JP3852338B2 - Method for disconnecting communication link of mobile station in road-to-vehicle communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for disconnecting a communication link of a mobile station in a road-vehicle communication system in which a mobile station on a road communicates with a radio base station arranged along the road. Specifically, the present invention relates to a road radio system in which microcells or picocells are arranged on a highway, an intersection, or a general road among a plurality of radio base stations, and relates to a communication link disconnection method of a mobile station for the radio base station.
[0002]
[Prior art]
In conventional mobile / car telephone systems, PHS, and the like, cell design has been performed so that cell coverage is not interrupted in order to provide users with continuous and stable communication services.
[0003]
On the other hand, in a road-to-vehicle communication system in which microcells having a cell diameter of about 30 m are continuously arranged on a road, since the cell size is very small, it is enormous to provide a continuous communication service without interruption in radio waves. It is necessary to install several base stations. Further, since only about 2 to 3 repetition frequencies can be secured, there is a high possibility that the line quality is deteriorated due to the influence of co-channel interference when the installation distance between the base stations is short.
[0004]
When a handover function is implemented in a road-vehicle communication system, it is expected that microcells or picocells are arranged at regular intervals. In this case, every time the mobile station enters a new cell, link connection and link disconnection are repeated with the base station, and information for handover is exchanged between the base stations in order to realize continuous communication. Need to do.
[0005]
According to the “Narrowband Communication (DSRC) System (ARIB STD-T75)”, which is the standard of the Radio Industries Association (ARIB), frequency selection is determined by the received signal strength and is periodically transmitted from the radio base station. It is recommended to connect to the radio base station based on the error test result of the control signal. However, specific parameters, determination conditions, and mounting methods for disconnecting the link connection are not clearly described, and are left to the manufacturer or the like who develops the wireless device.
[0006]
[Problems to be solved by the invention]
FIG. 6 is a graph showing a short-time simulation result for link disconnection in the road-vehicle communication system. The graph is a simulation evaluation of the link connection time when link connection and disconnection are performed using the error test result of the control signal in accordance with the standard described above, based on the actual measurement data. The horizontal axis 72 is time, the vertical axis 71 is the distance to the radio base station that the mobile station is trying to communicate with (shows a negative value as the distance increases), and plots 73 and 74 indicate that link connection and disconnection have been performed. . According to FIG. 6, it is shown that link connection or disconnection is repeated many times over time 2s to 4s and 5.5s to 7s (73-1, 73-2).
[0007]
FIG. 2 is a graph showing a short-time measurement result of received signal strength in the mobile station. As shown in FIG. 2, the received signal intensity in the road environment varies greatly due to reflected waves from the road surface and thermal noise inside the receiver. For this reason, the bit error rate varies greatly. Therefore, in the case where the frequency is simply selected based on the received signal strength in accordance with the above-mentioned standard and connection processing is performed using the error test result of the control signal, a stable received signal strength and error test result cannot be obtained. Thus, connection and disconnection are repeated in a short time. In addition, when the signal intensity equal to or higher than the threshold value is not obtained due to fluctuations in the received signal intensity even though the transmission / reception frequencies match, the process shifts to a process of selecting another frequency.
[0008]
Therefore, the present invention reduces the effects of reflected waves from the road surface, interference waves from adjacent areas, and thermal noise inside the receiver for a plurality of high-speed mobile stations in a road-vehicle communication system with a very small cell size. The purpose is to realize stable communication efficiently.
[0009]
[Means for Solving the Problems]
In order to achieve this object, the mobile station of the road-vehicle communication system according to the present invention provides:
A received signal strength detecting step for measuring the received signal strength;
A received signal strength determination step of determining whether the measured received signal strength has reached a threshold and deriving a received signal strength determination result;
An error test step for performing an error test on a control signal periodically transmitted from a radio base station and deriving an error test result;
When entering or leaving a communication area configured by a radio base station, determine whether communication with the radio base station is possible using a logical product or logical sum of the received signal strength determination result and the error test result when leaving the communication area. A communication availability determination step for deriving a communication availability determination result;
A communication link is connected or a link connection state is maintained if communication is possible based on a communication feasibility determination result , and a communication link is disconnected or a link disconnection state is maintained if communication is not possible, To do.
