Wireless communication system and transmission device   

This application is a continuation of U.S. patent application Ser. No. 11/128,285, filed on May 13, 2005, now pending, the entire disclosures of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Present Invention

The invention relates to a wireless communication system including a transmitting device having a plurality of antennas and capable of transmitting different radio signals from the respective antennas, and to the transmitting device.

2. Description of the Related Art

MIMO (Multi Input and Multi Output) communication system is given as a communication system capable of improving a transmission rate (transmission capacity) as a total by transmitting different pieces of data by use of same frequency band (and further the same spread code) from a plurality of antennas in parallel. The MIMO communication system is that plural pieces of data are transmitted from a plurality of transmitting antennas in parallel, and the signals synthesized while passing through a variety of communication paths are received by a plurality of receiving antennas. FIG. 7 is a diagram showing an outline of the MIMO communication system. FIG. 7 shows, in the MIMO communication system configured by i-pieces of transmitting antennas 500 and j-pieces of receiving antennas 510, how plural pieces of data (x1-xi) are transmitted to the receiving antennas 510 from the transmitting antennas 500, and the respective antennas obtain signals y1-yj synthesized with these pieces of data (x1-xi).

Note that when the transmission signal from each antenna is designated by a transmission vector x, the receipt signal received by each antenna is designated by a receipt vector y, a state of a radio path is expressed as a channel matrix H, and a noise vector is designated by n, there is established a relationship such as y=Hx+n.

In the MIMO communications as shown in FIG. 7, a receiving-side device receiving the signals transmitted from the plurality of antennas and then synthesized, utilizes a method called MLD (Maximum Likelihood Detection) defined as a maximum likelihood decoding method in order to acquire an excellent radio characteristic. By this method, the receiving-side device detects a necessary piece of data by separating the synthesized signals. The MLD is a method of detecting a data pattern by judging, with respect to combinations of all the transmission data patterns that can be transmitted by the transmitting side, if transmitted in such a manner, how much a possibly-acquired receipt signal gets approximate to the actual receipt signal (a degree of maximum likelihood) (see FIG. 8). In the MLD, however, in the case of transmitting the signals from, for example, four pieces of transmitting antennas by 16 QAM (Quadrature Amplitude Modulation) defined as a digital modulation method of transmitting 4-bit data with one symbol, there is a necessity of obtaining the likelihood of data patterns numbered as tremendously as 65536 (=164). In this case, it follows that the receiving-side device detects the data pattern exhibiting the maximum likelihood from within this tremendous number of data patterns. Thus, the MIMO communication system requires an enormous throughput for the data detection.

A method for solving this problem involves employing Pre-Rake, etc. shown in FIG. 9(B) in the transmitting-side device. The method typified by Pre-Rake is a method for reducing the receiving-side processes by the signal processing on the transmitting side. For instance, FIG. 9 shows wireless communications based on normal CDMA (Code Division Multiple Access) (FIG. 9(A)) and CDMA-based wireless communications using Pre-Rake (FIG. 9(B)). In the normal CDMA-based wireless communications shown in FIG. 9(A), the receiving side detects the data by the signal processing (channel compensation) based on the transmission path information. On the other hand, in the case of employing Pre-Rake shown in FIG. 9(B), the signal processing is previously executed based on the transmission path information of the signal before transmitting the signals.

In the Pre-Rake method, for example, in the case of a transmission environment (an environment where a path 1 and a path 2 shown in FIG. 10(A) exit) as shown in FIG. 10(A), though normally the receiving side makes channel compensation corresponding to the transmission environment, the transmitting side executes a channel compensation process equivalent to that on the receiving side.

For instance, a weighting synthesis (Rake creating) unit as shown in FIG. 10(B) multiplies the transmission signal by a weighting coefficient of each transmission environment. With this operation, the receiving-side signal processing can be reduced.

A technology disclosed in the document (“Examinations about Configuration of Transmitter/Receiver of MTMT Array System Using Weight Batchwise Control at Base Station”, written by Hoshida, B-5-54, General Meeting of Electronic Information Communication Institution in 2002) is proposed as a method of increasing a channel capacity by executing this type of signal processing employing the transmission path information on the transmitting side in the MIMO communication system.

That is, in the MIMO communication system, there are proposed a method of using an MLD receiver requiring an enormous throughput for acquiring an excellent radio characteristic and a method of employing a simple receiver requiring merely a low throughput by executing the signal processing that previously takes account of the transmission path on the transmitting side.

A base station performing the MIMO communications, however, has a case of desiring to separately use the MLD receiver and the simple receiver. In this case, there is none of a method of making the above methods coexistent with each other.

