JP3049387B2 - Wireless communication network and communication method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication network and a communication method in a wireless communication network, and more particularly, to an improvement in communication efficiency and an increase in data transmission delay in an environment where a plurality of terminals on a network execute data communication simultaneously. The present invention relates to a wireless communication network with improved time and a communication method in the wireless communication network.

[0002]

2. Description of the Related Art With the increase in the number of personal computer users and the spread of real-time applications such as video and audio, there has been a demand for faster communication networks.
In order to respond to such demands, in a network using a wired transmission medium, a transmission method capable of high-speed broadband transmission in a data link layer has been proposed and being realized. Also,
Regarding the physical layer, advances in optical fiber technology have made it possible to provide a sufficiently wide bandwidth.

[0003] However, in a network using a wireless transmission medium (hereinafter referred to as a wireless network), a high-speed broadband transmission technology in a data link layer has not yet been established. Furthermore, due to the finite nature of frequency resources, while research on high-speed broadband has been advanced, it has been a problem how to effectively use limited frequency resources. Therefore, as a method of covering a physical limit, it is considered to devise an access method at a data link level.

[0004] The access method of the communication network includes a fixed allocation method such as time division multiplexing or frequency division multiplexing in which a control station fixedly allocates time and frequency for transmission and reception to terminals, and each terminal autonomously transmits and receives. There is a random access method of a distributed control method. By the way, the document "N.
Abramson, "The ALOHA Sy
stem-Another alternative
e for computer communicat
ions, "Proc. of FallJoint
Comput. Conf. Pp. 177-18
6, May 1975 ", in time division multiplexing and frequency division multiplexing, time and frequency are divided in consideration of the maximum number of terminals, and the number of time slots and frequencies that are not actually used increases, resulting in waste. In addition, since the division is fixed, it is difficult to handle burst traffic. Attempts to enhance the capabilities of control stations to solve such problems have led to increasingly complex control stations, which have cost and reliability problems.

On the other hand, when the random access method is used, the above problem does not occur. However, since the transmission medium is used for another terminal, the control is performed by the access method. As a basic access control method, A
LOHA method, Slotted ALOHA method, CS
MA (Carrier Sense Multiple)
Access), CSMA / CD (Carrie)
r Sense Multiple Access w
i. Collision Detection) method. The ALOHA method is a method for starting transmission immediately after a transmission request occurs. When the load increases, the number of collisions sharply increases, and the average channel utilization efficiency is about 18% at the maximum, and the drop is severe at a high load. Here, the average channel utilization efficiency is the ratio of the average transmission success packet size per second to the transmission capacity.

In the Slotted ALOHA method, the time axis is divided into slots having the same length as the packet length, and transmission is not performed immediately even when a transmission request occurs, but transmission can be started only at the start of the slot. The maximum value of the average channel utilization efficiency of this system is twice as large as that of the ALOHA system, but also drops sharply under high load.

The basic operation of the CSMA system will be described with reference to FIGS. FIG. 16 shows a conceptual diagram of a terminal and a network. The terminal A, the terminal B, the terminal C, the terminal D, and the terminal E are terminals having a communication capability of executing communication via a transmission medium. The figure also shows a state where data is transmitted from the terminal A to the terminal E. In this method, each terminal, upon receiving a packet transmission request, checks the presence or absence of a carrier in the transmission medium before transmitting the packet, and transmits the packet if no carrier is present. If a carrier is detected, after waiting for a predetermined time, the presence or absence of a carrier is checked again, and after confirming that no carrier has been output, packet transmission is performed.

[0008] FIG. 17 is a time chart showing the use status of a channel. A packet is transmitted from terminal A to terminal E.
Thereafter, a packet is transmitted from terminal D to terminal B. This method generally has higher channel utilization efficiency than the above two methods, but also has a lower channel utilization efficiency under heavy load. CSMA / CD system is CSMA
Collision Detection (Collision Detective)
on) With the addition of the function, packet collision can be recognized during transmission. The channel use efficiency of the CSMA / CD system is the best compared to the other systems described above, and the channel use efficiency does not decrease even under a heavy load.

CSMA with the best channel utilization efficiency characteristics
As a means for further improving the characteristics of the / CD system, dividing a channel into a plurality of channels instead of a single channel is described in the literature "Nomura, Okada, Nakanishi," Multiple channels in a bus-type local area network. CSMA / CD system, "IEICE Journal, vo
l. J67-D, no. 9, pp. 949-95
9, September, 1984 ". According to this, the channel is divided into four as shown in FIG. 18, and each of the terminals A, B, C, D, and E can transmit and receive data on each channel. FIG. 19 shows the state of communication between terminals A and E and between terminals B and D at a certain point in time. Terminals A and E are CH2, terminals B and D
Can communicate using CH3. By using the different channels in the communication between the terminals, two or more different communication can be simultaneously performed.

