JP2001268633A - Radio communication system, radio base station, and mobile station - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evade deterioration in error rate due to the influence of a delay wave on a control channel sent and received with omini-directivity when a mobile communication system is structured by a spatial time-division multiple access system(SDMA). SOLUTION: The radio communication system, radio base station, and mobile station are provided which are constituted by using a spectrum-spread system hardly affected by a delay wave as a modulation system and a demodulation system for a control channel sent and received with omini-directivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an improvement of a mobile communication system using a space division multiple access system (SDMA).

[0002]

2. Description of the Related Art Generally, in a mobile communication system, communication between a base station and a plurality of mobile stations is performed using channels having different frequencies. According to this communication method, in order to increase the number of mobile stations that can be stored in the same call zone, it is necessary to increase the number of frequency channels allocated to each mobile station. Since there is a limit to the number of frequency channels that can be assigned to each mobile station, there is also a limit to the number of mobile stations that can be accommodated in the same call zone.

[0003] From such a background, a technique has been considered in which a plurality of mobile stations can secure a call with a base station while sharing the same frequency channel. This technique is a space division multiple access system (SDMA). The space division multiple access scheme (SDMA) is a multiple access scheme (Multi) in which a base station forms different directivities for a plurality of mobile stations and simultaneously communicates with the plurality of mobile stations on the same frequency channel.
i-Beam Adaptive Base-Stat
ion Antennas for Cellular
Land Mobile Radio System
m: S. C. Swales, IEEE VTC, 19
89).

The space division multiple access system (SDM)
The mobile communication system using A) has not been put to practical use yet.
Therefore, the prior art described here is a prior art under development. As shown in FIG. 5, the base station BS directs the main beams B1 and B2 to the mobile stations MS1 and MS2 in the same call zone ZN, so that the mobile stations MS1 and MS2 can simultaneously operate on the same frequency channel. Can make calls. By increasing the number of main beams B1 and B2, it is possible to increase the number of mobile stations that can simultaneously talk while using the same frequency channel.

On the other hand, as shown in FIG.
Performs transmission and reception with omni directional (circular directional), the same call zone Z on the same frequency channel
Within N, only one of the base station BS and the mobile stations MS1 and MS2 can talk. In other words, the use of the space division multiple access (hereinafter simply referred to as SDMA) technique has the advantage of increasing the subscriber capacity that can be accommodated in one frequency channel.

[0006] When the SDMA technology is put into practical use, a control signal, such as an incoming call signal and a broadcast signal, which needs to be transmitted to all mobile stations under the control of the base station BS, is transmitted. It is necessary to perform transmission and reception with the omni-directional pattern shown in FIG. Since the base station does not know the position of the mobile station, the incoming call signal needs to be broadcasted, so that it must be transmitted with omni-directionality. Also, a position information signal for identifying the control zone, a transmission control channel information signal for notifying the mobile station of the number of the transmission control channel being used, and a signal from the mobile station on the uplink transmission control channel that the mobile station is empty. The broadcast signal such as the idle line signal of the transmission control channel is a signal intended for all mobile stations, and needs to be transmitted with omni-directionality as well. still,
The above notification signal is a model case and may be different in other systems. On the other hand, the control channel associated with the speech channel and the speech channel for controlling the channel switching during the speech is a channel intended for a specific mobile station, and the directivity is directed to the specific mobile station and directed to the specific mobile station.
MA can be applied.

[0007]

Conventionally, a modulation / demodulation system such as a communication channel for forming directivity to a specific mobile station by using SDMA and a demodulation system for a control channel for transmitting and receiving with omni directivity are the same. Has been adopted. For example, when the QPSK modulation / demodulation method is used for the communication channel, the control channel for transmitting / receiving the omni-directional signal also uses the QPSK modulation / demodulation method.

SDMA for forming directivity to a specific mobile station
According to according to strongly receive the desired wave arriving from the direction of the main beam, to suppress the delayed wave arriving from other directions,
The characteristic which is hardly affected by the delayed wave can be obtained. But QPS
When a signal of the K modulation / demodulation method is received with omni-directional pattern, all delayed waves (reflected waves) input from all directions are received, and compared with the case where directivity is formed at a specific mobile station, a delayed wave is generated. There is a disadvantage that it is easily affected by

Therefore, when the control signal is transmitted and received with omni-directionality, the control signal is greatly affected by the delay wave, and a large drawback occurs in that the error rate of the control channel increases. An object of the present invention is to provide a radio communication system capable of reducing the error rate of a signal of a control channel that must transmit and receive with omni-directionality susceptible to delay waves, and a radio base station and a mobile station used for the radio communication system. To provide.

