JP2003284115A - Hand-over system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hand-over system capable of reducing a wireless out of synchronism detection time or a synchronism detection time. <P>SOLUTION: A mobile communication system comprises a plurality of base stations, a plurality of wireless zones covered by the base stations, and mobile stations moved in the wireless zones, and uses one of a plurality of channels to transceive voice and data between the base station and the mobile station, the first base station BS11 of a plurality of the base stations BS11 to BS51 informs of frequency information items f11 to f51 and the position information of the remaining one or more base stations BS11 to BS51, and the mobile station has a GPS receiver that receives the frequency information and the position information of the base stations notified by the first base station BS11 and detects a switching location of wireless zones on the basis of the data of the GPS receiver and the received position information, and a means that switches the frequency into the frequency of the succeeding base station BS12 on the opportunity of detection. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication system, and more particularly to an intelligent transportation system (ITS).
igent Transport Systems) Handover method for road-to-vehicle communication that realizes services in the field.

[0002]

2. Description of the Related Art ITS states that "using the latest information and communications, etc., we have constructed a system in which people, roads and vehicles are integrated,
Achieving improved safety, improved transportation efficiency, and improved comfort,
Intelligent transportation system that contributes to environmental conservation ",
Research and development is being carried out on a global scale centered on Japan, the US, and Europe. In addition, ITS will greatly contribute to the solution of various problems faced by road traffic today, such as traffic accidents and traffic congestion, as well as the expansion and new creation of the automobile / information and telecommunications-related industry market, and in the 21st century. It is expected to play an important role in realizing an advanced information and communication society.

[0003] ITS covers a wide range of fields such as roads, traffic, vehicles, and information and communications, and its development in Japan is carried out by four related ministries, including the National Police Agency, the Ministry of Economy, Trade and Industry, the Ministry of Internal Affairs and Communications, the Ministry of Land, Infrastructure, Transport and Tourism, and the industry, academia and government. It is a national project that can only be realized through collaboration and cooperation. Currently, development is being carried out in nine fields under the “whole concept of four ministries”. I in FIG.
The 9 development areas of TS and 20 user services are summarized. In order to realize these, it is necessary to construct a large-scale information communication system by using the latest technology with cooperation of related parties and understanding of users. There is "safe driving assistance" in one of the nine development fields mentioned above, and there are four user services in "safe driving assistance". This is the service assumed in the road-to-vehicle communication of the present invention, which will be described below.

The user service providing the traveling environment information uses various sensors on the road and vehicle to prevent accidents and the like in the daytime, nighttime, bad weather, and other situations where visibility is deteriorated. Understanding the driving environment of
The information providing device provides information to the driver who is driving in real time to assist the driver in recognizing the traveling environment.

In order to prevent accidents due to collisions, lane departures, etc., the danger warning user service collects the position and behavior of the own vehicle and surrounding vehicles and obstacle information ahead of the road by various sensors of the road and the vehicle. However, it assists the driver in determining the driving operation, such as giving a warning when it is determined to be dangerous from the vehicle position, the inter-vehicle distance, the traveling speed, and the like.

[0006] The driving assistance user service adds an automatic vehicle control function to the above-mentioned danger warning service to consider the position and behavior of the own vehicle and surrounding vehicles, obstacles, etc. Assists driver's driving operation by automatically performing speed control such as brake operation and steering wheel control.

In order to reduce the load on the driver and to reduce the risk of traffic accidents as much as possible, the automatic driving user service develops a driving assistance function capable of automatic control, and automatically operates according to the surrounding driving environment. By performing speed control such as brake operation and steering wheel control, safe and smooth inter-vehicle distance can be maintained and safe and smooth automatic driving can be achieved.

The system for providing the user service described above is the AHS (driving support road system). This system is the most technically advanced system in ITS. In addition to reducing the driver's burden by automating driving, the goal is to contribute to society by improving safe driving and increasing transportation effects by reducing accidents, and various technological ripple effects are expected. There is.

In Japan, the information providing system (AHS-
i), control support system (AHS-c), automatic driving system (AHS-a). Driving environment information and danger warning User service is AHS-i, Driving assistance user service is AHS-c, Automated driving user service is AHS-i
It corresponds to HS-a. The order of service provision is AHS-
The order is i → AHS-c → AHS-a.

