JP2002165254A - Handover system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate communications under environments of poor radio quality for reducing deficit of presentation information as much as possible, to hand over as soon as possible in a road-vehicle communication between a road side device and a vehicle. SOLUTION: A higher level than reception sensitivity of an on-vehicle material is set as a threshold. When lower than a prescribed number of times and the threshold within a predetermined time, the system transfers to a frequency switching procedure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an AHS (Advanc).
ed Cruise-Assist Highway S
system: a driving support road system) relates to a handover method between wireless zones in a road-to-vehicle communication system.

[0002]

2. Description of the Related Art In recent years, research and development of AHS aiming at a safe and comfortable road traffic system has been promoted mainly by the Ministry of Construction. Among them, as safe driving support services aimed at reducing traffic accidents, safe inter-vehicle maintenance, obstacle collision prevention, lane maintenance,
Services such as crosshead collision prevention, right-turn collision prevention, and pedestrian collision prevention are being studied.

In order to realize these services, it is necessary to provide appropriate information to a driver by performing wireless communication between a roadside facility installed on the roadside and a moving vehicle. For example, as an obstacle collision prevention service, a service that provides a driver with information to that effect in front of a curve when a faulty vehicle is stopped in front of a poor visibility curve or when there is a falling object is considered. In this service, it is necessary to maintain continuous information provision for several hundred meters before the curve. However, as for wireless communication for providing information, there is a limit to the distance that can be achieved with a given power.
In order to provide a service over several hundred meters as described above, a method of configuring a plurality of wireless zones has been adopted.

A technique called handover has been developed as a technique for logically maintaining a communication channel in order to continuously maintain communication between the road side and the vehicle in these plural wireless zones.

FIG. 1 is a block diagram for explaining a conventional road-vehicle communication system. 101 and 102 are wireless zones in which road-to-vehicle communication is covered. 103 and 104
Is an antenna for radiating radio waves for forming the wireless zone. Reference numerals 105 and 106 denote base stations connected to the respective antennas and control wireless transmission and reception. Each base station is connected to 107 base concentrators. The base central station monitors the status of a plurality of base stations and performs distribution processing of provided information. The base central station is connected to a 108 roadside processing device. Although not shown, the roadside processing device is also connected to a sensor device for monitoring road conditions or traffic conditions, and based on the information coming from these devices, provides danger / warning information between roadside vehicles below the base central station. It serves to notify the vehicle via the communication system.

FIG. 2 is a diagram for explaining a conventional handover method. The 201 wireless zone is formed by radio waves emitted by the 203 antenna 1. 202
The wireless zone is also formed by radio waves radiated by the 204 antenna 2. 205 and 206 are graphs respectively showing the relationship between the reception electric field strengths of the wireless zone 1 and the wireless zone 2 and the position in the zone. Although it depends on the angle of the antenna, the received electric field strength generally decreases as the distance from the antenna increases. In addition, since the rear of the antenna eliminates radio wave radiation, the curve shows a sharp decrease in the received electric field intensity near the antenna. The reception sensitivity value 207 generally indicates the reception capability of the vehicle-mounted device, and is a reception electric field strength for securing a predetermined transmission quality.

[0007] In the above-mentioned configuration, conventionally, when services are continuously provided in a plurality of wireless zones, a handover technique is used as a means for logically continuing a communication channel between a base station and a vehicle-mounted device. Have been.
For example, by using the fact that the received electric field strength of the frequency F1 of the wireless zone 1 is lowered in FIG. 2 and the frame synchronization cannot be obtained, a method of switching to the frequency of the next wireless zone 2 and pulling in the frame synchronization is considered. I have. The phenomenon that frame synchronization cannot be achieved is a phenomenon in which a predetermined synchronization signal cannot be detected even though a frame is not formed at a constant cycle.

FIG. 3 shows an example of a frame configuration. Reference numeral 301 denotes a signal generally called a unique word for synchronization detection. 302 is a signal related to the handover method,
It is a signal that reports frequency information of the next zone. Reference numeral 303 denotes a signal for notifying the contents of the frame. 30
Reference numeral 4 denotes a slot for notifying broadcast information for providing common information to vehicles existing in the wireless zone. Reference numeral 305 denotes an individual information slot for providing different information to each vehicle. Therefore, the individual information slots are subdivided into predetermined lengths in order to exchange information simultaneously with a plurality of vehicles.

