JPS62176235A - Data communication system - Google Patents

Abstract

PURPOSE:To attain the data communication between a master station and a slave station with less propagation delay by switching the system into a time division multiplex system when data collision takes place between slave stations due to increased traffic or the occurrence of data collision is estimated. CONSTITUTION:A radio channel is sectioned into a time slot of a prescribed length and plural slave stations S1-S5 send a data at random to the master station in synchronism with the time slot. When the traffic of the radio channel is increased and the data collision takes place between the slave stations or the occurrence of data collision is expected, the system is changed over into the time division multiplex system.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a data communication system in which a wireless channel is divided into time slots of a fixed length, and a slave station transmits data to a master station in synchronization with the time slots.

[Technical background of the invention and its problems]

There are roughly three types of data communication methods in which a wireless channel is divided into time slots of a fixed length, and a slave station transmits data to a master station in synchronization with the time slots.

The first method is a time division multiple access method in which a time slot is fixedly assigned to each slave station, and the second method is a reservation access method in which a slave station that has data to transmit to the master station reserves a time slot. The third method is a random access method in which the slave station randomly transmits data to the master station in synchronization with time slots. Among these methods, the random access method is suitable for satellite communications, mobile communications, etc. because the traffic of each slave station is small and the propagation delay to the master station is smaller than the other two methods when there are many slave stations. It is widely used as a data communication method for wireless channels. The details of this random access method can be found, for example, in ``Packet Switching Technology and Its Applications'' edited by the Institute of Electronics and Communication Engineers, p.205~
It is stated on page 222 (published on 420th day of the month of 1982).

By the way, in broadcast communication in which the master station performs simultaneous communication to all or specific slave stations, each slave station receives an ACK signal after receiving the broadcast communication signal from the master station due to the reliability of the system.
It is desirable to transmit an (Acknowledgment) signal to the master station.

Conventionally, when a random access method is adopted, an ACK signal for broadcast communication is also transmitted using the random access method. However, due to the priority of the ACK signal in broadcast communication,
After receiving the broadcast communication signal, it is expected that all of the plurality of slave stations will transmit ACK signals almost simultaneously. Therefore, as a matter of course, the ACK signals of each station collide and are retransmitted many times, resulting in a very large propagation delay until the ACK signal reaches the master station.

In this way, in the conventional random access method, the propagation delay was small and effective when the traffic at each station was small, but when the traffic temporarily increased due to broadcast communication or other reasons, the propagation delay was On the contrary, it becomes larger, so it has the disadvantage that it cannot necessarily be said to be an effective method, especially when there are large variations in traffic.

[Purpose of the invention]

This invention was made based on the above circumstances,
The purpose is to, regardless of the size of traffic,
It is an object of the present invention to provide a data communication system that allows data communication between a master station and a slave station with little propagation delay.

[Summary of the invention]

The present invention provides a data communication method in which a wireless channel is divided into time slots of a fixed length, and a plurality of slave stations randomly transmit data to a master station in synchronization with the time slots, when traffic on the wireless channel increases. The present invention is characterized in that the time slots of at least some of the slave stations are switched to be fixedly allocated.

〔Effect of the invention〕

According to the present invention, when the traffic is small, data is transmitted from the slave station to the master station using a random access method,
When traffic increases and a data collision occurs between slave stations, or when a data collision is expected, the system switches to time division multiplexing, so regardless of the size of the traffic, the transmission from the slave station to the master station is The propagation delay of data transmission can always be reduced.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 shows an example in which a master station sends a broadcast communication signal to a slave station, and the slave stations transmit an ACK signal to the master station in response. Note that the term "broadcast communication" is defined here as a broadcast communication signal in which a master station requests an ACK signal from a slave station. Further, here, the ACK signal and general data will be explained separately.

In the figure, TO to T9 are the times at which the time slots start, and specifically, each unique word contained in the data transmitted from the master station to the slave stations S1 to S5 at fixed time intervals using the downlink is This is the time after a certain period of time has elapsed after the slave stations S1 to S5 detected it. At time TO, data is being sent from the slave station S1 to the master station using the uplink in a random access method.

Now, if a broadcast communication signal is transmitted from the master station to all the slave stations S1 to S5 using the downlink during the period from TO to Tl, the uplink transmission signal will be determined from the unique word included in the broadcast communication signal. The time TI at which the next time slot begins is determined, and an ACK signal for broadcast communication is transmitted from each slave station 5l-85 to the master station from time TI. At this time, the communication method is Lang.

The system access method switches to the time division multiple access method. In this example, times Tl, T2. ..., each slave station Sl in each time slot starting from T5.

