JP4161506B2 - Time division multiplex communication method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a time division multiplex communication system, that is, a communication system in which 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]
[Prior art]
Conventionally, when one station communicates with multiple other stations using the time division multiplex communication method, a method of setting a time unit called a time slot and assigning this time slot to each other station is used. It has been. That is, when the time corresponding to one time slot is used only for communication with one of a plurality of counterpart stations, the time passes 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 other station. In this way, a method is used in which communication is performed with another partner station each time the time slot changes.
[0003]
Here, a predetermined number of time slots are grouped together by providing a plurality of time slots in a large unit time called a frame. The destination partner station is uniquely determined by the time slot order in this frame. That is, in a certain frame, the partner station to which the first time slot is assigned is the first partner station, and the partner station to which the second time slot is assigned is the second partner station. If the partner station to which the time slot is assigned is the nth partner station, even in another frame, the first time slot is the first partner station, and the second time slot is the second partner station. In the following, the nth time slot is sequentially assigned to the nth partner station. This relationship is common in all frames.
[0004]
For the time corresponding to this time slot, communication is performed with the partner station to which the time slot is assigned, and if the time passes and the time corresponding to another time slot is reached, the other party that has been communicating until then The communication with the station is terminated, and the communication with another partner station assigned with the other time slot is started.
In this way, communication with different partner stations is performed one after another, and this operation is periodically repeated for each frame, so that communication with a plurality of partner stations is performed in parallel. is there.
[0005]
At this time, the number of time slots in the frame depends on communication control application software. That is, the application software declares the number of time slots included in one frame in advance, and creates and communicates the time slots accordingly. The number of time slots was fixed.
[0006]
[Problems to be solved by the invention]
Such a communication technique is used for an ITS (Intelligent Road Information System) road-to-vehicle communication system. In ITS, communication is performed between a roadside station provided on the roadside and an in-vehicle station mounted on a vehicle traveling on a road near the roadside station, and a time slot is assigned to each in-vehicle station. So-called road-to-vehicle communication.
[0007]
At this time, all the first time slots in each frame are in the in-vehicle station of the first vehicle, all the second time slots are in the in-vehicle station of the second vehicle, and the nth time slot hereinafter. Are all assigned to the in-vehicle station of the nth vehicle, and one time slot is assigned to each in-vehicle station mounted on each vehicle. In this way, all in-vehicle stations can communicate with the roadside station in all frames for the time corresponding to the assigned time slot.
[0008]
Here, in a specific frame, the number of in-vehicle stations that should communicate with the roadside station varies depending on traffic conditions. In other words, within the time corresponding to a specific frame, communication is performed with the roadside station according to how many vehicles equipped with the in-vehicle station enter the communicable area that can communicate with the roadside station. The number of in-vehicle stations that should be changed. In response to this, 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 in-vehicle stations that can communicate with the roadside station in the frame.
[0009]
For such a problem, it is conceivable to assume the maximum possible number of counterpart stations and to determine the number of time slots per frame so as not to fall below that number at least. For example, in the road-to-vehicle communication system described above, it is assumed that the road is congested and the distance between vehicles is narrow. Or assume a traffic jam. In this situation, the maximum number of vehicles that can enter the communicable area covered by a single roadside station as an area where the roadside station and the vehicle can communicate is as simple as the number of vehicles accommodated in a flat parking lot. Therefore, the maximum number of partner stations can be estimated based on the number of vehicles that can enter, and the number of time slots per frame can be determined so as not to fall below that. By doing so, at least the problem that communication with some in-vehicle stations cannot be performed 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 in-vehicle station and cannot be assigned. This is because the time slot is substantially wasted. Since time is consumed without performing communication for the useless time slot, time similar to waiting time is wasted during communication.
[0011]
The improvement of communication efficiency to the maximum by eliminating such time waste is extremely important especially when communication is performed between an in-vehicle station and a roadside station mounted on a vehicle traveling at a high speed. This is an important issue. Because in this system, on the other hand, it is required to narrow the communicable area, which is a communicable area, to avoid confusion of multiple vehicles, and on the other hand, widen the communicable area and enable redundant communication etc. Because it is required.
