JPH08251187A - Radio communication system - Google Patents

Abstract

PURPOSE: To avoid collision while executing the transmission of a CSMA/CD (carrier sense multiple access/collection detection) system in a radio communication system to execute data transmission among plural radio equipments by a distributed control system. CONSTITUTION: In the case where a station A and the station C transmit request signals once at time t0 to the station B and the station D respectively, the stations B and D return ACK(acknowldge character) signals respectively after some period in which waiting time is set. When the priority of the station B is higher, the station B returns the ACK signal (time t1 ). This ACK signal is received by the stations A and C at time t2 , and since the station A judges it to be the ACK signal addressed to its own station, it transmits data in succession. On the contray, the station C recognizes the collision because the first ACK signal is not addressed to its own station, and it disconnects the transmission at the time of the transmission (time t3 ) and the reception (time t4 ) too of the ACK signal from the station D.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system using a plurality of wireless devices such as a wireless LAN, and more particularly to a communication system for avoiding collisions when a plurality of wireless devices simultaneously try to transmit.

[0002]

2. Description of the Related Art As a collision avoidance method in a wired LAN, CSMA / CD (Car) represented by Ethernet is used.
rier Sense Multiple Acces
The s / Collision Detection method is often used as a simple transmission control method. This method is
This is a distributed control method in which each terminal operates with the same logic and gives an access right to each terminal.

In the Ethernet, the signal of the coaxial cable is received immediately before the transmission is started, and it is confirmed that no signal is flowing in the transmission line (coaxial cable) before the transmission is started.

At this time, when a plurality of devices start transmission at the same time, transmission signals collide on the transmission path.

The Ethernet is provided with a hardware mechanism capable of detecting a collision when a collision occurs. Each transmitting station detects a collision on the transmission path, stops the transmission, and then restarts the transmission path after a pause time by a random number. The signal is monitored to check if there is no signal on the transmission path, and after confirming no signal, transmission is started.

With this algorithm, the probability of another collision is reduced, and the transmission line can be operated smoothly.

[0007]

In a wired LAN represented by Ethernet, multi-drop (N to N) transmission is possible with a relatively simple transmission device, and the CSMA / CD method is a method suitable for LAN. Can be said.

However, when trying to apply the CSMA / CD method to a wireless LAN, technical difficulties arise. This is because the collision detection method is more difficult than the wired method.

In the case of a cable, the cause of the decrease in the signal level between the transmission devices is due to the frequency characteristics of the coaxial cable, etc., and is basically defined by the length of the cable.

However, in the wireless LAN, the deterioration of the signal between the transmission devices is caused by the transmission loss of the radio wave, and basically depends on the characteristics of the antenna or the like.
It is defined by a three-dimensional distance in the Y and Z axis directions.

Broadly speaking, a wireless LAN is a wired LAN.
Compared with the above, the signal level difference between the transmission devices is increased by the cube of the distance.

In the wireless LAN, the signal difference between the respective transmission devices is larger than that in the wired LAN. Therefore, even if they are received at the same time, the signal of the transmission device having a large signal level is the signal of the transmission device having a small signal level. Since it is masked, it is difficult to detect a collision.

There is a centralized control system for avoiding a collision by using a radio device (centralized control device) that gives a transmission access right as a master station, but a special monitoring station is required as compared with the distributed control system.

An object of the present invention is to provide a wireless communication system capable of avoiding collision while transmitting in CSMA / CD system.

[0015]

In order to solve the above-mentioned problems, the present invention is a wireless communication system for transmitting data between a plurality of wireless devices by a distributed control method, in which a transmitting station does not communicate with other stations. When a request signal including the partner station address is sent, an ACK signal from another station is waited for, and when the ACK signal is received and the partner station address of the ACK signal is addressed to the own station, it is sent to the partner station The receiving station receives a request signal from another station and starts the transmission when the destination station does not address the station or when the ACK signal is not received for a certain period of time. When it is destined for each station, it waits for a time that is uniquely assigned to each station as a priority of each station, and then sends the ACK signal by broadcast. Characterized by comprising a transmission control means for performing reception.

[0016]

[Function] The request signal, the ACK signal, and the transmitted / received data include the address of the partner station, and the transmitter station and the receiver station transmit / receive the data by obtaining the communication right specifying the partner station by transmitting / receiving the request signal and the ACK signal. To do.

When the transmitting station transmits the request signal,
The receiving station ACKs after a response time with priority
By transmitting the signal, the radio wave mask can be transmitted and received while avoiding collision.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of the main part of a radio device, which comprises an antenna 1, a transmitter / receiver 2, a transmission control unit 3 and a computer unit 4 for controlling them. The algorithm of the transmission control unit 3 and the like is stored in the computer unit 4 as software, and control is performed by avoiding collision.

FIG. 2 shows a transmission algorithm by the computer unit 4. On the transmitting side, prior to transmission, it is first checked whether or not the communication with another station is completed in order to confirm the usage status of the transmission path (S1).

If the transmission line is idle in this check, a request signal is transmitted to the partner station (S2), and an ACK signal from another station for this request signal is waited (S2).
3). Address information of the partner station is attached to the information section of the request signal. Further, the receiving side sends back the ACK signal with the address information attached.

When this ACK signal is received (S4) and the address in the information part of the ACK signal is addressed to the own station (S5), the transmission is started as normal transmission to the partner station (S6), End the transmission.

