US20090325514A1 - Wireless communication system and transmission device - Google Patents

Abstract

The present invention relates to a wireless communication system to properly switch over a transmission method of radio signals corresponding to a configuration of a receiver. The wireless communication system according to the present invention includes a transmitting device having a plurality of antennas and capable of transmitting radio signals different from each other from these antennas, and a receiving device having at least one antenna and receiving the radio signals transmitted from the transmitting device. The receiving device comprises 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.

Description

CROSS-REFERENCE TO RELATED APPLICATION
• 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 transmittingantennas500 and j-pieces of receivingantennas510, how plural pieces of data (x₁-x_i) are transmitted to thereceiving antennas510 from thetransmitting antennas500, and the respective antennas obtain signals y₁-y_jsynthesized with these pieces of data (x₁-x_i).
• 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 inFIG. 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) (seeFIG. 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 inFIG. 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 inFIG. 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 inFIG. 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 apath1 and apath2 shown inFIG. 10(A) exit) as shown inFIG. 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 inFIG. 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 OF THE INVENTION
• 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.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
• 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 toFIG. 1.
• The MIMO communication system in the embodiment is comprised of, by way of an example, atransmitter11 and a plurality ofreceivers21,22, and23. For instance, thetransmitter11 has four pieces ofantenna elements10, thereceiver21 has oneantenna element200, thereceiver22 has oneantenna element201, and thereceiver23 has twoantenna elements203, respectively.
• Signals transmitted from theantenna elements10 of thetransmitter11 are received by therespective antenna elements201,202 and203, and data (carried on the signals) are detected by therespective receivers21,22,23. Further, pieces of transmission characteristic information of the signals received by the respective antennas are individually specified by signal processing of thereceivers21,22 and23 ((2) shown inFIG. 1). Then, the transmission characteristic information and information about the configuration of the receiver ((1) shown inFIG. 1) are transmitted to thetransmitter11 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 thetransmission antennas10 to each of the receivingantennas200,201,202 and203. 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.
• Thetransmitter11 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 thereceivers21,22 and23. 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 thereceivers21,22 and23 having the number of antennas as shown inFIGS. 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 toFIG. 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. Thetransmitter11 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 therespective receivers21,22 and23 reach the respective receivers, and transmits the signals. To be specific, thetransmitter11 performs the signal processing based on the transmission characteristic information on the signals so that one symbol data series directed to thereceivers21,22 each having one antenna reaches each of thereceivers21,22, and transmits the signals. Further, thetransmitter11 performs the signal processing on the signals so that two or less symbol data series (which are the data for two antennas) directed to thereceiver23 having two antennas reach the respective antennas as the symbol data of thereceiver23 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 thetransmitter11 will be explained.
• To start with, the signal sent from thetransmitter11 is influenced by a transmission environment of the respective channels between thetransmitter11 and therespective receivers21,22,23. 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 h_ijrepresents 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).
• $\begin{array}{cc}H=\left(\begin{array}{cccc}{h}_{11}& h_{12}& h_{13}& h_{14}\\ h_{21}& h_{22}& h_{23}& h_{24}\\ h_{31}& h_{32}& h_{33}& h_{34}\\ h_{41}& h_{42}& h_{43}& h_{44}\end{array}\right)& \left(1.1\right)\\ y=\mathrm{Hx}+n& \left(1.2\right)\end{array}$
• where n is a noise vector of each of the receiving antennas.
• The signal vectors of the signals received by thereceivers21,22 and23 are expressed by the formula (1.2), and hence thetransmitter11 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 thereceivers21,22 and23 to reach the respective receivers. Namely, thetransmitter11 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).
• $\begin{array}{cc}\begin{array}{c}F=\left(\begin{array}{cccc}{\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{11}& 0& 0& 0\\ 0& {\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{22}& 0& 0\\ 0& 0& f_{33}& f_{34}\\ 0& 0& f_{43}& f_{44}\end{array}\right)\\ =\left(\begin{array}{cccc}{h}_{11}& h_{12}& h_{13}& h_{14}\\ h_{21}& h_{22}& h_{23}& h_{24}\\ h_{31}& h_{32}& h_{33}& h_{34}\\ h_{41}& h_{42}& h_{43}& h_{44}\end{array}\right)·G\end{array}& \left(1.3\right)\end{array}$