SUMMARY

It is an object of the present invention to provide a wireless communication system capable of properly switching over a transmission method of a radio signal corresponding to a configuration of a receiver.

The present invention adopts the following configurations in order to solve the above-mentioned problems. Namely, the present invention is about a wireless communication system comprising a transmitting device having a plurality of antennas and capable of transmitting radio signals different from each other from the plurality of antennas, and a receiving device having at least one of antennas and receiving the radio signals transmitted from the transmitting device. In the present invention, the receiving device includes an information transmitting unit transmitting, to the transmitting device, configuration information about a configuration of the receiving device, and the transmitting device includes a transmitting unit transmitting the radio signals by a transmission method corresponding to the configuration information received from the receiving device.

In the present invention, the transmitting device is notified of the configuration information of the receiving device, and the transmitting device transmits the radio signals by a transmission method based on the notified configuration information.

Therefore, according to the present invention, the transmission method executed by the transmitting device can be changed corresponding to the configuration of the receiving device.

Further, in the present invention, the configuration information contains a piece of number-of-antenna information held by the receiving device, and the transmitting unit determines the transmission method on the basis of the number-of antenna information contained in the configuration information.

Hence, according to the present invention, the transmission method executed by the transmitting device can be changed corresponding to the number-of-antenna information of the receiving device.

Moreover, in the present invention, the receiving device further includes an extraction unit extracting, from the received radio signals, transmission characteristic information containing transmission path information corresponding to an environment where the radio signals are transmitted, the information transmitting unit transmits the configuration information and the transmission characteristic information, the transmitting device further includes a detection unit detecting the transmission path information from the transmission characteristic information received from the receiving device, and a transforming unit transforming the transmission signals on the basis of the detected transmission path information and the number-of-antenna information contained in the configuration information, and the transmitting unit transmits the radio signals corresponding to the transformed transmission signals.

In the present invention, the receiving device notifies the transmitting device of the transmission characteristic information and the configuration information of the receiving device. Then, the transmitting device detects the transmission path information from the notified transmission characteristic information. Further, the transmitting device transforms the transmission signals based on the detected transmission path information and the number-of-antenna information of the receiving device so that the receiving device can receive only the radio signals corresponding to the number-of-antenna information, and transmits the transformed signals.

Therefore, according to the present invention, it is possible to determine the transmission method corresponding to the number-of-antenna information of the receiving device having none of a high-level demodulating function by taking account of both of the number-of-antenna information of the receiving device and the transmission path information.

Note the present invention may be a program for actualizing any one of the functions described above. Moreover, the present invention may also be a readable-by-computer storage medium stored with such a program.

According to the present invention, it is feasible to actualize the wireless communication system capable of properly switching over the transmission method corresponding to the configuration of the receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an architecture of a MIMO communication system in an embodiment;

FIG. 2 is a diagram showing a principle of the MIMO communication system in the embodiment;

FIG. 3 is a diagram showing a functional configuration of the MIMO communication system in the embodiment;

FIG. 4 is a diagram showing an example of executing weighting of a transmission data symbol and controlling a transmission rate in accordance with transmission path information;

FIGS. 5A and 5B are diagram showing a modified example in a case where a transmission side can not know the transmission path information;

FIGS. 6A and 6B are diagram showing a modified example 2 in a case where a transmission side can not know the transmission path information;

FIG. 7 is a diagram showing an outline of the MIMO communication system;

FIG. 8 is a diagram showing an outline of MLD;

FIGS. 9A and 9B are diagram showing an outline of a Pre-Rake method; and

FIGS. 10A and 10B are diagram showing an outline of weighting synthesis by the Pre-Rake method.

An embodiment of a MIMO communication system according to the present invention will hereinafter be described with reference to the drawings. A configuration in the embodiment is an exemplification, and the present invention is not limited to the configuration in the embodiment.

.Device Configuration.

FIG. 1 is a diagram showing an outline of a hardware (H/W) architecture in the embodiment of the MIMO communication system according to the present invention. The outline of the H/W architecture in the embodiment of the present invention will be explained with reference to FIG. 1.

The MIMO communication system in the embodiment is comprised of, by way of an example, a transmitter 11 and a plurality of receivers 21, 22, and 23. For instance, the transmitter 11 has four pieces of antenna elements 10, the receiver 21 has one antenna element 200, the receiver 22 has one antenna element 201, and the receiver 23 has two antenna elements 203, respectively.