FIG. 20 shows the behavior of the average channel use efficiency with respect to the load, and FIG. 21 shows the behavior of the average transmission delay time with respect to the load. The load is a ratio of a transmission packet size per second to a transmission capacity. In other words, if the load is 100% and 1 Mbit packets are transmitted per second, 200% means that 2 Mbit packets are transmitted. However, since the transmission of a packet is not always successful, this load also includes an unsuccessfully transmitted packet.

The average channel utilization efficiency is an average of the ratio of the average transmission success packet size per second to the transmission capacity. That is, if 1 Mbits per second packet transmission is assumed to be 100% efficient, if the utilization efficiency is 50%,
This means that there are 500 kbits of successful transmission packets on average per second.

Referring to FIG. 20, a single channel CSMA / C
It is shown that the channel use efficiency is improved in the 4-channel CSMA / CD system compared to the D system.
Indicates that the transmission delay time of the 4-channel CSMA / CD system is shorter than that of the single-channel CSMA / CD system. These prove the superiority of the multi-channel in the CSMA / CD system.

[0013]

SUMMARY OF THE INVENTION As described above, CSMA
Multi-channeling in the / CD system has excellent characteristics in data communication. However, in a wireless network, collision detection of transmission data packets is difficult, so that the CSMA / CD method that is effective in a wired method cannot be directly applied to a wireless method. Therefore,
Even if multi-channeling is performed in a wireless network, collision detection (CollisionDetecti) is performed.
on) It was difficult to improve transmission efficiency by utilizing the features of the function.

An object of the present invention is to provide a data communication system and a communication method for improving data transmission efficiency in a wireless communication system in which it is difficult to use the CSMA / CD system.

It is another object of the present invention to provide a data communication system and a communication method in which channel utilization efficiency is improved and transmission delay time is improved, especially in a multi-channel communication system.

[0016]

In order to solve the above-mentioned problems, a wireless communication network according to the present invention is a wireless communication network in which a plurality of stations transmit and receive data by a random access method via a wireless communication medium. A data transmitting means for transmitting data by a random access method through a plurality of channels obtained by dividing a predetermined communication band, a transmitting station carrier detecting means for detecting a carrier for each of the plurality of channels, Data transmission channel selection means for selecting one of the channels for which no carrier is detected by the station carrier detection means as a data transmission channel by the data transmission means; clock means for measuring an elapsed time from the time of data transmission by the data transmission means; After the data transmission by the transmission means, If an ACK signal, which is a reception acknowledgment signal for the transmission data, is not received within the interval, carrier detection of each channel by the transmission station carrier detection means and channel selection by the data transmission channel selection means based on the carrier detection are executed again. A data transmission control unit for re-executing data transmission, a data reception station in the network comprising: a data reception unit for receiving data via filter means for separating each of the plurality of channels; Receiving station carrier detecting means for detecting a carrier for each of the channels, ACK transmitting channel selecting means for selecting one of the channels whose carrier is not detected by the receiving station carrier detecting means as an ACK signal transmitting channel, and ACK transmitting channel selecting Run through the channel selected by the means And having a ACK signal transmission means for performing transmission of the ACK signal by beam access method, the.

Further, the random access method in the contactless communication network of the present invention is a communication method based on the CSMA protocol.

Further, the transmitting station carrier detecting means in the data transmitting station in the contactless communication network of the present invention has a filtering means for separating each of the plurality of channels, and the filtering means separates each channel. It is characterized by detecting a carrier of a channel.

Further, the data transmission channel selecting means and the ACK transmission channel selecting means in the non-contact communication network of the present invention are characterized in that one channel is randomly selected from the channels from which no carrier has been extracted.

The number of channels in the contactless communication network of the present invention is 2 to 5.

Further, the communication band in the non-contact communication network of the present invention is characterized in that it is divided into a plurality of channels by a frequency division method.

Further, the communication band in the contactless communication network of the present invention is characterized in that it is divided into a plurality of channels by a code division system.

Further, the transmitting apparatus of the present invention includes a data transmitting means for transmitting data by a random access method via a plurality of channels obtained by dividing a communication band set in advance, and a carrier for each channel among the plurality of channels. A transmitting station carrier detecting means for detecting, a data transmitting channel selecting means for selecting one of the channels for which no carrier is detected by the transmitting station carrier detecting means, as a data transmitting channel by the data transmitting means, A timing means for measuring elapsed time;
After the data transmission by the data transmission means, an ACK, which is a reception acknowledgment signal for the transmission data, within a preset time
When no signal is received, data transmission control means for executing again carrier detection of each channel by the transmission station carrier detection means and channel selection by the data transmission channel selection means based on the carrier detection, and executing data transmission again. It is characterized by having.

