JP2002335559A - Radio communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the influence of an interference wave from other nearby cells using the radio channel of the same frequency in a radio communication method realizing radio communication by TDMA/TDD between radio base stations and subscriber stations in respective cells. SOLUTION: A first time slot TS1 in a fixed length, which is used in up-link communication and a second time slot TS2 in a fixed length, which is used in down-link communication, are arranged in a frame that the radio base stations of the respective cells use for bidirectional communication with the respective subscriber stations. The length of TS1 and that of TS2 are decided to be the same. Timing is synchronized between the first radio base station and the second radio base station, which constitute the two cells 201 and 202, which use the radio channels of the same frequency and which are in a specified position relation. The timing of the first time slot TS1 of the frame that the first radio base station uses for communication is adjusted to that of the second time slot TS2 of the frame which the second radio base station uses for communication.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio communication method usable for a fixed radio access system and the like, and more particularly to a radio communication method.
DMA (Time Division Multiple Access) / TDD (Time Division Duplex)
The present invention relates to a wireless communication method used for preventing interference of wireless signals between a plurality of cells when performing communication by using a wireless communication method.

[0002]

2. Description of the Related Art In a communication system for providing a fixed radio access service or the like, a relatively small service area is generally formed as a cell using one base station, and a large number of cells are arranged at regular intervals to provide a wide service as a whole. Configure the area. The subscriber station performs wireless communication with a specific base station forming a cell to which the subscriber station belongs.

In a radio communication system using a large number of cells, the same frequency channel needs to be commonly used by a plurality of cells in order to increase the efficiency of frequency use. However, it is necessary to perform control so that interference (collision) of radio signals does not occur between a plurality of cells using the same frequency channel. In order to prevent a plurality of communications using the same frequency channel from interfering with each other, the plurality of communications may be separated by a difference in transmission time. Therefore, in such a communication system, TDMA and CSMA have conventionally been used.
(Carrier Sense Multiple Access) / CA (Collision Avoidance) is employed.

[0004] In CSMA / CA, carrier sense is performed based on the reception level, and transmission is performed after confirming that the frequency to be used is not used by another station. But,
In the case of CSMA / CA, each subscriber station may transmit without noticing the existence of another station, and interference may occur. This is called the hidden terminal problem. On the other hand, TDM
In A, the time schedule used for communication between the base station and the subscriber station is managed collectively by the base station, and all communication is controlled by the base station. TDMA is used to provide a guarantee-type service that guarantees communication time in packet communication and is used to avoid the hidden terminal problem.

In communication in a communication system employing TDMA / TDD, a frame having a configuration as shown in FIG. 4 is generally used. That is, in this frame, time slots TSA and TSB for transmitting signals in the down direction from the base station to the subscriber station, and time slots TSC and TSC for transmitting signals in the direction from the subscriber station to the base station. There is TSD.

The time slot TSA is used to broadcast information of a time schedule determined by the scheduling of the base station to the subscriber station as broadcast information. Further, the time slot TSB is used for transmitting downlink user data. The time slot TSC is used for transmitting uplink user data. The time slot TSD is used for uplink random access for each subscriber station to request the base station to allocate a time slot.

When the dynamic slot assignment technique is used, the length of each of the time slots TSB and TSC used for transmitting user data is dynamically changed according to the traffic. However, the basic frame configuration is the same as in FIG. 4 and there is only one type.

[0008]

Here, it is assumed that a large number of cells are arranged at equal intervals to form a service area as shown in FIG. In this example, seven radio channels of frequencies f1, f2, f3, f4, f5, f6, and f7 are prepared for the entire system, and the radio channels are optimally assigned to each cell so that interference does not easily occur between adjacent cells. Assigned.

[0009] One cell represents a service area of one base station. For example, when communication is performed using a high frequency band such as a quasi-millimeter wave band, the radius of each cell is about several hundred meters. Although interference is not a problem between a plurality of cells using different frequencies, interference occurs between a plurality of cells using the same frequency and transmission quality deteriorates.
It is important to reduce such deterioration in transmission quality.