The radio frame having the above configuration is constantly and repeatedly transmitted, and its cycle is 10 ms here. The aforementioned lack of frame synchronization means that 1
It indicates a case where a 301 unique word is not detected where it should be detected every 0 ms. Generally, a transmission error occurs in wireless communication, and even if this error occurs in a unique word, frame synchronization is lost.
In order to discriminate whether synchronization is lost due to such a temporary error or loss of synchronization due to a decrease in the received electric field strength due to approaching the handover zone, the conventional handover is performed when the non-detection of the unique word, that is, loss of synchronization is detected a plurality of times in succession. The conditions for shifting to.

[0010]

As described above, under the handover condition for detecting the loss of synchronization a plurality of times in succession,
When the received electric field strength in the handover area decreases smoothly, good frequency switching is possible, but disadvantages may occur depending on the wireless environment. FIG. 4 is a typical example of measuring the reception electric field strength in the wireless zone. The horizontal axis shows the distance from the antenna position as a base point, but the level of the received electric field strength fluctuates in a complicated manner near the antenna position. In such a case, frame synchronization is lost or re-synchronization is established. Therefore, assuming that the handover condition in the previous period is three times consecutively out of synchronization, even if the out of synchronization occurs twice, if the unique word is correctly detected for the third time, the handover process is not performed and the communication in the current zone is continuously maintained. Will do.

[0011] In the case where the radio environment is not constant and the received electric field changes in a complicated manner as described above, the communication is not easily switched to the next zone and the communication continues in a state of poor radio quality, and the information provided to the vehicle-mounted device is lost. Causes a problem that the size becomes larger. Therefore, an object of the present invention is to provide means for quickly performing a handover by eliminating communication in an environment with poor wireless quality in order to minimize loss of provided information.

[Means for solving the problems]

As described above, in detecting out-of-synchronization depending on the receiving sensitivity of the vehicle-mounted device, communication is attempted to be continued in a state of poor communication quality, so that loss of provided information increases. Therefore, in the present invention, without depending on the receiving sensitivity of the vehicle-mounted device,
The frequency switching is performed by detecting a decrease in the received electric field strength.

[Action]

As described above, in order to shift to the handover process before the reception electric field changes in a complicated manner, a high level having a margin with respect to the reception sensitivity of the vehicle-mounted device is set as a threshold value.
When the threshold value falls below the predetermined number of times within the predetermined time period, the process is shifted to the handover process, so that communication can be continued while maintaining good radio quality.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 5 is a system configuration diagram for explaining an embodiment of the present invention. 501 and 502
Is a wireless zone, here 502 is a wireless zone from 501
An example will be described in which a handover is performed to a wireless zone. 503
And 504 are antennas for forming frontless zones 501 and 502, respectively. 505 and 506 are
FIG. 4 is a graph showing the received electric field intensity formed by the radio waves of the frequencies F1 and F2 radiated from the antennas 1 and 2, corresponding to the radio zone position.
Also, the relationship between the 507 reception sensitivity value and the 508 handover threshold is shown, and as shown in the figure, the handover threshold is set at a level much higher than the reception sensitivity value.
In this case, after passing the point A, the received electric field strength falls below the handover threshold value, so that the process shifts to the handover process near this point. In addition, at this point, the reception electric field strength of the frequency F2 of the wireless zone has already exceeded the handover threshold, and the condition that the frame synchronization in the wireless zone 2 can be sufficiently established has been established.

As described above, the handover is performed at a higher received electric field strength level as compared with the case where the handover is performed after the point B shown in the related art, so that the frequency is switched to the frequency of the next zone while the communication quality is good. Can be. Therefore, the loss of the provided information can be significantly reduced as compared with the related art.

