JPH08116323A - Data communication system - Google Patents

Abstract

PURPOSE: To detect collision by each transmission station while suppressing the reduction of throughput by transmitting a signal representing the collision of data by judging the detection of a carrier on a transmission line in a prescribed period as the collision of the data. CONSTITUTION: A transmission control circuit 11 performs the dividing processing of transmission data so as to reduce probability to detect the collision of a data frame and to set colliding frame length at the same length when a line is set in an idling state. Thence, the circuit 11 releases a carrier switch signal by transmitting to a changeover switch 1c via an inverter 1h to exclude the sneak path of a transmission signal to a reception system, and after that, transmits the data frame via a modulation circuit 1i and a high-frequency transmission circuit 1e. After transmission, a collision detection circuit 1k detects the collision by a carrier sense window when it is detected, and reports a jam signal representing the occurrence of the collision to a station in which the collision occurs and from which the transmission signal is transmitted, and performs re-processing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data communication system, and more particularly to a data communication system for detecting a data collision that occurs when a plurality of stations are connected via a transmission line.

[0002]

2. Description of the Related Art Conventionally, a plurality of wireless communication devices (hereinafter referred to as
It is called "station". ) Performs data communication between a plurality of stations using a transmission line such as a single carrier wireless line, data (hereinafter referred to as “frame”) transmitted from different stations causes a collision. , The frame may not be correctly received by the partner station.

Therefore, as a conventional access technology for preventing such frame collision, "IEEE 802.11 Committee materials"
DOC: IEE802.11-93 / 190 (1993) p.19-27 ", CSMA / CA (Carrier Sense Multiple Access with)
Collision Avoidance) method (hereinafter referred to as “first conventional technology”) and a signal collision detection method (hereinafter, referred to as “first prior art”) provided with a test period disclosed in Japanese Patent Laid-Open No. 4-373341.
This is called "second conventional technology". ) Is known.

First, CSMA / used in the first conventional technique
The CA method is an Ack (Acknowlege) frame or RTS (Reknow
This is a technique for confirming the occurrence of collision using a quest to send frame and a CTS (Clear to send) frame.

FIG. 12 shows CSMA using an Ack frame.
It is a figure which shows the time sequence of a / CA system.

As shown in FIG. 12A, in this case, 4
Among the stations A to D, the case is shown in which the frame is first transmitted from the station A to the station B, and then the frame is transmitted from the station C to the station D.

That is, first, station A receives data frame 1
Carrier sense 12a of wireless line prior to transmission of 2b
After confirming that the wireless line is in a state where there is no data transmission from another station (hereinafter referred to as “idle state”), the data frame 12b is transmitted to the B station.

Station B, which has completed reception of this data frame 12b, outputs an Ack frame 12c.

Here, when the station C performs the carrier sense 12d during the transmission of the data frame 12b, the C
Since the station can confirm that there is data transmission from another station (hereinafter, referred to as “busy state”), after the Ack frame 12c is received from the station B and a predetermined time (Tb) has passed, , The data frame 12e is transmitted.

As described above, in the CSMA / CA method using such an Ack frame, when the wireless line is busy, the transmission from other stations is suppressed until the Ack frame is transmitted, so that the frame is transmitted. Avoiding collisions.

However, according to this technique, as shown in FIG.
When a plurality of stations simultaneously output data frames as shown in (b), frame collision cannot be detected.

As shown in FIG. 12B, when the carrier sense 12g of the A station and the carrier sense 12h of the C station are performed at the same time, the wireless channels of the A station and the C station both become idle. Since it is recognized that the data is present, the data frame 12i transmitted by the A station and the data frame 12j transmitted by the B station cause a collision.

That is, CS using this Ack frame
According to the MA / CA method, if carrier senses of different stations are simultaneously performed, frame collision cannot be avoided.

Therefore, in this CSMA / CA system,
In addition to the Ack frame described above, RTS / CTS frames are often used.

FIG. 13 is a diagram showing a time sequence when an RTS / CTS frame is added to the CSMA / CA system shown in FIG.

As shown in FIG. 13A, in this case, the station A which has performed the carrier sense 13a confirms that the station A is in the idle state, and then transmits the RTS frame 1 to the station B.
3b is transmitted and a transmission request is made.

Then, the station B which has received the RTS frame 13b returns the CTS frame 13c to the station A as a response signal.

After that, the A station which has received the CTS frame 13c transmits the data frame 13d, and the B station which has completed the reception of the data frame 13d transmits the Ack frame 13e.

Here, while the station A is transmitting the data frame 13d to the station B, the station C carries out carrier sense 1
In the case of performing 3f, the C station transmits the Ac transmitted from the B station.
After receiving the k frame 13e, the RTS frame 13g is transmitted to make a transmission request.