Child station S2. . . . adopts a method of fixedly allocating and transmitting the ACK signal from the slave station S5.

If such a method is adopted, it is possible to avoid the inconvenience of the ACK signals being transmitted from the five slave stations S1 to S5 all at once and colliding with each other, and the transmission is completed by at least time T6. Therefore, the propagation delay is much smaller than when maintaining the random access method.

Next, from time T6, data communication is again switched to the random access method. After this point, the traffic is small, so even if data collides with each other, the propagation delay can be kept small.

Note that in the above-described embodiment, while each slave station S1 to S5 is transmitting an ACK signal to the master station, other data cannot be sent. Therefore, immediately after the ACK signal is transmitted, the traffic from each slave station temporarily increases, and there is a concern that the number of data collisions will increase.

Therefore, as shown in Fig. 2, each time slot used in the random access method is divided into a plurality of small slots, and an ACK signal is transmitted in synchronization with each small slot using a time division multiplexing method. One idea is to secure as much data transmission time as possible. Each time slot is
Subdivision is possible to the extent that each slave station S1 to S5 can reliably transmit an ACK signal in synchronization with the slot.

In FIG. 2(a), the time slot is divided into two, two small slots are provided in one time slot, and all ACK signals from slave stations Sl to S5 are transmitted between time Tl and time T4. This speeds up the time it takes to return to the random access method.

The method shown in FIG. 2(b) is a time division multiplexing method in which each time slot is divided into two, and an ACK signal is transmitted in the first half of each time slot, and data is transmitted in the second half. That is, time Tl~TI', T2~T2',
During the periods T3 to T3', T4 to T4', and T5 to T5', the ACK signals of the slave stations si to S5 are
I, ACK2゜..., ACK5 are respectively transmitted, and the times Tl' to T2. T2'-T3. T3'-T4. T4'
In the period from to T5, the slave stations S1 to S5 are assigned, respectively, and their transmittable data is transmitted.

This allows data transmission from the slave station to the master station even during the ACK signal transmission period.

Also, when a broadcast communication signal is sent from the master station to all or some of the slave stations, even if the slave station that received the broadcast communication is transmitting an ACK signal, all the slave stations Another possible method is to allow data to be randomly transmitted from the base station to the master station. Figure Z (c) shows such an example.
From the master station to the slave station St.

Child station S2. When broadcast communication is performed to the slave station S4, the first half of each time slot from time Tl to T4, that is, TI-Tl', T2 to T2'.

During the period from T3 to T3', slave station S1. Child station S8. The slave station S4 transmits ACK signals ACKI, ACK2 and ACK4, and transmits the second half, that is, Tl' to T2. T2'~T3
．． During the period from T3' to T4, data is transmitted from all slave stations 5l-35 to the master station in synchronization with the small slots using a random access method. This causes ACK
Even during signal transmission, part of the data can be transmitted from all slave stations S1 to S5. Then, from time T4, the random access method is used with the original time slot length.

It goes without saying that in each of the above cases, the division ratio of the small slots can be varied as much as possible.

゛The above was an example of switching to the time division multiple access method in advance before ACK signals collide, but this embodiment is not limited to broadcast communication, and can also be used in the event of a disaster or when the number of slave stations suddenly increases. is applicable. It is also effective to keep statistics on traffic and switch based on this.

On the other hand, when retransmitting data when data from a slave station actually collides, data from a particular slave station is transferred to data from another slave station.
It is also possible to prevent propagation delays by giving priority to retransmission in the evening.

In FIG. 3, data retransmission of a specific slave station is given priority over data retransmission of other slave stations depending on the type of frame in which a collision has been detected. Here, the wireless channel is configured by alternately arranging reference frames fO and superframes fs, and each superframe fs is
A plurality of frames fl, f2 . ...includes... Note that the frame length of the reference frame fO is f/, and the frame length of both the first frame f1 and the second frame f2 is F1, and the frame length of the f1 superframe is F.

Furthermore, for the purpose of explanation, it is assumed here that data from the master station to the slave station and data from the slave station to the master station are sent over the same line, but it goes without saying that they need not be sent over the same line.

The master station sends data to all slave stations during the reference frame fO. Each slave station S1, S2 uses this data as a reference for the first frame f1 or the second frame f2.
Data is sent to the master station during this period. Then, this is repeated for each super frame fs.

Now, assume that the master station sends data DO to the first slave station S1 and the second slave station S2 in a reference frame fO starting at time T3n (n is an integer).

