet, and the data packet is transmitted after receiving the response packet for the second control packet. A wireless packet communication apparatus, comprising: a second data packet transmission unit. A radio base station connected to a predetermined wired network and at least one radio terminal station that is dependent on the radio base station and performs radio packet communication with the radio base station, the radio base station and all radio terminals Prior to data transmission, the station detects the presence of radio waves on the wireless channel to be used and the intensity of received radio waves, and performs autonomous control while confirming or determining that there are no radio waves emitted from other radio stations. In a wireless packet communication device that identifies whether data transmission is possible and performs wireless packet communication by allowing packet collision,
The radio base station includes
The presence or absence of radio waves on the wireless channel during a predetermined time T Check, a busy period measurement means for integrating a busy period radio channel is busy when it detects a radio wave on the wireless channel,
A transmission mode determination timer for managing the time T;
Referring to the transmission mode determination timer acquires the busy period Tall measured previous SL busy period measuring means every time T is compared with a predetermined threshold value T1, busy at the time of the M-th control period of time T When the period Tall exceeds the threshold value T1, at the (M + 1) th time point of the control period of time T, a first control packet having a size smaller than that of the data packet is transmitted prior to transmission of the data packet. And a first data packet transmitting means for transmitting a data packet after receiving a response packet to the first control packet from another wireless station, and the wireless terminal station includes:
When the wireless base station of the communication partner recognizes that the first control packet having a size smaller than the data packet is transmitted prior to the transmission of the data packet having a predetermined size or less, the wireless terminal station A second control packet having a size smaller than that of the data packet is transmitted to the wireless base station prior to transmission of the data packet, and a data packet is transmitted after receiving a response packet to the second control packet. A wireless packet communication apparatus, comprising: a second data packet transmission unit.   4. The wireless packet communication apparatus according to claim 2, wherein the first data packet transmitting means needs to notify a subordinate wireless terminal station that the second control packet needs to be transmitted. In the case where the data packet on the transmission buffer is present, and if the data packet to be transmitted does not exist in the transmission buffer, the first control packet is transmitted independently from the data packet. Wireless packet communication device.

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