JP2508158B2 - Transmission control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wireless information transmission system between a plurality of stations, and more particularly to a transmission control system in which a transmission time varies depending on information to be transmitted.

[Conventional technology]

FIG. 3 is a structural example of a wireless information transmission system between a plurality of stations. The system configuration shown in Fig. 3 is used when wireless information transmission between PCs or e-mail is performed wirelessly within a restricted area such as one floor of a building.
Taken as the simplest configuration. In such a system, the quality of transmitted information has been improved by the development of error correction technology. However, there is a problem of electric field fluctuation due to fading. For example, in the case of completely transmitting one piece of information to a partner station under fading, there is a problem of signal collision as described below.

In FIG. 3, it is assumed that information is transmitted from station A to station B. At this time, the other stations C and D confirm that there is no received radio wave and perform transmission. If this confirmation is incomplete, for example, if station C starts transmitting at the same radio frequency while transmitting radio wave is being emitted from station A, station B cannot correctly receive information.

FIG. 4 is an example of a signal configuration and a received electric field strength for explaining the determination of the presence or absence of a radio wave and the transmission control by the conventional method. The information transmitted from station A is a preliminary signal, information I _k
And an end signal, and is transmitted for a time T. At the station C, the received electric field E fluctuates due to fading.

Station C can transmit under the following conditions. That is,
(I) When the end signal is received, or (ii) When the received electric field strength E is lower than a certain reference value E _o and time τ has elapsed.

Here, in the case of (ii), that is, when the received electric field strength E becomes equal to or lower than E _o during reception of the information I _k becomes a problem. At this time, station C cannot determine whether the termination signal has not been received even though the transmission from station A has stopped, or whether station A is transmitting but the received electric field has only weakened.

Therefore, in the past, the time τ was chosen to be sufficiently large and the time τ
If E <E _o remains as above, the transmission from station A is considered to have been completed and the transmission from station C can be performed.

[Problems to be solved by the invention]

The above-mentioned conventional transmission control method has a limit in setting the time τ. That is, if the time τ is long, there is a problem in that the station that has not received the termination signal cannot transmit for a while even if the transmission from the station A is stopped. On the other hand, when the time τ is short, the probability of signal collision increases because station A is also transmitting from other stations during transmission.

Therefore, τ was selected to be several hundreds of msec, but in actual fading, the electric field may weaken in seconds, for example, when a person comes between radios connected to a personal computer, and the signal is weakened. The problem of collision has been a major obstacle to practical use.

On the other hand, there is a limit to measuring the received electric field strength,
The quality of information and the electric field strength did not always correspond due to temperature changes. In particular, when the quality of the information is high due to the error correction function, the information can be received even in a weak electric field, but there is a drawback that the electric field strength measuring circuit does not respond in a weak electric field. That is, even if the information was received, it was sometimes judged that the information was not received.

In view of the above problems, it is an object of the present invention to provide a transmission control method capable of reliably preventing signal collision between a plurality of stations.

[Means for solving problems]

In the transmission control method according to the present invention, a plurality of stations respectively
When transmitting information having different transmission times, the apparatus is provided with a means for transmitting by including time information until the transmission starts or during transmission during the transmission, and at least the time corresponding to the time information when the time information is received. It is characterized by having means for restricting not to transmit only.

In the transmission control method according to the present invention, when the transmission time varies depending on the information to be transmitted, the transmission is started by including the time information until the transmission is completed or in the middle of the transmission, and the station receiving this time information transmits the time information. , The transmission is restricted so that it is not transmitted at least for the time corresponding to the time information.

For this reason, the limiting means in the present invention is, specifically, the time information detecting unit and, when the time information is detected by the detecting unit, starts the output for the time corresponding to the time information. When the received electric field level is above the reference value, the timer rises, and when the received electric field level is above the reference value, it rises, and the received electric field level is below the reference value. A second timer that falls after a predetermined time has elapsed from the time point, and is configured to clear the second timer when the first timer falls, the output of the first timer and the second timer. The transmission is restricted so that it does not occur when any one of the outputs of the timers of No. 2 rises.

〔Example〕

FIG. 1 shows an embodiment for realizing the present invention. Here, as shown in FIG. 2, the case where the information transmission is performed including the time information and the end signal will be postponed.

 Regarding transmission, it operates as follows.

Information to be transmitted is information I ₁ , information I ₂ , and information I _3, and corresponding time information is time information TI ₁ and time information TI.
₂ and time information TI ₃ and these are memory 1, 2, 3,
It is stored in 4,5,6.

When the transmission switch 8 of the transmission operation unit 7 is turned on in the non-reception state, this signal passes through the OR circuit 10 and the transmitter 11
And transmission is activated for the control unit 12. Then, first, a preliminary signal is output from the preliminary signal pattern generating unit 13 according to a command from the control unit 12, and is transmitted as a radio wave from the transmitter 11 through the combining unit 14.

Next, the switch circuits 16 and 17 are switched by the setting operation of the information selecting operation unit 15, and the information I _k selected by the information selecting operation unit 15 and the corresponding time information IT _k are transmitted through the combining unit 14, respectively. Sent from machine 11. When the transmission of the information I _k ends, an end signal is output from the end signal pattern generation unit 16 according to a command from the control unit 12, and is transmitted from the transmitter 11 through the combining unit 14.

Regarding reception, the transmission control means described below operates as follows.