[0010]
According to another embodiment of the present invention, it is also preferable that the received signal strength detection step performs a moving average processing operation on the received signal strength measured over a certain time width.
[0011]
Further, according to another embodiment of the present invention, the moving average processing operation includes the i- th acquired received signal strength S (i) , the weighting factor λ (0 ≦ λ ≦ 1) , and the i− 1th moving average. It is also preferable that the moving average at the i- th is obtained by using M (i-1) and M (i) = ( S (i) + λ M (i-1) ) / (1 + λ) .
[0012]
Also, according to another embodiment of the present invention, the error verification step comprises:
The number of backward protection stages that prescribes the number of normal receptions of error verification results for connection determination of communication links, and the number of forward protection stages that prescribes the number of abnormal receptions of error inspection results for judgment of communication link disconnection,
Link disconnection state that is disconnected from the radio base station, link connection standby state in which the number of times that the error test result is normal is less than the number of backward protection steps, link connection state that is in communication with the radio base station, and error test result A transition state having a link disconnection waiting state in which the number of times of an error is less than the number of forward protection stages is changed according to a communication link state with the radio base station and an error test result;
Determining that the link connection is possible if the number of times that the error test result is normal reaches the number of backward protection steps; and
It is also preferable to have a step of determining that the link is disconnected if the number of times that the error test result is abnormal has reached the number of forward protection steps.
[0013]
Also, in the received signal strength determination step, the threshold value used for determining link connection during link disconnection and the threshold value used for determining link disconnection during link connection are independently provided, so that when the communication area exits, averaging processing is performed. The effect of dullness can be reduced and stable communication can be provided.
[0014]
Furthermore, according to another embodiment of the present invention, the communication availability determination step designates separately the determination condition for determining that the communication link can be connected and the determination condition for determining that the communication link is disconnected. Is also preferable. For example, when the logical product of the received signal strength and the error test result is used as the link connection determination condition and the logical sum of the received signal strength and the error test result is used as the link disconnection condition, a reliable link connection process and a quick Link disconnection processing can be performed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0016]
FIG. 1 is a system configuration diagram of a road-vehicle communication system according to the present invention. According to FIG. 1, a plurality of radio base stations 4-1 to 4 -N (N is an arbitrary natural number) are continuously arranged on the road 8 and connected to the local area network 3. It is configured to be able to communicate with all the radio base stations connected to the external network, the local server 2 and the local area network 3. Further, the radio base stations 4-1 to 4-N configure radio cells 6-1 to 6-N on the road 8 using f1 to fN of the radio frequencies 5-1 to 5-N, and travel directions 9, communication in the upward direction 10 and the downward direction 11 is performed with the moving vehicle 7 that travels at a high speed.
[0017]
In FIG. 1, when the moving vehicle 7 enters the wireless cell area 6-1, the moving vehicle 7 receives the control signal 11 periodically transmitted from the wireless base station 4-1. It recognizes that it has entered the service area provided by the base station 4-1. Next, the mobile vehicle 7 sends a request signal for establishing a communication link to the radio base station 4-1, and the communication link is established by receiving the request signal at the radio base station 4-1. At this time, as information exchanged for establishing a communication link, an identification code of a mobile station, an identification code of a radio base station, applicable application information, and the like are assumed. In the following description, it is assumed that an information download service in the downlink direction is used as an application.
