JP3993115B2 - Wireless packet transmission method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wireless packet transmission method used in a wireless communication system.
[0002]
[Prior art]
For example, in a wireless communication system such as a wireless LAN system, communication is performed by forming a wireless line between a wireless base station and one or a plurality of wireless terminals, or a wireless line is connected between a plurality of wireless terminals. Form and communicate.
When performing such communication, data is transmitted in the form of a wireless packet. In addition, when there are a plurality of transmitting stations, if they transmit radio packets at the same time, a communication failure occurs due to collision of the radio packets.
[0003]
Therefore, collision is conventionally avoided by control of CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance).
That is, when data to be transmitted is generated, the transmission source terminal performs carrier sense and checks whether other wireless terminals are transmitting using the same wireless line. If no transmission from another wireless terminal is detected for a certain time (Td), the wireless packet is transmitted.
[0004]
On the other hand, when receiving the wireless packet, the destination wireless terminal transmits a reception response (ACK) to the transmission source. When the transmission source terminal receives this reception response, a series of transmission sequences is completed.
Further, after the transmission at the transmission source terminal is completed, when there are still packets to be transmitted in the transmission buffer of the transmission source terminal, carrier sense is performed again. The carrier sense time in this case is determined by adding a time (random backoff time: Tb) randomly selected from a certain range to the certain time (Td). If no transmission from another wireless terminal is detected, the wireless packet is transmitted, and thereafter the same processing is repeated to transmit the packet.
[0005]
Therefore, for example, a signal appears on the wireless line at the timing shown in FIG.
By the way, in the wireless communication system as described above, there is also a wireless communication system that can select one transmission speed from a plurality of types of transmission speeds (bit rates) when transmitting a wireless packet.
[0006]
Also in such a wireless communication system, the length of time of carrier sense is determined to be the same as that of a general wireless communication system.
When wireless terminals that transmit at two different transmission speeds coexist, for example, a signal as shown in FIG. 8B appears on the wireless line.
[Non-Patent Document 1]
Fujita et al: “System evaluation based on throughput of broadband wireless LAN using CSMA / CA”, IEICE Technical Report, RCS 2002-168, October 2002.
[Non-Patent Document 2]
K. Saito. Et al. “An Effective Data Transfer Method By Integrating Priority Control into Multirate Mechanism For IEEE802.11 Wireless LANs,” VTC2002 Spring.
[0007]
[Problems to be solved by the invention]
As described above, in the conventional wireless packet transmission method, even when a wireless packet is transmitted at any transmission speed, every time one wireless packet is transmitted, the same time (Td or Td + Tb) is used. The carrier sense is executed, and the wireless packet is transmitted only when transmission from another wireless station is not detected.
[0008]
When the transmission speed is low, the time required for transmission of one wireless packet becomes long, but when the transmission speed is high, one wireless packet can be transmitted in a short time.
However, when the transmission speed is increased, the time required to transmit one wireless packet is shortened, but the ratio of waiting time (overhead) required for carrier sense increases, so the transmission efficiency deteriorates and the actual time per unit time is reduced. In reality, the amount of information transmission, that is, the effective transmission rate, is not improved much compared to the increase in transmission rate.
[0009]
In addition, when a wireless packet is transmitted by selecting one transmission speed from a plurality of transmission speeds, a wireless packet transmitted at a low speed and a wireless packet transmitted at a high speed are on the same wireless line. May be mixed.
In such a case, as shown in FIG. 8B, a low-speed wireless packet occupies a wireless line for a longer time than a high-speed wireless packet. It is necessary to wait for a long time until the transmission of the wireless packet is completed. As a result, there is a problem that the overhead increases and the effective transmission rate does not improve much even if the transmission rate is increased.
[0010]
An object of this invention is to provide the radio | wireless packet transmission method which can improve the efficiency of transmission.
[0011]
[Means for Solving the Problems]
The first aspect of the present invention performs carrier sense for a certain period of time before the transmitting wireless station transmits a wireless packet, and transmits the wireless packet only when transmission from another wireless station is not detected. In a wireless packet transmission method for confirming completion of transmission of a wireless packet by receiving a reception response from a transmission destination wireless station, a reception response from the transmission destination wireless station to a wireless packet already transmitted by the transmission source wireless station is received. after receiving the data to be transmitted next exists in the source of the radio station, and when a predetermined condition is satisfied, the length of time for or the carrier sense to omit the carrier sense The present invention is characterized in that the next radio packet is transmitted with a shorter time than the fixed time used for carrier sense before transmission of the radio packet.