• With the transmission of the signals subjected this change of variable, it follows that thereceivers21 and22 each having the single receiving antenna receive one self-addressed data series, and thereceiver23 having the two antennas receive the two data series in parallel. Herein, f is an appropriate complex number. Namely, let x₀be a pre-transformation symbol data vector, and the receiving data vector y can be expressed by a calculation formula as by the formula (1.4).
• $\begin{array}{cc}\begin{array}{c}y=\mathrm{Hx}={\mathrm{HGx}}_0={\mathrm{<figure-callout\; label="Fx"\; filenames="US20090325514A1-20091231-D00005.png"\; state="\{\{state\}\}">Fx</figure-callout>}}_0\\ =\left(\begin{array}{cccc}{\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{11}& 0& 0& 0\\ 0& {\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{22}& 0& 0\\ 0& 0& f_{33}& f_{34}\\ 0& 0& f_{43}& f_{44}\end{array}\right)x_{0}\end{array}& \left(1.4\right)\end{array}$
• As can be understood also from the formula (1.4), with the multiplication by the change-of-variable matrix G, thetransmitter21 may simply consider only the signals influenced by only the element f₁₁, i.e., the signals that are transmitted from the transmittingantenna1 and should be received by thereceiver11 without taking account of the synthesis of the signals transmitted from other antennas. That is, the influence of the signals transmitted from other antennas can be already restrained at a stage of receiving the signals by the self-antenna.
• This is the same with thereceiver22. Thereceiver23, as the influence of the transmission signals from other antennas were already restrained at the stage of receiving the signals by the self-antenna, may simply consider the signals influenced by elements f₃₃, f₃₄, f₄₃, and f₄₄, i.e., the signals received by the two antennas possessed by thereceiver23.
• .Functional Configuration.
• Next, functions of the respective devices in the MIMO communication system in the embodiment will be described with reference toFIG. 3.FIG. 3 is a diagram showing a functional configuration of the MIMO communication system in the embodiment. The functional units shown inFIG. 3 actualize the principle of the system described earlier.FIG. 23 shows thetransmitter11 and thereceiver23 illustrated inFIG. 1. Thereceivers21,22 unillustrated inFIG. 3 have the same configuration as that of thereceiver23 except that each of thereceivers21,22 has a single piece of antenna and has none of high-level demodulating function (which is a signal separating function exemplified as below).
• To begin with, the functional configuration of thetransmitter11 will be explained as follows. Thetransmitter11 is constructed of a variable changing unit111 (corresponding to a transmission unit and a transformation unit according to the present invention), asignal separating unit112, atransmission processing unit113,antenna elements10, anantenna element100, areceipt processing unit114 and a transmission characteristic information/receiver configuration information detecting unit115 (corresponding to a detection unit according to the present invention).
• ..Variable Changing Unit111..
• The variable changingunit111 obtains (updates), based on transmission characteristic information and receiver configuration information inputted from the transmission characteristic information/receiver configurationinformation detecting unit115, the change-of-variable matrix G that satisfies the formula (1.3). A method by which thevariable changing unit111 obtains the change-of-variable matrix G will be explained in depth in an item of <Operational Example>.
• The variable changingunit111, when a data transmission request is given, multiplies the transmission symbol data by this change-of-variable matrix G, and outputs the transmission symbol data after being multiplied to thesignal separating unit112.
• ..Signal Separating Unit112..
• Thesignal separating unit112 separates the serially-arranged symbol data signals inputted from the variable changingunit111 in parallel for every antenna to which the data signal is transmitted, and outputs the data signal to thetransmission processing unit113 for sending from each of theantenna elements10. Thesignal separating unit112, when separating the signals, by a use of the symbol data signal inputted from the variable changingunit111, determines the antenna to which the symbol data signal should be transmitted. This transmitting antenna is determined based on the transmission signal transformed by the variable changingunit111.
• ..Transmission Processing Unit113..
• Thetransmission processing units113 output, to theantenna elements10, high-frequency signals obtained by performing a modulation process upon the transmission signals inputted from thesignal separating unit112. Simultaneously, thetransmission processing units113 transmit a plurality of different known signals (which will hereinafter be referred to as transmission characteristic estimation signals) having signal patterns orthogonal to each other in order to make thereceiver23 estimate a transmission path characteristic. Note that thetransmission processing units113 in the embodiment are configured in the form of being divided for everyantenna element10 and may also be made to operate in the form of being organized into one unit.
• ..Antenna Element10..
• Theantenna element10 is an antenna for transmitting the high-frequency signals outputted from thetransmission processing units113 to thereceiver23. Though explained later on, theantenna element10 can be constructed as a transmitting/receiving dual-purpose antenna by use of a duplexer, etc.