When the ACK signal is not addressed to the own station (S5),
As a collision occurs, transmission cancellation processing is performed (S7), and the other station waits for the end of communication by the other station because the other station has a higher priority (S7).
1).

When the ACK signal is not received (S4), the reception waiting timer waits (S8), and when the ACK signal is not received until the time is up (S4), it is determined that the partner station is abnormal and the transmission is canceled. (S9), wait for the end of communication of the other station (S1).

FIG. 3 shows a reception algorithm by the computer unit 4. On the receiving side, when a request signal from another station is received (S11) and the address held in the information section is addressed to the own station (S12), a time determined uniquely to each station is generated according to the own station address, etc. After waiting for this time (S13), an ACK signal is transmitted (S1).
4).

This ACK signal is composed of the address of its own station and the global address, and is a simultaneous broadcast received by all stations. Further, as described above, the address of the partner station is also added to the ACK signal as information, which is used for checking the address of the own station in the process (S5) on the transmitting side.

After the transmission of the ACK signal, when the received data is addressed to the own station (S15), data reception is performed (S1).
6) The reception is completed.

When there is reception from another station but it is not addressed to itself (S12) and when the received data is not addressed to itself (S1)
In 5), the next reception is awaited (S11).

According to the transmission / reception algorithm described above, the transmission side determines whether or not it is addressed to itself by the address of the partner station provided in the information part of the ACK signal for the transmission of the request signal, and transmits.

When waiting for an ACK signal, first ACK addressed to the own station
The station that receives the signal gets the transmission right. Therefore, if the first ACK signal is not addressed to the local station on the transmitting side, the ACK is not returned, and the transmission is terminated when the ACK signal waiting time is up.

The receiving side waits for a certain time when receiving the request signal, but the priority of each station can be changed by the method of generating this time. The method of determining the priority will be described below.

(1) In case of fixed priority.

The waiting time of each station is a unique fixed time. Normally, the address of each station is set uniquely, and a unique fixed time is obtained by multiplying this address by a certain multiple to determine the waiting time.

In this method, the priority of each station at the time of collision is fixed. The address is calculated by the transmission address of the request signal.

(2) In the case of variable priority.

As represented by Ethernet, this is a method of determining the waiting time with a random number. In this case, the ACK signals may collide.

(3) In the case of semi-fixed priority.

Although the waiting time of each station is fixed, it has a plurality of waiting times, and the shorter the time, the higher the priority. Each station operates at a low priority first, but when a transmission wait occurs due to a collision or the like, the priority of that station is increased.

FIG. 4 shows a specific example in which this embodiment is applied to a wireless communication system. Of the four stations, station A and station B are located at a short distance, and station C and station D are located at a short distance.
The case where station B and stations C and D are located at a long distance is shown.

In the configuration shown in the figure, station A becomes B at time t _0.
FIG. 5 shows a time chart in the case where the station C simultaneously transmits the request signal to the station C and the station C to the station D at the same time.

In this case, the signals of stations A and C are strong in stations B and D, respectively, and the signals of stations at long distances are likely to be masked.

In response to the request signal at this time, B,
Station D returns an ACK signal after a certain waiting time, but if station B has a high priority,
The station first sends back an ACK signal (time t ₁ ).

This ACK signal is received by stations A and C at time t ₂ , but station A first determines that the ACK is addressed to itself, while station C initially transmits data. The ACK signal is not addressed to the own station, so that the collision is recognized, and the transmission is terminated when the ACK signal is transmitted from the D station (time t ₃ ) and when it is received (time t ₄ ).

[0043]

As described above, according to the present invention, the request signal, the ACK signal, and the transmitted / received data include the address of the partner station, and the transmitter station and the receiver station transmit and receive the request signal and the ACK signal. Data is transmitted and received with the communication right specifying the station. Then, when the transmitting station transmits the request signal, the receiving station transmits the ACK signal after the response time giving priority,
It has the following effects.

(1) The transmission similar to the CSMA / CD system can be performed even by the distributed control system such as the wireless LAN which is difficult to detect the collision.

(2) As can be seen in the centralized control system, collision avoidance can be performed without the need to provide a special monitoring station such as a master station for avoiding collision on the transmission path. This enables a distributed processing type wireless LAN.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a main part of a wireless device according to an embodiment of the present invention.

FIG. 2 is a transmitter algorithm of a wireless device according to an embodiment.

FIG. 3 is a receiving side algorithm of a radio device according to an embodiment.

FIG. 4 is an example of a wireless communication system.

FIG. 5 is a time chart of collision avoidance according to the embodiment.

[Explanation of symbols]

 1 ... Antenna 2 ... Transceiver 3 ... Transmission control unit 4 ... Computer unit

Claims (1)

[Claims] 1. In a wireless communication system for performing data transmission between a plurality of wireless devices by a distributed control method, a transmitting station transmits a request signal including a partner station address from another station when there is no communication with the other station. Wait for the ACK signal of, and start transmitting to the partner station when the ACK signal is received and the partner station address included in the ACK signal is addressed to the partner station If the receiving station receives a request signal from another station and the destination station address is addressed to itself, the receiving station receives the request signal from the other station for a time determined uniquely to each station. A transmission control means for transmitting the ACK signal by broadcast after waiting and for receiving data when the received data corresponding to the ACK signal is addressed to itself is provided. Communication system.