Patent ID: 12199710

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.FIG.1is a block diagram showing a configuration of a wireless communication system100according to the present embodiment. The wireless communication system100includes a radio transmitting station apparatus1and a radio receiving station apparatus2.

The radio transmitting station apparatus1includes a bit data generating unit11, a data signal modulating unit12, a training signal generating unit13, a transmission beam formation processing unit14, (transmission beam formation processor), a transmission signal transforming unit15, a reception signal transforming unit16, and M-number of antennas17-1to17-M, where M is an integer that is equal to or larger than 2.

The bit data generating unit11generates bit data of transmission data to be transmitted to the radio receiving station apparatus2. The bit data generating unit11may perform error correction encoding and interleaving when generating the bit data. The data signal modulating unit12transforms the bit data generated by the bit data generating unit11into a data signal according to a modulation system. As the modulation system, for example, quadrature amplitude modulation (QAM) is applied.

The training signal generating unit13generates a training signal determined in advance which is also known to the radio receiving station apparatus2. The transmission beam formation processing unit14performs processing for forming a transmission beam based on a transmission weight matrix calculated by a transmission/reception weight calculating unit24of the radio receiving station apparatus2. The transmission beam formation processing unit14may perform normalization of transmission power when forming the transmission beam.

The transmission signal transforming unit15performs processing for transforming a transmission beam formed by the transmission beam formation processing unit14into an analog transmission signal to be sent by radio waves from each of the antennas17-1to17-M. The antennas17-1to17-M perform transmission and reception of radio waves to and from the radio receiving station apparatus2. The reception signal transforming unit16transforms an analog reception signal corresponding to a radio wave received by the antennas17-1to17-M into a digital signal. The reception signal transforming unit16outputs a transmission weight matrix included in the transformed digital signal to the transmission beam formation processing unit14.

The radio receiving station apparatus2includes a reception signal transforming unit22, a communication path estimating unit23(communication path estimator), the transmission/reception weight calculating unit24(transmission/reception weight calculator), a transmission signal transforming unit25, a reception beam formation processing unit26(reception beam formation processor), a data signal demodulating unit27, a transmission data detecting unit28, and N-number of antennas21-1to21-N, where N is an integer that is equal to or larger than 2. N may be either a same value as M or a value that differs from M.

The antennas21-1to21-N perform transmission and reception of radio waves to and from the radio transmitting station apparatus1. The reception signal transforming unit22transforms an analog reception signal corresponding to a radio wave received by the antennas21-1to21-N into a digital signal.

When a training signal is included in the transformed digital signal, the reception signal transforming unit22reads the training signal from the digital signal. The reception signal transforming unit22outputs the read training signal to the communication path estimating unit23. In addition, when a data signal prior to reception beam formation is included in the transformed digital signal, the reception signal transforming unit22reads the data signal prior to reception beam formation from the digital signal. The reception signal transforming unit22outputs the read data signal prior to reception beam formation to the reception beam formation processing unit26.

The communication path estimating unit23estimates a communication path matrix h(z) based on the training signal output by the reception signal transforming unit22. The transmission/reception weight calculating unit24calculates a transmission weight matrix and a reception weight matrix based on the communication path matrix h(z) estimated by the communication path estimating unit23. The transmission/reception weight calculating unit24outputs the calculated transmission weight matrix to the transmission signal transforming unit25. The transmission/reception weight calculating unit24outputs the calculated reception weight matrix to the reception beam formation processing unit26.

The transmission signal transforming unit25performs processing for transforming the transmission weight matrix into an analog transmission signal to be sent by radio waves from each of the antennas17-1to17-M.

The reception beam formation processing unit26forms a reception beam based on the reception weight matrix output by the transmission/reception weight calculating unit24and N-number of data signals prior to reception beam formation corresponding to the antennas21-1to21-N and restores the data signals.

