Wireless communications system, wireless communications method, and wireless communications apparatus
In an SVD-MIMO transmission using a singular value decomposition, the amount of information fed back to a transmitter from a receiver is reduced. Instead of feeding back to the transmitter, a transmission weighting vector V obtained by performing a singular value decomposition of a channel information matrix obtained by the receiver, the receiver sends reference symbols to the transmitter, which obtains the channel information matrix and performs the singular value decomposition to yield the vector V necessary when transmitting data. In the procedure of obtaining the vector V, a noncoincidence between channel matrices in the opposite directions is compensated for, by performing a calibration for compensating an error between transmitting and receiving analog devices on the part of both the transmitter and the receiver.
1. A wireless communications system for a communication between a transmitter and a receiver each having a plurality of antennas, over a communications channel by multiplexing a signal, the system comprising:
a reference signal sender which feeds back reference signals for respective antennas of the receiver from the receiver to the transmitter;
a first channel information acquirer which calculates, based on the reference signals received by the transmitter, a channel information matrix H whose elements represent transfer functions of respective communication sub-channels of the channel each of which links one of the antennas of the transmitter and one of the antennas of the receiver;
an SVD unit which performs a singular value decomposition of the channel information matrix H to yield UDV H , so as to obtain a transmit antenna weighting coefficient matrix V whose entries represent weighting vectors for the respective antennas of the transmitter; and
a signal sender which sends the components of a reference signal from the respective antennas of the transmitter to the receiver with the components weighted by the transmit antenna weighting coefficient matrix V;
a second channel information acquirer which calculates, based on the weighted reference signals received by the receiver, a channel information matrix H′ corresponding to the transmit antenna weighting coefficient matrix V and respective antennas of the receiver;
a receive antenna weighting coefficient matrix decision unit, in the receiver, configured to determine a receive antenna weighting coefficient matrix based on the channel information matrix H′; and
a decoder, in the receiver, configured to decode a received signal, which is received after obtaining the receive antenna weighting coefficient matrix based on the received antenna weighting coefficient matrix.
2. A wireless communications system taking account of a transfer function of a communications channel between a transmitter and a receiver each having an antenna, the system comprising:
a calibration coefficient obtainer which obtains a calibration coefficient for each of the antennas of the transmitter and the receiver by calculating a ratio of a transfer function of each of a transmission circuit and a reception circuit corresponding to each of the antennas;
a reference signal feedback unit which feeds back a reference signal as compensated on the part of the receiver by using the calibration coefficient for the antenna of the receiver, to the transmitter;
a transfer function calculator which compensates, on the part of the transmitter, the received calibrated reference signal by using the calibration coefficient for the antenna of the transmitter, and obtains a transfer function based on the compensated reference signal; and
a data sender which transmits data using the transfer function.
3. The system of claim 2 ,
wherein each of the transmitter and the receiver has a plurality of antennas, and a communication between the transmitter and the receiver is performed by multiplexing a signal indicative of data such that components of the signal is sent over respective sub-channels of the channel each of which links one of the antennas of the transmitter and one of the antennas of the receiver,
wherein the calibration coefficient obtainer obtains calibration coefficients of the respective antennas on the part of both the transmitter and the receiver,
wherein the reference signal feedback unit sends, by time division, the reference signals for the respective antennas of the receiver as compensated by using the respective calibration coefficients;
wherein the transfer function calculator operates on the part of the transmitter to: compensate the reference signals received by the antennas of the transmitter, by using the calibration coefficients for the respective antennas; calculate the transfer functions based on the compensated reference signals; obtain a channel information matrix H′ in the inverse direction from the receiver to the transmitter, whose elements represent the transfer functions of the respective sub-channels; and acquire a transmit antenna weighting coefficient matrix V whose entries represent weighting vectors of the respective antennas of the transmitter, by performing a singular value decomposition of the channel information matrix H′ to yield U′D′V′ H , and
wherein the data sender sends the components of the signal indicative of the data from the respective antennas of the transmitter to the receiver with the components weighted by the respective weighting vectors.