In order to realize AHS, a function of recognizing a road traffic environment (other vehicles, obstacles, road surface conditions and traveling vehicle position), a control function of guiding the vehicle by judging surrounding conditions, an information communication function. Road side infrastructure functions such as the above are required. Furthermore, support by systems other than AHS is also essential, and information on traffic conditions, weather, road alignment, etc. is also required.

On the other hand, the vehicle has a function of detecting road obstacles,
Speed control function, steering wheel control function, MMI function, obstacle avoidance function, etc. are required. The required functions described above are selected and used at each practical level of AHS-i, c, and a.

Communication supporting such ITS is shown in FIG.
As shown in FIG. 4, it can be roughly divided into four types: wide-area wired communication, wide-area wireless communication, road-vehicle communication (dedicated short-distance communication), and inter-vehicle communication.
Build an information and communication system for ITS services as a whole.
These communication technologies should be developed in consideration of being used as a platform for various ITS services, rather than being spent on unique ITS services.

Wide area wired communication and wide area wireless communication are based on ISDN.
It is composed of existing technologies such as, PDC, PHS, and GSM.
An information communication system that provides an ITS service is constructed by using these existing technologies and unique technologies described below.

Communication technologies peculiar to ITS include road-vehicle communication and vehicle-to-vehicle communication. The purpose of these communications is to communicate automatically and in real time between vehicles and roads or between vehicles to make driving of drivers and duties of road traffic managers safer, more comfortable, and more efficient.

Road-to-vehicle communication is communication between a communication infrastructure such as a beacon laid along a road and an in-vehicle device mounted on an automobile. It is classified into spot communication type and continuous communication type. In the spot communication type, small wireless zones are intermittently arranged on the road, and communication is performed at the moment when a vehicle passes through this zone. VICS (road traffic information and communication system) and ETC (automatic toll collection system) are typical and have already been put to practical use. On the other hand, the continuous communication type is applied to the roadside and the vehicle to continuously communicate with each other to perform a danger warning such as a collision prevention and a cooperative driving / autonomous driving. It is the key to realizing AHS (driving support road system).

The inter-vehicle communication is mainly intended for exchanging data among the front seat information (vehicle control information), which has a particularly short information update cycle and is directly connected to vehicle control.
It is attracting attention as one of the elemental technologies essential for the realization of ITS including future cooperative driving and autonomous driving. Since it does not depend on infrastructure like road-to-vehicle communication, it can be expected to be used on general roads.

Of the above-mentioned ITS-specific communication techniques, the present invention describes a handover method between a roadside communication device (base station: BS) and an on-vehicle device (mobile station: MS) that provides an AHS service. .

As a road-vehicle communication protocol, DSRC (Ded
icated Short Rang Communications). DSRC
Is dedicated mobile communication related to a vehicle traveling on a road. DSRC is an important basic technology for communication in ITS and contributes to the informatization of roads, traffic, and vehicles, which is the purpose of ITS. In a broad sense, it includes vehicle-to-vehicle communication, but generally refers to road-to-vehicle communication performed between a vehicle traveling on a road and a roadside machine. Road-to-vehicle communication is communication between a communication infrastructure such as a beacon (base station) laid along a road as described above and an in-vehicle device mounted on a vehicle. It is classified into spot communication type and continuous communication type.

As described above, in the spot communication type, small wireless zones are intermittently arranged on the road and communication is performed at the moment when the vehicle passes through this zone. On the other hand, the continuous communication type is applied to the roadside and the vehicle to continuously communicate with each other to perform a danger warning such as a collision prevention and a cooperative driving / autonomous driving. AHS
It is the key to realizing (driving support road system).

FIG. 11 shows the specified range of DSRC. The physical layer of layer 1, the data link layer of layer 2, and the application layer of layer 7 are defined ranges. Since it is necessary to finish the communication within a limited time while the vehicle moves in the communication zone, the structure of 7 layers is simplified to 3 layers. That is, layers 3 to 6 are not specified. Layer 7
Is configured to appropriately include the functions of layers 3 to 6.