The data signal demodulating unit27demodulates a data signal using a demodulation system corresponding to the modulation system used for modulation by the data signal modulating unit12of the radio transmitting station apparatus1and restores bit data. The transmission data detecting unit28detects transmission data from the bit data demodulated by the data signal demodulating unit27. When the bit data generating unit11has performed error correction encoding, the transmission data detecting unit28performs error correction decoding, and when the bit data generating unit11has performed interleaving, the transmission data detecting unit28performs de-interleaving.

(Processing by Wireless Communication System)

FIG.2is a sequence diagram showing a flow of processing by the wireless communication system100according to the present embodiment.

The training signal generating unit13of the radio transmitting station apparatus1generates a training signal (step S101). The training signal generating unit13outputs the generated training signal to the transmission beam formation processing unit14.

The transmission beam formation processing unit14forms a transmission beam based on the training signal output by the training signal generating unit13. The transmission signal transforming unit15performs processing for transforming the transmission beam formed by the transmission beam formation processing unit14into an analog transmission signal to be sent from each of the antennas17-1to17-M. Subsequently, the transmission signal transforming unit15transmits the analog transmission signal by radio waves to the radio receiving station apparatus2via the antennas17-1to17-M (step S102). At a time point of step S102, the transmission beam formation processing unit14has not been provided with a transmission weight matrix. Therefore, the transmission beam formation processing unit14forms a transmission beam without using a transmission weight matrix. As a result, an unweighted transmission signal is to be transmitted from each of the antennas17-1to17-M.

Each of the antennas21-1to21-N of the radio receiving station apparatus2receives the transmission signal transmitted by each of the antennas17-1to17-M of the radio transmitting station apparatus1(step S103). The reception signal transforming unit22transforms an analog reception signal corresponding to the transmission signal received by each of the antennas21-1to21-N into a digital signal. The reception signal transforming unit22reads the training signal included in each of the plurality of transformed digital signals. The reception signal transforming unit22outputs the plurality of read training signals to the communication path estimating unit23.

The communication path estimating unit23estimates a communication path matrix h(z) based on the plurality of read training signals (step S104). Specifically, the communication path estimating unit23calculates the communication path matrix h(z) being an N×M matrix indicated by expression (7) below having, as an element of the matrix, expression (1) above which approximates a transfer function of CIR using a transfer function of FIR. In applying expression (1), a CIR length is denoted by “L”, any one arbitrary antenna among the antennas17-1to17-M of the radio transmitting station apparatus1is denoted by nt, and any one arbitrary receiving antenna among the antennas21-1to21-N of the radio receiving station apparatus2is denoted by nr. The communication path estimating unit23outputs the estimated communication path matrix h(z) to the transmission/reception weight calculating unit24.

[Math.7]h⁡(z)=[h1⁢1(z)…h1⁢M(z)⋮⋱⋮hN⁢1(z)…hNM(z)](7)

The transmission/reception weight calculating unit24inputs the communication path matrix h(z) output by the communication path estimating unit23. The transmission/reception weight calculating unit24calculates a transmission weight matrix and a reception weight matrix according to singular value decomposition in a frequency domain with respect to the input communication path matrix h(z). The transmission/reception weight calculating unit24first calculates a communication path matrix H(f) of the frequency domain by performing a discrete Fourier transform (DFT) on the communication path matrix h(z) as shown in expression (8) below (step S105).

[Math.8]h⁡(z)∈N×M⟶DFTH⁡(f)∈N×M(8)

As shown in expression (8), the communication path matrix H(f) of the frequency domain belongs to a group of N×M matrices in a similar manner to the communication path matrix h(z) of the time domain and is therefore an N×M matrix.

By performing singular value decomposition as shown in expression (9) below with respect to the communication path matrix H(f) of the frequency domain, the transmission/reception weight calculating unit24calculates an N-row, N-column unitary matrix U(f) and an adjoint matrix (step S106). The adjoint matrix is an M-row, M-column complex conjugate transposed matrix V(f)Hof the unitary matrix.
[Math. 9]
H(f)=U(f)Σ(f)V(f)H(9)

In expression (9), Σ(f) denotes an N-row, M-column diagonal matrix of which a diagonal element is a singular value.