As described above, in this conventional technique, the transmission source station makes a transmission request (RTS) after carrying out carrier sensing, and confirms whether a collision occurs before transmitting a data frame. .

FIG. 13B is a diagram showing a time sequence when the A station and the C station simultaneously perform carrier sensing.

As shown in FIG. 13B, when the carrier sense 13h of the station A and the carrier sense 13i of the station C are simultaneously performed, the wireless line is in the idle state at that time, so Transmits an RTS frame, and this RTS frame collides.

That is, according to this conventional technique, the collision of the data frames can be avoided by detecting the collision of the RTS frames before the collision of the data frames to be originally transmitted.

Note that, in FIG. 13B, a portion which is actually processed is shown by a solid line, and a portion which is not processed is shown by a dotted line.

As described above, in the first conventional technique, the collision of the data frames is avoided by using the Ack frame and the RTS / CTS frame.

Next, the second conventional technique will be described.

The second prior art is CSMA / CD.
(Carrier Sense Multiple Accesswith Collision Dete
In order to realize the communication method on a wireless line, a plurality of predetermined pulse signals are transmitted at random time intervals for a certain period prior to frame transmission, and while other pulse signals are not transmitted from other stations. This is a signal collision detection method in which when a pulse signal is detected, it is determined that a collision has occurred, transmission of a data frame is stopped, and a retransmission procedure is started.

FIG. 14 is a diagram showing a time sequence when the second conventional technique is used.

In this figure, the carrier sense 14a of the station A, which attempts to transmit the data frame to the station B, and the D
It shows a case where the carrier sense 14b of the C station which is going to transmit the data frame to the station is simultaneously performed.

As shown in FIG. 14, the station A transmits a pulse signal 14c before transmitting a data frame after confirming that the wireless line is in the idle state by the carrier sense 14a.

Similarly, station C also performs pulse signal 1 after transmitting carrier frame 14b after performing carrier sense 14b.
4d is transmitted.

At the A station, the pulse signal 1 from its own station
Since the pulse signal 14d transmitted from the C station is received while transmitting 4c, it is determined that a collision has occurred, and transmission of the data frame is stopped.

As described above, in the second conventional technique, the collision of data frames is detected in advance by transmitting the pulse signals having different patterns from each other prior to the data frame transmission.

[0034]

However, the Ack frame and RTS / CTS frame used in the first prior art are
Since the frame structure is added with control data such as a flag and a CRC code, there is a problem that throughput is reduced.

In particular, the transmission of this Ack frame must be performed after receiving the data frame, and the transmission of the RTS / CTS frame must be performed before transmitting the data frame. Therefore, the accumulation of such frames lowers the throughput. .

On the other hand, also in the second prior art, a test time is always required to perform a test using a pulse signal before transmitting a data frame.

Then, in order to check whether or not a pulse from another station is received between a plurality of pulse signals emitted from the own station, a certain test period is required, which lowers the throughput.

As described above, the first prior art and the second prior art
No matter which of the above-mentioned conventional techniques is used, there is a problem that a decrease in throughput cannot be avoided when detecting data collision.

Therefore, it is an object of the present invention to solve the above problems and provide a data communication system capable of detecting a data collision while suppressing a decrease in throughput.

[0040]

To achieve the above object, the first invention is to connect a plurality of stations via a transmission line,
In a data communication system in which each station transmits data to another station via the transmission line after confirming that there is no carrier on the transmission line, data transmission means (in FIG. 1) transmitting data having different data lengths. 1l), carrier detecting means for detecting a carrier on the transmission path (1g in FIG. 1), and carrier on the transmission path by the carrier means within a predetermined period after the data transmission is completed by the data transmitting means. When a collision is detected by the collision detection means (1k in FIG. 1) that determines that the data collides with another data transmitted from another station, Is a collision signal transmitting means (11 in FIG. 1) for transmitting a signal indicating that data collision has occurred to the other station after the other station finishes transmitting data. Characterized in that the equipped in each station.

In the second invention, a plurality of stations are coupled via a transmission line, each station confirms that there is no carrier on the transmission line, and then transmits data to another station via the transmission line. In a data communication system for transmitting data, data transmission means (1l in FIG. 1) for transmitting data having different data lengths, carrier detection means (1g in FIG. 1) for detecting a carrier on the transmission path, and After the transmission is completed, a first period and a second period subsequent to the first period are set, and when a carrier on the transmission path is detected in the first period, a first collision state occurs. Collision detecting means (1 in FIG. 1) that determines the second collision state when the carrier on the transmission path is detected only during the second period.
k) and if the collision detection means determines that the first collision state has occurred, it is determined that the data collision has occurred to the other station after the other station finishes transmitting the data. Collision signal transmitting means for transmitting the indicated signal (1l in FIG. 1)
Each station is equipped with and.