Further, in the transmitting apparatus according to the present invention, the random access method is a communication method based on the CSMA protocol.

The receiving apparatus according to the present invention further comprises a data receiving unit for receiving data via a filter means for separating each of a plurality of channels obtained by dividing a predetermined communication band constituting a wireless communication medium. Receiving station carrier detecting means for detecting a carrier for each of the plurality of channels, ACK transmitting channel selecting means for selecting one of the channels for which no carrier is detected by the receiving station carrier detecting means as an ACK signal transmitting channel,
ACK signal transmission means for executing transmission of an ACK signal by a random access method via a channel selected by the transmission channel selection means.

Further, in the receiving apparatus according to the present invention, the random access method is a communication method based on the CSMA protocol.

A communication method according to the present invention is a communication method in a wireless communication network in which a transmitting station and a receiving station wirelessly communicate using a plurality of channels obtained by dividing a communication band having a predetermined frequency range, The transmitting station detects the presence or absence of a carrier of a plurality of channels, selects one of the channels on which the carrier is not detected as a data transmission channel, transmits data by a random access method via the selected channel, and Means for counting the time elapsed since the transmission of the data, the receiving station extracting the carriers of the plurality of channels, and if the extracted carrier is data transmitted to the receiving station, And after receiving the data, detect carriers of a plurality of channels, find a channel on which no carrier is detected, and There select one channel as ACK transmission channel transmits an ACK signal by the random access method via the selected channel, the transmission station,
If an ACK signal transmitted by the receiving station is not received even after a preset time has elapsed from the start of timing by the timing means, carrier detection and channel selection of a plurality of channels are performed again, and the data signal A retransmission is attempted.

In the communication method according to the present invention, the random access method is a communication method based on the CSMA protocol.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION A wireless communication network according to the present invention realizes multi-channel in communication by a random access method, and executes data communication by a plurality of terminals connected by a wireless communication medium. The terminal used in the present invention is a radio channel filtering means,
It has a carrier detection unit, a wireless channel selection control unit, a data link control unit, and an ACK timing unit, and performs communication between terminals via a multi-channel wireless communication medium by frequency division or code division. In selecting a channel by a terminal, first, carrier detection of a channel is performed, and one channel is randomly selected from vacant channels in which no carrier has been detected and used as a communication channel. When the packet transmission on the selected communication channel ends, the packet transmitting terminal confirms the success of the transmission by receiving an ACK (acknowledgement) message from the packet receiving terminal.

[0030]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a system conceptual diagram of a plurality of terminals and a wireless communication network in an embodiment of the present invention. The terminal A, the terminal B, the terminal C, the terminal D, and the terminal E are terminals having a communication capability via a wireless communication medium. In this embodiment, the transmission medium is divided into three channels by a method such as frequency division or code division (CH1, CH2, respectively).
2, CH3), and each terminal A-E is configured to be able to transmit and receive data using each of the plurality of channels.

A schematic configuration of the terminal is shown for terminal A in FIG. Other terminals BE have the same configuration as terminal A. As shown for terminal A, the terminal has ACK timing means 1, data link control means 2, radio channel control means 3, carrier detection means 4, and radio channel filtering means 5, and the terminal is connected via transmission medium 6. Performs data communication with other terminals. The ACK timing means 1 has a function of measuring a time from when a data packet is transmitted from a terminal to another terminal to when an ACK packet including a success message regarding packet transmission is received from the data receiving terminal. The data link control means 2 is a means for transmitting a packet using the channel selected by the wireless channel selection control means 3. The wireless channel selection control means 3 is a means for selecting one channel used for communication from the channels for which no carrier has been detected by the carrier detection means 4. The carrier detecting means 4 has a function of detecting a carrier of a channel on the wireless communication network based on a signal obtained from the wireless channel filtering means 5. The wireless channel filtering means 5 has a function of extracting a received signal for each of a plurality of channels.

The transmission medium in FIG. 1 is a wireless communication medium, and is divided into three channels in this embodiment. Channel division is achieved, for example, by frequency division shown in FIG. 2 or code division using spread spectrum shown in FIG. 2 and 3, the horizontal axis f indicates the frequency. In the case of frequency division, channels (CH1, C
H2 and CH3), and in the case of code division, a code using spread spectrum is allocated to each channel, thereby enabling identification of each channel.

While terminal A shown in FIG. 1 is performing data communication with terminal E using channel CH1 in the wireless communication medium, terminal D uses terminal CH to use channel CH3 in the same wireless communication medium. 4, 5 and 6 show a state in which data transmission is to be carried out in chronological order.

