JP2001223660A - Time division multiplex communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly decide a slot number for improving communication efficiency in the time division multiplex communication, where a plurality of slots are provided to each frame. SOLUTION: In a step 2, the number of slots is increased upon the receipt of a communication request from an on-vehicle station and in a step 10, the number of the slots is decreased when communications with a vehicle are completed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiplex communication system, that is, a communication system in which a communication time is divided into short unit times called time slots and each unit time is used for communication with a different partner station.

[0002]

2. Description of the Related Art Conventionally, when one station communicates with a plurality of partner stations by using a time division multiplex communication system, a time unit called a time slot is set, and this time slot is assigned to each partner station. Is used. That is, the time corresponding to one time slot is used only for communication with one of the plurality of partner stations, and when that time elapses and the time corresponding to the next time slot is reached, This is a method in which the next time slot is used only for communication with another assigned station. In this way, a method is used in which communication is performed with another partner station one after another every time the time slot changes.

[0003] Here, a predetermined number of time slots are put together by providing a plurality of time slots in a large unit time called a frame. The order of the time slot in this frame uniquely determines the partner station to which the frame is assigned. That is, in a certain frame, the partner station to which the first time slot is assigned is defined as the first partner station, and the partner station to which the second time slot is assigned is defined as the second partner station. If the partner station to which the time slot is assigned is the n-th partner station, in another frame, the first time slot is assigned to the first partner station and the second time slot is assigned to the second partner station. The nth time slot is sequentially assigned to the station, and then to the nth partner station. This relationship is common in all frames.

[0004] Only for the time corresponding to this time slot,
Communication is performed with the partner station to which the time slot is assigned, and when the time elapses and the time corresponding to another time slot is reached, the communication with the partner station that has been communicating up to that time is terminated, and the other terminal is disconnected. Starts communication with another station to which the time slot is assigned. In this way, communication with different partner stations is performed one after another, and by repeating this operation periodically for each frame, communication with a plurality of partner stations is performed as if performed in parallel. is there.

At this time, the number of time slots in a frame depends on communication control application software. That is, the application software preliminarily declares the number of time slots included in one frame, creates a time slot according to the declaration, and performs communication. The number of this time slot was fixed.

[0006]

Such a communication technique is used for a road-to-vehicle communication system of ITS (Intelligent Information System). In the ITS, communication is performed between a roadside station provided on the roadside and a vehicle-mounted station mounted on a vehicle running on a road near the roadside station, and a time slot is assigned to each vehicle-mounted station. hand,
A so-called road-to-vehicle communication is performed.

At this time, all the first time slots in each frame are transmitted to the vehicle-mounted station of the first vehicle,
On-vehicle stations mounted on individual vehicles, such as all the second time slots are on the on-vehicle station of the second vehicle, all the following n-th time slots are on the on-vehicle station of the n-th vehicle, and so on. , One time slot is assigned from each frame. In this way, all the on-vehicle stations can communicate with the roadside station for the time of the assigned time slot in all the frames.

Here, in a specific frame, the number of on-vehicle stations that should communicate with the roadside station fluctuates according to the traffic situation. That is, within the time corresponding to the specific frame, within the communicable area that can communicate with the roadside station,
The number of in-vehicle stations that should communicate with the roadside station fluctuates depending on how many vehicles equipped with in-vehicle stations enter. Accordingly, the number of time slots to be provided in one frame also varies. This is because the number of time slots provided in one frame defines the upper limit of the number of vehicle-mounted stations that can communicate with the roadside station in the frame.

In order to solve such a problem, it is considered that the number of time slots per frame is determined so as not to be less than the maximum possible number of the partner stations. Can be For example, in the road-to-vehicle communication system described above, it is assumed that the road is congested and the inter-vehicle distance is reduced. Or assume a traffic congestion situation. In this situation, the maximum number of vehicles that can enter the communicable area covered by one roadside station as an area where the roadside station and vehicles can communicate is simply the number of vehicles that can be accommodated in a flat ground parking lot. Therefore, it is sufficient to estimate the maximum number of partner stations based on the number of vehicles that can enter, and determine the number of time slots per frame so as not to fall below the maximum number. By doing so, at least the problem of not being able to communicate with some in-vehicle stations can be avoided.

[0010] On the other hand, from the viewpoint of communication efficiency, this is not the best method, because the time slot allocation in one frame is one time slot for one vehicle-mounted station, This is because time slots that have not been allocated are substantially wasted. Since the time is consumed without performing the communication by the useless time slot, a waste of time similar to the waiting time occurs during the communication.