[0042]

According to the first aspect of the invention, each station confirms that there is no carrier on the transmission line by using the carrier detection means, and then uses the data transmission means to transmit the data having different data lengths through the transmission line. When the carrier on the transmission path is detected by using carrier detection means after transmitting the data to another station via the carrier detection means and the carrier on the transmission path is detected by the carrier means within a predetermined period. Is a collision detection means, the data and other data transmitted from another station is determined to have collided, collision signal transmission means, after the other station has finished transmitting data,
A signal indicating that a data collision has occurred is transmitted to the other station.

Therefore, each of the transmitting stations can detect a data collision that occurs when a plurality of stations determine that there is no carrier on the transmission path and start transmitting data at the same time while reducing the decrease in throughput. You can

According to the second aspect of the invention, each station uses the carrier detecting means to confirm that there is no carrier on the transmission line, and then uses the data transmitting means to transmit the data having different data lengths. When the carrier on the transmission path is detected by using the carrier detecting means after transmitting the data to another station via the path and the data is transmitted, and the carrier on the transmission path is detected in the first period, The first collision state is judged by the collision detection means, and when a carrier on the transmission path is detected only during the second period, it is judged as the second collision state and the first collision state is detected by the collision detection means. When it is determined that the state is in the state, the collision signal transmitting means transmits the signal indicating that the data collision has occurred to the other station after the other station finishes transmitting the data.

Therefore, it is possible to prevent the station that has received the signal indicating that the data collision has occurred from outputting the same signal further, and to improve the throughput.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a wireless communication system will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a wireless communication system according to the present invention and a detailed configuration of stations that join the wireless communication system.

As shown in FIG. 1, this radio communication system is a system in which four stations A, B, C and D having the same function communicate with each other using a single carrier radio line.

When transmitting a data frame to another station, each station that joins the wireless communication system first carries out carrier sense on the wireless line and transmits the data frame if the communication path is idle.

It should be noted that each station is provided with a function of detecting the collision of data frames by carrying out carrier sensing again after the end of data frame transmission.

Next, the configuration of each station will be specifically described by taking the station A as an example.

Station A has an antenna 1a, a circulator 1b, a changeover switch (SW) 1c, a high frequency receiving circuit 1d, a high frequency transmitting circuit 1e, a demodulating circuit 1f, a carrier detecting circuit 1g, an inverter 1h, and Modulation circuit 1i
, A memory 1j, a collision detection circuit 1k, and a transmission control circuit 1l.

The circulator 1b is a high frequency transmission circuit 1
The high frequency signal received from e is output to the antenna 1a, and the reception signal from the antenna 1a is output to the high frequency receiving circuit 1d via the changeover switch 1c.

The change-over switch 1c disconnects the circulator 1b and the high-frequency receiving circuit 1d from each other when data transmission is performed to prevent the transmission signal from sneaking into the receiving system. Connecting.

The high frequency receiving circuit 1d demodulates the received signal obtained by removing the harmonic component from the received signal from the antenna.
f and the carrier detection circuit 1g.

The high frequency transmission circuit 1e amplifies the transmission signal received from the modulation circuit 1i and outputs it to the circulator 1b.

The demodulation circuit 1f demodulates the reception signal received from the high frequency reception circuit 1d and writes the demodulated reception data in a predetermined location of the memory 1j.

The carrier detection circuit 1g outputs the carrier display signal detected from the reception signal received from the harmonic wave reception circuit to the collision detection circuit 1k and the transmission control circuit 1l.

When the received signal strength of the received signal is above a certain level, the carrier display signal is turned on,
In other cases, the carrier display signal is turned off.

The modulation circuit 1i modulates the transmission data received from the transmission control circuit 11 and outputs it to the harmonic transmission circuit 1e.

The memory 1j is a memory for exchanging data with a data processing unit (not shown).
The transmission data written in the predetermined location of the above is subjected to the transmission processing, and the reception data written in the predetermined location is read out by the data processing unit.

The collision detection circuit 1k, based on the carrier switch signal received from the transmission control circuit 11 and the carrier display signal received from the carrier detection circuit 1g,
Whether or not there is a data frame collision is confirmed, and when a data frame collision is detected, a collision detection signal is output to the transmission control circuit 11.

The transmission control circuit 1l is the carrier detection circuit 1
carrier indication signal received from the g and the collision detection circuit 1
Based on the collision detection signal received from k, switching control of the changeover switch 1c and data frame transmission control are performed.

The transmission control unit 1l also performs data division and jam signal generation, which will be described later.

As is apparent from the above configuration, this station A
It can be seen that a collision detection circuit 1k for detecting a data frame collision is added to the conventional station configuration, and a data division function and the like are added to the transmission control circuit 11.

Next, the concept of the present invention in which the collision detection circuit 1k is introduced will be described with reference to the time chart shown in FIG.