4. The system of claim 3 , further comprising:
a reference signal feedforward unit which sends the reference signals for the respective antennas, from the transmitter to the receiver by time division;
a second transfer function calculator which operates, on the part of the receiver, to: calculate transfer functions based on the reference signals received by the respective antennas; obtain a channel information matrix H in the forward direction whose elements represent the transfer functions of the respective sub-channels; and obtain a receive antenna weighting coefficient matrix U whose entries represent weighting vectors for the respective antennas of the receiver; and
a data receiver which operates, on the part of the receiver, to receive the components of the signal indicative of the data sent from the transmitter by the respective antennas, and decodes the signal by using the receive antenna weighting coefficient matrix U H .
5. A wireless communications method for a communication between a transmitter and a receiver each having a plurality of antennas, over a communications channel by multiplexing a signal, the method comprising:
feeding back reference signals for respective antennas of the receiver from the receiver to the transmitter;
calculating, based on the reference signals received by the transmitter, a channel information matrix H whose elements represent transfer functions of respective communication sub-channels of the channel each of which links one of the antennas of the transmitter and one of the antennas of the receiver;
performing a singular value decomposition of the channel information matrix H to yield UDV H , so as to obtain a transmit antenna weighting coefficient matrix V whose entries represent weighting vectors for the respective antennas of the transmitter;
sending the components of a reference signal from the respective antennas of the transmitter to the receiver with the components weighted by the transmit antenna weighting coefficient matrix V;
calculating, based on the weighted reference signals received by the receiver, a channel information matrix H′ corresponding to the transmit antenna weighting coefficient matrix and respective antennas of the receiver;
determining a receive antenna weighting coefficient matrix based on the channel information matrix H′; and
decoding a signal received after obtaining the receive antenna weighting coefficient matrix based on the received antenna weighting coefficient matrix.
6. A wireless communications method taking account of a transfer function of a communications channel between a transmitter and a receiver each having an antenna, the method comprising steps of:
obtaining a calibration coefficient for each of the antennas of the transmitter and the receiver by calculating a ratio of a transfer function of each of a transmission circuit and a reception circuit corresponding to each of the antennas;
feeding back a reference signal as compensated on the part of the receiver by using the calibration coefficient for the antenna of the receiver, to the transmitter;
compensating, on the part of the transmitter, the received calibrated reference signal by using the calibration coefficient for the antenna of the transmitter, and obtaining a transfer function based on the compensated reference signal; and
sending data using the transfer function.
7. The method of claim 6 , employing a communications system wherein each of the transmitter and the receiver has a plurality of antennas, and a communication between the transmitter and the receiver is performed by multiplexing a signal indicative of data such that components of the signal is sent over respective sub-channels of the channel each of which links one of the antennas of the transmitter and one of the antennas of the receiver,
wherein the calibration coefficient obtaining step comprises obtaining calibration coefficients of the respective antennas on the part of both the transmitter and the receiver,
wherein the reference signal feeding back step comprises sending, by time division, the reference signals for the respective antennas of the receiver as compensated by using the respective calibration coefficients;
wherein the compensating step comprises, on the part of the transmitter: compensating the reference signals received by the antennas of the transmitter, by using the calibration coefficients for the respective antennas; calculating the transfer functions based on the compensated reference signals; obtaining a channel information matrix H′ in the inverse direction from the receiver to the transmitter, whose elements represent the transfer functions of the respective sub-channels; and acquiring a transmit antenna weighting coefficient matrix V whose entries represent weighting vectors of the respective antennas of the transmitter, by performing a singular value decomposition of the channel information matrix H′ to yield U′D′V′ H , and
wherein the data sending step comprises sending the components of the signal indicative of the data from the respective antennas of the transmitter to the receiver with the components weighted by the respective weighting vectors.
8. The method of claim 7 , further comprising steps of:
sending the reference signals for the respective antennas, from the transmitter to the receiver by time division;
on the part of the receiver, calculating transfer functions based on the reference signals received by the respective antennas; obtaining a channel information matrix H in the forward direction whose elements represent the transfer functions of the respective sub-channels; and obtaining a receive antenna weighting coefficient matrix U whose entries represent weighting vectors for the respective antennas of the receiver; and
on the part of the receiver, receiving the components of the signal indicative of the data sent from the transmitter by the respective antennas, and decoding the signal by using the receive antenna weighting coefficient matrix U H .