• ..Antenna Element100..
• Theantenna element100 is an antenna for receiving the high-frequency signals transmitted from anantenna element200 of thereceiver23. The high-frequency signals received by theantenna element100 are outputted to thereceipt processing unit114.
• ..Receipt Processing Unit114..
• Thereceipt processing unit114 acquires the receipt signals by effecting an amplifying process upon the high-frequency signals inputted from theantenna element100. Thereceipt processing unit114 outputs the receipt signals to the transmission characteristic information/receiver configurationinformation detecting unit115.
• ..Transmission Characteristic Information/Receiver ConfigurationInformation Detecting Unit115..
• The transmission characteristic information/receiver configurationinformation detecting unit115 detects data of the transmission characteristic information and data of the receiver configuration information from the inputted receipt signals (receipt signals received from each of the receivers). The detected transmission characteristic information and the detected receiver configuration information are outputted to the variable changingunit111. Note that the transmission characteristic information and the receiver configuration information are detected and generated by thereceiver23. Incidentally, the receiver configuration information may be acquired from a upper device side. For example, the receiver configuration information is stored in an HLR (Home Location Register), and is downloaded as the necessity may arise. On this occasion, the respective terminal configurations may be distinguished from each other by use of terminal IDs, etc.
• Next, the functional configuration of thereceiver23 will be explained as below. Thereceiver23 is constructed of anantenna element203, areceipt processing unit231, a transmission characteristic estimating unit232 (corresponding to an extraction unit according to the present invention), a signal separating/data detecting unit233, a transmission characteristic information/receiver configuration information generating unit234, a transmission processing unit235 (corresponding to an information transmitting unit according to the present invention), and anantenna element200.
• ..Antenna Element203..
• Theantenna element203 is an antenna for receiving the signals transmitted from theantenna elements10 of thetransmitter11. The high-frequency signals received by theantenna element203 are outputted to thereceipt processing unit231. As will be explained later on, theantenna element203 may be constructed as a transmitting/receiving dual-purpose antenna as in the case of theantenna100.
• ..Receipt Processing Unit231..
• Thereceipt processing unit231 acquires the receipt signals by executing the amplifying process, etc. upon the high-frequency signals inputted from theantenna element203. The receipt signals are outputted to the signal separating/data detecting unit233 and to the transmissioncharacteristic estimating unit232.
• ..TransmissionCharacteristic Estimating Unit232..
• The transmissioncharacteristic estimating unit232 obtains a transmission path matrix H of the transmission paths between theantenna elements10 and theantenna elements203 by use of the known signals, etc. from the inputted receipt signals, and estimates transmission characteristic information expressed by a transmission characteristic matrix F (=HG) in a form multiplied by a change-of-variable matrix G by which thevariable changing unit111 of thetransmitter11 multiplies the transmission signals. In the embodiment, the transmission characteristic matrix F is a matrix expressed by the formula (1.4), and it follows that the change-of-variable matrix G can be updated with this estimated value, corresponding to, even when the transmission path changes, this change. Further, the transmission characteristic information is matrix elements f₃₃, f₃₄, f₄₃, and f₄₄of the transmission characteristic matrix F shown in the formula (1.4) in the transmissioncharacteristic estimating unit232 of thereceiver23. Note that the matrix elements f₁₁and f₂₂of the transmission characteristic matrix F shown in the formula (1.4) are estimated in theunillustrated receivers21 and22.
• Then, the transmissioncharacteristic estimating unit232 outputs the transmission characteristic information to the signal separating/data detecting unit233. This transmission path matrix H, the transmission path becoming different corresponding to each antenna element on the receiving side, as a matter of course, changes for every antenna element receiving the signal. Accordingly, the transmissioncharacteristic estimating unit232 is prepared for everyantenna element203 and estimates the transmission characteristic information from the signals received by each antenna. An in-depth description of how the transmissioncharacteristic estimating unit232 estimates the transmission characteristic information, will be given in the item of <Operational Example>.
• ..Signal Separating/Data Detecting Unit233..
• The signal separating/data detecting unit233 separates the receipt signals (which will hereinafter be called a signal separating function) based on the MIMO method by employing the transmission characteristic information (the matrix elements f₃₃, f₃₄, f₄₃, and f₄₄shown in the formula (1.4)) inputted from the transmissioncharacteristic estimating unit232, and detects the receiving data. Note that the detection of the receiving data may involve employing MLD, etc.
