WO2010050631A1

WO2010050631A1 - Mobile communication repeating method in moving object and repeater thereof

Info

Publication number: WO2010050631A1
Application number: PCT/KR2008/006353
Authority: WO
Inventors: Duk-Yong Kim
Original assignee: Kmw Inc.
Priority date: 2008-10-28
Filing date: 2008-10-28
Publication date: 2010-05-06

Abstract

A method for relaying radio communication in a moving object is provided. The method includes previously defining a radio map made by databasing information on a radio environment of a preset area; comparing current position information and moving direction information of the moving object with data in the radio map; and adjusting, according to the comparison result, an antenna for a relay mounted on the moving object so as to always face a serving base station now in service, or to face a direction in which a signal from the serving base station is best received.

Description

MOBILE COMMUNICATION REPEATING METHOD IN MOVING OBJECT AND REPEATER THEREOF

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a radio communication relay technology in a moving object, and in particular, to a method for relaying radio communication in a moving object and a relay thereof, in which while a moving object is moving, a relay adjusts a relay antenna(s) mounted on the moving object to allow the relay antenna to face a serving base station from which it is now receiving a service, or to face the direction in which a signal from a corresponding base station is best received, thereby reducing the number of handoffs and thus improving management efficiency of wireless channel resources of the base station.

2. Description of the Related Art

As illustrated in FIG. 1, in a mobile communication system, when a mobile station 110 leaves a serving cell area 130 of a serving base station 120 from which it is now receiving a service, and enters another area, for example, another channel, sector, base station, base station controller, exchange, etc., a handoff function for continuously maintaining a call path of the mobile station is performed.

As to the handoff function, when radio strength decreases during a call of a mobile station due to mobility of the mobile station, the mobile station replaces the old radio resources with new radio resources to continue the call. In this function, the mobile station continuously searches signal strength of the serving base station from which it is now receiving a service, and signal strengths of neighboring base stations, and compares the searched signal strengths of the base stations with each other, thereby switching its call to a target base station where it can continuously maintain the current ongoing call.

The mobile station compares the searched pilot strengths of base stations with several predetermined thresholds, and classifies the pilots into 4 sets of an active set, a candidate set, a neighbor set, and a remaining set. The active set is a set of PN codes (=pilots) with which call channels are now allocated to a mobile station. The candidate set, though it is not the active set now, is a set of PN codes having pilot strength sufficient for demodulation. The neighbor set, though it is neither the active set nor the candidate set now, is a set of PN codes that can be candidates for handoff. Finally, the remaining set is a set of PN codes, none of which is included in the above three sets.

A service area of one base station is commonly several kilometers (KM) wide. In some cases, however, the service area is several tens of meters (M) in the high-population area such as metropolitan area.

When a distance between a base station and another base station is close in this way, frequency of handoff occurrence increases.

Meanwhile, when strength of a signal transmitted from a place having a special radio environment, i.e., from a base station which is geographically adjacent to a mobile station, is lower than that of a signal received from a base station which is farther from the mobile station, due to an obstacle such as buildings, the mobile station performs handoff to the remote base station having a good radio environment, rather than performing handoff to the adjacent base station, and repeatedly performs handoff back to the adjacent base station once it passes the special area.

In particular, when there are many surrounding obstacles or the moving object moves frequently, multi-fading is severe, increasing a handoff rate.

For these reasons, the mobile station suffers from the high possibility that a call will be dropped in a process of frequently repeating handoff, causing a possible influence on the entire system quality.

Soft handoff adopts a Connect-Before-Break scheme of connecting a call through an interim process of simultaneously capturing signals from a plurality of base stations. However, during handoff, a plurality of adjacent base stations commonly allocate call channels to one mobile station in a duplicated manner, causing a considerable decrease in management efficiency of wireless channel resources. In particular, as to the base stations situated in the path through which public transportation means such as bus, subway, train, etc. moves, numerous passengers make calls through the base stations, and they pass through a plurality of base stations for a short time. Therefore, handoff occurs frequently, causing an abruptly decrease in management efficiency of wireless channel resources of the base stations.