As one technique for reducing interference between a plurality of cells, an antenna tilt technique is known. That is, the directional characteristics of the base station antenna in the vertical direction are adjusted so that the radio signal is attenuated in the direction of an area farther than the service area. Also, a technique is known in which a plurality of sector antennas having a wide-angle directivity of about 30 to 90 degrees are installed in a base station, and the directivity of the antenna is switched by switching the sector antenna for each radio burst packet in order to reduce interference. Have been.

In the example shown in FIG.
It is assumed that a sector antenna of a sector is provided in a base station of each cell, and 360 degrees around each cell is divided into 60-degree sectors, and communication directions are separated into six sector directions. For different sector directions, no signal is transmitted at the same time and no interference occurs. However, as shown in FIG. 2, there is only one other cell using the same frequency at a position relatively close to each cell in each sector direction.

For example, assuming that the directivity of the antenna is directed to the direction of the sector 5 in FIG.
And the cell 202 may cause interference. That is, interference cannot be sufficiently reduced only by separating the communication direction of the base station into a plurality of parts by the sector antenna.
Regarding the occurrence of interference between a plurality of cells, actually, four types of patterns P1, P2, P3 and P3 as shown in FIG.
P4 can be assumed.

The pattern P2 in FIG. 3 indicates that the radio wave transmitted from the base station of another cell affects the reception of the base station of the own cell as an interference wave. But,
Actually, the antenna gain of the subscriber station of the own cell that transmits the desired wave is about 10 dB larger than the antenna gain of the base station of the other cell that transmits the interference wave. Received at a sufficiently high level, and the effects of interference are of little concern.

The reason why the antenna gain of the subscriber station is higher than that of the base station is as follows. Since the subscriber station only needs to communicate with a specific base station constituting the cell to which the subscriber station belongs, the subscriber station uses an antenna with a sharp directivity and a high gain to direct the antenna toward a specific base station. In general, the directivity of the light is directed. On the other hand, since the base station needs to communicate with a large number of subscriber stations, the base station generally uses an antenna having a wide-angle directivity and a low gain.

A pattern P4 in FIG. 3 represents a case where a radio wave transmitted from a subscriber station of another cell affects reception of a subscriber station belonging to a specific cell (own cell) as an interference wave. ing. However, in practice, the propagation path between the subscriber station of the own cell and the subscriber station of another cell is low and long. Moreover, an obstacle such as a building is generally present in the middle of the propagation path between the subscriber station of the own cell and the subscriber station of another cell, and the propagation path is blocked. . Therefore, the problem of interference hardly occurs.

Therefore, only two types of patterns P1 and P3 shown in FIG. 3 actually pose a problem. Pattern P1,
In any of P3, interference occurs in the same direction, that is, in the up direction or in the down direction. The present invention reduces the influence of an interference wave from another cell in the vicinity using a wireless channel of the same frequency in a wireless communication method for performing wireless communication by TDMA / TDD between a wireless base station and a subscriber station of each cell. The purpose is to do.

[0017]

A small service area formed by a fixed radio base station for a nearby subscriber station is defined as one cell, and a plurality of cells are arranged to form a large service area. A wireless communication method using a wireless communication system for forming and allocating a specific wireless channel to each cell and performing wireless communication by TDMA / TDD between a wireless base station and a subscriber station of each cell, A frame used by the radio base station of each cell for bidirectional communication with each subscriber station includes a first time slot having a fixed length used exclusively for uplink communication and a fixed time slot used exclusively for downlink communication. A second time slot having the same length, the length of the first time slot and the length of the second time slot are determined to be the same, and radio channels of the same frequency are used. And the communication timing is synchronized between a first radio base station and a second radio base station constituting two cells having a specific positional relationship, and a frame used by the first radio base station for communication. And the second time slot of a frame used for communication by the second radio base station is set to the same timing.

[0018] In the first aspect, a frame used in communication of a first cell formed by a first radio base station and a second frame are used.
A first time slot used for uplink communication and a second time slot used for downlink communication between frames used in communication of a second cell formed by the wireless base station. The relationship is opposite in time. That is, the timing of the second time slot transmitted by the base station in the first cell matches the timing of the first time slot received by the base station in the second cell. Accordingly, when the own cell and the other cell shown in FIG. 3 are associated with the first cell and the second cell, respectively, the pattern P1
The desired wave and the interference wave appear at different timings from each other, so that the interference of the pattern P1 is prevented.