FIG. 6 is a diagram for explaining an algorithm for shifting to handover in the present invention. T1
Is a timer for measuring a predetermined period, for example, 50
ms. T2 is a timer for sampling the received electric field strength, which is set to 5 ms here. Also RS
SI is a reception signal level corresponding to the reception electric field strength, and here, for example, a handover threshold is set to 60 dBm. In addition, it is assumed that the reception sensitivity value of the vehicle-mounted device has a value of, for example, about 80 dBm for such a handover threshold value. In this case, each time the timer T2 expires, the measurement of the reception electric field strength is performed. As a result, if the reception electric field strength is equal to or less than the handover threshold value of 60 dBm, the counter value is incremented. If the measurement result of the received electric field strength is 60 dBm or more, the counter is not incremented and waits for the next timer T2 to expire.

[0017] Thus repeated and the 50ms timer T1 expires, will be to migrate predetermined number n observe the value of the counter in the dictionary, for example, 5 times a handover process Tara ultra Etei. Therefore, 5 times or more every 5 ms 6
When the reception electric field strength of 0 dBm or less is detected, the process shifts to the handover process. Here, the synchronization is performed by switching to the week fraction of the next zone. In the present invention, as for the frequency of the next zone, the next zone frequency information is reported in a radio frame transmitted from the roadside infrastructure as shown in FIG. As described above, the method of transitioning to the handover process when the value falls below the handover threshold for a predetermined number of times or more in a predetermined time has been described, but the following describes the predetermined interval and the predetermined number of times according to the traveling speed of the vehicle. Is made variable.

FIG. 4 shows an embodiment of the reception electric field strength in the radio zone. In general, a drop in the reception electric field may occur in the radio zone due to road surface reflection, surrounding buildings or running vehicles. In such a case, if handover processing is performed by erroneously recognizing the handover area as a temporary decrease in the received electric field, the radio wave of the next zone frequency may be insufficient and frequency switching may not be performed. At this time, since information is not provided to the vehicle during the handover processing organization, information is lost. To prevent such inconvenience,
It is necessary not to shift to the handover process when the reception electric field strength decreases instantaneously. Therefore, the predetermined time and the predetermined number of times may be increased, but this is not preferable because the frequency switching time in the normal handover area increases. So the for the decline in temporary reception field strength, since the time through a drop in response to the running speed of the vehicle is different, in the high-speed set small for a predetermined time and a predetermined number of times, the predetermined time and predetermined at a low speed By increasing the number of times, it is possible to prevent erroneous handover processing for a drop in the received electric field strength in the wireless zone outside the original handover area while suppressing the time required for frequency switching.

[0019]

As described above in detail in the embodiment of the present invention, in order to perform a handover process at a high receiving electric field strength level, the frequency is switched to the next frequency with good communication quality. Can be. Therefore, loss of the provided information can be significantly reduced as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram for explaining a conventional example.

FIG. 2 is a diagram for explaining a conventional handover method.

FIG. 3 is an example of a radio frame.

FIG. 4 is a diagram showing actual measured values of received electric field strength in a general wireless zone.

FIG. 5 is a diagram for explaining an embodiment of the present invention.

FIG. 6 is a diagram for explaining an algorithm for shifting to a handover process;

[Explanation of symbols]

101, 102, 201, 202, 501, 502-Wireless zone 103, 104, 203, 204, 503, 504-Antenna 105, 106-Base station 107-Base central station 108-Roadside processing device 205, 206, 505.506 -Received field strength 207, 507-OBE reception sensitivity value 508-Handover threshold value 301-Unique word 302-Next zone frequency information slot 303-Frame control information slot 304-Broadcast information slot 305-Individual information slot

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H180 AA01 BB04 FF13 FF27 LL01 LL04 LL15 5K067 AA33 BB12 EE02 EE10 FF16 HH22 JJ39

Claims (3)

[Claims] In a road-to-vehicle communication performed between a roadside apparatus and a vehicle, a level higher than a receiving sensitivity of an on-vehicle device is set as a threshold, and a frequency is switched a predetermined number of times within a predetermined time by falling below the threshold. A handover method characterized by shifting to a procedure. 2. The handover method according to claim 1, wherein the threshold value is at least 10 dBm higher than the receiving sensitivity of the vehicle-mounted device. 3. The handover method according to claim 1, wherein the predetermined time and the predetermined number of times are variable depending on a traveling speed of the vehicle.