Control function of communication line (communication medium) physical layer
It is called (L1), and has a function of converting the data passed from the upper layer into a form for transmission on an actual communication medium. DSRC L
The specification No. 1 is shown as a radio wave standard (specifications of the physical layer are shown in FIG. 5).

The data link layer (L2) defines the frame structure, the control parameters, and the transmission error control.
L2 defines a communication control procedure for realizing data communication with a roadside device when an in-vehicle device passes through a communication zone, and its configuration is defined by a logical link layer (LLC sublayer) and a medium access control layer (M
AC sublayer).

The LLC sublayer is ISO / IEC8802-
2: It is based on 1994 (Local Area Network),
Some features have been removed to accommodate DSRC.
The MAC sublayer has a data processing function mainly for communication management of the transmission medium. FIG. 12 shows the structure and function of the data link layer.

The application layer (L7) provides DSRC communication means for applications such as ETC. The DSRC L7 includes all the functions related to the communication between the roadside device and the in-vehicle device that are not supported in the lower layers (L1 and L2). The main processing functions of L7 are performed by three kernels, and perform initialization processing, bidirectional data transfer processing, broadcast data transfer processing, and the like. FIG. 13 shows the configuration and function of the application layer.

In the Japanese DSRC standard, the structure of the communication protocol adopts a synchronous structure capable of supporting full-duplex and half-duplex communication. The synchronous structure is a fixed length of a basic unit (slot) of data in downlink and uplink. The slots have a fixed length, and n slots are combined to form a frame. Frame is 1
Each roadside device is configured to be able to communicate with a plurality of vehicle-mounted devices at the same time, and communication is sequentially started from the vehicle-mounted device that has been registered for communication with the roadside device. This series of communication between the roadside device and the on-vehicle device is called a transaction, and a procedure from the start to the end of one communication is defined.

FCMS (Frame Control M
essage Slot: Frame control message slot), MD
There are S (Message Data Slot) and ACTS (Activation Slot) (FIG. 14). The FCMS is a slot that synchronizes frames and provides slot allocation information to the vehicle-mounted device because the roadside device controls communication, and is dedicated to the downlink (FIG. 14). The MDS is a slot containing actual communication data, and the acknowledgment of data communication is also included in this slot. MDS is an MDC (Message Data) for data transfer.
a Channel: message data channel) and MD
It is composed of two ACKCs (Acknowledge Channels) for transmitting the reception result of C as a normal / abnormal code to the other party. There are downlinks and uplinks
(Figure 15).

The ACTS is used when the vehicle-mounted device starts communication.
A slot that requests the roadside device to allocate an MDS slot, and is composed of a plurality of ACTCs (Activation Channels). The in-vehicle device randomly selects ACTC, and requests the roadside device for communication registration. It is dedicated to the uplink (Fig. 16).

Depending on the communication system, there are half-duplex communication frames and full-duplex communication frames. Half-duplex communication frame is MD
The FCMS has a variable-length frame structure in which the total number of S and ACTC is 8 or less, and FCMS is added to the head. It can be applied not only to bidirectional communication but also to a communication frame for one-way only (broadcast) from a roadside device to an on-vehicle device (FIG. 17). The full-duplex communication frame has a variable-length frame structure including slots each having an MDS number and an ACTC number of 4 or less. Each of the uplink and downlink performs transmission / reception (FIG. 18).

A series of communications between the roadside device and the on-vehicle device is called a transaction. The communication protocol of DSRC allows communication between a roadside device and an in-vehicle device that moves in a limited communication zone.
This is done by exchanging information in basic units called slots. FIG. 19 shows an example of a transaction. When the vehicle enters the communication zone and the in-vehicle device can communicate, the first frame FCMS is used for synchronization. With respect to the ACTS designated by the FCMS, an arbitrary ACTC among them is selected, and the communication registration ID randomly generated is transmitted. When the roadside device receives the registration of the vehicle-mounted device, it allocates a slot with which the vehicle communicates and notifies it by FCMS. The vehicle-mounted device that has received the FCMS transmits the uplink data by the designated MDS. After the in-vehicle device transmits the uplink data, the MD
ACKC is received in the latter half of S.