Signals transmitted from the antenna elements 10 of the transmitter 11 are received by the respective antenna elements 201, 202 and 203, and data (carried on the signals) are detected by the respective receivers 21, 22, 23. Further, pieces of transmission characteristic information of the signals received by the respective antennas are individually specified by signal processing of the receivers 21, 22 and 23 ((2) shown in FIG. 1). Then, the transmission characteristic information and information about the configuration of the receiver ((1) shown in FIG. 1) are transmitted to the transmitter 11 by use of, e.g., dedicated antennas (unillustrated). As a matter of course, the illustrated antennas can be also employed. The transmission characteristic information is characteristic information of a transmission path along which the signal is transmitted from each of the transmission antennas 10 to each of the receiving antennas 200, 201, 202 and 203. The configuration information of the receiver can contain at least one item among items such as the number of receivers, the number of antenna elements possessed by each receiver, a demodulation method of each receiver, and performance (a processing speed, a degree of signal processability) of the receiver.

The transmitter 11 receiving the configuration information of the receiver and the transmission characteristic information, after effecting signal processing upon the signals on the basis of these items of information, transmits these signals to the receivers 21, 22 and 23. Note that for an easy understanding of the description in the embodiment, only unidirectional wireless communications are illustrated in separation into the transmitter and the receivers, however, each device may have both of the receiving function and the transmitting function, whereby bidirectional communications may be performed.

Further, the MIMO communication system in the embodiment exemplifies the receivers 21, 22 and 23 having the number of antennas as shown in FIGS. 1 and 2, however, this is nothing but the exemplification, and there may be a single receiver having four pieces of antennas and may also be two receivers each having two pieces of antennas. Namely, the MIMO communication system in the embodiment limits neither the configuration of the receiver nor the configuration of the transmitter.

.Principle of System.

Next, the principle of the MIMO communication system having the H/W architecture described above in the embodiment will be explained with reference to FIG. 2. FIG. 2 is a diagram showing the principle of the MIMO communication system in the embodiment.

In the MIMO communication system in the embodiment, the transmitting side previously executes the signal processing corresponding to, e.g., the number of antennas held by the receiver. The transmitter 11 performs the signal processing on the signals so that the symbol data series of which the number is equal to or smaller than the number corresponding to the number of receiving antennas possessed by the respective receivers 21, 22 and 23 reach the respective receivers, and transmits the signals. To be specific, the transmitter 11 performs the signal processing based on the transmission characteristic information on the signals so that one symbol data series directed to the receivers 21, 22 each having one antenna reaches each of the receivers 21, 22, and transmits the signals. Further, the transmitter 11 performs the signal processing on the signals so that two or less symbol data series (which are the data for two antennas) directed to the receiver 23 having two antennas reach the respective antennas as the symbol data of the receiver 23 itself, and transmits the signals. For instance, the signal processing may also be performed so that first and second symbol data series reach both of first and second antennas, and so that the first symbol data series reach the first antenna and the second symbol data series reach the second antenna.

Herein, the principle of the signal processing by the transmitter 11 will be explained.

To start with, the signal sent from the transmitter 11 is influenced by a transmission environment of the respective channels between the transmitter 11 and the respective receivers 21, 22, 23. Further, in the MIMO communication system, plural items of data are transmitted from the plurality of transmitting antennas, and hence the signals sent therefrom pass through a variety of communication paths and are received by the respective receiving antennas in the form of being synthesized with the signals sent from other antennas. Therefore, in the case of transforming the channel transmission environment into numerical values, this can be expressed by a matrix corresponding to the number of antennas held by the transmitter and the number of antennas held by the receiver.

Specifically, in the MIMO communication system in the embodiment, when hij represents transmission characteristics of transmission paths from four pieces of transmitting antennas i to four pieces of receiving antennas j, whereby the channel transmission environment can be expressed by a matrix H (which will hereinafter be called a transmission path matrix H) in a formula (1.1).

Then, when the transmission signal and the receipt signal are expressed in vector, a transmission signal vector x and a receipt signal vector y can be expressed by a formula (1.2).

H = ( h 11 h 12 h 13 h 14 h 21 h 22 h 23 h 24 h 31 h 32 h 33 h 34 h 41 h 42 h 43 h 44 ) ( 1.1 ) y = Hx + n ( 1.2 )

where n is a noise vector of each of the receiving antennas.

The signal vectors of the signals received by the receivers 21, 22 and 23 are expressed by the formula (1.2), and hence the transmitter 11 executes the following process in order for the symbol data series of which the number corresponds to the number of antennas of the receiving antennas held by the receivers 21, 22 and 23 to reach the respective receivers. Namely, the transmitter 11 executes the process of multiplying the transmission symbol data by a 4-row/4-column matrix G (which will hereinafter be called a change-of-variable matrix G) that satisfies the following formula (1.3).

F =  ( f 11 0 0 0

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