System and method for wireless communications with codebook quantization

A method for controller operation, the method comprising:

• receiving, by the controller, an index from a communications device, the index corresponding to a codeword in a rank n codebook, and the codeword representing a quantized channel estimate, where n is a non-negative integer value representing a number of transmit antennas at a controller;
• computing a precoding matrix from the codeword;
• precoding data to be transmitted to the communications device in accordance with the precoding matrix;
• and
• transmitting the precoded data to the communications device,
• wherein the rank n codebook comprises 2K codewords with each codeword comprising n columns of a transformed base matrix of dimension Nt×Nt, where K is a positive integer number representing a number of bits in the rank n codebook, and Nt is a number of transmit antennas at the controller, and
• wherein an i-th codeword of the rank n codebook is expressible as Ci=diag(ui)×DFTNt, where DFTNt is the base matrix, ui(n)=ejπ sin(k sin(θt))n, iε[0, . . . , 2K−1], nε[0, . . . , Nt−1], k is a constant, and θiε[0,2π], and diag( ) is a function that returns diagonal elements of ui.

A communications device comprising:

• a channel estimate unit coupled to a signal input, the channel estimate unit configured to estimate a channel between the communications device and a controller serving the communications device;
• a quantization unit coupled to the channel estimate unit, the quantization unit configured to quantize the channel estimate in accordance with a rank n codebook and to output an index to a codeword from the rank n codebook in accordance with a codeword selection mechanism;
• a codebook store coupled to the quantization unit, the codebook store configured to store the rank n codebook;
• and
• a transmitter coupled to the quantization unit, the transmitter configured to transmit the index to the controller,
• wherein the rank n codebook comprises 2K codewords with each codeword comprising n columns of a transformed base matrix of dimension Nt×Nt, where K is a positive integer number representing a number of bits in the rank n codebook, and Nt is a number of transmit antennas at the controller, and
• wherein an i-th codeword of the rank n codebook is expressible as Ci=diag(ui)×DFTNt, where DFTNt is the base matrix, ui(n)=ejπ sin(θt))n, iε[0, . . . , 2K−1],nε[0, . . . , Nt−1], k is a constant, θiε[0,2π], and diag( ) is a function that returns diagonal elements of ui.

A controller comprising:

• a feedback decoder coupled to a signal input, the feedback decoder configured to decode feedback information from a communications device to produce an index, where the index corresponds to a codeword in a rank n codebook, the codeword corresponding to a quantized version of channel state information for a communications channel between the controller and the communications device;
• a beamforming vector compute unit coupled to the feedback decoder, the beamforming vector compute unit configured to compute a beamforming vector from the codeword;
• a transmit beamforming unit coupled to the beamforming vector compute unit and to a data input, the transmit beamforming unit configured to apply the beamforming vector to data provided by the data input;
• and
• a transmitter coupled to the transmit beamforming unit and to an antenna, the transmitter configured to transmit beamformed data provided by the transmit beamforming unit to a source of the feedback information using the antennas,
• wherein the rank n codebook comprises 2K codewords with each codeword comprising n columns of a transformed base matrix of dimension Nt×Nt, where K is a positive integer number representing a number of bits in the rank n codebook, and Nt is a number of transmit antennas at the controller, and
• wherein an i-th codeword of the rank n codebook is expressible as Ci=diag(ui)×DFTNt, where DFTNt is the base matrix, ui(n)=ejπ sin(k sin(θt))n, iε[0, . . . , 2K−1], nε[0, . . . , Nt−1], k is a constant, θiε[0,2π], and diag( ) is a function that returns diagonal elements of ui.