[0010]

According to the first aspect of the present invention, a control channel for transmitting signals for all mobile stations under the control of a base station, such as an incoming call signal and a broadcast signal, is omni-directional. A channel for transmitting and receiving signals and transmitting a signal intended for a specific mobile station, such as a communication channel and a control channel associated with the communication channel, is transmitted to a specific mobile station using a space division multiple access technique. In a wireless communication system that performs transmission and reception with directivity, a modulation and demodulation method of a control channel signal that performs transmission and reception with omni directivity is a spread spectrum method.

According to a second aspect of the present invention, a first signal processing section for multiplying a complex amplitude of each output of a plurality of antenna elements by a complex weight to form a summation in order to form a reception directivity of a communication channel, The signal to be transmitted to the mobile station is divided into a plurality of signals to form the transmission directivity of the communication channel,
A second signal processing unit that multiplies each of the plurality of branched signals by a complex weight, inputs each of the signals to an antenna element, emits the air with directivity, and a sum of sums obtained by the first signal processing unit. A communication channel receiver for demodulating a signal, a communication channel transmitter for providing a signal to be transmitted to the second signal processing unit, and a spread spectrum system for transmitting a control signal from a mobile station received by an omni-directional antenna A control channel receiver for demodulating with, a control channel transmitter for applying to an antenna having omni directivity, and modulating a control signal to be transmitted to a mobile station by spread spectrum modulation,
The phase difference between signals induced by the plurality of antenna elements and transmitted from the mobile station is measured, the direction in which the mobile station is located is determined, and this direction information is input to the first signal processing unit and the second signal processing unit. The present invention proposes a radio base station constituted by azimuth measuring means for controlling the reception directivity and the transmission directivity of a communication channel to the azimuth where the mobile station exists.

According to a third aspect of the present invention, in the wireless base station according to the second aspect, N first signal processing units, second signal processing units, speech channel receivers, and speech channel transmitters are provided, respectively. We propose a radio base station characterized in that it can communicate with N mobile stations in the same call zone. According to a fourth aspect of the present invention, there is provided a transmission / reception antenna, a control channel receiver for demodulating a control signal transmitted from the radio base station and induced by the transmission / reception antenna by a spread spectrum method, and a transmission / reception antenna transmitted from the radio base station. Channel receiver that demodulates the communication channel signal induced by the signal, a control channel transmitter that provides a control signal modulated by the spread spectrum method to the transmission / reception antenna, and applies a communication signal to be transmitted to the radio base station to the transmission / reception antenna. And a mobile station configured by using a transmitter for a communication channel.

[0013]

According to the radio communication system proposed in the present invention, since the spread spectrum modulation / demodulation system is used in the control channel for transmitting and receiving signals with omni-directionality, the spread spectrum modulation / demodulation system is less susceptible to delay waves. Therefore, the error rate of the control channel can be kept low. As a result, there is obtained an advantage that it is possible to construct a wireless communication system in which the operation of the control channel is stable while employing the communication method using SDMA.

Further, according to the configuration of the radio base station proposed in claim 3, N mobile stations can talk on the same frequency channel in the same call zone. As a result, the original purpose of the SDMA for effectively utilizing the frequency channel can be realized.

[0015]

FIG. 1 shows an embodiment of a radio base station used in a radio communication system according to the present invention. SDM
Since it is necessary to form directivity for a specific mobile station by A, a plurality of antennas are required. FIG. 1 shows a case where K array antenna elements AN1 to ANK are provided. The plurality of array antenna elements AN1 to ANK have N
Signal processing units 11A to 11N are connected. These N
Signal processing units 11A to 11N, N traffic channel receivers 12A to 12N, N traffic channel transmitters 13A to 13N, and one control channel receiver 14
, One control channel transmitter 15, one azimuth measuring means 16, and one system controller 17.
This shows a case where a base station capable of communicating with a plurality of mobile stations is configured.

Each of the N signal processing units 11A to 11N has the same number of complex weight multipliers B1 to BK as the number of array antenna elements AN1 to ANK, and an addition and branching unit D.
And a weight control unit CC. That is, the signal processing units 11A to 11N operate as first signal processing means for forming directivity in the array antenna elements AN1 to ANK at the time of reception, and are directed to the radiation characteristics of the array antenna elements AN1 to ANK at the time of transmission. It operates as a second signal processing means for giving the property.