• Further, theunillustrated receivers21 and22 may not have the signal separating function with the signal processing performed by thetransmitter11 as the transmitting side so that each of the receivers receives only the signals that should be received by the self-receiver.
• ..Transmission Characteristic Information/Receiver Configuration Information Generating Unit234..
• The transmission characteristic information/receiver configuration information generating unit234 generates the receiver configuration information of the self-device (e.g., stores the configuration information on an unillustrated memory, reads the information therefrom and generates the information), and also generates the transmission data to be transmitted together with the transmission characteristic information estimated by the transmissioncharacteristic estimating unit232 to thetransmitter11. In the embodiment, it is assumed that the receiver configuration information contains information about the number of antennas held by the receiver23 (this is the same with other receivers).
• ..Transmission Processing Unit235..
• Thetransmission processing unit235 performs the modulation process upon the transmission signals in order to transmit, to thetransmitter11, the transmission data containing the transmission characteristic information and the receiver configuration information inputted from the transmission characteristic information/receiver configuration information generating unit234 by a use of signaling etc., and outputs the high-frequency signals to theantenna element200. Simultaneously, thetransmission processing unit235 transmits the transmission characteristic estimation signals with their signal patterns orthogonal to each other to make thetransmitter11 estimate the transmission path characteristic.
• Note that the known signals for the transmission characteristic estimation may be transmitted in the form of being distinguished from the actual transmission data by employing a timewise separating method with respect to the data, a spread-code based separating method utilizing CDMA, a sub-carrier frequency based separating method utilizing OFDM (orthogonal Frequency Division Multiplexing) and a combined method of these separating methods.
• ..Antenna Element200..
• Theantenna element200 is an antenna for transmitting, to thetransmitter11, the high-frequency signals outputted from thetransmission processing unit235.
• .Receiver Configuration Information.
• Next, the receiver configuration information of which each of the receivers21-23 notifies thetransmitter11, will be explained as follows.
• An example of employing the number of antennas for every receiver is given as the receiver configuration information in the embodiment. The receiver configuration information can be also categorized as below by way of other example. Further, it is also possible to categorize in a way that combines the following categorizations.
• .Categorization 1. Categorization corresponding to the number of antennas held by the receiver.
• .Categorization 2. Categorization corresponding to the demodulation method held by the receiver. The demodulation method connoted herein can exemplify the aforementioned signal separating function. There is considered a case, wherein the receiver is categorized as a receiver capable of demodulating received signals into which radio signals transmitted from the transmitter are synthesized with radio signals transmitted from other antenna possessed by this transmitter, or a receiver capable of demodulating only the signals received in the form of being separated so as not to be synthesized with the radio signals transmitted from other antenna, or a receiver capable of demodulating by sue of signals that are partially separated and received by other receiving antenna. An operation of thetransmitter11 in this case will be explained in detail in an item of <<Generation of Change-of-Variable Matrix G Suited to Configuration of Receiver>>.
• .Categorization 3. Categorization corresponding to a data identifying method held by the receiver. For instance, there is considered a case of categorization depending on whether MLD or MMSE (Minimum Mean Square Error).
Operational ExampleEstimation of Transmission Characteristic Information by TransmissionCharacteristic Estimating Unit232
• The transmissioncharacteristic estimating unit232 estimates the transmission characteristic information from the received signals. This transmission characteristic information is estimated by the following method as elements of the transmission characteristic matrix F expressed by the formula (1.4) and comprising of the transmission path matrix H reflecting the transmission path environment and the change-of-variable matrix G multiplied by thetransmitter11.
• The transmissioncharacteristic estimating unit232 estimates the transmission characteristic information by use of the transmission characteristic estimation signals as the known signals given from thetransmitter11. To be specific, the transmissioncharacteristic estimating unit232 estimates the matrix elements f₃₃, f₃₄, f₄₃, and f₄₄shown in the formula (1.4).