The spot-type DSRC road-vehicle communication system, which is being put into practical use internationally, is very effective for ETC, navigation, etc., but it is continuous for realizing functions related to AHS such as driving assistance and automatic driving. Communication-type DSRC is suitable, and research and development are underway in each country. In addition, inter-vehicle communication, which is a means of communication between vehicles, is important for autonomous driving, and is being studied in various countries.

Conventionally, such DSRC has been used to perform the following handover to realize continuous communication.

FIG. 20 shows an example of a system configuration for continuous communication. In the example, there are 5 base stations (BS1 to BS5) and the frequency f
1 to f4 are assigned. Roadside processing device is a base station
(BS) management (setting of radio frequency, etc.), data transmission / reception, etc. to provide AHS services. Mobile station (MS) is BS
It enters the wireless zone of No. 1 and sequentially passes through BS2 to BS5 to receive the AHS service through DSRC. MS
1 transmits and receives at frequency f1 in the wireless zone of BS1,
In the wireless zone S2, frequency f2, in the wireless zone BS3, frequency f3, in the wireless zone BS4, frequency f4,
In the wireless zone of BS5, the base station at frequency f1
Send and receive data with (BS).

Handover when crossing between wireless zones is performed as follows, for example. MS1 knows the frequency of BS1 by using, for example, a lane marker (FIG. 21). The lane marker describes that the frequency of BS1 is f1 and the type of AHS service. MS1 passes over the lane marker before entering BS1 and reads the written data. When the MS 1 can receive the provided AHS service, the radio frequency is set to f1 and data is transmitted / received to / from the BS 1. The radio frequency f2 of the next zone BS2 is written in the FCMS of the frame transmitted by the BS1, and the MS1 stores it. When MS1 passes through the radio zone of BS1, the radio frequency f1 is out of synchronization. MS1 is determined to have passed the wireless zone of BS1, triggered by this, sets the frequency of the wireless device to the stored wireless frequency f2, and transmits and receives data to and from BS2. Similarly, the radio frequency f3 of the next zone BS3 is included in the FCMS of BS2.
However, the radio frequency f4 of the next zone BS4 is written in the FCMS of BS3, and the radio frequency f1 of the next zone BS5 is written in the FCMS of BS4. In contrast, BS5
Since the next zone frequency is not applied to FCMS,
BS5 can know the end of the AHS service. In this way, when the radio zone is crossed, the radio frequency is switched to the frequency of the next zone to realize the handover.

The handover method described above is applied to the AHS
When applied to the continuous communication type assuming services etc., there are the following problems.

In the above-mentioned handover method, the frequency is switched when the synchronization is lost when the wireless zone is crossed.
There is time when communication is lost. Usually, the communication quality of mobile communication is poor, so synchronization is protected so that synchronization cannot be easily lost. Since the synchronization protection takes several times as many as the frame, it takes about 100 ms until the frame loss is actually detected, for example, if the frame time is 25 ms. Also,
It takes more time to detect the loss of synchronization and switch the radio frequency to establish the synchronization. AH
The S service provides information about vehicle safety,
Loss of communication due to handover causes significant problems.

[0036]

SUMMARY OF THE INVENTION The present invention has been made under the above circumstances, and an object thereof is to provide a handover method capable of shortening the wireless out-of-synchronization detection time or the synchronization detection time. There is.

[0037]

In order to solve the above problems, the present invention comprises a plurality of base stations, a plurality of radio zones covered by the base stations, and a mobile station moving in the radio zones, In a mobile communication system in which voice and data are transmitted and received between a base station and a mobile station using one of a plurality of channels, a plurality of wireless zones form a continuous wireless zone, and the first of the plurality of base stations The base station broadcasts the frequency information and position information of the remaining one or more base stations, and the mobile station has a GPS receiver and receives the frequency information and position information of the base station broadcast from the first base station. However, it has means for detecting the switching location of the wireless zone from the data of the GPS receiver and the received position information, and switching to the frequency of the next base station when triggered by this.