When operating as the first signal processing means, the complex amplitudes X1 to XK, which are the outputs of the array antenna elements AN1 to ANK, are multiplied by complex weights W1 to WK by complex weight multipliers B1 to BK. D operates as an adder, and obtains sum outputs Y1 to YN as an addition result. By appropriately selecting the complex weights W1 to WK, the directivity of the array antenna elements AN1 to ANK can be changed. When operating as the second signal processing means, the adder and splitter D operates as a splitter, divides the transmission signal output from the communication channel transmitter 13A into K in this example, and divides the transmission signal into the K-divided signals. By multiplying the complex weights W1 to WK by the complex weight multipliers B1 to BK and applying the complex amplitude multiplied by the complex weight to each of the array antenna elements AN1 to ANK, radio waves having directivity are emitted. .

A method for determining the directivity of the array antenna elements AN1 to ANK will be described. The azimuth measuring means 16 is connected to each of the array antenna elements AN1 to ANK through, for example, couplers J1 to JK. Direction measuring means 16
Captures a control signal transmitted from the mobile station for each time slot assigned to each mobile station, measures the phase difference between signals induced in each of the array antenna elements AN1 to ANK,
The arrival direction of the radio wave of each mobile station is determined based on the phase difference.

When the direction of arrival of the radio wave is determined, the direction measuring means 16 inputs the direction information of each mobile station to the system controller 17 and causes the system controller 17 to transfer the weight information to each weight controller CC. The directivity of each of the signal processing units 11A to 11N is directed to the azimuth obtained by measurement by the azimuth measuring means 16. Several algorithms are known as a directivity forming method when performing SDMA. Classification based on prior knowledge about the desired wave can be divided into two systems.

One is a method using a replica (reference wave) of a desired wave as prior knowledge. The MMSE (RL) which forms directivity by the least square method using the replica as a reference signal.
S, LMS). Another method is to use the direction of arrival (DOA) of the desired wave as prior knowledge, and algorithms called MSN and DCMP are known (for details, see "Adaptive signal processing by array antenna: Nobuyoshi Kikuma, Science Technology publishers "). In addition, there is also an algorithm called CMA, which forms a directivity blindly without using prior knowledge using the property of constant envelope of a signal. In these methods, a main beam is directed to a desired wave, while null (a direction of zero gain) is directed to an interference wave. In addition, instead of pointing the null to the interference wave, the main beam is directed to the desired wave, and a fixed beam that suppresses the interference wave by forming a directional pattern with low gain in directions other than the desired wave A forming method can also be used in SDMA. The description so far has been directed to the case of the first signal processing unit at the time of reception. However, at the time of transmission, the addition or the branching unit D may be operated as a branching unit to reverse the signal flow.

The control channel receiver 14 and the control channel transmitter 15 are communication channel receivers 12A to 12N.
The operation timings of the communication channel transmitters 13A to 13N are time-divisionally operated. FIG. 2 shows this state.
In the time slot T1, the control channel receiver 14 and the control channel transmitter 15 operate to exchange control signals with the mobile station. In the time slot T2, the communication channel receivers 12A to 12N and the communication channel transmitter 1
3A to 13N operate to form a communication line with each mobile station.

In the time slot in which the control channel receiver 14 and the control channel transmitter 15 operate, the weight control unit CC sets only the complex weight W1 to 1, sets the other complex weights W2 to WK to zero, and sets the array antenna element to zero. A signal is given to only AN1, and transmission / reception is performed with omni-directionality. Next, the configuration of the present invention will be described. The configuration of the present invention is characterized by the communication channel receivers 12A to 12A.
When the modulation method of the 12N and the communication channel transmitters 13A to 13N uses, for example, QPSK, the control channel receiver 14 and the control channel transmitter 15 use a spread spectrum modulation / demodulation receiver and transmitter. It is.

Since the spread spectrum modulation / demodulation method is already well known, its description is omitted here. However, by adopting the spread spectrum method, the resistance to the influence of a delayed wave (reflected wave) can be increased. . The reason is that the spread spectrum has a feature that the RAKE reception can be realized, the delayed waves are combined and used effectively, and the characteristic deterioration due to the delayed waves hardly occurs. FIG. 3 shows another embodiment of the radio base station according to the present invention. The embodiment shown in FIG. 3 shows an embodiment in which the control channel antenna M having omni-directionality is provided independently of the array antenna elements AN1 to ANK used for the communication channel. Therefore, in this case, the system control device 17 and the weight control unit CC use the array antenna elements AN1 to AN
It is not necessary to have a program for switching K to omni-directional. The other configuration is the same as the configuration of the wireless base station shown in FIG. 1, and therefore, further description of FIG. 3 will be omitted.