SUMMARY OF THE INVENTION

An aspect of the present invention is to provide a radio communication method in a moving object, in which a radio map is made by measuring radio environment information in a moving path of the moving object or in a special area, and a relay with an antenna whose facing direction is adjustable is mounted in the moving object to adjust the facing direction of the antenna based on current position information and direction information of the moving object and data in the radio map, so that a radio signal of a base station from which the relay is now receiving a service is maintained at higher strength, making it possible to reduce handoff occurrence and preventing several adjacent base stations from allocating call channels to one mobile station in a duplicated manner.

Another aspect of the present invention is to provide a radio communication method in a moving object, in which a radio map is made by measuring radio environment information in a moving path of the moving object or in a special area, and a relay with antennas fixed to a plurality of directions is mounted in the moving object to select an arbitrary antenna based on current position information and direction information of the moving object and data in the radio map, so that a radio signal of a base station from which the relay is now receiving a service is maintained at higher strength, making it possible to reduce handoff occurrence and preventing several adjacent base stations from allocating call channels to one mobile station in a duplicated manner.

Further another aspect of the present invention is to provide a radio communication method in a moving object, in which a radio map is made by measuring radio environment information in a moving path of the moving object or in a special area, and a relay with antennas fixed to a plurality of directions is mounted in the moving object to select an arbitrary antenna based on current position information and direction information of the moving object and data in the radio map, so that when a handoff state occurs, the radio communication method additionally selects an antenna facing a target base station to which the relay will perform handoff, other than an antenna facing a serving base station from which the relay is now receiving a service, by checking surplus channel information of the target base station, and adjusts received signal strength of a base station, received from the selected antenna, in a predetermined ratio so that handoff is performed with a time difference, thereby making it possible to distribute load of the base stations according to surplus channel environment of the target base station.

Yet another aspect of the present invention is to provide a radio communication method in a moving object, in which a radio map is made by measuring radio environment information in a moving path of the moving object or in a special area, and a relay with a plurality of antennas whose facing directions are adjustable is mounted in the moving object to adjust facing directions of the antennas based on current position information and direction information of the moving object and data in the radio map, so that when a handoff state occurs, the radio communication method additionally selects an antenna used for receiving a signal of a target base station to which the relay will perform handoff, other than an antenna used for receiving a signal of a serving base station from which the relay is now receiving a service, by checking surplus channel information of the target base station, so as to adjust facing directions thereof, and adjusts received signal strengths of the base stations, received from the selected antennas, in a predetermined ratio so that handoff is performed with a time difference, thereby making it possible to distribute load of the base stations according to surplus channel environment of the target base station.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for a description of handoff in a mobile communication system;

FIG. 2 is a block diagram according to a first embodiment of the present invention; FIG. 3 is a block diagram according to a second embodiment of the present invention;

FIG. 4 is a block diagram according to a third embodiment of the present invention; and FIG. 5 is a block diagram according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the accompanying drawings, a detailed description will now be made of a radio communication method in a moving object according to the present invention.

The moving object can be classified into bus, car, train, subway, etc. A description of the present invention will be given with reference to the bus, one of the moving objects, by way of example.

Although the present invention will be described for an exemplary case where a moving object moves along a regular moving path, by way of example, the present invention can also be applied to a moving object that moves along an irregular.

The bus is a typical moving object that can carry several tends of passengers along a regular path at a speed of about 60KM.

Assuming that all passengers on the bus are enjoying communication, each time handoff occurs, a plurality of base stations should allocate as many channels as the number of corresponding passengers in a duplicated manner, causing inefficient management of wireless channel resources.

First Embodiment

First, a radio map is made by measuring and databasing radio environments in the moving path of the bus.

The radio environments include base station information for each received signal's strength in a particular position, base station's azimuth information in a particular position, and information on a direction in which a signal of a corresponding base station in a particular position is best received. Such measurement of the radio environments and making of the radio map can be previously performed by the service provider intended to support the present invention by means of separate measurement equipments. Thereafter, information on the generated radio map is stored in a radio communication relay according to the present invention.

Next, a relay is mounted on the bus so that it can relay signals inside the bus. Referring to FIG. 2, an antenna 260 whose facing direction is adjustable by a driver 262 is mounted as a relay antenna.