Each of FIGS. 4, 5, and 6 is a diagram sequentially showing a change in the use status of each channel. Three channels CH divided by frequency division or the like in a wireless communication medium
For each of CH1, CH2, and CH3, the data transfer status on the time axis t is shown. First, in FIG. 4, data transmission is performed from terminal A to terminal E using channel CH1, and during this data transmission, terminal D transmits all channels (CH1, CH2) for data transmission.
2, CH3) is sensed to detect a channel free state.

FIG. 5 shows a state in which the terminal D detects the presence or absence of a carrier by the carrier sense of each channel and selects one channel from a plurality of channels as a communication channel. Here, two vacant channels CH2 and CH3 other than the channel CH1 are detected, and the channel CH3 is determined as the channel used by the terminal D from the vacant channels of these CH2 and CH3.

FIG. 6 shows a state in which terminal D is performing data transmission to terminal B using channel CH3 determined as a communication channel. Data transmission from terminal D to terminal B can be performed simultaneously with data transmission from terminal A to terminal E. In any of the states shown in FIGS. 4, 5, and 6, the carrier sense of the channel by the terminal does not prevent data transmission.

FIG. 7 is a block diagram of a terminal device according to the embodiment of the present invention. In the embodiment described below, an example of a communication terminal applied to communication using a wireless communication medium in which a communication channel is divided into a plurality of channels by frequency division will be described.

As shown in FIG. 7, the terminal device is roughly divided into an upper layer 10, a data link unit 20, and a radio receiving unit 3.
0, a wireless transmission unit 40, and a physical interface unit 50, and perform data communication with other terminals via a transmission medium 60.

The upper layer 10 is a software module corresponding to the OSI third layer (network layer). If there is data to be sent to another terminal, the data link control unit 21 is requested to send the data. Data link unit 20
Is composed of a data link control unit 21 and an ACK timing unit 22. The data link control unit 21 is a module having a function of controlling transmission of a data packet in response to a request from the upper layer 10 and a function of performing a process related to a data packet received from another terminal, and can be realized by an LSI. Here, the data packet is packetized data transmitted from the upper layer 10. The ACK timer 22 has n timers, which is a number corresponding to the number n of channels, and can simultaneously measure a plurality of channels.

The flow of the function of the data link unit 20 when transmitting a data packet will be described with reference to FIG. At the time of packet transmission, first, a command is sent to the carrier detection unit 33 to perform carrier sense (step 802), and the presence or absence of a carrier of each channel is confirmed (step 803). If there is a channel with no carrier, one channel selected from the radio channel selection control unit 41 is notified (step 806). If carriers are detected in all channels, the back-off time is calculated (step 804), and after waiting for that time (step 805), each channel is sensed again (step 8).
02). The back-off time is, for example, C shown below.
Truncated used in SMA / CD format
Binary Exponential Backoff
f is used.

[0041]

## EQU1 ## In this equation, the back-off time T is set as follows: T = t ・ n0 ≦ n <2k (k = min (m, 10)) m: Number of collisions t is a constant, which is a 512-bit packet transmission time.

As a method of setting the back-off time different from the above method, a predetermined positive integer, for example, 5
It is also effective to select one number at random from values from 1 to 512 with 12 as the maximum value, and multiply that number by the maximum propagation delay time to obtain the backoff time.

After receiving the notification of the selected transmission channel from the wireless channel selection control unit 41, the transmission of the packet is started using the notified channel (step 80).
7) Then, when the transmission is completed (step 808), a command for starting the time measurement is issued by the timer unit 22 corresponding to the packet transmission channel, and an ACK packet for the transmitted packet while the time measurement is started is awaited (step 808). Step 8
09). T which is a preset allowable ACK waiting time
_{If an} ACK packet is received by _ACK seconds, a stop time command is issued to the ACK timer 22 to end transmission (step 81).
0,812). However, if an ACK packet is not received even after the elapse of the predetermined waiting time T _ACK seconds, a timeout notification is output from the ACK timer 22 and transmission is considered to have failed, and the packet is retransmitted (step Steps 802) to 811 are performed.

[0044]

[Equation 2] T_ACKIs a predetermined value.
If T _ACK= Maximum round-trip propagation delay time + Average packet processing time.