[0012]
In order to satisfy this contradictory requirement, even if the communication efficiency is improved, the time required to complete the entire communication is shortened, and the communicable area is shortened and the communicable time is shortened, sufficient communication is achieved. It is extremely useful to be able to complete In addition, if the communicable area is narrowed so that the confusion of a plurality of vehicles can be avoided, the above request can be met.
As described above, in time division multiplex communication, it is an extremely important issue to eliminate waste of time slots and improve communication efficiency.
[0013]
[Means for Solving the Problems]
In order to solve the above-described problems, in the present invention, in the road-to-vehicle communication system, the number of time slots in one frame is variable.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described by way of examples.
FIG. 1 shows a system external view 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 location 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 approaches the roadside station 2, communication is possible between the roadside station 2 and the in-vehicle station mounted on the vehicle 3 even when the vehicle 3 is traveling.
[0015]
An appropriate place for installing the roadside station 2 is a place that matches the purpose of managing the passage of vehicles on the road 1. For example, a place where a manned toll gate is installed on a conventional highway.
[0016]
FIG. 2 shows a protocol used for communication performed between the roadside station 2 and the in-vehicle station.
A series of columns from FCM to END shown in the figure indicates a signal group having a predetermined length used for communication. This entire signal group is called a frame. This frame is configured by continuously transmitting individual signal sequences from FCM, MDS, or END, which are divided by a square frame in the figure. Each individual signal sequence is called a time slot or simply a slot. Hereinafter, the time slot is simply referred to as a slot.
[0017]
In this column, the left shows an earlier time and the right shows a later time. Therefore, the signal is first transmitted from the FCM, then transmitted in order of MDS, 1, 2, and finally END is transmitted, and transmission for one frame is completed. Here, in the slot of the FCM, a special signal indicating the number of slots in the frame and the usage of the slot is stored, and the slot of the FCM is always transmitted at the beginning of the frame.
[0018]
Here, the information transmitted between the roadside station 2 and the in-vehicle station is placed in the middle 1 to 8. That is, 1 to 4 shown as UPLINK in the figure are assigned to transmission from the vehicle to the roadside station 2, and 5 to 8 shown as DOWNLINK in the figure are assigned to transmission from the roadside station 2 to the vehicle.
[0019]
FIG. 3 is a diagram schematically illustrating a state in which actual communication is performed based on the protocol.
The actual communication is performed in such a form that the in-vehicle station first transmits a communication request to the roadside station 2, and the roadside station 2 that has received the communication request returns a signal to the in-vehicle station.
[0020]
First, the in-vehicle station transmits a communication request. This communication request is made on the UPLINK, but the in-vehicle station itself does not recognize which slot is empty, that is, available 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, arbitrarily selects a slot 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 in-vehicle station continues the communication as it is. However, if there is no signal from the roadside station, the in-vehicle station correctly sends the communication request to the roadside station. As the possibility of not reaching 2 is reached, a slot is again arbitrarily selected and the communication request is retransmitted.
[0021]
For this reason, for example, when a plurality of in-vehicle stations simultaneously transmit a communication request by selecting the same slot, this communication request is not correctly recognized by the roadside station 2. At this time, each in-vehicle station generates a random number again and arbitrarily selects a slot. In this case, since it is not realistic for a plurality of vehicles to select the same slot again, the same phenomenon is not repeated.
After that, the roadside station 2 that has received the communication request analyzes the received communication request and generates a signal in response to each of the in-vehicle stations.
[0022]
Next, a signal generated for each in-vehicle station is assigned to a DOWNLINK slot, and transmitted to the in-vehicle station for each assigned slot. In this way, a series of frame communication is completed.
[0023]
FIG. 4 shows a flowchart of time slot assignment and deletion to be performed before and after communication.
In FIG. 4, first, at step 1, the presence or absence of a communication request from the vehicle is examined. 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, the number of slots is added in step 2.
[0024]
The concept of adding the number of slots is shown in FIG. In FIG. 5, the upper is the frame configuration before the processing in step 2, and the lower is 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.