Further, it has means for synchronizing the frame transmission timings of a plurality of base stations. Further, the mobile station has means for making the timing of switching to the frequency of the next base station the end of the frame or the start of the frame.
The mobile station has two radios, one transmitting and receiving at the frequency of the current base station's radio zone, the other waiting at the frequency of the next base station's radio zone to determine the switching timing of the radios. It has a means to be the beginning of the frame or the end of the frame.

According to the handover method for road-to-vehicle communication of the present invention, the switching time of the wireless zone can be completed in a short time.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the system configuration of the present invention. Roadside processing device, base stations BS11, BS21, BS3
1, BS41, BS51 and mobile station MS11. BS11 is a base point base station. The roadside processing device sends the base station BS11 to base station BS21 to base station BS51.
The frequency information and the position information of the base station are notified. The radio frequency of the base point base station BS11 is set to f11 by default, and the mobile station MS11 uses the radio frequency f1 of the base station BS11.
1 is set as the initial frequency. FIG. 2 shows a format example. The base station position information is notified in three dimensions xyz, but since the vehicle travels on the road, there is no problem even if there is no height z. Further, the actual position information is not the position directly below the base station antenna, but the position where the wireless zones shown in FIG. 3 intersect, for example.

FIG. 4 shows the configuration of the base station. The base station is composed of a roadside radio, a DSRC controller, an optical module and a CPU. The roadside radio implements the physical layer as shown in FIG. 5 and sets the frequency under the control of the CPU.
The DSRC control unit mainly implements the MAC sublayer of the data link layer and operates under the control of the CPU. The optical module transmits and receives data between the base station and the roadside processing device under the control of the CPU. The CPU controls the roadside wireless device, the DSRC control unit, the optical module, and the like to operate the base station.

FIG. 6 shows an example of the configuration of the vehicle-mounted device. The in-vehicle device includes an in-vehicle wireless device, a DSRC control unit, a GPS receiver and a CPU. The in-vehicle wireless device is equipped with a physical layer as shown in FIG. 5, and the frequency is set under the control of the CPU. The DSRC control unit is mainly the M of the data link layer.
It implements the AC sublayer and operates under the control of the CPU. The GPS receiver notifies the CPU of the current position information of the mobile station. The CPU controls the in-vehicle wireless device, the DSRC control unit and the like to operate the mobile station.

In the above configuration, the operation is performed according to the handover flow of FIG. After the start-up of each device, the roadside processing device sets, for example, a radio frequency according to the notification data of FIG. 2 to each base station, and subsequently transmits a start command,
Further, the broadcast data of FIG. 2 is transmitted to the base point base station BS11. After starting up, each base station starts transmitting a frame by a start command from the roadside processing device. As a result, the frame transmission timing of each base station is aligned.

The base point base station (BS11) uses the radio frequency (f
11) is set and the operation is started. The annunciation data received from the roadside processing device is stored, and thereafter, the annunciation data is transmitted in an arbitrary slot every frame.

The mobile station MS11 sets a radio frequency in the base point base station BS11, starts operation, and runs a vehicle.
When entering the wireless zone of the base point base station BS11, wireless synchronization is established and a connection request is transmitted to the base point base station BS11. Upon receiving the connection request from the mobile station MS11, the base point base station allocates the slot transmitting the broadcast data.

The mobile station MS11 receives and stores the annunciation data in the slot assigned to the base point base station BS11. Compare the location information of the notification data with the GPS data,
The switching position to the next wireless zone is detected. When detected, the radio is set to the frequency f21 of the next radio zone. The switching position is where the waves of f11 and f21 intersect, and immediately synchronizes with the frequency of f21. After the synchronization is established, the connection request is transmitted to the base station BS21. Upon receiving the connection request from the mobile station MS11, the base station BS21 allocates a slot.

The above operation is performed at frequencies f31, f41, f5.
Repeat 1 and frequency setting change until the last position information,
Handover between base stations is executed.

In this handover method, since the handover is carried out based on the position information instead of the conventional handover triggered by the out-of-synchronization, the out-of-synchronization detection time can be shortened and a more feasible AHS service can be provided. Become.