Next, an embodiment of the function of the data link control unit 21 when receiving a data packet will be described with reference to FIG. Waiting for reception of a data packet from another terminal (step 90)
2) Then, the reception of the packet determined to be the packet addressed to the own terminal by the data signal determination unit is started, and when the reception of the data packet is completed (from step 902 to step 903), the ACK packet is transmitted to the terminal that transmitted the data packet. Is transmitted to the carrier detection unit 33 in order to transmit the carrier, and the presence or absence of a carrier of each channel is confirmed (steps 903 and 904). When the carrier detector 33 notifies that there is a channel with no carrier (steps 904 to 907), the radio channel selection controller 41 is notified of the channel with no carrier. After that, one channel selected by the radio channel selection control unit 41 from the notified channels without carriers is notified (step 907). If carriers are detected in all channels (steps 904 to 905),
After calculating the back-off time (step 905) and waiting for the back-off time (step 906), each channel is sensed again (from step 906 to step 90).
3) Yes.

After receiving the notification of the selected transmission channel from the radio channel selection control unit 41, the ACK packet is transmitted using that channel. The ACK timer 22 is a module having a function of measuring the time from when the terminal transmits a packet to when the terminal receives an ACK packet from a transmission partner, and can be realized by an IC including a clock circuit. When the ACK timing start notification for a certain channel is received from the data link control unit 21, the timing for the channel is started. After the elapse of T _ACK seconds, the timer stops counting and notifies the data link control unit 21 of a timeout. If the data link control unit 21 has notified the time stop command before the elapse of T _ACK seconds, the time stop is performed at the time of notification of the command. Also, since a plurality of channels can be used simultaneously, when the number of channels is n (n is an integer of 2 or more), a total of n timepieces (Timer clocks) are provided for each channel.
1, Timer 2, Timer 3, ..., Timer
n).

The ACK clock unit in the data link unit 20 has n clocks corresponding to the number n of channels as in the above embodiment, and each clock measures the time of one channel corresponding to the ACK clock. Although a common timer is configured for a plurality of channels, the data link controller 21 holds a table for managing a packet transmission time and an ACK packet waiting time, so that the time measurement of a plurality of channels can be performed by the common timer. It may be configured to do so.

The radio receiving section 30 comprises a radio channel filtering section 31, a demodulation section 32, a carrier detection section 33, and a data signal judgment section 34. The wireless channel filtering unit 31 has a function of filtering a signal received from the physical interface 50 for each channel, and can be realized by, for example, a bandpass filter. In order to handle a plurality of channels, when the number of channels is n (n is an integer of 2 or more), one band-pass filter is assigned to each channel, and a total of n band-pass filters (BPFs) are used.
1, BPF 2, BPF 3,..., BPF n) constitute a radio channel filtering unit 31. Note that the wireless channel filtering unit may be configured not to have a plurality of bandpass filters but to perform channel classification by a scan method. The demodulation unit 32 has a function of demodulating the carrier filtered by the radio channel filtering unit 31 to a baseband signal.
Can be realized.

The carrier detector 33 detects a data packet or A
A module having a function of detecting a carrier of each channel before transmitting the CK packet, and notifies the data link control unit 21 of the detected channel. One-chip I
This can be realized by a C module or the like. Data signal determination unit 34
Is a module that determines whether a received signal is addressed to its own terminal based on a terminal-specific address such as a MAC address based on a signal obtained from the demodulation unit 32, and can be realized by an LSI or the like.

The radio transmission section 40 comprises a radio channel selection control section 41 and a modulation section 42. The wireless channel selection control unit 41 determines which channel to transmit based on the detection result of the carrier detection unit 33, and can be realized by a one-chip IC module or the like. As the channel, one is randomly selected from the channels for which no carrier is detected.

The modulator 42 has a function of modulating the baseband signal to a transmission frequency corresponding to the channel determined by the radio channel selection controller 41 and sending the modulated signal to the physical layer interface 50, and can be realized by an LSI or the like. Modulation unit 42
May have a configuration in which a modulator for converting a frequency according to the channel is provided for each channel. For example, if there are five channels, five modulators are provided, and the modulator to be used is determined according to the selected channel.

The physical layer interface unit 50 is connected to the transmission medium 6
0 and an interface portion of the terminal device, and if it is wireless, an antenna and an RF circuit module. Transmission medium 6
0 is a wireless transmission medium.

In the above embodiment, an example in which multi-channeling is performed by frequency division has been described. However, as described above, the radio channel filtering unit 31 is a primary demodulation circuit using a spreading code, and the modulation unit 42 is a base demodulation circuit. By combining the primary modulation circuit that modulates the band signal with the carrier frequency and the secondary modulation circuit that uses a spreading code,
Multi-channel using code division can be realized. That is, it is required that the channel filtering means and the modulator in the terminal have a configuration corresponding to a multi-channel scheme applied in communication.

Although frequency division can secure more channels, when the error rate of the wireless transmission path is large, code division using spread spectrum is more resistant to noise and is superior to frequency division. Therefore, frequency division is effective where the error rate of the wireless transmission path is small, and code division is effective where the error rate is large.