[0012]
In claim 1, when the same wireless station intends to transmit a plurality of wireless packets continuously, the length of time for performing carrier sensing or omitting carrier sensing after transmitting one wireless packet Therefore, it is possible to transmit a plurality of wireless packets in a short time.
Therefore, when wireless packets with a high bit rate and wireless packets with a low bit rate are mixed on the same wireless circuit, carrier sense is omitted or shortened in a wireless station that transmits high-speed wireless packets. By doing so, the time taken by the low-speed radio packet to occupy the radio line is relatively reduced, so that the transmission overhead is reduced for the radio station transmitting the high-speed radio packet, and the effective transmission rate is improved. .
[0013]
The radio packet transmission method according to claim 2, wherein the number of times that the carrier sense is omitted or the time is continuously reduced, or an elapsed time from the start of transmission of the first radio packet is managed, and the number of times Alternatively, when the elapsed time reaches a predetermined threshold, the carrier sense omission or the time shortening operation is stopped.
[0014]
According to the second aspect of the present invention, the number of times carrier sense is omitted or the number of time reductions is limited, or the time for which continuously transmitted radio packets occupy the radio channel is limited. Can be prevented.
According to a third aspect of the present invention, in the wireless packet transmission method according to the second aspect, when the information transmission rate regarding the wireless packet can be selected, a threshold for the number of times the carrier sense is omitted or the time is continuously reduced is set. The information is automatically changed according to the difference in information transmission speed.
[0015]
According to the third aspect of the present invention, the number of times of omitting the carrier sense or the number of time reductions is determined according to the information transmission speed that is actually used. .
The fourth aspect of the present invention performs carrier sense for a certain period of time before a transmission source radio station transmits a radio packet, and transmits a radio packet only when transmission from another radio station is not detected. In the wireless packet transmission method for confirming completion of transmission of a wireless packet by receiving a reception response from a transmission destination wireless station, transmission of the transmission source wireless station is completed when the carrier sense in the transmission source wireless station is completed. When data of a plurality of packets is accumulated in the buffer and can be transmitted at an information transmission rate higher than a reference information transmission rate among a plurality of selectable information transmission rates, the plurality of packets in the transmission buffer are The transmission frame is combined to form one transmission frame, and the transmission frame is allocated to one of the wireless packets for transmission.
[0016]
In claim 4, when the same radio station intends to transmit a plurality of radio packets continuously, a transmission frame including a plurality of packets can be transmitted by one radio packet, so that more radio packets can be transmitted by one radio packet. Information can be sent.
Therefore, when wireless packets with a high bit rate and low-speed wireless packets are mixed on the same wireless line, a wireless station that transmits a high-speed wireless packet transmits a transmission frame including a plurality of packets. Since the time during which the low-speed wireless packet occupies the wireless line is relatively reduced, the effective transmission rate of the wireless station that transmits the high-speed wireless packet is improved.
[0017]
According to a fifth aspect of the present invention, in the wireless packet transmission method according to the fourth aspect, when configuring the transmission frame, the number of packets included in the transmission frame or a time during which the wireless packet of the transmission frame occupies a line is predetermined. It is characterized by limiting to the threshold value.
[0018]
According to the fifth aspect of the present invention, the number of packets included in the transmission frame or the time that the wireless packet of the transmission frame occupies the line is limited, so that only a specific wireless station is prevented from occupying the wireless line for a long time it can.
According to a sixth aspect of the present invention, in the wireless packet transmission method according to the fifth aspect, when the information transmission rate regarding the wireless packet can be selected, the number of packets included in the transmission frame is automatically set according to the difference in the information transmission rate. It is characterized by changing.
[0019]
According to the sixth aspect of the present invention, the number of packets included in the transmission frame is determined according to the information transmission rate that is actually used, so that the time for which continuously transmitted wireless packets occupy the wireless line can be limited.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
One embodiment of the wireless packet transmission method of the present invention will be described with reference to FIGS. This form corresponds to claims 1 and 2.
[0021]
FIG. 1 is a flowchart showing a transmission operation (1) of a radio station. FIG. 2 is a time chart showing an example (1) of a signal appearing on the wireless line. FIG. 3 is a block diagram illustrating a configuration example of a radio station.