In each time chart shown below,
It is assumed that data is transmitted from station A to station B and from station C to station D, and only the time charts of stations A and C on the transmitting side are shown in each figure.

FIG. 2 (a) is a diagram showing a case where station C performs carrier sense while station A is transmitting a data frame. In this case, as in the prior art, station A
When the station finishes transmitting the data frame,
After the elapse of b), the station C will transmit the data frame.

By the way, in the present embodiment, after transmitting the data frame, the carrier sense window 2a is provided to detect the collision of the data frame.

Therefore, this carrier sense window 2
A will be described with reference to FIG.

FIG. 2B is a diagram showing a case where the carrier sense 2b by the station A and the carrier sense 2c by the station C are performed at the same time. In this case, the stations A and C are both connected to the wireless channel. A to recognize that it is idle
The data frame 2d transmitted from the station collides with the data frame 2e transmitted from the station C.

At this time, data frame 2 transmitted by station C
The frame length of e is the data frame 2d transmitted by station A.
Since it is shorter than the frame length of C, station C performs carrier sense immediately after the end of transmission of data frame 2e. That is, when the released switch 1c is closed, carrier sense is performed after Tc time after data transmission, so that the presence of the data frame 2d transmitted from the A station can be detected.

As described above, if there is a difference in data frame length from each other, the carrier sense window 2 according to the present invention.
By using a, a data frame collision can be detected.

In this case, like the station C, a station that has transmitted a data frame having a short frame length can detect a collision, but the other station cannot detect a collision. It is configured to transmit a jam signal indicating the presence or absence of a collision.

The functional unit for performing collision detection using the carrier sense window is the collision detection circuit 1k.

Next, the data transmission processing procedure of station A,
The processing procedure of the collision detection circuit 1k in this processing will be specifically described with reference to FIGS. 3 and 4.

FIG. 3 is a flow chart showing the data transmission processing procedure of station A shown in FIG.

As shown in FIG. 3, station A first carries out carrier sense (step 301) and checks whether or not the wireless line is busy (step 302). If it is busy, it waits for a certain period of time. After that, the process shifts to step 301 and the above process is repeated to wait for the idle state.

Specifically, the transmission control circuit 1l confirms the carrier display signal obtained from the carrier detection circuit 1g, and while the carrier display signal is on, recognizes that the wireless line is busy, When the display signal is turned off, it is recognized as in the idle state.

Then, after confirming that the wireless line is in the idle state, the transmission control circuit 11 carries out the division processing of the transmission data (step 303).

Here, if the frame lengths of the data frames that start transmission at the same time are equal to each other, the collision of the data frames cannot be detected, so that the probability that the frame lengths of the colliding data frames become the same will be reduced. The division is done. The division of the transmission data will be described later.

Next, in order to prevent the transmission signal from sneaking into the receiving system, the transmission control circuit 1l transmits the carrier switch signal to the changeover switch 1c via the inverter 1h, and after releasing the changeover switch (step 304), The transmission data is modulated by the modulation circuit 1i and the modulated transmission data is amplified by the high frequency transmission circuit 1e (step 30).
5) Transmit a transmission signal, that is, a data frame (step 306).

When the transmission of the transmission signal is completed, the carrier sensing is performed again, and it is detected whether or not the collision of the transmission signals occurs based on the result of the carrier sensing (step 307).

When it is recognized that a collision has occurred, a jam signal indicating that a collision has occurred is notified to another station that has transmitted the transmission signal causing the collision (step 309), and then the retransmission processing is performed. (Step 310) and the process ends.

Next, the collision detection processing performed by the collision detection circuit 1k shown in step 307 will be specifically described.

FIG. 4 is a flowchart showing a collision detection processing procedure performed by the collision detection circuit 1k.

As shown in FIG. 4, this collision detection circuit 1k
Then, it is confirmed whether or not the transmission of the data frame is finished (step 401), and when the transmission of the data frame is finished, the operation of the built-in timer is started (step 4).
02) and confirms whether the carrier display signal output from the carrier detector 1g is ON (step 403).

The reason for checking whether or not the carrier display signal is ON is that the carrier detection circuit 1g turns the carrier display signal ON only when a carrier is detected, that is, when a data frame collision occurs. This is because.

Therefore, when it is confirmed that the carrier display signal is ON, a collision detection signal indicating that a data frame collision has occurred is turned ON and transmitted to the transmission control unit 11 (step 404).

On the other hand, if the carrier display signal is not turned ON for a predetermined time (step 405), since collision of data frames does not occur, the process is terminated as a timeout.

As described above, in this embodiment, after the data frame is transmitted, the collision detection circuit 1k is used to detect the collision by the carrier sense window, and when the collision is detected, the jam signal is transmitted. There is.