Next, simulation results showing the performance of the multi-channel communication system using the CSMA system of the present invention will be described with reference to FIGS. 10, 11, 12, and 13.

[0056]

[Table 1] The simulation conditions are as follows. Number of stations: 10 Number of channels at the time of channel division: 2, 3, 4, 5, 6 Cell size: 6000 m Maximum propagation delay time: 20.0 μsec Packet length: 512 bits Transmission capacity: 1 Mbps

FIG. 10 shows the behavior of the average channel utilization efficiency with respect to the load on the transmission medium 60. 2,
In order to compare the result of the present method in the case of 3, 5 channels with the conventional method, the one-channel CSMA method, the CSMA / CD
Simulation results of the method under the same conditions are also shown.

Here, the load is a ratio of the transmission packet size per second to the transmission capacity. In other words, when the load is 100% under the above simulation conditions, it means that 1 Mbit packets are transmitted per second. However, since the transmission of the data packet is not always successful, this load is a value including the unsuccessfully transmitted packet.

Here, the average channel utilization efficiency is the average of the ratio of the average transmission success packet size per second to the transmission capacity. That is, when the channel utilization efficiency is 50% under the above simulation conditions, it means that there is an average of 500 kbits of successful transmission packets per second.

From this figure, it can be seen that, compared to the conventional one-channel CSMA system, the two- to five-channel system of the present invention has higher average channel utilization efficiency. It is clear that the number is twice that of the CSMA method. Also, as the number of channel divisions increases, the use efficiency becomes less likely to decrease under a high load, and the performance is remarkably improved as compared with the conventional one-channel CSMA system in which the use efficiency decreases rapidly with an increase in load.

FIG. 11 shows the behavior of the average transmission delay time of a packet with respect to the load on the transmission medium 60. Here, the load is the same as that described in FIG. Here, the average transmission delay time of a data packet is measured from a time point when a data packet transmission request is generated to a time point when transmission is actually started when transmission is successfully completed. From FIG. 11, it can be seen that the multi-channel system of the present invention has a small average transmission delay time, and is particularly advantageous under a heavy load. Also, the delay time becomes smaller as the number of channels increases.

FIG. 12 is a graph in which the vertical axis represents the improvement rate of the average channel utilization efficiency, the horizontal axis represents the number of channels, and the vertical axis represents the improvement rate of the average transmission delay time, and the horizontal axis represents the number of channels. It is created and shown by changing (75%, 175%, 275%). The improvement rate is an improvement rate from the conventional one-channel CSMA method. From FIG. 12, it can be seen that, when the load is 75% and the number of channels is 6, both the channel utilization efficiency and the average transmission delay time deteriorate the performance. When the load is further increased to 175%, the improvement rate gradually increases from the second channel to the fifth channel, but it can be seen that increasing the number of channels to six causes a decrease in the improvement rate. When the load is further increased to 275%, the improvement rate of 6 channels is finally slightly higher than the improvement rate of 5 channels. From the above, it can be seen that the range of the optimal number of channels is the range of the number of channels from 2 to 5, and even if the number of channels is 6 or more, improvement in performance cannot be expected. This is because as the number of channels increases, the transmission capacity per channel decreases, and transmission takes time. In addition, an increase in the number of channels leads to an increase in cost, and the number of channels for which a sufficient effect of the present invention can be expected without a significant increase in cost is 2 to 5.

FIG. 13 shows the behavior of the average packet transmission delay time with respect to the average utilization efficiency of the channel. The average utilization efficiency of the channel corresponds to the throughput viewed from the application layer, not from the throughput viewed from the data link layer, which counts all the packets including the amount of retransmission and transmission failure packets. Therefore, this value directly affects the operation of the application. For example, in the case of a real-time application requiring a strict delay, it is better that the delay does not increase even if the throughput increases. Further, when the load becomes high (increase in throughput as viewed from the data link layer), the transmission delay time increases, but the throughput decreases. Therefore, two values of the transmission delay time correspond to the same throughput value. . For this reason, in applications that use throughput as a parameter for observing network behavior, the transmission delay time becomes larger than expected from the throughput value,
It interferes with application control. Looking at FIG. 13 from the viewpoint of these effects, it can be said that the multi-channel system of the present invention is more suitable for real-time applications than the CSMA system.

Also, the ALOHA system applicable to wireless communication like the CSMA system is made multi-channel (three channels), and the average channel use efficiency and the average transmission delay time are set to the same parameters as in the simulation of the multi-channel CSMA system. The results measured by the used simulation are shown in FIGS. As can be seen from these figures, in the ALOHA system, the channel use efficiency and the transmission delay time do not improve so much even in the case of multi-channel.
It can be seen that it is more effective to apply multi-channel to the SMA method. This is because, in the CSMA scheme, one channel is selected from channels without carriers, whereas
This is because, in the ALOHA method, since a channel including a carrier is selected from among them, the probability of collision is higher than that in the CSMA method.