• The transmission characteristic estimation signals involve using data patterns (1, 1, 1, 1), (1, −1, 1, −1) (1, 1, −1, −1) and (1, −1, −1, 1) defined as the known signals with their signal patterns orthogonal to each other. Note that each data pattern is transmitted from each of the transmitting antennas. Then, preferably, the known signals orthogonal to each other are transmitted from the respective receiving antennas of the receiver and also received by the transmitting antenna of the transmitter in order for the transmitter to estimate the transmission path (H) between each of the receiving antennas of each receiver and the transmitting antenna of the transmitter.
• From the left element in the brackets, there are shown the first symbol data, the second symbol data, the third symbol data and the fourth symbol data. In thereceiver23 receiving the transmission characteristic estimation signals, the data received by one of the two receiving antennas are expressed such as y_1,1and y_1,2in the formula (2.1) and the formula (2.2). The symbol y_1,1represents the first symbol receipt data, and the symbol y_1,2represents the second symbol receipt data. With this operation, the transmissioncharacteristic estimating unit232 of thereceiver23 estimates f₃₃by adding the two symbols and estimates f₃₄by subtracting the symbols. Note that the estimations of f₃₃and f₃₄employ only the first symbol data and the second symbol data, however, as a matter of course, the third symbol data and the fourth symbol data may also be used.
• The data y_2,1and y_2,2received by the other receiving antenna are subjected to the same processing, thereby estimating f₄₃and f₄₄.
• 
  y_1,1=f₃₃+f₃₄  (2.1)
• 
  y_1,2=f₃₃−f₃₄  (2.2)
• 
  y_2,1=f₄₃+f₄₄  (2.3)
• 
  y_2,2=f₄₃−f₄₄  (2.4)
• Note that the known signals for the transmission characteristic estimation may be transmitted in the form of being distinguished from the actual transmission data by employing the timewise separating method with respect to the data, the spread-code based separating method utilizing CDMA (Code Division Multiple Access), the sub-carrier frequency based separating method utilizing OFDM (Orthogonal Frequency Division Multiplexing) and the combined method of these separating methods.
• ..Generation of Change-of-Variable Matrix G byVariable Changing Unit111..
• The transmission path environment momentarily changes, and hence, unless the change-of-variable matrix G is used in response to changing in the transmission path environment, the communications exhibiting a high-level wireless characteristic can not be performed. Such being the case, the way of how the variable changingunit111 obtains the change-of-variable matrix G reflecting the latest transmission path environment, will be next described as below.
• At first, the variable changingunit111 obtains the latest transmission path matrix H by making use of the transmission characteristic information to be transmitted to thetransmitter11 from each of thereceivers21,22,23. Namely, the transmission characteristic information (f₁₁, f₂₂, f₃₃, f₃₄, f₄₃, and f₄₄) transmitted from therespective receivers21,22,23 consists of the change-of-variable matrix G by that the variable changingunit111 multiplies the transmission data last time and the transmission path matrix H reflecting the transmission path environment at that time (F=HG), and therefore the variable changingunit111 acquires the transmission path matrix H by employing the change-of-variable matrix G used last time, which corresponds to this transmission characteristic matrix F. Then, the variable changingunit111 obtains a new change-of-variable matrix G by use of the latest transmission characteristic information F received and the formula (1.3) from the obtained transmission path matrix H.
• Further, on the occasion of getting the feedback about the transmission characteristic information and the receiver configuration information to the transmitter from the receiver, when thetransmission processing unit235 utilizes TDD (Time Division Duplex), the different and orthogonal known signals (the transmission characteristic estimation signals) may be transmitted from the respective receivers. With this operation, the variable changingunit111 estimates the transmission path matrix H by employing the transmission characteristic estimation signals, thereby acquiring the change-of-variable matrix G. Namely, as the proper transmission characteristic information F (e.g., as shown inFIG. 3, other elements excluding a part of the elements (which is set to, e.g., 1) are set to 0), the change-of-variable matrix G is obtained by using the formula (1.3) and can be employed for converting the transmission signal.
• Note that the first setting of the change-of-variable matrix G, in the case of adopting, e.g., the TDD method employing the same frequency and so on, can be done by the transmitter estimating the transmission path between each receiving antenna of each receiver and the transmitting antenna of the transmitter.
• In short, the orthogonal known signals are transmitted from the respective receiving antennas of the receiver and received by the transmitting antenna of the transmitter, thereby estimating the transmission path matrix H. If the TDD method is adopted, bidirectional paths can be deemed as the same transmission paths, and hence there are obtained the estimated transmission path matrix H and the change-of-variable matrix G as the proper transmission characteristic information F (e.g., as shown inFIG. 3, other elements excluding a part of the elements (which is set to, e.g., 1) are set to 0), and these matrixes can be employed for the conversion of the transmission signals. On this occasion, as a matter of course, it is desirable that the receiver configuration information be also employed.