In the relay are installed a controller 200 for adjusting the relay antenna 260 according to the properties of the present invention while performing a common radio communication relay operation; a memory 210 for storing data for the previously made radio map; a Global Positioning System (GPS) device 240 for obtaining information on the current position and moving direction of the bus; a sensor 220; and a service antenna 230 for performing radio communication with a mobile station(s) in the bus.

The controller 200 adjusts a facing direction of the relay antenna based on current position information and moving direction information of the bus, and data in the radio map.

A detailed description thereof will be given below.

When the bus moves, the controller 200 calculates the current position and moving direction information.

The current position and moving direction information of the bus can be calculated using a general method based on a sensor 220 for directional information detection, composed of the GPS device 240, a gyroscope and a compass.

Further, the controller 200 calculates position information of the base station from which it is now receiving the service, stored in the radio map. The controller 200 compares the current position information and moving direction information of the bus with the base station's position information, and adjusts the facing direction of the antenna so that the relay antenna can well receive the signal of the serving base station from which it is now receiving the service.

The relay antenna's facing direction adjustment operation can be performed on a temporary basis, or on a real-time basis.

When adjusting the relay antenna's facing direction, the controller 200 can either adjust the relay antenna to face the base station from which it is now receiving the service according to a previously set program, or adjust the relay antenna to face the direction in which a signal of the base station from which it is now receiving the service is best received at the highest strength. Actually, of course, the relay itself adjusts the relay antenna's facing direction to the direction which is simply set in the corresponding position according to the currently set program.

As a result, no matter in which direction the bus moves, the relay antenna always faces the base station from which the relay is now receiving the service, or the direction in which a signal of the corresponding base station is best received.

If the relay adjusts the antenna's facing direction in this manner, the radio signal of the base station from which the relay is now receiving the service is maintained at higher power, making it possible to reduce handoff occurrence and to reduce the number of base stations that allocate duplicate channels to one mobile station.

Second Embodiment

First, as done in the first embodiment, a radio map is made by measuring and databasing radio environments in the moving path of the bus.

The radio environments include base station information for each received signal's strength in a particular position, base station's azimuth information in a particular position, and information on a direction in which a signal of a base station in a particular position is best received.

Next, a relay is mounted on the bus, and the number of mounted relay antennas is 2 or more.

For example, as shown in FIG. 3, 4 antennas 360 can be provided so that they can be mounted in the east/west/south/north directions, or more than 4 antennas can be provided so that they can be mounted in the subdivided directions.

In the relay are installed a switching unit 362 for selecting any one of the plurality of antennas; a controller 200 for outputting a control signal for controlling the switching unit; a memory 210 for storing data for the previously made radio map; and a GPS device 250 for obtaining the current position and moving direction information of the bus.

The controller 200 selects an arbitrary one of the plurality of antennas based on the current position information and moving direction information of the bus, and data in the radio map.

A detailed description thereof will be given below.

Further, the controller 200 calculates position information of the serving base station from which it is now receiving the service, stored in the radio map.

The controller 200 compares the current position information and moving direction information of the bus with the base station's position information.

Based on the comparison result, the controller 200 checks the antennas 360 which are facing the serving base station in their current positions. The controller 200 controls the switching unit 362 so that the corresponding antennas are selected.

The controller 200 can either select the antennas facing the base station from which it is now receiving the service according to a previously set program, or select the antennas facing the direction in which a signal of the base station from which it is now receiving the service is best received at the highest strength.

As a result, no matter in which direction the bus moves, the relay can always select the antennas facing the base station from which it is now receiving the service, or the antennas facing the direction in which a signal of the corresponding base station is best received.

Third Embodiment First, as done in the first and second embodiments, a radio map is made by measuring and databasing radio environments in the moving path of the bus.

For example, as shown in FIG. 4, 4 antennas 360 can be provided so that they can be mounted in the east/west/south/north directions, or more than 4 antennas can be provided so that they can be mounted in the subdivided directions.