Although omitted for convenience of explanation, even when the carrier display signal is turned on and the collision detection signal is turned on, carrier detection by the carrier detection circuit 1g is terminated and the carrier display signal is turned off. If so, the collision detection signal is naturally turned off.

Next, the mutual relation of the signals output from each component of the station will be described with reference to FIG.

FIG. 5 (a) is a diagram showing a time chart of each signal output from each component of the station C which has completed the transmission of the data frame first.

As shown in the figure, in station C, the transmission control circuit 1l turns on the carrier switch signal (5a) to switch the changeover switch 1c (5b), and the circulator 1b.
And disconnect the high-frequency receiving circuit 1d,
The transmitted harmonic data is output to the wireless line (5c).

Further, since the data frame length transmitted by the C station is shorter than the data frame length of the A station which starts transmission at the same time, the A station transmits the data at the time when the transmission of the harmonic data of the C station is completed. It means that frame transmission is continuing.

Therefore, after the transmission harmonic data is turned off, the reception harmonic data is turned on (5d),
The carrier display signal output from the carrier detection circuit 1g and the collision detection signal output from the collision detection circuit 1k are also ON (5e).

When the transmission of the harmonic data by the station A is completed, the station C outputs a jam signal to the station A (5f) to notify that the data frame collision is detected.

From these, it can be seen that the carrier switch signal, the transmission harmonic data, and the time sequence of the changeover switch correspond to each other, and the reception harmonic data, the carrier display signal, and the time sequence of the collision detection signal correspond to each other.

Further, as shown in FIG. 5B, station A, which continues transmitting data frames at the end of transmission by station C,
Since the jam signal transmitted from station A is received after the data frame is transmitted, the carrier display signal is ON (5g).
At the same time, the collision detection signal output from the collision detection circuit 1k also becomes ON (5h).

In the present embodiment, also in the A station, after the data frame transmission is completed, the carrier switch signal is turned on to release the changeover switch, and the jam signal is transmitted (5i).

Next, the carrier sense window (t
The carrier detection time by cw) will be described.

First, when the frame length of the data frame transmitted by another station is longer than that of the data frame transmitted by the own station, carrier detection is started immediately after the data frame transmission of the own station is completed. can do.

However, when the frame length of the data frame transmitted by another station is shorter than that of the data frame transmitted by the local station, the propagation delay time (t
The carrier detection period needs to be determined in consideration of d) and the time (tj1) from when the station detects the end of transmission to when the jam signal is transmitted.

That is, in the case shown in FIG. 6, the station A needs to perform carrier detection at least until the jam signal is notified from the station C after the transmission of the data frame a is completed. The data frame transmission end time is tn, the time until the own station recognizes that a jam signal has been received is tcd, and the maximum transmission delay time between stations is tdm.
If it is ax, it is necessary to detect the carrier at least up to tn + (2tdmax + tj1 + tcd).

Incidentally, these tdmax, tj1 and tcd
In fact, since it is a minute time, it is possible to detect the carrier quickly.

By the way, in the above embodiment, the jam signal is transmitted not only to the station C which has finished the transmission of the data frame but also to the station A which has finished the transmission of the data frame.

However, when the jam signal is received from station C, A
If the station sends the jam signal again to the C station that has already detected the collision, it results in unnecessary traffic.

Therefore, a second embodiment will be described in which a station that has already received a jam signal from another station does not transmit the jam signal.

FIG. 7 is a time chart showing a case where the data frame a transmitted from the A station and the data frame c transmitted from the C station compete with each other.

As shown in FIG. 7, in the second embodiment, two types of carrier sense windows (tcw1, tcw1, tcw1, tcw1, tcw1, tcw1) are used.
cw2) is provided.

That is, in the first embodiment, if a signal is input within the carrier sense window, a collision of data frames can be detected regardless of whether the signal is a data frame or a jam signal. In the second embodiment, the first carrier sense window (tcw1) for carrying out carrier sensing of the data frame and the carrier sense window (t for carrying out carrier sensing of the jam signal are provided in the second embodiment.
cw2).

As described above, the reason for providing the two types of carrier sense windows is that the window for carrying out the carrier sense of the data frame and the window for carrying out the carrier sense of the jam signal are separated so that the jam signal is received by each station. This is so that they can be recognized.

In other words, in the second embodiment, each station is configured to be able to recognize a jam signal coming from another station, thereby preventing a new jam signal from being transmitted to another station. Is there.

Next, the collision detection processing procedure of the second embodiment for performing collision detection using the above two carrier sense windows will be described.

FIG. 8 is a flow chart showing the collision detection processing procedure of the second embodiment according to the present invention.

As shown in FIG. 8, the collision detection circuit 1k is
It is confirmed whether or not the transmission of the data frame is completed (step 801), and when the transmission of the data frame is completed, the operation of the built-in timer 1 and timer 2 is started (step 802), and the carrier detector 1g is operated. It is confirmed whether the output carrier display signal is ON (step 803).