After receiving the reference data from the master station, the first slave station S1 and the second slave station S2 synchronize with the frame from the reference synchronization signal included in the data DO from the master station. 1 frame fl or the second from time T an+2
Data Dl and D2 are randomly sent out during frame f2. For example, when data Dl from the first slave station S1 and data D2 from the second slave station S2 collide as shown at time T 3m+1, the first slave station S1 Since the confirmation signal from the master station for the data D1 of the first slave station S1 is not received, it is known that the data has collided.

If the first slave station S1 is the first slave station from time T3n+1,
When detecting a collision between the data from the second slave station S1 and the data sent by itself in frame f1, the first slave station S1 immediately retransmits the same data. In this case, the second slave station S2 can use the first frame f1 only after a delay of N (F+f') (N is an arbitrary integer) after the data collision. That is, during this period, data from the first slave station S1 is assigned preferentially to the first frame f1. Therefore, the first frame f1 is referred to herein as a first slave station priority frame.

On the other hand, the second slave station S2 receives the second slave station from time T3n+2.
When detecting a collision between the data from the first slave station S1 and the data sent by itself in frame f2, the second slave station S2 immediately retransmits the same data. In this case, the first slave station S1 or the second frame f2 can be used only after a time delay of N'(F+f'')(N' is an arbitrary integer) after the data collision. In other words, During this period, for the second frame f2, the second slave station S2
Priority will be given to data from Therefore, the second
The frame f2 is herein referred to as the second slave station priority frame.

According to the above method, when a data collision occurs in the first frame f1, it becomes possible to immediately retransmit the same data from the first slave station without collision after the collision is detected, and after the collision, the data is randomly transmitted. The propagation delay can be shorter than the conventional method, which retransmits data every second. The same can be said about the second frame.

FIG. 4 shows the configuration of a slave station for realizing the access method shown in FIG. 3. Here, we will take as an example a case where the master station pools free wireless lines and allocates the free lines in response to a call request from a slave station.

A call request signal a from a terminal or an exchange is sent to a signal generator 1.
1 and generates data b based on a predetermined format. Data b is input to the modulation unit 13 via the synchronization unit 12 for determining the timing of transmitting data from the slave station to the master station, modulated on a determined channel fm, and sent as a modulated signal to the master station. . On the other hand, the master station sends data e to all slave stations at regular intervals on the same channel fa+. This data e also includes a line number etc. assigned by the master station in response to a call request from a slave station. Data e is input to demodulation section 14, demodulated, and sent to signal extraction section 15 as data g. Signal extractor 15
Now, let's decompose the manually generated data g. A part of the decomposed data, such as the assigned line number, is sent to the terminal or exchange as data h. Further, a reception confirmation signal from the master station to the slave station, a test signal, etc. included in the data g are sent to the signal generation section 11 and the retransmission control section 16 as data i. The signal generation unit 11 generates a response signal from the data i if necessary.

On the other hand, data b is sent to the synchronization unit 12 based on the call request signal a.
, the synchronization unit 12 generates a timer signal for time measurement, and sends this timer signal to the retransmission control unit 16. The retransmission control unit 16 measures the time based on the timer signal, and if the reception confirmation signal included in the data i at the master station is not obtained within a certain period of time, it is determined that the data from the slave station has collided. The retransmission time of the colliding data is determined by the method described above, and the retransmission of the colliding data is controlled. The retransmission control unit 16 receives a retransmission control signal k indicating the retransmission time.
is sent to the synchronization unit 12. In addition, the signal extraction unit 15 extracts the reference signal j included in the data g from the master station,
This is sent to the synchronization section 12. The synchronization unit 12 determines a frame for retransmission based on the input reference signal j and the retransmission control signal, and sends the data b to the modulation unit 13 at the frame interval.

With the above configuration, data retransmission control can be performed.

Note that the present invention provides, for example, a system in which only the first slave station has the right to transmit data during the first frame fl, based on the data transmitted from the master station using a wireless channel during the reference frame fO. , prohibits the second slave station from sending data to the master station during the first frame fl, and
During the second frame f2, both the first and second slave stations can access, but in the event of a collision, data retransmission from the second slave station may be prioritized.

The method of retransmitting data regarding collisions is the same as that described in FIG. According to this method, for example, if the traffic of the first slave station is higher than that of the second slave station, data from the first slave station can be reliably sent in the first frame, and data from the second slave station can be reliably sent in the first frame. Frame efficiency can be sufficiently increased by sharing the frame with a second slave station with low traffic.

Also, contrary to the above example, only the second slave station can access the second frame f2, and the first and second slave stations can access the first frame f1, but there is a collision. In this case, it is also possible to give priority to the first slave station.

Note that the present invention is also applicable to cases where there are three or more access stations. For example, in Figure 5, the slave station is (m + n)
This figure shows an overview of the access method when there are multiple users.