[0011] To maximize the communication efficiency by eliminating such a waste of time, especially when communication is carried out between a vehicle-mounted station mounted on a vehicle running at high speed and a roadside station. Is a very important issue. Because, in this system, it is required to narrow the communicable area, which is a communicable area, on the one hand to avoid confusion of a plurality of vehicles, and on the other hand, to expand the communicable area to enable redundant communication and the like. Is required.

In order to satisfy this conflicting demand, it is necessary to improve the above-mentioned communication efficiency, shorten the time required to complete a single communication, shorten the communicable area and shorten the communicable time, It is extremely effective to be able to complete the communication sufficiently. Then, by narrowing the communicable area and avoiding confusion of multiple vehicles,
Meet the above requirements. As described above, it is extremely important to reduce waste of time slots and improve communication efficiency in time division multiplex communication.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, in the present invention, in a road-to-vehicle communication system, the number of time slots in one frame is made variable.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to examples. FIG. 1 shows an external view of a system illustrating an embodiment of the present invention. In the figure, 1 is a road, 2 is a roadside station (communication device) provided at an appropriate place on the road 1, and 3 is a vehicle equipped with an in-vehicle station (communication device) not shown. In such a configuration, the vehicle 3 travels on the road 1 as shown in the figure. At this time, when the vehicle 3 is approaching the roadside station 2, communication is possible between the roadside station 2 and the vehicle-mounted station mounted on the vehicle 3 even when the vehicle 3 is running.

An appropriate place for installing the roadside station 2 is a place that meets the purpose of managing the passage of vehicles on the road 1. For example, a place where a manned tollgate is installed on a conventional highway.

FIG. 2 shows a protocol used for communication between the roadside station 2 and the on-vehicle station. A series of columns from FCM to END shown in the figure shows a signal group of a predetermined length used for communication. The entire signal group is called a frame. This frame is represented by F
It is configured by continuously transmitting individual signal strings up to CM, MDS, or END. These individual signal sequences are called time slots or simply slots. Here, a time slot is simply referred to as a slot hereinafter.

In this column, an earlier time is shown on the left side, and a later time is shown on the right side. Therefore, the first signal is FC
Starting with M, the data is transmitted in order of MDS, 1, 2, and finally END is transmitted, and the transmission of one frame is completed. Here, the FCM slot stores a special signal indicating the number of slots in the frame and the purpose of the slot, and the FCM slot is always transmitted at the beginning of the frame.

Here, information transmitted between the roadside station 2 and the on-vehicle station is placed in intermediate 1 to 8. That is, 1 to 4 shown as UPLINK in the figure.
Indicates transmission from the vehicle to the roadside station 2, and in the figure, DOWNL
5 to 8 designated as INK are respectively assigned to the transmission from the roadside station 2 to the vehicle.

FIG. 3 is a diagram schematically showing a state in which actual communication is performed based on the above protocol. In actual communication, first, the onboard station transmits a communication request to the roadside station 2,
The roadside station 2 that has received the communication request transmits a signal to the return vehicle-mounted station.

First, the in-vehicle station transmits a communication request. This communication request is made on UPLINK, but the on-vehicle station itself does not know which slot is empty, that is, which slot can be used for communication. Therefore, the in-vehicle station has a pseudo-random number generation function, generates a pseudo-random number using this function prior to a communication request, selects a slot arbitrarily based on the generated random number, and places it in the selected slot. To send a communication request. As a result, if the communication request is normally received and a signal is transmitted from the roadside station 2, the vehicle-mounted station continues the communication as it is, but if there is no signal from the roadside station, the vehicle-mounted station determines that the communication request has been successfully completed. Assuming that the communication request may not have reached 2, the slot is arbitrarily selected again and the communication request is retransmitted.

Therefore, for example, when a plurality of vehicle-mounted stations transmit a communication request at the same time, that is, select the same slot, the communication request is not correctly recognized by the roadside station 2. At this time, each in-vehicle station newly generates a random number and arbitrarily selects a slot again. In this case, since it is not realistic that a plurality of vehicles select the same slot again, the same phenomenon will not be repeated. Thereafter, the roadside station 2 that has received the communication request analyzes the received communication request, and generates a signal responsive to the request for each vehicle-mounted station.

Next, the signal generated for each vehicle-mounted station is represented by D
It is assigned to an OWNLINK slot, and transmitted to the vehicle-mounted station for each assigned slot. Thus, communication of a series of frames is completed.

FIG. 4 shows a flowchart of time slot allocation and erasure to be performed before and after communication. In FIG. 4, first, in step 1, the presence or absence of a communication request from the vehicle is checked. If there is no communication request, the operation of step 1 is repeated in preparation for receiving a new communication request. If there is a communication request, step 2
Add the number of slots.