Further, the timing of the first time slot transmitted by the subscriber station in the first cell coincides with the timing of the second time slot received by the subscriber station in the second cell. Therefore, if the own cell and the other cell shown in FIG. 3 are respectively associated with the first cell and the second cell, the desired wave and the interference wave of the pattern P3 appear at different timings from each other. Is prevented.

According to a second aspect of the present invention, in the wireless communication method according to the first aspect, the wireless base station of each cell performs communication using a sector antenna capable of switching the direction of directivity, and responds according to the directivity of the sector antenna. The two cells are determined by the following method. In claim 2, since the radio base station switches the direction of the directivity of the sector antenna,
For example, if the direction of the sector is distinguished as shown in FIG. 2, it is possible to reduce the number of other cells that may cause interference as shown in FIG. Can be. Therefore, interference can be prevented by reversing the timing of uplink communication and downlink communication between the own cell and one other cell.

According to a third aspect of the present invention, in the wireless communication method according to the first aspect, each subscriber station performs wireless communication using a directional antenna directed to a specific wireless base station. According to the third aspect, since the directivity of the antenna of each subscriber station is limited only to the specific base station, it is possible to prevent interference from occurring in directions other than the specific base station. Further, since the gain of the antenna at the subscriber station is increased, it is possible to prevent the interference of the pattern P2 shown in FIG. 3 from occurring.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the wireless communication method according to the present invention will be described with reference to FIGS. This form corresponds to all claims. FIG. 1 is a schematic diagram showing time slot allocation of a plurality of related cells. FIG. 2 is a plan view showing an example of a cell arrangement of the wireless communication system.

In this embodiment, it is assumed that the wireless communication method of the present invention is applied to a wireless communication system as shown in FIG. In FIG. 2, each of a number of hexagons represents a small service area called a cell. One fixed radio base station (hereinafter simply referred to as a base station) is provided at the center of each cell. Also, at least one subscriber station exists in each cell. Each subscriber station can perform radio communication with a base station of a cell to which the subscriber station belongs using a radio channel of one predetermined frequency. TDMA / TDD is used as a wireless communication method.

In this example, wireless channels of seven frequencies f1, f2, f3, f4, f5, f6, f7 are used in the entire system. In order to prevent interference between adjacent cells, a radio channel is assigned to each cell so that adjacent cells do not use the same frequency. Also,
The base station of each cell is provided with sector antennas of 60 sectors at 60 degrees. That is, the range of 360 degrees in the horizontal plane is set to 60
It is divided into 6 sectors at a time, and the directivity is 60
Transmission and reception can be performed within a range of degrees. In practice, the directivity of the sector antenna can be switched for each wireless burst packet.

Each subscriber station has an antenna having a sharp directivity. The direction of the antenna of the subscriber station is directed toward the base station of the cell to which the subscriber station belongs. In FIG. 2, for example, when the cell 201 performs communication using the sector 5 of the sector antenna, there is only one cell 202 that uses the same frequency f3 as the cell 201. Therefore, interference between the cell 201 and the cell 202 as shown in FIG. 3 may occur.

Therefore, in order to suppress the interference between the patterns P1 and P3 shown in FIG. 3, communication is performed using the following method. In communication of each cell, all base stations use a frame having a configuration as shown in FIG. Each frame is provided with a time slot TS1 used for downlink communication (direction from the base station to the subscriber station) and a time slot TS2 used for uplink communication (direction from the subscriber station to the base station). .

The length of each of the time slots TS1 and TS2 is set to a half of the frame length T, and the length of the frame length T and each of the time slots TS1 and TS2 is set to a fixed length.
The time slot TS1 is further divided into two types of time slots TS11 and TS12. Time slot TS
Reference numeral 11 is used to broadcast information of the time schedule determined by the base station as broadcast information from the base station to the subscriber station. The time slot TS12 is used for transmitting user data from the base station to the subscriber station.

The time slot TS2 is further divided into two types of time slots TS21 and TS22. The time slot TS21 is used for transmitting user data from the subscriber station to the base station. The time slot TS22 is used for uplink random access for each subscriber station to request the base station to allocate a time slot.