Here fO is the reference frame, f11. ...,fl
a+.

f21. −, f 2n are slave stations S 11
．． -, S 1m.

S21. ..., frames for S2n (all frame lengths are f), and F is frame f 11.・・・
・.

f 1m, f 21. ..., f represents the length of the superframe fs that includes 2n. The slave station Sll can send data in the period of the frame flll and the period of the frame f21, but the frame flll is the priority frame of the slave station Sll. That is, if there is a collision with data from the slave station S21 during the frame rtt, the data from the slave station Sll is prioritized and retransmitted. Access from slave station S21 is prohibited for a certain cycle. Similarly, slave station S1
m can transmit data during the period of frame f1m and the period of frame f2m. Furthermore, the slave station S2n is capable of transmitting data during the period between frames f in and frame f 2n, and if there is a collision with data from the slave station Sin during the frame f2n, the data from the slave station S2n will be transmitted. Give priority to the data and resend it. Access from the slave station Sin is prohibited for a certain cycle.

As shown in the figure, for example, at time Tm+1, data from slave station Sll and data from slave station S12 collide, and by time T, the reference frame fO from the master station to all slave stations, which is received at regular intervals, is When the slave station SIL and the data reception confirmation signal of the slave station 521 are not sent to the data, the slave station SIL
1 and the slave station S21 determine that there has been a collision, and the slave station S21 retransmits the collision data at time Te+a++1. On the other hand, the slave station Sll prohibits access to the priority frame of S21 from time T by an integral multiple of the sum of the length f' of the reference frame fO and the length F of the super frame fs, that is, NCF1f'). and time T no 10N (f'10F)
Access is possible from 10f'+mf.

From the above, even when there are three or more access stations, by providing a priority frame for each slave station, if a collision occurs in the priority frame, data from that slave station can be retransmitted immediately after the collision is detected. , the propagation delay can be made shorter than before.

Furthermore, the case of FIG. 5 may be extended as follows. That is, during the period of frame fil, only the slave station S11 is allowed to access, and access from the slave station SL2 is prohibited. Similarly, during the frame f1m, only the slave station S1m is allowed to access, and access from the slave station S2o+ is prohibited. Furthermore, in the period of frame f21, the slave station Sl
1 and the slave station S21, but in the event of a collision, retransmission of data from the slave station S21 takes priority. The method of retransmitting data regarding collisions is similar to the method described in FIG. Similarly, during the frame f21, only access from the slave station S2n is permitted, and the slave station Si[
Access from Il is prohibited. Data access from the slave station Sin and slave station S2n is permitted during the period of frame f in, but the same applies to the case where priority is given to the slave station Sin in the event of a collision. As a result, even if there are variations in traffic, for example, the slave stations S 11°..., 5
iI11's traffic is high, and slave station S21. ....

When the traffic of S2n is small, the slave station S11.・
....

The data from Sl[11 is guaranteed to be in frame f11.
....

f Lm, and further frames f21. ...,
f2n to slave station S21. . . , can be shared with S2n, and the frame efficiency can be sufficiently increased.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the concept of a data communication system according to an embodiment of the present invention, FIG. 2 is a schematic diagram illustrating various improvement examples of the data communication system, and FIG. FIG. 4 is a block diagram showing the configuration of a slave station for realizing the communication method, and FIG. 5 is a schematic diagram showing the concept of a data communication system according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the concept of a data communication method. Sl -35, SLl~Sin, S21~S2n
・=Slave station, 11... Signal generation section, 12... Synchronization section,
13...Modulation section, 14...Demodulation section, 15...Signal extraction section, 16...Reproduction control section. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2

Claims (7)

[Claims] (1) In a data communication system in which a wireless channel is divided into time slots of a certain length and multiple slave stations randomly transmit data to a master station in synchronization with the time slots, when the traffic on the wireless channel increases, , a data communication system characterized in that time slots of at least some slave stations are switched to be fixedly allocated. (2) After the broadcast signal is transmitted from the master station to the slave stations, the ACK signal transmitted from each slave station to the master station is transmitted by time division multiplex communication. Data communication method described. (3) When it is detected that signals from slave stations collide,
2. The data communication system according to claim 1, wherein time slots are allocated between colliding slave stations. (4) The data communication system according to claim 1, wherein each slave station knows in advance the allocated time slot. (5) The data communication system according to claim 1, characterized in that information on time slots to which each slave station is assigned is transmitted from the master station to the slave stations. (6) When it is detected that signals from slave stations collide,
2. The data communication system according to claim 1, wherein data from a specific slave station among the colliding slave stations is preferentially retransmitted. (7) The data communication system according to claim 1, wherein a priority slave station is determined according to the position of a time slot in which data collides.