FIG. 8 shows an example of the configuration of an in-vehicle device equipped with two in-vehicle wireless devices. For example, the radio A is the base station BS11
When the radio device B is synchronized with the frequency f11, the radio device B sets the frequency f21 in the next radio zone. When the wireless device B receives the wave of f21, synchronization is established. When the DSRC control unit detects the establishment of synchronization of the wireless device B, it switches the selection circuit to receive the data from the wireless device B. The radio A sets the frequency f31 of the next radio zone. In this handover method,
Since the handover is performed when the synchronization of the standby radio is established, the base station position information is unnecessary.

According to the above handover method, the synchronization establishment time is further shortened as compared with the case where there is one wireless device.

Although not shown, the DSRC control unit has a frame generation function. As mentioned above, GPS
Radio frequency switching is completed when the data and position information match, or at the timing of synchronization establishment of the standby radio (A / B), but at this time the frame generation function and arbitrary timing (first or last frame) It is also possible to switch after synchronizing with). By doing so, it becomes possible to switch during the frame guard time, and it is possible to minimize frame destruction and the like.

[0052]

As described above, according to the handover method of the present invention, there is an effect that the out-of-synchronization detection time of radio or the synchronization detection time can be shortened.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration example according to the present invention.

FIG. 2 is a diagram showing an example of broadcast data of a base point base station.

FIG. 3 is a diagram showing an example of base station position information.

FIG. 4 is a diagram showing a configuration of a base station.

FIG. 5 is a drawing showing specifications of a physical layer.

FIG. 6 is a diagram showing an example of a configuration of an in-vehicle device.

FIG. 7 is a handover flow chart.

FIG. 8 is a diagram showing another configuration example of an in-vehicle device.

FIG. 9 is a diagram showing nine development fields of ITS and twenty user services.

FIG. 10 is a diagram showing a communication field of ITS.

FIG. 11 is a diagram showing a specified range of DSRC.

FIG. 12 is a diagram showing a structure and a function of a data link layer.

FIG. 13 is a diagram showing a configuration and a function of an application layer.

FIG. 14 is a diagram showing a configuration of FCMS.

FIG. 15 is a diagram showing a configuration of an MDS.

FIG. 16 is a diagram showing a structure of an ACTS.

FIG. 17 is a diagram showing a configuration example of a half-duplex communication frame.

FIG. 18 is a diagram showing a full-duplex communication frame structure.

FIG. 19 is a diagram showing an example of a transaction.

FIG. 20 is a diagram showing an example of a system configuration of continuous communication.

FIG. 21 is a diagram showing a configuration example when a lane marker is used.

[Explanation of symbols]

BS11, BS21, BS31, BS41, BS51
Base station MS11 Mobile station

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Claims (6)

[Claims] 1. A base station comprising a plurality of base stations, a plurality of radio zones covered by the base stations, and a mobile station moving in the radio zones, wherein one of the plurality of channels is used between the base station and the mobile stations. In a mobile communication system for transmitting and receiving voice and data, the plurality of radio zones form a radio zone continuously with each other, and the first base station of the plurality of base stations is the frequency of the remaining one or a plurality of base stations. Information and location information, the mobile station comprises a GPS receiver,
The frequency information and the position information of the base station notified from the first base station are received, the switching location of the wireless zone is detected by the data of the GPS receiver and the received position information, and the frequency of the next base station is simultaneously detected. A handover method characterized by switching and continuing communication between a base station and a mobile station. 2. The handover system according to claim 1, wherein the frame transmission timings of the plurality of base stations are synchronized. 3. The handover system according to claim 1, wherein the timing at which the mobile station switches to the frequency of the next base station is at the end of the frame. 4. The handover system according to claim 1, wherein the timing at which the mobile station switches to the frequency of the next base station is set to the beginning of the frame. 5. The mobile station comprises two radios, one transmitting and receiving at the frequency of the current base station radio zone, and the other one.
3. The handover method according to claim 1, wherein one of the base stations waits at the frequency of the radio zone of the next base station, and the switching timing of the radio is set to the beginning of the frame. 6. The mobile station comprises two radios, one transmitting and receiving at the frequency of the current base station's radio zone, and the other one.
3. The handover method according to claim 1 or 2, wherein one of the base stations waits at the frequency of the radio zone of the next base station, and the switching timing of the radio is set to the end of the frame.