In the relay are installed a switching unit 362 for selecting any one or more of the plurality of antennas according to a control signal; signal strength adjusters 462, connected to the plurality of antennas, respectively, for adjusting received signal strengths of the corresponding antennas according to a control signal; a controller 200 for outputting to the switching unit 362 a control signal CS for controlling the signal strength adjusters 462 and a switching signal CS for selecting antennas in order to proportionally adjust strengths of received signals of the serving base station from which it is now receiving the service, and a target base station to which it will perform handoff; a memory 210 for storing data for the previously made radio map; and a GPS device 250 for obtaining the current position and moving direction information of the bus.

The controller 200 selects one or more of the plurality of antennas based on current position information and moving direction information of the bus, data in the radio map, and surplus channel information of a handoff target base station.

A detailed description thereof will be given below.

The controller 200 determines which of the plurality of antennas it will select, based on the current position information and moving direction information of the bus, and the base station's position information.

Meanwhile, when the handoff state occurs (i.e., the current position corresponds to an area where handoff occurs), the controller 200 receives surplus channel information of the target base station, and if there is any surplus in channel capacity, the controller 200, as done in the second embodiment, selects the antennas facing the handoff target base station.

The third embodiment is equal in operation to the second embodiment up to here.

However, if there is no surplus in the channel capacity of the target base station, the controller 200 simultaneously selects the antennas facing the base station from which it is now receiving the service, and the antennas facing the target base station to which it will perform handoff. Further, the controller 200 proportionally adjusts strengths of signals received via the selected antennas according to the surplus channel environment of the target base station so that handoff is performed with a time difference.

That is, the controller 200 receives signals of both the serving base station and the target base station, and if there is no surplus in the channel capacity of the target base station, the controller 200 sets received signal strength of the target base station to be less than received signal strength of the serving base station by an arbitrary ratio so that only some mobile stations undergo handoff.

Thereafter, when there is an enough surplus in channel capacity of the target base station, the controller 200 inversely sets received signal strength of the serving base station to be less than received signal strength of the target base station so that the remaining mobile stations undergo handoff.

After the handoff is completed for all mobile stations, the selection of the antennas facing the serving base station is cancelled.

In this case, the relay receives the channel capacity signals provided from the target base station, and based on this information, the controller 200 controls the handoff-related antenna selection and signal strength adjustment operation.

In addition, information on the handoff target base station is previously set in the radio map, and the number of the additionally selected target base stations can be one or more.

For reference, if surplus channels of the handoff target base station are too less in number, it is also possible to select one more handoff target base station. That is, the controller 200 can select the current serving base station and 2 target base stations, thereby distributing the handoff.

As a result, no matter in which direction the bus moves, the relay can always receive a good signal of the base station from which it is now receiving the service, and can reduce handoff occurrence. Thus, the relay can reduce the number of base stations that allocate duplicate channels to one mobile station.

Further, the controller 200 can distribute load of base stations by allowing handoff to be performed according to the surplus channel environment of the target base station with a time difference.

Fourth Embodiment

As done in the third embodiment, a relay is mounted on the bus, and 2 or more antennas whose facing direction is adjustable by drivers 262 are installed as relay antennas.

In the relay are installed a switching unit 362 for selecting any one or more of the plurality of antennas according to a control signal; signal strength adjusters 462, connected to the plurality of antennas, respectively, for adjusting received signal strengths of the corresponding antennas according to a control signal; a controller 200 for outputting a control signal to the drivers 262 to adjust facing direction of the relay antennas, outputting a control signal to the signal strength adjusters 462 to proportionally adjust received signal strengths of the serving base station from which it is now receiving the service, and the target base station to which it will perform handoff, and outputting a control signal for selecting antennas to the switching unit 362; a memory 210 for storing data for the previously made radio map; and a GPS device 250 for obtaining the current position information and moving direction information of the bus.

An operation will now be described below.

When the bus moves, the controller 200 calculates current position and moving direction information. The controller 200 selects an arbitrary antenna among the plurality of antennas.

The controller 200 adjusts the selected antenna to face the serving base station, based on the current position information and moving direction information of the bus, and the base station's position information.