By performing an inverse discrete Fourier transform (IDFT) with respect to U(f)Hthat is a complex transposed matrix of the N-row, N-column unitary matrix U(f) as shown in expression (10) below, the transmission/reception weight calculating unit24calculates a matrix in the time domain. Let the matrix calculated by the transmission/reception weight calculating unit24based on expression (10) below be a reception weight matrix wr(z).

[Math.10]U⁡(f)H⟶IDFTu^(z)H=wr(z)(10)

In addition, by performing an inverse discrete Fourier transform (IDFT) with respect to V(f) that is a complex transposed matrix of the adjoint matrix V (f)Has shown in expression (11) below, the transmission/reception weight calculating unit24calculates a matrix in the time domain. Let the matrix calculated by the transmission/reception weight calculating unit24based on expression (11) below be a transmission weight matrix wt(z) (step S107).

[Math.11]V⁡(f)⟶IDFTv^(z)=wt(z)(11)

The transmission/reception weight calculating unit24outputs the calculated transmission weight matrix wt(z) to the transmission signal transforming unit25. The transmission/reception weight calculating unit24outputs the reception weight matrix wr(z) to the reception beam formation processing unit26. The reception beam formation processing unit26inputs the reception weight matrix wr(z) output by the transmission/reception weight calculating unit24.

The transmission signal transforming unit25inputs the transmission weight matrix wt(z) output by the transmission/reception weight calculating unit24. The transmission signal transforming unit25transforms the input transmission weight matrix wt(z) into an analog transmission signal. The transmission signal transforming unit25transmits a radio wave corresponding to the transformed analog transmission signal to the radio transmitting station apparatus1via the antennas21-1to21-N(step S108).

The reception signal transforming unit16of the radio transmitting station apparatus1transforms an analog reception signal corresponding to the radio wave received via the antennas17-1to17-M into a digital signal. The reception signal transforming unit16reads the transmission weight matrix wt(z) included in the transformed digital signal (step S109). The reception signal transforming unit16outputs the read transmission weight matrix wt(z) to the transmission beam formation processing unit14. The transmission beam formation processing unit14inputs the transmission weight matrix wt(z) output by the reception signal transforming unit16.

Subsequently, processing for transmitting transmission data is started. The bit data generating unit11generates bit data of transmission data to be provided from the outside. The data signal modulating unit12transforms the bit data generated by the bit data generating unit11into a data signal according to a modulation system determined in advance (step S110). The data signal modulating unit12outputs the transformed data signal to the transmission beam formation processing unit14.

The transmission beam formation processing unit14inputs the data signal output by the data signal modulating unit12. The transmission beam formation processing unit14forms an FIR filter-type transmission beam based on the input data signal and the transmission weight matrix wt(z) (step S111).

The transmission signal transforming unit15performs processing for transforming the transmission beam formed by the transmission beam formation processing unit14into an analog transmission signal to be sent from each of the antennas17-1to17-M. The transmission signal transforming unit15transmits a radio wave corresponding to the analog transmission signal to the radio receiving station apparatus2via the antennas17-1to17-M (step S112).

The reception signal transforming unit22of the radio receiving station apparatus2transforms an analog reception signal corresponding to the radio wave received via the antennas21-1to21-N into a digital signal (step S113). The reception signal transforming unit22reads a data signal prior to reception beam formation from the transformed digital signal. The reception signal transforming unit22outputs the read data signal prior to reception beam formation to the reception beam formation processing unit26.

The reception beam formation processing unit26inputs the data signal prior to reception beam formation output by the reception signal transforming unit22. The reception beam formation processing unit26restores the data signal by forming an FIR filter-type reception beam based on the input data signal prior to reception beam formation and the reception weight matrix wr(z) (step S114).