[0025]
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 increased any more, so the determination in step 4 to be described below is omitted, and the acceptance of further communication requests is terminated, and the process proceeds to step 6.
[0026]
If the maximum number has not been reached, it is determined in step 4 whether a predetermined time has elapsed. If the predetermined time has not elapsed, it is possible to accept a communication request from another vehicle, and the process returns to step 1 again. If the predetermined time has elapsed, communication with the vehicle that has already requested communication must be started. Therefore, the acceptance of further communication requests is discontinued regardless of whether or not there is a margin for accepting communication requests, and Step 6 is started. Transition.
[0027]
Next, in step 6, a time slot is assigned to the communication request. At this time, there are various ways of assigning slots. For example, slots may be assigned in the order of early communication requests. That is, slot 1 may be assigned sequentially to the first received communication request, slot 2 to the next received communication request, and so on.
[0028]
Further, in step 7, FCM allocation data is generated. The allocation data for FCM includes information indicating how many slots are included in one frame and to which communication request each slot is allocated, that is, to which in-vehicle station. The in-vehicle station that has received the signal from the roadside station 2 can read this allocation data and determine which slot data is necessary for the host vehicle. As a result, the slot determined to be data for other vehicles may be ignored on the in-vehicle station side.
[0029]
The allocation data reflects the result of adding the number of slots in step 2. That is, when the number of slots is changed in the process of step 2, the number of changed slots is shown.
[0030]
Next, in step 8, actual communication is performed. The communication here is a one-way communication from the roadside station 2 to the in-vehicle station. For each slot that has not been added by adding in step 2 or omitting the processing in step 2, an individual in-vehicle station is assigned. Allocation is performed, and actual communication is performed between the roadside station 2 and each in-vehicle station based on the allocation.
[0031]
Thereafter, in step 9, it is determined whether or not all communication with a specific in-vehicle station has been completed. If completed, it is not necessary to communicate with the in-vehicle station in the next frame, and no signal is transmitted to the in-vehicle station. Therefore, in step 10, the number of slots is decremented by one. If not completed, step 10 is omitted, and the number of slots is not subtracted.
[0032]
The concept of subtracting the number of slots is shown in FIG. In FIG. 6, the upper is the frame configuration before the processing in step 10, and the lower is 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.
[0033]
Next, in step 11, it is determined whether or not the determination in step 9 has been made for all in-vehicle stations to which the current slot is assigned. If there are still in-vehicle stations that have not been determined, the processes after step 9 are similarly performed for the in-vehicle stations that have not been determined. When the determination is finished for all the in-vehicle stations, the series of processes is terminated.
[0034]
【The invention's effect】
As described above, in the present invention, since the number of slots is made variable according to the communication request from the in-vehicle station, the number of frames is appropriately increased or decreased according to the number of communication requests from the in-vehicle station. As a result, the slot can be used effectively, and the time length of the frame can be shortened as much as possible. For this reason, 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 is applicable.
FIG. 2 is an explanatory diagram showing a concept of a protocol for time division multiplex communication.
FIG. 3 is an explanatory diagram showing a communication state.
FIG. 4 is an explanatory diagram showing a procedure of communication processing.
FIG. 5 is an explanatory diagram showing a concept of addition of 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)

A time division multiplex communication method in which one specific station communicates with a plurality of partner stations, and includes a set of start signal transmission time and end signal transmission time, and the start signal transmission time and end signal transmission time. has a large unit time including small unit time a predetermined number between, assign a small unit of time according to a predetermined order for each individual large unit time to each remote station, a small unit of time allocated In a communication method for performing communication with a partner station to which the unit time is assigned,
A predetermined number of the small unit times included in the large unit time,
A time division multiplex communication method, characterized in that it is variable in response to a communication request received from a partner station prior to communication with the partner station . 2. The communication method according to claim 1, wherein the predetermined number of the small unit times is increased every time a communication request is received from a partner station . 3. The communication method according to claim 1 , wherein the predetermined number of the small unit times is reduced every time communication with the partner station is completed . 4. The communication method according to claim 1, wherein the predetermined number of the small unit times is made to coincide with the number of the counterpart stations that can communicate with the specific station. Communication method.

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