In the simulation in the above-described embodiment, when it is assumed that the packet size is changed, the values of the average channel use efficiency and the average transmission delay time are predicted to change according to the change in the packet size. Focusing on the transmission opportunity, the change in the packet size due to the change in the packet size causes the same change in all the stations, so the relative relationship to the change in the number of channels does not change, and the number of channels shown in FIG. It is expected that the tendency of the change of the improvement rate with the change of will not change. Therefore, the optimal number of channels is in the range of 2 to 5 regardless of the transmission packet size.

Also, assuming that the number of stations is changed in the above simulation, assuming that the total amount of traffic generated from all stations is the same, the traffic amount per station changes, and the average channel utilization efficiency increases. And the average transmission delay time are expected to change, but since the same traffic volume change occurs in all stations, the relative relationship does not change either, and the improvement rate with the change in the number of channels shown in FIG. It is predicted that there will be no large deviation in the tendency of the change in Therefore, even if the number of stations changes, the optimum number of channels is in the range of 2 to 5.

[0067]

According to the communication system of the present invention, the channel utilization efficiency is improved as compared with the conventional single channel CSMA system, so that the radio wave resources can be effectively used. Further, since the transmission delay can be suppressed to a low level until the load becomes high, there is an effect that the operation of the real-time application is hardly adversely affected.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a terminal and a wireless communication network according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of channel division by frequency division in an embodiment of the present invention.

FIG. 3 is a conceptual diagram of channel division by code division in an embodiment of the present invention.

FIG. 4 is a diagram illustrating a carrier detection state by a terminal before data transmission is started in the embodiment of the present invention.

FIG. 5 is a diagram illustrating a state of determining a communication channel by a terminal before starting data transmission in the embodiment of the present invention.

FIG. 6 is a diagram illustrating a state of data transmission according to the embodiment of the present invention.

FIG. 7 is a block diagram illustrating a configuration of a terminal device according to an embodiment of the present invention.

FIG. 8 is a flowchart illustrating an operation of the transmission control unit when transmitting a packet in the terminal device according to the embodiment of the present invention.

FIG. 9 is a flowchart illustrating an operation of the transmission control unit when the terminal device transmits an ACK packet according to the embodiment of the present invention.

FIG. 10 is a diagram showing a comparison of simulation results of average channel use efficiency when the multi-channel system of the present invention is used.

FIG. 11 is a diagram showing a simulation result of an average transmission delay time when the multi-channel system of the present invention is used.

FIG. 12 is a diagram illustrating a simulation result of the average channel use efficiency and the average transmission delay time improvement efficiency when the multi-channel system of the present invention is used.

FIG. 13 is a diagram illustrating a relationship between an average channel use efficiency and an average transmission delay time when the method of the present invention is used.

FIG. 14 is a diagram showing a simulation result of average channel use efficiency when the ALOHA method is multi-channel.

FIG. 15 is a diagram illustrating a simulation result of an average transmission delay time when the ALOHA method is multi-channel.

FIG. 16 is a conceptual diagram of a terminal and a network in the one-channel CSMA scheme.

FIG. 17 is a transmission time chart in the one-channel CSMA system.

FIG. 18 is a conceptual diagram of terminals and channels in the multi-channel CSMA / CD system.

FIG. 19 is a diagram illustrating a state of each channel when transmitting data in the multi-channel CSMA / CD system.

FIG. 20 is a diagram illustrating simulation results of average channel use efficiency when the CSMA / CD scheme is multi-channel.

FIG. 21 is a diagram showing a simulation result of an average transmission delay time when the CSMA / CD system is multi-channel.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 ACK timing means 2 data link control means 3 wireless channel selection control means 4 carrier detection means 5 wireless channel filtering means 6 transmission medium 10 upper layer 20 data link unit 21 data link control unit 22 ACK timing unit 30 wireless reception unit 31 wireless channel Filtering unit 32 Demodulation unit 33 Carrier detection unit 34 Data signal determination unit 40 Radio transmission unit 41 Radio channel selection control unit 42 Modulation unit 50 Physical interface unit 60 Transmission medium

Claims (13)