Here, the timer 1 is a timer corresponding to the first carrier sense window (tcw1). When the tcw1 is closed, the timer 1 times out, and similarly, the timer 2 receives the second window. (Tcw
Corresponds to 2).

Then, if it is confirmed that the carrier display signal is ON, it is confirmed whether or not the timer 1 has timed out (step 804). If it has not timed out, that is, the carrier detection is within tcw1. If so, the notification signal is turned on (step 8).
At the same time, the collision detection signal is turned ON (step 806).

The notification signal is a signal indicating whether or not the jam signal is transmitted to another station. When the collision detection circuit 1k turns on the notification signal and transmits it to the transmission control circuit 1l, the jam signal is sent. The signal is transmitted to other stations.

On the other hand, when the timer 1 has timed out, that is, when carrier detection is performed within tcw2, the notification signal is held in the OFF state and only the collision detection signal is turned ON ( Step 806).

The above process is repeated until the timer 2 times out (step 807), and the process is terminated when the timer 2 times out.

By processing the notification signal and the collision detection signal using the timer 1 and the timer 2, the jam signal can be transmitted only when the carrier is detected in tcw1.

Next, the carrier detection time of the first carrier sense window (tcw1) and the carrier detection time of the second carrier sense window (tcw2) will be described with reference to FIG.

First, since this tcw1 is a dedicated window for detecting the carrier of the data frame, it is possible that the frame length of the data frame transmitted from another station is longer than the data frame transmitted from the own station. I need to think.

That is, in this case, similarly to the case described in the first embodiment, the carrier detection can be started immediately after the transmission of the data frame from the own station is completed.

Since this tcw1 does not detect a jam signal transmitted from another station, it is the final time of receiving a data frame transmitted from another station, that is, tm + td + tcd (however, tm + td + tcd Is sufficient to detect the carrier until the maximum long frame transmission time).

On the other hand, since tcw2 is a dedicated window for detecting a jam signal, it is necessary to consider the case where the data frame transmitted by another station is shorter than the data frame transmitted by the own station. There is.

In this case, as a general rule, the carrier detection may be started from the end time of the carrier detection of tcw1. However, at least before the earliest arrival of the jam signal from another station, the carrier detection should be started. I need to put it.

That is, at the minimum time when a jam signal transmitted from another station can reach its own station, that is, at tn + (2tdmin + tj1 + tcd), carrier detection by tcw2 must be started.

The end of the carrier detection of tcw2 needs to be set later than the final time when the jam signal described in the first embodiment arrives, that is, tn + (2tdmax + tj1 + tcd).

By thus setting the carrier detection times of tcw1 and tcw2 respectively, it becomes possible to separate the carrier detection of the data frame and the jam signal and prevent the unnecessary jam signal from being transmitted. .

As described above, in the first and second embodiments, the collision of data frames is detected by providing the carrier sense window for detecting the carrier after transmitting the data frame. .

Therefore, the present invention is premised on that the other station continues to transmit the data frame when its own station finishes transmitting the data frame.

However, when the data length of the data to be transmitted is long, since the data is divided by the maximum frame length, the data frames transmitted from each station have the same frame length.

For example, when Ethernet is used, the upper limit of the data length included in the frame is 15
Since it is defined as 00 bytes, a large number of maximum length frames having 1500 bytes of transmission data will be transmitted.

Therefore, hereinafter, a data division method for reducing the occurrence probability of the same frame length when the data length of the data to be transmitted is longer than the maximum frame length will be described with reference to FIG.
It will be described using 0.

The division of the transmission data is performed by the transmission control circuit 11 as described with reference to FIG.

FIG. 10A is a diagram showing a first data division method in which a difference is provided in the data length itself included in the data frame.

In this first data division method, the frame length of each data frame is determined using random numbers.

That is, if the maximum data length that can be included in a frame is M, the minimum difference between the frame lengths in which collision detection is possible in the present invention is n, and a random number consisting of a positive integer is RND, the data included in each frame is The length (Fi) is divided so that Fi = M−n × RND.

Then, a header such as a flag is added to each of the divided data to generate a plurality of data frames having different frame lengths.

As described above, by providing the difference in the data length itself included in the data frame, it is possible to provide the difference in the frame length of the data frame.

Depending on the application or the like, there are cases where a large number of frames of a specific length, which are shorter than the maximum frame length, are transmitted.

In this case, if the data length included in the frame of the specific length is G, the minimum difference between the frame lengths in which collision detection is possible in the present invention is n, and the random number consisting of a positive integer is RND,
The probability of occurrence of the same frame can be reduced by generating a frame with G + nxRND, which is obtained by adding nxRND to the data length G, as the data length.