The signal received from the receiver 24 is processed by the information processing unit 18 such as a microcomputer. For the presence or absence of radio waves, the first timer 22 and the second timer
20 gives the judgment result. That is, if both timer outputs are low level, it means that there is no radio wave transmitted from another station.

The electric field detection unit 19 is for determining whether or not the received electric field strength E is higher than a certain reference value E _o , and raises the output of the timer 20 when E> E _o . If the output of the electric field detector 19 continues to fall for the time τ, the output χ20 of the timer 20 also falls. When the end signal is detected by the end signal detector 21, the timer 20 is cleared through the OR circuit 25, and the output χ20 also falls at this time.

Further, the timer 22 responds to the output of the time information detecting unit 23. That is, in the time information detection unit 23, the time information TI _k
When is detected, the output of the timer 22 rises for a time T _k corresponding to that. At the time when the output of the timer 22 falls after a lapse of time T _k from once rising, the falling detection unit 26 catches this and outputs a narrow pulse, and clears the timer 20 through the OR circuit 25.

The fall detection unit 26 includes an inverter 27, an AND circuit 28, a resistor 29, and a capacitor 30. Resistor 29 and capacitor 30 are used to slightly delay the output of timer 22. Therefore, at the moment when the output of the timer 22 falls (at the moment when the output of the inverter 27 rises), the AND circuit
The two inputs of 28 are both in the logic "1" state, and a narrow pulse is generated at the output of the AND circuit 28 at this point.
This pulse width is determined by the time constants of the resistor 29 and the capacitor 30, and is selected sufficiently smaller than the set time L of the timer 20.

As is clear from the above description, in FIG. 1, the timer 20 that determines that radio waves of other stations are being emitted using the result of electric field detection and the time from the time when the time information is received due to transmission restrictions. Timer 22 that determines that there is radio wave from another station during T _k
Is used.

Next, the operation of transmission restriction according to the present invention will be described with reference to FIG. The information transmitted is a preliminary signal, time information TI _k ,
It _{consists of the} information I _k and the end signal and is transmitted for a time T.

In the present invention, transmission is not possible even if the time τ elapses with the received electric field strength E lower than the reference value E _o . That is, if the time information TI _k is received, the corresponding time T
Transmission is restricted because _k is receiving a signal (there is a radio wave from another station).

When the time T is long in the time T in which the information is received, it is quite possible that the condition of E <E _o continues for a time τ or longer. However, if the time information TI _k is received,
_{Since k} is limited in transmission, there is no risk of transmission even if the state of E <E _o continues for τ or more.

Of course, under fading, the time information TI _k may not be received. Maximum non-detection rate of time information is 1/10
Even if it is assumed, the probability that it will not be detected during radio wave emission of another station and will be transmitted will be 1/10 compared to the conventional one, so there is a practical effect.

Furthermore, if the non-detection rate of time information is made sufficiently small by error correction or the like, the transmission control method of the present invention becomes more reliable.

Further, in the present invention, not only the timer 20 detects the end signal but also the timer 22 detects the time T _k from the time information detection time.
It is cleared when it is judged that the time has passed. Therefore, when the end time cannot be detected, unnecessary transmission restrictions are not imposed.

Although FIG. 1 and FIG. 2 have explained the case where the end signal is included, it is clear that the same effect can be obtained by applying the present invention even when the end signal is not included. In this case, in FIG. 1, the end signal pattern generator 16, the end signal detector 21, and the OR circuit 25 are unnecessary, and the fall detector 26
Output pulse of is directly connected to clear timer 20.

〔The invention's effect〕

As described above, the transmission control method of the present invention is not limited to whether the received electric field strength is equal to or higher than the reference value,
The time transmission determined by the time information included in the received signal is limited, and the probability of signal collision is greatly reduced compared to the conventional method. In the case of the present invention,
The end of transmission is detected more reliably than in the past, and it is possible to prevent unnecessary transmission restrictions.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment for realizing the transmission control system of the present invention, and FIG. 2 is a signal configuration and reception electric field strength for explaining the presence / absence of a radio wave and the transmission control by the method of the present invention. FIG. 3 is a diagram showing an example of the configuration of an information transmission system to which the present invention is applied, and FIG. 4 is a signal for explaining the presence / absence of radio waves and transmission control by a conventional method. The figure which showed the example of a structure and received electric field strength. In the figure, 1 to 6 are memories, 8 is a transmission switch, 14 is a combining unit, 16 and 1
7 is a switch circuit.

Claims (2)

(57) [Claims] 1. In wireless information transmission between a plurality of stations within a limited area, each station starts transmission at the time of transmitting information having different transmission times or ends transmission during transmission. The transmission control means is provided with means for transmitting the time information inclusive, and when the time information is received, the transmission control means is provided for restricting transmission at least for a time corresponding to the time information.
The time information detection unit, a first timer that raises the output for a time corresponding to the time information when the time information is detected by the detection unit, the electric field detection unit, and the received electric field level is a reference value. And a second timer that rises and falls after a predetermined time elapses from the time when the received electric field level becomes equal to or lower than the reference value, and the second timer that falls at the time when the first timer falls A transmission control method characterized in that the second timer is configured to be cleared, and transmission is not performed when one of the first timer output and the second timer output rises. . 2. The transmission control system according to claim 1, further comprising means for adding an end signal at the end of transmission at each station, wherein the transmission control means has a detector for detecting the end signal, Either the first timer output or the second timer output is configured to clear the second timer at the time of detecting the reception of the end signal or at the time of the fall of the first timer. A transmission control method characterized by limiting transmission so that it does not occur when is activated.