[0018]
FIG. 3 is a state transition diagram showing an example of a communication link connection disconnection method according to the present invention. When the mobile station is in the link disconnection state 31, when receiving a control signal periodically transmitted from the radio base station (32-1), the signal strength determination of the received control signal and the error of the received control signal (34-1). When the signal strength determination result exceeds the threshold and the error test result is normal (35-2), the state of the mobile station transitions from the link disconnection state 31 to the link connection state 36. When the signal strength determination result is less than the threshold value or the error test result is abnormal (35-1), the mobile station waits in the link disconnection state 31.
[0019]
When the mobile station is in the link connection state 36, the mobile station receives a control signal periodically transmitted from the radio base station (32-2), determines the signal strength of the received control signal, and tests the received control signal for error. (34-2). When the signal strength determination result is less than the threshold and the error test result is abnormal (35-4), the state of the mobile station transitions from the link connection state 36 to the link disconnection state 31. When the signal strength determination result exceeds the threshold value or the error test result is normal (35-3), the mobile station state holds the link connection state 36.
[0020]
Further, when the mobile station is in the link disconnection state 31, when the control signal cannot be received for a certain period of time (33), the mobile station sequentially switches the channel frequency to be received until the control signal is normally received. Repeatedly receive and receive control signals.
[0021]
In the example shown in FIG. 3, the logical product of the received signal strength determination and the error test result is used as the determination condition. However, as the determination condition, (1) the logical sum of the received signal strength determination and the error test result, (2) Only the received signal strength determination or (3) only the error test result may be used.
[0022]
In addition, it is more effective to use different conditions for determining the link connection and disconnection conditions, for example, error test only when the link is connected, and logical sum of the received signal strength and the error test result when the link is disconnected. In some cases.
[0023]
However, in the method shown in FIG. 3, since the received signal strength fluctuates as shown in FIG. 2, the effect of suppressing the short-time connection as shown in FIG. 6 is small. When the threshold value of the received signal strength is set low, the communication area is widened, but link connection / disconnection is repeated in a short time due to fluctuations in the received signal strength. On the other hand, when the threshold value of the received signal strength is set high, link connection / disconnection is not repeated due to fluctuations in the received signal strength, but the communication area becomes narrow. Therefore, a method of moving average processing the received signal strength of control signals for several frames is added.
[0024]
FIG. 4 is a graph of the result of moving average processing of received signal strength in a mobile station. Here, moving average of control signals for 10 frames is performed. As shown in FIG. 4, since the fluctuation due to the thermal noise inside the receiver is smoothed and the influence of the dip due to the road surface reflected wave is reduced, the effect of suppressing the short-time connection is increased. Therefore, it is possible to set the threshold value of the received signal strength used for connection determination to be low to some extent.
[0025]
Furthermore, a moving average processing method using a weighting coefficient is shown. Assuming that the i-th acquired received signal strength is S (i) and the weighting coefficient is λ (0 ≦ λ ≦ 1), the i-th moving average M (i) is expressed as follows.
[0026]
M (i) = (S (i) + λM (i-1)) / (1 + λ)
[0027]
Here, when λ is close to 1, M (i) is close to a moving average from infinite time before weighting, and when λ is close to 0, M (i) is close to S (i).
[0028]
A more effective moving average by adjusting λ depending on whether the fluctuation of the received signal intensity is an instantaneous value fluctuation due to the influence of thermal noise or a short-term fluctuation due to the influence of a dip due to a reflected wave from the road surface, etc. Processing can be performed. Specifically, it is possible to obtain an average received signal strength close to the bit error rate characteristic by increasing λ when the influence of thermal noise is large, and decreasing λ when the influence of reflected wave is large. .
[0029]
FIG. 5 is a state transition diagram of the communication link connection disconnection method using the number of protection stages for error verification according to the present invention.
[0030]
When the mobile station is in the link disconnection state 51, when receiving a control signal periodically transmitted from the radio base station, the mobile station performs an error test on the received control signal. When the error test result is normal (53-1), the state of the mobile station transitions from the link disconnection state 51 to the link connection standby state 52-1. When the error test result is abnormal (54-0), the mobile station stands by in the link disconnection state 51.