Meanwhile, when the handoff state occurs, the controller 200 receives surplus channel environment information of the target base station, and if there is any surplus in channel capacity, the controller 200, as done in the first embodiment, adjusts the antennas to face the handoff target base station.

However, if there is no surplus in channel capacity of the target base station, the controller 200 allows the relay to receive a signal of the handoff target base station via the remaining antennas.

That is, the controller 200 allows the relay to simultaneously receive signals of the serving base station from which it is now receiving the service, and the target base station to which it will perform handoff.

In addition, the controller 200 proportionally adjusts strengths of signals received via two antennas according to the surplus channel environment of the target base station so that handoff is performed with a time difference.

That is, the controller 200 receives signals of both base stations, and if there is no surplus in channel capacity of the target base station, the controller 200 sets received signal strength of the target base station to be less than received signal strength of the serving base station by an arbitrary ratio so that only some mobile stations undergo handoff.

Thereafter, if there is an enough surplus in channel capacity of the target base station, the controller 200 inversely sets received signal strength of the serving base station to be less than received signal strength of the target base station so that the remaining mobile stations undergo handoff. After the handoff is performed on all mobile stations, the controller 200 cancels the selection of the antennas via which the relay was receiving a signal of the serving base station from which it is now receiving the service, and adjusts only the antennas via which the relay receives the signal of the target base station.

Meanwhile, the third and fourth embodiments can allow the relay to always select more than 2 antennas, instead of removing the switching unit 362, and then adjust received signal strength of the antennas via which signals are received, thereby providing the effect of selecting antennas.

That is, after selecting all of the antennas facing the serving base station and the antennas facing the target base station, if the controller 200 sets received signal strength of the antennas that always fact the serving base station, to 100, and sets received signal strength of the antennas that always face the target base station, to O', only the signals of the serving base station are eventually received, providing the effect of selecting antennas even without the switching unit.

In this case, the controller 200 can either adjust the relay antenna to face the base station from which it is now receiving the service according to a previously set program, or adjust the relay antenna to face the direction in which a signal of the base station from which it is now receiving the service is best received at the highest strength.

As a result, no matter in which direction the bus moves, the relay can always receive a good signal of the base station from which it is now receiving the service, and can reduce the number of base stations that allocate duplicate channels to one mobile station.

In addition, it is possible to distribute load of base stations by allowing handoff to be performed according to the surplus channel environment of the target base station with a time difference.

Meanwhile, in the first to fourth embodiments, in some cases, strength of a signal transmitted from a place having a special radio environment, i.e., from a base station which is geographically adjacent to a mobile station, is lower than that of a signal received from a base station which is farther from the mobile station, due to an obstacle such as buildings.

In this case, the conventional mobile station performs handoff to the remote base station having a good radio environment, rather than performing handoff to the adjacent base station, and repeatedly performs handoff back to the adjacent base station once it passes the special area.

In order to reduce such frequent handoff state, a handoff target base station to which the first handoff will be performed, can be previously set during generation of the radio map.

That is, in the case where even though a signal received from the remove base station is higher in strength than the signal received from an adjacent base station in a particular position, the signal received from the adjacent base station becomes higher again in strength once the mobile station passes the particular place, the present invention can reduce the number of handoffs by continuously maintaining the call with the adjacent base station without performing handoff to the remove base station.

As described in detail above, the radio communication method in a moving object according to the present invention allows the relay antenna mounted on the moving object to face the serving base station from which the relay is now receiving the service, or to face the direction in which a signal from a corresponding base station is best received; or allows the relay to select an antenna facing the serving base station from which it is now receiving the service, or to select an antenna facing the direction in which a signal of the serving base station is best received, among a plurality of relay antennas mounted on the moving object, so that the radio signal of the base station from which the relay is now receiving the service is maintained at higher strength, making it possible to reduce the handoff occurrence and to prevent several adjacent base stations from duplicately allocating call channels to one mobile station, and thus contributing to an increase in management efficiency of wireless channel resources of the base stations. In addition, when the handoff state occurs, the proposed radio communication method simultaneously receives signals of the serving base station and the target base station according to the channel capacity environment of the target base station, and proportionally adjusts received signal strength of the serving base station and received signal strength of the target base station, thereby allowing handoff to be performed with a time difference, and thus providing the effect of distributing load of the base stations.