The minimum difference n between the frames is the time (ta) from carrier sense before transmission to frame transmission.
And the time from transmission end to carrier sense (tb)
And the sum (ta + tb + tcd) of the time (tcd) until it is determined to be busy after receiving the signal.

FIG. 10B is a diagram showing a second data division method in which a variable-length additional signal 10b is added to transmission data to form a data frame.

In the second data division method, an additional signal created by using random numbers is added to the transmission data divided into fixed lengths.

That is, M is the maximum data length that can be included in a frame, n is the minimum difference between the frame lengths in which collision detection is possible in the present invention, and RND, RN are random numbers consisting of positive integers.
When the maximum value of D is m, the transmission data is divided into a plurality of data 10a having a length of (M-m).

Then, for each of the above data 10a,
(M−m) + n × RND added with (n × RND) becomes the data length of the transmission data included in each data frame. By adding a header such as a flag to each transmission data, the frame A plurality of data frames having different lengths are generated.

As described above, by dividing the transmission data into fixed-length data and constructing the data frame based on the data obtained by adding the additional signal 10b to the data, a difference in the frame length of the data frame can be provided. it can.

If the probability that frames are transmitted at the same time is P and the probability that the frames have the same length are Q, the probability R that a collision cannot be detected is R = P × Q. By using the division method and the second data division method to reduce the probability Q that frames have the same length, it is possible to reduce the probability R that a collision cannot be detected.

Next, the reason why the present invention improves the throughput will be described with reference to FIG.

FIG. 11 is a diagram showing a comparison of the time charts of the above-mentioned conventional technique and the present invention.

Ac of CSMA / CA, which is the first conventional technique
When the k method is used, the receiving station needs to send the Ack frame 11a after receiving the data frame.
When the TS method is used, the RTS frame 11b and CTS frame 11c are required.

Further, in the second conventional technique, a test period 11d for conducting a test using a pulse signal is required before transmitting a data frame.

On the other hand, in the present invention, the carrier sense window 11e is provided after transmitting the data frame.

Therefore, in the following, the medium occupancy time by the carrier sense window 11e of the present invention and the case of the above Ac when the collision does not occur and when the collision occurs.
The medium occupation time and the test period 11d by the k frame 11a, the RTS frame 11b, and the CTS frame 11c are compared.

First, considering the case where no collision occurs,
In the case of the present invention, the medium occupancy time by the carrier sense window 11e depends on the jam signal transmission time except for the minute time such as the delay time and the transmission / reception switching time, and the jam signal transmission time allows the carrier sense. Therefore, it is not necessary to set the length longer than the preamble length of the carrier sense performed prior to the transmission of the data frame.

On the other hand, the first prior art Ack frame 11a, RTS frame 11b and CTS frame 11c are used.
Since the frame has a frame structure, the medium occupancy time is increased as compared with the present invention due to various flags and check codes necessary for the frame.

The pulse signal itself used in the second prior art has the same medium occupation time as the jam signal of the present invention, but in the second prior art, a plurality of pulse signals are arranged, Since the configuration is used in which pulses transmitted from other stations are received during the pulse transmission, the medium occupation time increases as the collision detection probability is increased.

From this, it can be seen that the present invention improves the throughput as compared with the above-mentioned prior art in the case where no collision occurs.

Next, the throughput when a collision occurs will be described.

Since the present invention confirms the data frame collision after the fact, when focusing on only the frame in which the collision has occurred, the data frame collision is detected in advance and the unnecessary data frame is transmitted. It is considered that the first conventional technique using the non-RTS / CTS frame and the second conventional technique using the test period are more efficient.

However, considering all the frames including the frames in which no collision occurs, the present invention improves the throughput.

That is, of the I transmission frames, J
Assuming that a collision occurs in the number of frames, according to the present invention, the time T1 until all the frames are transmitted is T1 = I
X (DATA + carrier sense time) + J x DATA.

On the other hand, using the first conventional technique using the RTS / CTS frame, the time T2 until all the frames are transmitted is: T2 = I × (RTS + CTS + DATA) + J × (RTS + CTS) −J
× DATA, and the time T3 until all frames are transmitted using the second conventional technique is T3 = I × (test time + DATA) + J × (test time)
-J × DATA.

Here, in an actual operating environment, J /
Considering that I is sufficiently small, the merit of preventing the transmission of the collision data frame is small,
It can be seen that the present invention improves throughput.

From this, it is understood that according to the present invention, the throughput is improved not only when the collision does not occur but also when the collision occurs.

As described above, in this embodiment, after a data frame is transmitted from one station to another station via a wireless line, carrier detection is performed using the carrier sense window, and if a carrier is detected, For example, since the jam signal is configured to be transmitted to the other station that has transmitted the data frame in which the collision has occurred, it is possible to prevent a decrease in throughput at both the stations that have transmitted the data frame,
Data frame collisions can be detected.