The data signal prior to reception beam formation input by the reception beam formation processing unit26or, in other words, a communication path response is to be represented by h(z)wt(z) obtained by multiplying the communication path matrix h(z) by the transmission weight matrix wt(z). A multiplication of the reception weight matrix wr(z) and the data signal prior to reception beam formation is to be represented as expression (12) below.

[Math.12]wr⁢(z)⁢h⁢(z)⁢wt⁢(z)=u^(z)H⁢u⁢(z)⁢∑(z)⁢v⁡(z)H⁢v^⁢(z)=∑(z)={[Δ0](N<M)Δ(N=M)[Δ0](N>M)}(12)

In expression (12), Δ denotes a matrix shown in expression (13) which is a diagonal matrix having transfer functions λ1(z) to λq(z) of a singular value as elements.
[Math. 13]
Δ=diag(Δ1(z), . . . ,Δq(z))  (13)

In expression (13), q=rank [matrix h(z)] and q≤(N,M). Therefore, with respect to a result of multiplication of the reception weight matrix wr(z) and the data signal prior to reception beam formation, the reception beam formation processing unit26multiplies each of λ1(z)−1to λq(z)−1for each row or, in other words, for each stream. Accordingly, inter-symbol interference can be suppressed and signals can be separated for each stream. Δ may be made an identity matrix by having the transmission beam formation processing unit14process λ1(z)−1to λq(z)−1of each stream when forming the transmission beam.

The reception beam formation processing unit26outputs the restored data signal to the data signal demodulating unit27.

The data signal demodulating unit27inputs the data signal output by the reception beam formation processing unit26. The data signal demodulating unit27demodulates the input data signal and restores bit data (step S115). The transmission data detecting unit28detects transmission data from the bit data demodulated by the data signal demodulating unit27. The transmission data detecting unit28outputs the detected transmission data to the outside.

The wireless communication system100according to the embodiment described above includes the radio transmitting station apparatus1having the plurality of antennas17-1to17-M and the radio receiving station apparatus2having the plurality of antennas21-1to21-M. In the radio receiving station apparatus2, the communication path estimating unit23estimates a communication path matrix h(z) based on a training signal received from the radio transmitting station apparatus1. The transmission/reception weight calculating unit24transforms the communication path matrix h(z) estimated by the communication path estimating unit23into a frequency domain, transforms, into a time domain, a complex conjugate transposed matrix of each of a unitary matrix U(f) and an adjoint matrix V(f)Hobtained by performing singular value decomposition for each frequency with respect to the transformed communication path matrix of the frequency domain, and adopts each as a reception weight matrix wr(z) and a transmission weight matrix wt(z). The reception beam formation processing unit26performs reception beam formation based on the reception weight matrix wr(z). In the radio transmitting station apparatus1, the transmission beam formation processing unit14performs transmission beam formation based on the transmission weight matrix wt(z) received from the radio receiving station apparatus2. Accordingly, the wireless communication system100according to the embodiment described above is capable of performing FIR filter-type transmission beam formation and reception beam formation even when the numbers of antennas on a transmission side and a reception side differ from each other or, in other words, even when the communication path matrix h(z) is non-square.

In addition, in the wireless communication system100described above, as shown at the end of expression (12), regardless of the number “M” of the antennas17-1to17-M of the radio transmitting station apparatus1and the number “N” of the antennas21-1to21-N of the radio receiving station apparatus2being the same or different, a gain of each stream is to be dependent on transfer functions λ1(z) tO λq(Z) of each singular value. Therefore, when correlation of the communication path matrix h(z) is high, several singular values are to be 0 or, in other words, q<min (M,N). In this case, since a part of the singular values is 0, although there is a possibility that some of the streams become low throughput or non-communicable, communication will not be disabled in all streams.