In this embodiment, it is assumed that the radio station 10 (transmission source) configured as shown in FIG. 3 transmits a radio packet to the transmission destination second radio station via a radio channel. There is also a third wireless station (another transmitting station) that transmits wireless packets to the same wireless line.
[0022]
As shown in FIG. 3, the radio station 10 includes an antenna 11, a transmission / reception unit 12, a transmission / reception buffer 13, a control unit 14, and a carrier sense unit 15.
Data to be transmitted is sequentially input to the radio station 10 in the form of a predetermined packet from an external terminal (not shown). This data is temporarily stored in the transmission buffer in the transmission / reception buffer 13 and is converted into a predetermined transmission signal by the transmission / reception unit 12 when the transmission is possible, and transmitted from the antenna 11 as a radio packet signal.
[0023]
A radio packet addressed to the local station is received by the antenna 11, demodulated by the transmission / reception unit 12, and output as a reception packet to an external terminal via the reception buffer in the transmission / reception buffer 13.
The carrier sense unit 15 detects the presence / absence of a radio signal received via the antenna 11 when attempting transmission, and identifies whether a signal transmitted from another transmitting station exists on the radio line. To do. The control unit 14 determines the transmission timing based on the detection state of the carrier sense unit 15.
[0024]
In this form, the radio station 10 performs control as shown in FIG. 1 during transmission. The operation shown in FIG. 1 will be described below.
When one or more packets to be transmitted appear in the transmission buffer in the transmission / reception buffer 13, the wireless station 10 starts carrier sense in step S11. If a signal (carrier) from another transmitting station is not detected for a predetermined time Td or (Td + Tb) (other transmitting stations are not transmitting), the process proceeds from step S12 to S13.
[0025]
The time Td is a predetermined time, and the time Tb is a back-off time that is randomly determined within a predetermined range.
In step S13, a counter for counting the number of times of transmission Nx or the occupation time Tx is initialized.
In step S14, one packet is transmitted as a wireless packet. Also, a reception response ACK is received from the transmission destination for the transmitted wireless packet.
[0026]
In step S15, the number of times of transmission Nx or the occupation time Tx is incremented by one.
In step S16, it is confirmed whether or not there is untransmitted data (packet) in the transmission buffer. If there is an untransmitted packet, the process proceeds to the next step S17.
[0027]
In step S17, the number of transmissions Nx is compared with a predetermined threshold value Nmax, or the occupation time Tx is compared with a predetermined threshold value Tmax. When the condition of (Nx <Nmax) or (Tx <Tmax) is satisfied, the process proceeds from step S17 to S18, and when the condition is not satisfied, the process returns to step S11.
In step S18, carrier sense is performed or waits for the predetermined time Ts, and then the process returns to step S14.
[0028]
Accordingly, assuming that the threshold Nmax is 3, for example, an operation as shown in FIG. 2 is realized.
That is, when the radio station 10 starts carrier sense from time t0 in FIG. 2 and does not detect a signal from another transmitting station before the time Td elapses, the radio station 10 transmits one transmission packet P1 at time t1. Transmit as a wireless packet. By this transmission, the number of times of transmission Nx becomes 1.
[0029]
The transmission destination radio station that has received the transmission packet P1 performs error detection, and if there is no error, returns a reception response ACK after a predetermined time Ts from reception. Since (Ts <Td), even when another wireless station attempts transmission, the transmission destination wireless station transmits ACK first. For this reason, ACK transmission from the destination wireless station is not hindered by other wireless stations.
[0030]
In the wireless station 10 that has transmitted the transmission packet P1, after the reception response ACK is received at time t2, if there is a remaining packet to be transmitted next (Nx <Nmax), the process proceeds from step S17 to S18. move on.
Accordingly, in this case, carrier sense is omitted, and at time t3 when the time Ts has elapsed, the next transmission packet P2 is immediately transmitted in step S14. By this transmission, the number of times of transmission Nx becomes 2.
[0031]
Even when the wireless station 10 transmits the transmission packet P2, since (Ts <Td), even when another wireless station attempts transmission, the wireless station 10 transmits the transmission packet P2 first. . For this reason, transmission of the transmission packet P2 is not hindered by other radio stations.