Further, since the first carrier sense window for detecting the data frame and the second carrier sense window for detecting the jam signal are provided, the station receiving the jam signal does not need an unnecessary jam. Signal transmission can be stopped and throughput can be improved.

Further, when the transmission data length is longer than the maximum frame length, the transmission data is divided so that each data frame length has a different size by using a random number, so that the probability of collision detection is improved. Can be achieved.

In this embodiment, the case where the present invention is applied to the wireless communication system has been described. However, the present invention is not limited to wireless, and can be applied to a wired case.

Further, in the present embodiment, the jam signal is used as means for notifying the occurrence of a collision event to other transmitting stations.
This jam signal can be used not only by other transmitting stations but also by each station as a signal indicating the line status.

[0175]

As described in detail above, according to the first invention, the carrier on the transmission line is detected after transmitting the data from the transmitting station, and the carrier on the transmission line is detected within a predetermined period. In this case, it is determined that the data has collided with other data transmitted from another station, and after the other station finishes transmitting the data, a signal indicating that the data collision has occurred is transmitted. Since it is configured to transmit to other stations, data collision that occurs when multiple stations determine that there is no carrier on the transmission path and start transmitting data at the same time while reducing the decrease in throughput. It becomes possible to detect at each transmitting station.

According to the second invention, the carrier on the transmission path is detected after transmitting the data from the transmitting station, and the first
When a carrier on the transmission path is detected during the period of, the first collision state is determined, and after another station finishes transmitting data, a signal indicating that data collision has occurred is sent to the other station. The signal is transmitted to the station, and when the carrier on the transmission path is detected only during the second period, the second collision state is determined, so that the signal indicating that the data collision has occurred is received. It is possible to improve the throughput by preventing the above-mentioned station from outputting the same signal.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a wireless communication system and a detailed configuration of a station according to the present invention.

FIG. 2 is a time chart showing collision detection performed by the station shown in FIG.

FIG. 3 is a flowchart showing a data transmission processing procedure of the station shown in FIG.

4 is a flowchart showing a collision detection processing procedure performed by the collision detection circuit shown in FIG.

5 is a time chart showing the interrelationship of signals output from each component of the station shown in FIG.

FIG. 6 is a time chart showing carrier detection and notification using tcw.

7 is a time chart showing another example of collision detection performed by the station shown in FIG.

8 is a flowchart showing another collision detection processing procedure performed by the collision detection circuit shown in FIG.

FIG. 9 is a time chart showing carrier detection and notification using tcw1 and tcw2.

10 is a diagram showing a data division method performed by the transmission control circuit 11 shown in FIG.

FIG. 11 is a diagram showing a comparison between time charts of a conventional technique and the present invention.

FIG. 12 is a diagram showing a time sequence in the case of using a conventional technique provided with an Ack frame.

FIG. 13 is a diagram showing a time sequence in the case of using a conventional technique provided with an Ack frame and an RTS / CTS frame.

FIG. 14 is a diagram showing a time sequence in the case where a conventional technique for providing a test time is used.

[Explanation of symbols]

A, B, C, D stations, 1a antenna, 1b circulator, 1c changeover switch, 1d high frequency receiving circuit, 1e high frequency transmitting circuit, 1f demodulating circuit, 1
g carrier detection circuit, 1h inverter, 1i modulation circuit, 1j memory, 1k collision detection circuit, 1l
Transmission control circuit

Claims (2)

[Claims] 1. A data communication system in which a plurality of stations are coupled via a transmission line, each station confirms that there is no carrier on the transmission line, and then transmits data to another station via the transmission line. In the above, data transmission means for transmitting data having different data lengths, carrier detection means for detecting a carrier on the transmission path, and carrier means within a predetermined period after the data transmission by the data transmission means is completed. When a carrier on the transmission path is detected by, a collision detection unit that determines that the data collides with another data transmitted from another station, and a collision is detected by the collision detection unit Is a collision signal transmitting means for transmitting a signal indicating that data collision has occurred to the other station after the other station finishes transmitting data. Data communication system characterized by comprising a. 2. A data communication system in which a plurality of stations are coupled via a transmission line, each station confirms that there is no carrier on the transmission line, and then transmits data to another station via the transmission line. In data transmission means for transmitting data having different data lengths, carrier detection means for detecting carriers on the transmission path, and a first period and a first period after the transmission of the data is completed. A second period that follows is set, and when a carrier on the transmission line is detected in the first period, it is determined as a first collision state, and a carrier on the transmission line is detected only in the second period. In this case, a collision detection unit that determines the second collision state, and, if the collision detection unit determines that the first collision state, the other station, after the other station has finished transmitting data, To the station Data communication system, wherein a collision over data has and a collision signal transmitting means for transmitting a signal indicating that occurred each station.