• ..Generation of Change-of-Variable Matrix G Suited to Configuration of Receiver..
• As described above, the receiver configuration information (for example, the number of antennas) is fed back to thetransmitter11, whereby the variable changingunit111 of thetransmitter11 obtains the change-of-variable matrix G corresponding to the receiver configuration information.
• Given hereunder is an example of the operation of the variable changingunit111 of thetransmitter11 that obtains the change-of-variable matrix G in accordance with, herein, the demodulation method of the receiver in the receiver configuration information (Categorization 2) described above. To be specific, the operation of the transmitter in the case of differing from the configuration of the receiver in the MIMO communication system in the embodiment shown inFIGS. 1 and 2, will be described as below.
• .First Configuration.
• In the MIMO communication system in the embodiment, thereceiver23 holding the two antennas has the configuration that the signal separating/data detecting unit233 has the signal separating function. The first configuration, which will be described herein, is a case of being constructed of the receiver capable of demodulating only the signals received in the form of being separated so as not to be synthesized with the radio signals transmitted from other antennas.
• In this case, the transmission characteristic information/receiver configuration information generating unit234 of thereceiver23 organizes the receiver configuration information so as to contain a piece of category information showing that the receiver has the demodulation method as described above. Then, the variable changingunit111 obtains, based on the category information, a change-of-variable matrix G that will be given as follows. Subsequently, the variable changingunit111 multiplies the transmission data by this change-of-variable matrix G and transmits the data, and each receiver may detect the data per antenna.
• The transmitter configuring the MIMO communication system according to the present invention can correspond to the case where such a simple receiver exists.
• $\begin{array}{cc}F=\mathrm{HG}=\left[\begin{array}{cccc}{\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{11}& 0& 0& 0\\ 0& {\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{22}& 0& 0\\ 0& 0& f_{33}& 0\\ 0& 0& 0& f_{44}\end{array}\right]& \left(1.5\right)\end{array}$
• .Second Configuration.
• A second configuration is a case in which there is one single receiver holding four pieces of antennas, and the receiver has the following demodulation method. The receiver in the second configuration enables simple modulation in the way that the receiver provides predetermined order per antenna, the data are detected with respect to the signals received by the antennas in this order, and a result of the data detection in the earlier order is utilized on the occasion of the data detection.
• In this case, the transmission characteristic information/receiver configuration information generating unit234 of thereceiver23 organizes the receiver configuration information so as to contain a piece of information showing that the demodulation method described above is adopted. Then, the variable changingunit111 obtains, based on this information, the change-of-variable matrix G shown in the formula (1.6). Subsequently, the variable changingunit111 multiplies the transmission data by this change-of-variable matrix G, and transmits the data, whereby the receiver can demodulate the data received from the antennas in the predetermined order.
• Namely, in this example, the signal received by the receiving antenna corresponding to the first row in the following matrix or a transmission signal x₁is obtained. Next, a transmission signal x₂is obtained by use of a signal received by the receiving antenna corresponding to the second row in the following matrix and the transmission signal x₁, sequentially, and results that are thus acquired in the order from the top are utilized at the receiving time, thereby making it possible to easily regenerate the transmission signals.
• Note that the respective elements such as f₁₁, etc. can be estimated by use of the known signals, and it follows that unknown transmission signals are easily obtained while giving a degree of freedom to some extent to the elements of the matrix F.
• $\begin{array}{cc}F=\mathrm{HG}=\left[\begin{array}{cccc}{\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{11}& 0& 0& 0\\ f_{21}& {\mathrm{<figure-callout\; label="f"\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">f</figure-callout>}}_{22}& 0& 0\\ f_{31}& f_{32}& f_{33}& 0\\ f_{41}& f_{42}& f_{43}& f_{44}\end{array}\right]& \left(1.6\right)\end{array}$
• .Third Configuration.
• A third configuration is a case of the receiver capable of demodulating the signals obtained by synthesizing the radio signals transmitted from the transmitter with the radio signals transmitted from other antenna possessed by this transmitter and received.
• Even in the case of this receiver having the highest-level data detecting function, the variable changingunit111 obtains the change-of-variable matrix G shown in the formula (1.7) by which a transmission capacity can be maximized without any restraint condition. Namely, the variable changingunit111 sets the elements fixed to “0” less than a half, ideally, to zero (0).