For example, when the cell 201 shown in FIG. 2 performs communication by selecting the sector 5, these cells 201 and 202 are used to prevent interference between the cell 201 and the cell 202.
As shown in FIG. 1, the timing of the frame is relatively shifted by a half of the frame length T between the time periods 02 and 02. That is, when two cells 201 and 202 for which interference should be prevented are determined, after synchronizing the frame timing between the base station of the cell 201 and the base station of the cell 202, both base stations use the same. The timing of one frame is delayed or advanced by T / 2 so that a time difference of T / 2 as shown in FIG.

In the example shown in FIG.
The frame used at 02 is delayed by T / 2. Since the communication timing of the subscriber station in each cell is controlled according to the time schedule determined by the base station, the base station and the subscriber station belonging to the same cell perform communication according to the same frame timing. When the timing of each frame of the two cells 201 and 202 is determined as shown in FIG. 1, when the downlink communication is performed in the time slot TS1 in the cell 201, the uplink in the time slot TS2 is performed in the cell 202. Perform communication. Also, cell 20
When the uplink communication is performed in the time slot TS2 in 1, the downlink communication is performed in the cell 202 in the time slot TS1 of the next frame.

That is, between the cell 201 and the cell 202, the timing of the upstream communication and the timing of the downstream communication are opposite, so that the upstream communication is not performed at the same timing, and the downstream communication is not performed at the same timing. No direction communication is performed. Accordingly, as shown in a pattern P1 shown in FIG. 3, the base station of the own cell (cell 201) and the other cell (cell 202)
And do not perform downlink communication at the same time,
The interference of the pattern P1 is prevented. Further, since the subscriber station of the own cell and the subscriber station of another cell do not simultaneously perform uplink communication as in the pattern P3 shown in FIG. 3, interference of the pattern P3 is also prevented.

The two cells to be controlled (20
When the frame timing is actually controlled between (1, 202), for example, the communication may be performed between base stations of two cells and the timing may be adjusted by autonomous control of each base station. In the case where a higher-level base station that manages a plurality of base stations is provided, communication is performed between each base station and the higher-level base station, and the timing of the frame of each base station is adjusted by controlling the higher-level base station. You may.

[0033]

According to the present invention, the pattern P shown in FIG.
Since interference of P1 and P3 can be suppressed, for example, when a large number of cells are arranged to secure a wide service area as shown in FIG. 2, a radio channel of a limited frequency is effectively used. In addition, the communication quality can be prevented from deteriorating.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing time slot allocation of a plurality of related cells.

FIG. 2 is a plan view showing an example of a cell arrangement in a wireless communication system.

FIG. 3 is a perspective view showing an interference generation pattern.

FIG. 4 is a schematic diagram showing a configuration of a frame generally used in TDMA / TDD communication.

[Explanation of symbols]

201, 202 cells TS1, TS2, TS11, TS12, TS21, TS
22 time slot T frame length P1 to P4 pattern

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K028 AA02 BB04 CC02 CC05 DD02 LL02 5K067 AA03 AA11 CC04 DD25 EE02 EE10 EE46 EE71 GG03 KK02

Claims (3)

[Claims] 1. A small service area formed by a fixed radio base station with respect to a nearby subscriber station is defined as one cell, a plurality of cells are arranged to form a large service area, and a specific service area is specified for each cell. Radio channels are allocated and TDMA between the radio base station and the subscriber station of each cell is performed.
A wireless communication method using a wireless communication system for performing wireless communication according to / TDD, wherein a wireless base station of each cell is used exclusively for uplink communication in a frame used for bidirectional communication with each subscriber station. A fixed-length first time slot and a fixed-length second time slot used exclusively for downlink communication are provided, and the length of the first time slot and the length of the second time slot are the same. The first wireless base station and the second wireless base station, which use two wireless cells having the same frequency and which are in a specific positional relationship, synchronize communication timing with each other, A first time slot of a frame used for communication by the first radio base station and a second time slot of a frame used for communication by the second radio base station are set at the same timing. Wireless communication method characterized by and. 2. The radio communication method according to claim 1, wherein the radio base station of each cell performs communication using a sector antenna capable of switching the direction of directivity, and the radio base station according to the direction of the sector antenna. A wireless communication method comprising determining one cell. 3. The wireless communication method according to claim 1, wherein each subscriber station performs wireless communication using a directional antenna directed to a specific wireless base station.