FIG. 4 shows an embodiment of a mobile station proposed in the present invention. The mobile station proposed in the present invention comprises a speech channel receiver 21, a speech channel transmitter 22, a control channel receiver 23, a control channel transmitter 24, and a system control device 25 for controlling these operations. Composed of The feature of the present invention lies in that the control channel receiver 23 is constituted by a spread spectrum demodulation type receiver and the control channel transmitter 24 is constituted by a spread spectrum modulation type transmitter.

With this configuration, a spread spectrum modulated control signal can be sent to the radio base station shown in FIG. 1 or FIG. 3, and a spread spectrum control signal sent from the base station can be received. Can be.

[0026]

As described above, according to the present invention, the spread of the control channel transmitted and received in the omni-directional pattern is achieved by using the spread spectrum method for the modulation and demodulation of the control channel transmitted and received in the omni-directional pattern in the base station. It is possible to increase the resistance to the influence of waves, improve the error rate characteristics of the control channel, and thereby obtain the advantage that a highly reliable wireless communication system using SDMA can be constructed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a position embodiment of a radio base station according to the present invention.

FIG. 2 is a time chart for explaining the operation of FIG. 1;

FIG. 3 is a block diagram showing a modified embodiment of the radio base station according to the present invention.

FIG. 4 is a block diagram showing an embodiment of a mobile station according to the present invention.

FIG. 5 is a conceptual diagram of the SDMA system.

FIG. 6 is a conceptual diagram for explaining omni directivity applied to a control channel of the SDMA scheme.

[Explanation of symbols]

AN1 to ANK Array antenna elements X1 to XK Complex amplitude W1 to WK Complex weight J1 to JK Combiner B1 to BK Complex weight multiplier CC1 to CCK Weight control units 11A to 11N First signal processing unit (second signal processing unit) 12A １２12N Receiver for communication channel 13AＡ13N Transmitter for communication channel 14 Receiver for control channel 15 Transmitter for control channel 16 Direction measurement means 17 System controller

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shuji Kubota 2-3-1 Otemachi, Chiyoda-ku, Tokyo F-term in Nippon Telegraph and Telephone Corporation (reference) 5J021 AA05 AA06 AA11 AB01 DB01 FA13 FA14 FA16 FA32 GA02 HA10 5K022 EE01 EE23 EE31 5K067 AA02 CC10 DD42 EE02 EE10 EE53 KK02 KK03

Claims (4)

[Claims] A control channel for transmitting a control signal for all mobile stations under the control of a base station, such as an incoming call signal and a broadcast signal, performs transmission and reception with omni-directionality. A channel for transmitting a signal intended for a specific mobile station, such as a control channel attached to a communication channel, is a radio channel for transmitting and receiving directivity to a specific mobile station using a space division multiple access technique. In a communication system, a modulation and demodulation method of a signal of a control channel that performs transmission and reception with the omni-directional pattern is a spread spectrum method. 2. A: a first signal processing unit for multiplying a complex amplitude of outputs of a plurality of antenna elements by a complex weight to form a reception directivity of a communication channel to obtain a sum; and B: transmitting a communication channel. A signal to be transmitted to the mobile station is formed into a plurality of signals in order to form directivity, and each of the plurality of branched signals is multiplied by a complex weight. C, a communication channel receiver for demodulating the sum signal obtained by the first signal processing unit, and D: a communication for providing a signal to be transmitted to the second signal processing unit. E, a control channel receiver for demodulating a control signal from a mobile station received by an antenna having omni directivity by a spread spectrum method, and F, an antenna having omni directivity, A control channel transmitter for modulating a control signal to be transmitted to a mobile station by spread spectrum modulation; and G, a phase difference between signals induced from the plurality of antenna elements and transmitted from the mobile station. Azimuth measuring means for determining an existing azimuth, inputting the azimuth information to the first signal processing unit, and controlling the reception directivity of the communication channel to the azimuth where the mobile station is present. Characteristic radio base station. 3. The radio base station according to claim 2, wherein the first signal processing unit, the second signal processing unit, the communication channel receiver, and the communication channel transmitter are provided N each, and the number of the first signal processing unit, the second signal processing unit, and the communication channel transmitter are N. A radio base station capable of communicating with N mobile stations. 4. A transmission / reception antenna, B: a control channel receiver for demodulating a control signal transmitted from the radio base station and induced by the transmission / reception antenna by a spread spectrum method, C: transmission from the radio base station A communication channel receiver for demodulating a communication channel signal induced by the transmission / reception antenna; and D; a control channel transmitter for providing a control signal modulated by a spread spectrum method to the transmission / reception antenna; A mobile station characterized by comprising: a communication channel transmitter for applying a communication signal to be transmitted to a radio base station to an antenna.