FIG. 5 shows the concept of adding the number of slots.
In FIG. 5, the upper part shows the frame configuration before the processing in step 2, and the lower part shows the frame configuration after the processing in step 2. In the figure, TS7 is added by adding 1 to the number of slots in DOWNLINK.

Next, in step 3, it is determined whether or not the number of slots has reached the maximum. When the maximum number is reached, the number of slots cannot be further increased, so that the determination in step 4 described below is omitted, the acceptance of further communication requests is terminated, and the process proceeds to step 6.

If the maximum number has not been reached, it is determined in the next step 4 whether or not a predetermined time has elapsed. If the predetermined time has not passed, it is possible to accept a communication request from another vehicle,
Return to step 1 again. If the predetermined time has passed,
Since it is necessary to start communication with the vehicle for which the communication request has already been made, the reception of the further communication request is terminated and the process proceeds to step 6 irrespective of whether there is room to accept the communication request.

Next, in step 6, a time slot is assigned to the communication request. At this time, there are various ways of allocating the slots. For example, the slots may be allocated in the order of earlier communication requests. That is,
Slots may be sequentially assigned to the first received communication request, the second slot to the next received communication request, and so on.

Further, in step 7, allocation data for FCM is generated. The FCM allocation data includes information on how many slots are included in one frame, and on which communication request each slot is allocated, that is, which vehicle-mounted station is allocated. The in-vehicle station that has received the signal from the roadside station 2 reads this allocation data and can determine which slot data is needed for the own vehicle. as a result,
A slot determined to be data for another vehicle may be ignored by the vehicle-mounted station.

The allocation data is stored in step 2
Reflects the result of adding the number of slots. That is, when the number of slots has been changed in the process of step 2, the number of changed slots is shown.

Next, in step 8, actual communication is performed. The communication here is one-way communication from the roadside station 2 to the vehicle-mounted station.
Each of the in-vehicle stations is assigned to each of the slots that have not been added by omitting the processing described above, and actual communication is performed between the roadside station 2 and each in-vehicle station based on this assignment.

Thereafter, in step 9, it is determined whether or not all communications with the specific vehicle-mounted station have been completed.
If it has been completed, it is not necessary to perform communication with the on-vehicle station in the next frame, and there is no need to transmit a signal to the on-vehicle station. If not completed, step 10 is omitted and the number of slots is not subtracted.

FIG. 6 shows the concept of subtraction of the number of slots.
In FIG. 6, the upper part shows the frame configuration before the processing in step 10, and the lower part shows the frame configuration after the processing in step 10. In the figure, slot 7 is deleted by subtracting 1 from the number of slots in DOWNLINK.

Next, in step 11, step 9
Is determined for all in-vehicle stations to which the current slot is assigned. If there is an in-vehicle station that has not yet been determined, the processing from step 9 onward is similarly performed for the in-vehicle station that has not been determined. When the determination has been completed for all the in-vehicle stations, a series of processing ends.

[0034]

As described above, in the present invention, the number of slots is made variable in accordance with the communication request from the vehicle-mounted station, so that the number of frames can be appropriately changed according to the number of communication requests from the vehicle-mounted station. As a result, the slot can be used effectively, and the time length of the frame can be reduced as much as possible. Therefore, time-efficient communication can be performed.

[Brief description of the drawings]

FIG. 1 is an external view showing an outline of a road-vehicle communication system to which the present invention can be applied.

FIG. 2 is an explanatory diagram showing the concept of a protocol of time division multiplex communication.

FIG. 3 is an explanatory diagram showing a communication state.

FIG. 4 is an explanatory diagram showing a procedure of a communication process.

FIG. 5 is an explanatory diagram showing the concept of adding the number of slots.

FIG. 6 is an explanatory diagram showing the concept of subtraction of the number of slots.

[Explanation of symbols]

 1 road 2 roadside station

Claims (4)

[Claims] 1. A time-division multiplexing communication method in which one specific station communicates with a plurality of partner stations, comprising a large unit time including a predetermined number of small unit times, and each large unit A communication method in which a small unit time is allocated to each partner station according to a predetermined order for each time, and the allocated small unit time communicates with the partner station to which the unit time is allocated. The predetermined number of the small unit time included in the unit time is:
A time division multiplex communication method characterized by being variable. 2. The time division multiplexing method according to claim 1, wherein the predetermined number of the small unit times is made equal to the number of the other stations that can communicate with the specific station. Communication method. 3. The communication method according to claim 2, wherein the other station is movable. 4. The communication method according to claim 3, wherein when the other station approaches the specific station, the approached opposite station becomes communicable with the specific station. Time division multiplex communication method.