• $\begin{array}{cc}F=\mathrm{HG}=\left[\begin{array}{cccc}{f}_{11}& f_{12}& f_{13}& f_{14}\\ f_{21}& f_{22}& f_{23}& f_{24}\\ f_{31}& f_{32}& f_{33}& f_{34}\\ f_{41}& f_{42}& f_{43}& f_{44}\end{array}\right]& \left(1.7\right)\end{array}$
Modified Example 1
• In the MIMO communication system in the embodiment, the transmitter executes the signal processing based on the configuration of the receiver, however, the transmission path matrix H as the transmission path information is employed on the occasion of effecting the signal processing.
• Namely, the transmitter side knows the transmission path information, and hence the signal processing may be executed to perform the high-speed data transmission on the transmission path exhibiting a high quality of the transmission path, and to perform the low-speed data transmission on the low-quality transmission path (which corresponds to a transmission rate control unit according to the present invention).
• With this contrivance, the high-speed data transmission can be performed as a whole of the system.
Modified Example 2
• Further, the higher-speed data transmission may additionally be conducted on the high-quality transmission path by increasing the electric power for transmission, and the lower-speed data transmission may be effected on the low-quality transmission path by decreasing the electric power for transmission. With this contrivance, the higher-speed data transmission can be done as a total system because of getting approximate to the power control based on Water Filling Principal. In this case, for example, when constructed of the simple receiver as in the aforementioned (first configuration), the transmitter may execute processing as below.
• The transmitter at first effects weighting in a way that multiplies the change-of-variable matrix G given in the formula (1.8) with respect to the transmission path matrix H by a weighting coefficient w_iso that an electric power weight P_iwith respect to a diagonal section a_iof the matrix A shown in the formula (1.9) meets the formula (1.10). Herein, H represents Conjugate Transpose, max (x, y) indicates that the larger of x and y is selected, and λ and σ2 are constants determined from average transmission power and noise power. The transmitter multiplies the weighted signal by the change-of-variable matrix G in the same way as in the embodiment, and transmits this signal.
• $\begin{array}{cc}G=H^{-1}& \left(1.8\right)\\ A=G^HG& \left(1.9\right)\\ P_i=\max \left(0,\frac{\lambda }{a_i}-{\mathrm{<figure-callout\; label="\sigma "\; filenames="US20090325514A1-20091231-D00000.png,US20090325514A1-20091231-D00001.png"\; state="\{\{state\}\}">\sigma </figure-callout>}}^{2}\right)& \left(1.10\right)\\ w_i=\sqrt{P_i}& \left(1.11\right)\\ C_i\propto \log \left(1+\frac{w_{i}^2}{{\sigma }^2}\right)& \left(1.12\right)\end{array}$
• The transmitter may further effect rate matching upon each symbol data series so as to gain a transmission rate proportional to C_ishown in the formula (1.12), and may thus transmit the symbol data series.
• FIG. 4 is a diagram showing an example of the transmitter that executes power weighting corresponding to the transmission path information and transmission rate control. The transmitter shown inFIG. 4 puts a weight w₁-w₄on the transmission signal controlled to have a transmission rate of a transmission rate C₁-C₄for every transmitting antenna.
• With this contrivance, the high-speed data transmission can be done as the total system.
Modified Example 3
• The system described so far has the configuration in which the transmission side can know the transmission path information and may also take a configuration in which the transmission side can not know the transmission path information. In this case also, it is possible to adopt the transmission method corresponding to the receiver by notifying the transmission side of the receiver configuration information.
• FIGS. 5(A) and 5(B) show the MIMO communication system in the case of a configuration in which the transmitter can not know the transmission path information. InFIG. 5(A), the transmitter is notified of the number of antennas held by the receiver and thereby transmits the signals from one arbitrary transmitting antenna to the receiver having the single antenna. Similarly, inFIG. 5(B), the signals are transmitted from the two transmitting antennas to the receiver having the two antennas.
• Moreover, there are categorized, according to not the number of antennas but a type of receiver, into a case of being a MLD receiver and a case of being an MMSE (Minimum Mean Square Error) receiver, and the transmitter may control the transmission rate.FIG. 6(A) shows the case of having the MLD receiver, andFIG. 6(B) shows the example of having the MMSE receiver. The transmitter in this case controls the transmission rate to perform the high-speed data transmission to the MLD receiver exhibiting a high wireless characteristic and to perform the low-speed data transmission to the MMSE receiver inferior in characteristic to the MLD receiver.
• With this contrivance, even in the case where the transmitter has such a configuration as to be unrecognizable of the transmission path information, it is possible to conduct the transmission corresponding to the configuration of the receiver.
• <Others>
• The disclosures of Japanese patent application No.JP2005-006352, filed on Jan. 13, 2005 including the specification, drawings and abstract are incorporated herein by reference.