(57) [Claims] 1. A wireless communication network in which a plurality of stations transmit and receive data via a wireless communication medium, wherein a data transmitting station in the network performs random access via a plurality of channels obtained by dividing a communication band set in advance. Data transmitting means for transmitting data according to a method; transmitting station carrier detecting means for detecting a carrier for each of the plurality of channels; and data transmitting one of the channels for which no carrier is detected by the transmitting station carrier detecting means. Data transmission channel selecting means for selecting as a data transmission channel by means, time measuring means for measuring an elapsed time from the time of data transmission by the data transmitting means, and within a preset time after data transmission by the data transmitting means. A which is a reception confirmation signal for the transmission data
When a CK signal is not received, data transmission control for re-executing carrier detection of each channel by the transmission station carrier detection means and channel selection by the data transmission channel selection means based on the carrier detection, and re-executing data transmission. Means, the data receiving station in the network comprises: a data receiving means for receiving data through a filter means for separating each of the plurality of channels; and a carrier for each of the plurality of channels. Receiving station carrier detecting means for detecting, ACK transmitting channel selecting means for selecting one of the channels for which no carrier is detected by the receiving station carrier detecting means as an ACK signal transmitting channel, and a channel selected by the ACK transmitting channel selecting means Through the random access method Wireless communication network comprising: the ACK signal transmitting means, a to perform transmission of that ACK signal. 2. The wireless communication network according to claim 1, wherein the random access method is a communication method based on a CSMA protocol. 3. The wireless communication network according to claim 1, wherein the transmitting station carrier detecting means in the data transmitting station includes a filter means for separating each of the plurality of channels, and the filter comprises: A wireless communication network characterized by detecting a carrier of each channel after channel separation by the means. 4. The wireless communication network according to claim 1, wherein the data transmission channel selection unit and the ACK transmission channel selection unit randomly select one channel from channels from which no carrier has been extracted. A wireless communication network. 5. The wireless communication network according to claim 1, wherein the number of channels is two to five. 6. The wireless communication network according to claim 1, wherein said communication band is divided into a plurality of channels by a frequency division method. 7. The wireless communication network according to claim 1, wherein said communication band is divided into a plurality of channels by a code division method. 8. A transmitting apparatus used in a wireless communication network in which a plurality of stations transmit and receive data by a random access method via a wireless communication medium, wherein a random number is transmitted through a plurality of channels obtained by dividing a predetermined communication band. Data transmitting means for transmitting data by an access method; transmitting station carrier detecting means for detecting a carrier for each of the plurality of channels; and transmitting one of the channels on which no carrier is detected by the transmitting station carrier detecting means to the data. A data transmission channel selecting means for selecting as a data transmission channel by the transmission means; a timer means for measuring an elapsed time from the time of data transmission by the data transmission means; and a predetermined time after data transmission by the data transmission means. In the acknowledgment signal for the transmitted data That A
When a CK signal is not received, data transmission control for re-executing carrier detection of each channel by the transmission station carrier detection means and channel selection by the data transmission channel selection means based on the carrier detection, and re-executing data transmission. And a transmitting device. 9. The transmitting apparatus according to claim 8, wherein the random access scheme is a communication scheme based on a CSMA protocol. 10. A receiving apparatus used in a wireless communication network in which a plurality of stations transmit and receive data by a random access method via a wireless communication medium, wherein a predetermined communication band constituting the wireless communication medium is divided. Data receiving means for receiving data via a filter means for separating each of the plurality of channels, a receiving station carrier detecting means for detecting a carrier for each of the plurality of channels, and a receiving station carrier detection ACK transmission channel selecting means for selecting one of the channels for which no carrier is detected by the means as the ACK signal transmitting channel; and transmitting the ACK signal by the random access method via the channel selected by the ACK transmission channel selecting means. ACK signal transmitting means Receiving apparatus according to claim and. 11. The receiving apparatus according to claim 10, wherein the random access scheme is a communication scheme based on a CSMA protocol. 12. A communication method in a wireless communication network in which a transmitting station and a receiving station wirelessly communicate using a plurality of channels obtained by dividing a communication band in which a frequency range is determined in advance, wherein the transmitting station comprises: Detecting the presence or absence of a carrier of the channel, selecting one of the channels on which the carrier was not detected as a data transmission channel, transmitting data by a random access method via the selected channel, and Starting timing of the elapsed time from transmission, the receiving station extracts carriers of the plurality of channels, and receives the data when the extracted carrier is data transmitted to the receiving station. Then, after receiving the data, a carrier of the plurality of channels is detected, and a channel on which no carrier is detected is obtained. One of the non-transmitted channels is selected as an ACK transmission channel, an ACK signal is transmitted through the selected channel by a random access method, and the transmitting station starts timing by the timing unit and sets a preset ACK signal. If the ACK signal transmitted by the receiving station is not received even after a lapse of time, carrier detection and channel selection of the plurality of channels are performed again, and retransmission of the data signal is attempted. A communication method in a communication network. 13. The communication method according to claim 12, wherein the random access method is a communication method based on a CSMA protocol.