Claims

1. A method for relaying radio communication in a moving object, the method comprising: previously defining a radio map made by databasing information on a radio environment of a preset area; comparing current position information and moving direction information of the moving object with data in the radio map; and adjusting, according to the comparison result, an antenna for a relay mounted on the moving object so as to always face a serving base station now in service, or to face a direction in which a signal from the serving base station is best received.

2. A method for relaying radio communication in a moving object, the method comprising: previously defining a radio map made by databasing information on a radio environment of a preset area; comparing current position information and moving direction information of the moving object with data in the radio map; and selecting, according to the comparison result, an antenna facing a serving base station now in service, or an antenna facing a direction in which a signal from the serving base station is best received, among a plurality of antennas for a relay mounted on the moving object.

3. A method for relaying radio communication in a moving object, the method comprising: previously defining a radio map made by databasing information on a radio environment of a preset area; comparing current position information and moving direction information of the moving object with data in the radio map; selecting, according to the comparison result, an antenna facing a serving base station now in service, or an antenna facing a direction in which a signal from the serving base station is best received, among a plurality of antennas for a relay mounted on the moving object; when a handoff state occurs, checking surplus channel information of a target base station to which handoff will be performed; when there is a surplus in channel of the target base station, selecting an antenna facing the target base station, and canceling the selection of the antenna facing the serving base station; and when there is no surplus in channel of the target base station, additionally selecting an antenna facing the target base station, simultaneously receiving signals of the target base station and the serving base station, and proportionally adjusting strengths of the received signals.

4. A method for relaying radio communication in a moving object, the method comprising: previously defining a radio map made by databasing information on a radio environment of a preset area; selecting one of a plurality of antennas for a relay mounted on the moving object; comparing current position information and moving direction information of the moving object with data in the radio map; adjusting, according to the comparison result, the selected antenna among the plurality of antennas for the relay mounted on the moving object so as to face a serving base station now in service, or to face a direction in which a signal from the serving base station is best received; when a handoff state occurs, checking surplus channel information of a target base station to which handoff will be performed; when there is a surplus in channel of the target base station, adjusting the selected antenna so as to face the target base station; and when there is no surplus in channel of the target base station, additionally selecting another antenna, simultaneously receiving signals of the target base station and the serving base station, and proportionally adjusting strengths of the received signals.

5. The method of any one of claims 1 to 4, wherein a base station to which handoff will be performed in a moving path is previously set.

6. The method of any one of claims 1 to 4, wherein information on the radio environment comprises adjacent base station information for each received signal's strength, base station's azimuth information, and information on a direction in which a signal of a corresponding base station is best received.

7. The method of claim 3 or 4, wherein the number of the added target base stations is one or more.

8. A relay for radio communication, which is mounted in a moving object, the relay comprising: at least one relay antenna which is installed for radio communication with a base station and its facing direction is adjustable by a driver; a controller for adjusting the relay antenna; a memory for storing data for a radio map made by databasing information on a radio environment of a preset area; a Global Positioning System (GPS) device for obtaining current position and moving direction information of the moving object, and a sensor for sensing a moving direction; and a service antenna for radio communication with mobile stations in a bus; wherein the controller adjusts a facing direction of the relay antenna based on the current position information and moving direction information of the bus, and data in the radio map.

9. A relay for radio communication, which is mounted in a moving object, the relay comprising: a plurality of relay antennas which are installed for radio communication with a base station; a switching unit for selecting any one of the plurality of antennas; a controller for controlling a selection operation of the switching unit; a memory for storing data for a radio map made by databasing information on a radio environment in a preset area; a Global Positioning System (GPS) device for obtaining current position and moving direction information of the moving object, and a sensor for sensing a moving direction; and a service antenna for radio communication with mobile stations in a bus; wherein the controller selects at least one of the plurality of relay antennas based on the current position information and moving direction information of the bus, and data in the radio map.

10. The relay of claim 8 or 9, further comprising a signal strength adjuster, connected to each relay antenna, for adjusting received signal strength of a corresponding antenna according to a control signal of the controller.