Claims (3)

1. A wireless communication system including a transmitting apparatus that includes a plurality of antennas and can transmit different radio signals from the respective antennas, and a receiving apparatus that includes at least one antenna and receives the radio signals transmitted from the transmitting apparatus,

the receiving apparatus comprising:

an information notification unit to expressly notify the transmitting apparatus of information on the number of antennas of the receiving apparatus or information on the number of multiplexed signals concurrently-processable by the receiving apparatus,

the transmitting apparatus comprising:

a transforming unit to transform transmitting signals based on the information on the number of antennas or the information on the number of multiplexed signals which are received from the receiving apparatus; and

a transmission unit to transmit radio signals corresponding to the transformed transmitting signals.

2. A wireless communication system including a transmitting apparatus that includes a plurality of antennas and can transmit different radio signals from the respective antennas, and a receiving apparatus that includes at least one antenna and receives the radio signals transmitted from the transmitting apparatus,

the receiving apparatus comprising:

an information transmission unit to transmit, to the transmitting apparatus, configuration information on configuration of the receiving apparatus, the configuration information including information on the number of antennas of the receiving apparatus or information on the number of multiplexed signals concurrently-processable by the receiving apparatus,

the transmitting apparatus comprising:

a detection unit to detect the information on the number of antennas or the information on the number of multiplexed signals from the configuration information received from the receiving apparatus;

a transforming unit to transform transmitting signals based on the detected information on the number of antennas or the detected information on the number of multiplexed signals; and

a transmission unit to transmit radio signals corresponding to the transformed transmitting signals.

3. A wireless communication system including a transmitting apparatus that includes a plurality of antennas and can transmit different radio signals from the respective antennas, and a receiving apparatus that includes at least one antenna and receives the radio signals transmitted from the transmitting apparatus,

the receiving apparatus comprising:

an extraction unit to extract, from received radio signals, transmission characteristic information including transmission path information corresponding to an environment where the received radio signals have been transmitted; and

an information transmission unit to transmit, to the transmitting apparatus, configuration information on configuration of the receiving apparatus and the extracted transmission characteristic information, the configuration information including information on the number of antennas of the receiving apparatus or information on the number of multiplexed signals concurrently-processable by the receiving apparatus,

the transmitting apparatus comprising:

a detection unit to detect the information on the number of antennas or the information on the number of multiplexed signals from the configuration information received from the receiving apparatus, and detect the transmission path information from the transmission characteristic information received from the receiving apparatus;

a transforming unit to transform transmitting signals based on the detected information on the number of antennas or the detected information on the number of multiplexed signals and based on the detected transmission path information; and

a transmission unit to transmit radio signals corresponding to the transformed transmitting signals.

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