[0031]
When the mobile station is in the link connection standby state 52-1 to 52- (K-1), when the error test result of the received control signal is normal (53-1 to 53- (K-1)), The normal count is incremented and the normal count is determined. Here, when the number of normal times has reached the number of backward protection stages (52-K), the mobile station transitions to the link connection state 55. When the normal number is less than the number of backward protection stages, the mobile station is held in the link connection standby state. When the mobile station is in the link connection standby state 52-1 to 52- (K-1), when the error test result of the received control signal is abnormal (54-1 to 54- (K-1)), The mobile station transits to the link disconnection state 51.
[0032]
When the mobile station is in the link connection state 55 and the error test result of the received control signal is abnormal (57-1), the mobile station transitions from the link connection state 55 to the link disconnection standby state 56-1. . When the error test result is normal (58-0), the state of the mobile station is held in the link connection state 55.
[0033]
When the mobile station is in the link disconnection standby state 56-1 to 56- (L-1), when the error test result of the received control signal is abnormal (57-2 to 57-L), the number of abnormalities is set to 1. Increase (one transition in the left direction in the figure). When the error test result of the received control signal is normal (58-1 to 58- (L-1)), the number of abnormalities is decremented. After performing the error test, the mobile station determines the number of abnormalities, and when the number of abnormalities reaches the number of forward protection stages (56-L), when the number of abnormalities is 0 (58-1). Transition to the link connection state 55. When the number of abnormalities is not 0 and the number of forward protection stages has not been reached, the state of the mobile station is held in the link disconnection standby states 56-1 to 56- (L-1).
[0034]
According to the various embodiments of the present invention described above, various changes, modifications, and omissions within the scope of the technical idea and the viewpoint of the present invention can be easily made by those skilled in the art. The above description is merely an example, and is not intended to be restrictive. The invention is limited only as defined in the following claims and the equivalents thereto.
[0035]
【The invention's effect】
As described above, the present invention described in detail has the following effects.
(1) In a road-to-vehicle communication system composed of spot beams having a cell diameter of about 30 m continuously arranged on a road, link connection / disconnection corresponding to high-speed movement of the vehicle can be realized accurately and efficiently. It becomes possible.
(2) Since the short-time repetition of communication connection disconnection can be suppressed and the frequency selection frequency can be reduced, the throughput characteristics of the road-vehicle communication system can be improved.
(3) Since the link connection disconnection caused by the movement of the vehicle can be performed promptly and reliably, the throughput characteristics of the road-to-vehicle communication system can be improved within the communication service area composed of a plurality of radio cells.
(4) Since a control signal is not basically exchanged between a radio base station and a radio base station that controls a plurality of radio base stations as in a cellular system, a costly dedicated line becomes unnecessary.
(5) Since the link connection disconnection control is performed only between the mobile station and the limited radio base station, the traffic amount of the control signal flowing on the network connecting all the radio base stations can be minimized.
(6) With respect to ETC (Electronic Toll Collection, automatic toll collection system) that has already been put into practical use, it is possible to implement a function for a communication link connection disconnection method without performing a major device modification. .
[0036]
FIG. 7 is a graph showing the effect of the communication link connection disconnection method in the road-vehicle communication system according to the present invention. According to FIG. 7, it is possible to provide efficient communication in which a link connection is cut only once in one communication area.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a road-vehicle communication system according to the present invention.
FIG. 2 is a graph showing a short-time measurement result of received signal strength in a mobile station.
FIG. 3 is a state transition diagram showing an example of a communication link connection disconnection method according to the present invention. FIG. 4 is a graph showing a result of moving average processing of received signal strength in a mobile station.
FIG. 5 is a state transition diagram of a communication link connection disconnection method using the number of protection stages for error verification according to the present invention.
FIG. 6 is a graph showing a short-time simulation result of link connection disconnection in a road-to-vehicle communication system. FIG. 7 is a graph showing the effect of the communication link connection disconnection method according to the present invention.