In addition, in the wireless communication system100described above, the transmission weight matrix wt(z) and the reception weight matrix wr(z) are calculated in the frequency domain and processing for multiplying the transmission weight matrix wt(z) and the reception weight matrix wr(z) or, in other words, processing for forming a transmission beam and a reception beam is performed in the time domain. Therefore, since processing of formation of a transmission beam and a reception beam in the time domain can be sequentially performed with respect to a data signal, processing delay can be reduced as compared to adopting a method of performing a discrete Fourier transform with respect to a data signal.

In the processing by the transmission/reception weight calculating unit24in the embodiment described above, a fast Fourier transform can be applied in place of a discrete Fourier transform and an inverse fast Fourier transform can be applied in place of an inverse discrete Fourier transform.

In addition, while the radio receiving station apparatus2includes the transmission/reception weight calculating unit24in the embodiment described above, alternatively, the radio transmitting station apparatus1may include the transmission/reception weight calculating unit24and calculate the reception weight matrix wr(z) and the transmission weight matrix wt(z). In this case, the transmission signal transforming unit15of the radio transmitting station apparatus1is to receive the reception weight matrix wr(z) from the transmission/reception weight calculating unit24and transmit the reception weight matrix wr(z) to the radio receiving station apparatus2.

Furthermore, while the radio transmitting station apparatus1includes the training signal generating unit13and the radio receiving station apparatus2includes the communication path estimating unit23in the embodiment described above, alternatively, the radio receiving station apparatus2may include the training signal generating unit13, the radio transmitting station apparatus1may include the communication path estimating unit23, and the radio transmitting station apparatus1may estimate the communication path matrix h(z). In this case, when the radio receiving station apparatus2includes the transmission/reception weight calculating unit24, the transmission signal transforming unit15of the radio transmitting station apparatus1is to receive the communication path matrix h(z) from the communication path estimating unit23and transmit the communication path matrix h (z) to the radio receiving station apparatus2.

In addition, while the radio receiving station apparatus2includes the plurality of antennas21-1to21-N in the embodiment described above, alternatively, there may be a plurality of radio receiving station apparatuses2including a single antenna21-1or a plurality of radio receiving station apparatuses2including the plurality of antennas21-1to21-N.

The radio transmitting station apparatus1and the radio receiving station apparatus2in the embodiment described above may be realized by a computer. In this case, a program for realizing the functions may be recorded in a computer-readable recording medium and the program recorded in the recording medium may be realized by having a computer system load and execute the program. It is assumed that a “computer system” as used herein includes an OS and hardware such as peripheral devices. In addition, a “computer-readable recording medium” refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM or a storage apparatus such as a hard disk that is built into the computer system. Furthermore, a “computer-readable recording medium” may also include a recording medium that dynamically holds a program for a short period of time such as a communication wire when the program is to be transmitted via a network such as the Internet or a communication line such as a telephone line as well as a recording medium that holds a program for a certain period of time such as a volatile memory inside a server or a computer system to become a client. Moreover, the program described above may be any of a program for realizing a part of the functions described above, a program capable of realizing the functions described above in combination with a program already recorded in a computer system, and a program for realizing the functions using a programmable logic device such as an FPGA (Field Programmable Gate Array).

While an embodiment of the present invention has been described in detail with reference to the drawings, it is to be understood that specific configurations are not limited to the embodiment and that the present invention also includes designs and the like which do not constitute departures from the gist of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is applicable to radio communication in which SC-MIMO transmission is to be performed.

REFERENCE SIGNS LIST

1Radio transmitting station apparatus2Radio receiving station apparatus11Bit data generating unit12Data signal modulating unit13Training signal generating unit14Transmission beam formation processing unit15Transmission signal transforming unit16Reception signal transforming unit17-1to17-M Antenna21-1to21-N Antenna22Reception signal transforming unit23Communication path estimating unit24Transmission/reception weight calculating unit25Transmission signal transforming unit26Reception beam formation processing unit27Data signal demodulating unit28Transmission data detecting unit