When the wireless station 10 receives the reception response ACK from the transmission destination for the transmission packet P2 at time t4 and there remains a packet to be transmitted next (Nx <Nmax), steps S17 to S18 are performed. Proceed to
[0032]
Therefore, at this time, carrier sense is omitted and at time t5 when time Ts has elapsed, the next transmission packet P3 is immediately transmitted in step S14.
As a result of this transmission, the transmission count Nx becomes 3. Therefore, the next time step S17 is executed, (Nx = Nmax), and the process returns from step S17 to S11. Therefore, after transmitting three wireless packets continuously, normal carrier sense is executed.
[0033]
For this reason, the overhead regarding the carrier sense at the time of transmission is reduced, and the effective information transmission speed improves.
(Second Embodiment)
One embodiment of the wireless packet transmission method of the present invention will be described with reference to FIGS. This form corresponds to claims 4 to 6.
[0034]
FIG. 4 is a flowchart showing the transmission operation (2) of the radio station. FIG. 5 is a time chart showing an example (2) of the signal appearing on the wireless line. This form is a modification of the first embodiment, and assumes a case where a radio station 10 having the same configuration as that of FIG. 3 is used.
In this embodiment, it is assumed that the bit rate R used for transmission can be selected from a plurality of types. In this form, the radio station 10 performs control as shown in FIG. 4 at the time of transmission. Hereinafter, the operation shown in FIG. 4 will be described.
[0035]
When one or more packets to be transmitted appear in the transmission buffer in the transmission / reception buffer 13, the wireless station 10 starts carrier sense in step S21. Then, if a signal (carrier) from another transmitting station is not detected for a predetermined time Td or (Td + Tb) (other transmitting stations are not transmitting), the process proceeds from step S22 to S23.
[0036]
In step S23, the radio station 10 acquires the bit rate R currently used for transmission. In the next step S24, the maximum number of packets Kmax is determined according to the bit rate R. Specifically, for example, the following calculation formula is used.
Kmax = K0 ・ R / R0
K0: number of reference packets (constant: 1 for example)
R0: Reference bit rate (constant)
In step S25, it is confirmed whether or not there is untransmitted data (packet) in the transmission buffer. If there is an untransmitted packet, the process proceeds to the next step S26.
[0037]
In step S26, a transmission frame is constructed from untransmitted data (packets) in the transmission buffer within the range of the maximum number of packets Kmax determined in step S24.
For example, when (Kmax = 3) and three or more untransmitted packets exist in the transmission buffer of the radio station 10, three transmission packets P1, P2, P3 and One transmission frame is configured using the header HD and the Taylor TL. If the number of existing packets is 2, a transmission frame including two packets is formed even if (Kmax = 3).
[0038]
In step S27, one transmission frame is transmitted as a wireless packet. Also, a reception response ACK is received from the transmission destination for the transmitted wireless packet.
When controlling in this way, for example, as shown in FIG. 5, even when a wireless packet with a high bit rate and a wireless packet with a low bit rate are mixed on one wireless line, The time for one high-speed wireless packet to occupy the wireless line and the time for one low-speed wireless packet to occupy the wireless line can be set to the same length.
[0039]
For this reason, when the bit rate is high, a plurality of packets can be transmitted with one wireless packet (transmission frame), and transmission overhead associated with carrier sense can be reduced. That is, the packet transmission efficiency is improved and the effective information transmission rate is increased.
(Third embodiment)
One embodiment of the wireless packet transmission method of the present invention will be described with reference to FIGS. This form corresponds to claim 3.
[0040]
FIG. 6 is a flowchart showing the transmission operation (3) of the radio station. FIG. 7 is a time chart showing an example (3) of the signal appearing on the wireless line.
This form is a modification of the first embodiment, and assumes a case where a radio station 10 having the same configuration as that of FIG. 3 is used. In FIG. 6, the steps corresponding to those in FIG. 1 are given the same numbers. The following description of the same parts as those in the first embodiment is omitted.
[0041]
In this embodiment, it is assumed that the bit rate R used for transmission can be selected from a plurality of types. In this form, the radio station 10 performs control as shown in FIG. 6 during transmission. Hereinafter, the operation shown in FIG. 6 will be described.
In step S31, the radio station 10 acquires the bit rate R currently used for transmission. In the next step S32, the maximum number of transmissions Nmax is determined according to the bit rate R. Specifically, for example, the following calculation formula is used.