DESCRIPTION OF SYMBOLS 1 Gateway 2 Local server 3 Local network 4-1 to 4-N Radio base station 5-1 to 5-N Radio frequency 6-1 to 6-N Radio cell 7 Moving vehicle 8 Road 9 Moving direction 10 Request signal 11 Control signal 21 Received signal strength axis 22 Time axis 23 Received signal strength data 31 Link disconnection state 32-1 to 22-2 Reception of control signal from radio base station 33 Frequency selection timeout 34-1 to 34-2 Received signal strength judgment and error Test 35-1 to 35-4 Link connection or disconnection condition 41 Received signal strength axis 42 Time axis 43 Received signal strength data 51 subjected to moving average processing 51 Link disconnected state 52-1 to 52-K Link connection standby state 53-1 53-K Error test result in link connection standby state normal 54-0 to 54- (K-1) Error detection in link connection standby state Result error 55 Link connection status 56-1 to 56-L Link disconnection waiting state 57-1 to 57-L Error test result error in link disconnection standby state 58-0 to 58- (L-1) Error in link disconnection standby state Test result Normal 71 Distance axis 72 with radio base station to be linked Link time axis 73-1 to 73-2 Repeated short time of link connection / disconnection 74-1-74-2 Normal link connection / disconnection 81 Link connection Distance axis 82 with time base 83-1 to 83-2 Normal link connection / disconnection

Claims (4)

In the mobile station communication link connection disconnection method in a road-vehicle communication system in which a mobile station on a road communicates with a radio base station arranged along the road, the mobile station includes:
A received signal strength detecting step for measuring the received signal strength;
A reception signal strength determination step of determining whether the measured reception signal strength has reached a threshold and deriving a reception signal strength determination result;
An error test step for performing an error test on a control signal periodically transmitted from the radio base station and deriving an error test result;
When entering the communication area configured by the radio base station, it is determined that communication with the radio base station is possible only when the received signal strength determination result exceeds a threshold and the error test result is normal. Or, when leaving the communication area, it is determined that communication with the radio base station is possible only when the received signal strength determination result exceeds a threshold value or the error test result is normal, A communication availability determination step for deriving a determination result; and
When communication is possible when entering the communication area based on the communication availability determination result, a communication link is connected and a link disconnection state is maintained when communication is not possible, or communication is possible when leaving the communication area A communication link connection disconnection method for a mobile station, comprising the step of maintaining the communication link connection state and disconnecting the communication link in the case of communication failure .   2. The communication link connection disconnection method of a mobile station according to claim 1, wherein the received signal strength detecting step performs a moving average processing operation on the received signal strength measured over a certain time width.   The moving average processing operation uses the i-th acquired received signal strength S (i), the weighting coefficient λ (0 ≦ λ ≦ 1), and the i−1th moving average M (i−1), M ( 3. The mobile station communication link disconnection method according to claim 2, wherein the i-th moving average is obtained by i) = (S (i) + λM (i−1)) / (1 + λ). . The error test step includes:
A back protection stage number that defines the number of normal receptions of the error test result for connection determination of a communication link, and a front protection stage number that defines the number of abnormal receptions of the error test result for determination of communication link disconnection,
A link disconnection state in which the wireless base station is disconnected, a link connection standby state in which the number of times the error test result is normal is less than the number of back protection stages, a link connection state in communication with the wireless base station, The transition state having the link disconnection standby state in which the number of times the error test result becomes abnormal is less than the number of forward protection stages is shifted according to the communication link state with the radio base station and the error test result. Steps,
Determining that the link connection is possible if the number of times that the error test result is normal reaches the number of backward protection steps;
4. The mobile station link according to claim 1, further comprising: determining that the link is disconnected if the number of times that the error test result is abnormal has reached the number of forward protection stages. 5. Disconnection method.

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