[0042]
Nmax = N0 ・ R / R0
N0: Reference number (constant: 1 for example)
R0: Reference bit rate (constant)
Therefore, in this embodiment, the upper limit (Nmax) of the number of times of continuous transmission of a plurality of radio packets with carrier sense omitted or shortened is determined according to the bit rate R used for transmission.
[0043]
In the example shown in FIG. 7, transmission packets P1, P2, and P3 are continuously transmitted by three wireless packets that appear continuously when the bit rate is high, and one wireless packet when the bit rate is low. Each time a packet is transmitted, normal carrier sense is performed.
Note that when there are only two types of bit rates that can be used for transmission, high speed and low speed, general conventional control is performed when the speed is low, and only when high speed is selected, FIGS. You may control to perform operation | movement as shown in FIG.
[0044]
【The invention's effect】
As described above, according to the present invention, a plurality of wireless packets can be transmitted continuously, or a plurality of packets can be transmitted in a single transmission, so that the overhead during transmission is relatively reduced. The effective packet rate is improved.
In addition, when one transmission rate can be selected from a plurality of types of transmission rates, the number of times wireless packets are continuously transmitted and the number of packets included in one wireless packet are determined according to the transmission rate. Even when low-speed wireless packets and high-speed wireless packets coexist on the same wireless line, it is possible to prevent the proportion of time taken by low-speed wireless packets from occupying the wireless line from increasing. Efficiency is improved.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a transmission operation (1) of a radio station.
FIG. 2 is a time chart showing an example (1) of a signal appearing on a wireless line.
FIG. 3 is a block diagram illustrating a configuration example of a radio station.
FIG. 4 is a flowchart showing a transmission operation (2) of the wireless station.
FIG. 5 is a time chart showing an example (2) of a signal appearing on a wireless line.
FIG. 6 is a flowchart showing a transmission operation (3) of the radio station.
FIG. 7 is a time chart showing an example (3) of a signal appearing on a wireless line.
FIG. 8 is a time chart showing an example (conventional example) of a signal appearing on a wireless line.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Radio station 11 Antenna 12 Transmission / reception part 13 Transmission / reception buffer 14 Control part 15 Carrier sense part

Claims (6)

Before the source radio station transmits a radio packet, carrier sense is performed for a certain period of time, and only when no transmission from another radio station is detected, the radio packet is transmitted. In a wireless packet transmission method for confirming completion of transmission of a wireless packet by receiving a reception response from a station,
After receiving a reception response from the destination radio station for the radio packet already transmitted by the source radio station, the data to be transmitted next exists in the source radio station and satisfies the predetermined condition The carrier sense is omitted, or the length of time for performing the carrier sense is shorter than a predetermined time used for carrier sense before transmission of the wireless packet, and the next wireless packet is transmitted. A wireless packet transmission method. The wireless packet transmission method according to claim 1, wherein the number of times the carrier sense is omitted or the time is continuously reduced, or the elapsed time from the start of transmission of the first wireless packet is managed, A radio packet transmission method characterized in that, when a predetermined threshold value is reached, the carrier sense omission or time reduction operation is stopped. 3. The wireless packet transmission method according to claim 2, wherein when the information transmission rate relating to the wireless packet can be selected, a threshold for the number of times the carrier sense is omitted or the time is continuously reduced is set as the information transmission rate. A wireless packet transmission method characterized by automatically changing according to a difference. Before the source radio station transmits a radio packet, carrier sense is performed for a certain period of time, and only when no transmission from another radio station is detected, the radio packet is transmitted. In a wireless packet transmission method for confirming completion of transmission of a wireless packet by receiving a reception response from a station,
When the carrier sense in the transmission source radio station is completed, data of a plurality of packets is accumulated in the transmission buffer of the transmission source radio station, and a reference information transmission rate is selected from a plurality of selectable information transmission rates. A plurality of packets in the transmission buffer are combined to form one transmission frame, and the transmission frame is allocated to one of the wireless packets and transmitted when the transmission is possible at a high information transmission rate. A wireless packet transmission method. 5. The wireless packet transmission method according to claim 4, wherein when configuring the transmission frame, the number of packets included in the transmission frame or the time for which the wireless packet of the transmission frame occupies the line is limited to a predetermined threshold. A wireless packet transmission method. 6. The wireless packet transmission method according to claim 5, wherein when the information transmission rate regarding the wireless packet can be selected, the number of packets included in the transmission frame is automatically changed according to the difference in the information transmission rate. A wireless packet transmission method characterized by the above.

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