Process for Beamforming Data to be Transmitted by a Base Station in a MU-MIMO System and Apparatus for Performing the Same

A method of beamforming data to be transmitted in a Multi-User-Multiple Input, Multiple Output (MU-MIMO) communication system comprising a base station and a selected set of User Equipment (UE) communicating with the base station, comprising:

• precoding the data by the base station in accordance with a beamforming matrix complying with a precoding matrix Vcu according to the equation
• V
• CU
• =
• 1
• M
• 
• DPA
• ,
• where
• M is the number of transmit antennas,
• D is a diagonal unitary matrix of the form D=diag (1, exp(jφ1), exp(jφ2), . . . exp(jφM-1)),
• P is a permutation matrix interchanging only the last M−1 rows, and
• A is a general Hadamard matrix;
• and
• transmitting, from the base station to the UE at least a first and a second index which are representative of D, P and A.

A method of processing data to be transmitted to a plurality of User Equipment (UE) in a Multi-User-Multiple Input, Multiple Output (MU-MIMO) communication system, the data being precoded by a Constant Unitary Beamforming process for suppressing interference at reception, the method comprising the steps of:

• receiving channel estimations provided by the multiple UEs;
• selecting one cost function to be optimized;
• computing a precoding matrix (Vcu) according to the equation:
• V
• CU
• =
• 1
• M
• 
• DPA
• ,
• where
• M is the number of transmit antennas
• D is a diagonal unitary matrix of the form D=diag (1, exp(jφ1), exp(jφ2), . . . exp(jφM-1)),
• P is a permutation matrix interchanging only the last M−1 rows, and
• A is a general Hadamard matrix;
• executing an optimization algorithm of the selected cost function to compute the optimized representation D, P and A of the precoding matrix Vcu;
• quantizing the result of the optimization algorithm to generate a quantized vector;
• generating at least a first and a second index representative of the quantized vector and the permutation matrices;
• transmitting the at least first and second indexes to the UEs;
• and
• computing Vcu and using it for coding data to be transmitted to the UE.

A method, executed by a User Equipment (UE), of processing received data that was precoded by a base station in accordance with a beamforming matrix in a Multi-User-Multiple Input, Multiple Output (MU-MIMO) communication system, the method comprising the steps of:

• estimating the channel characteristics;
• transmitting the estimated channel characteristics to the base station;
• receiving from the base station at least a first and a second index representative of a beamforming precoding utilized by the base station for beamforming the data transmitted to the UE;
• using the first and second indexes to generate
• a diagonal unitary matrix of the form D=diag (1, exp(jφ1, exp(jφ2), . . . exp(jφM-1)),
• a permutation matrix P interchanging only the last M−1 rows, and
• a Hadamard matrix A;
• computing a precoding matrix Vcu according to the equation
• V
• CU
• =
• 1
• M
• 
• DPA
• where M is the number of transmit antennas;
• wherein the at least first and second index are representative of D, P and A;
• and
• receiving from the base station precoded data;
• and
• processing the received, precoded data by applying the precoding matrix.

A base station operative in a Multi-User-Multiple Input, Multiple Output (MU-MIMO) communication system to transmit data to a plurality of User Equipment (UE), comprising:

• a controller operative to precode the data in accordance with a beamforming matrix complying with a precoding matrix Vcu according to the equation
• V
• CU
• =
• 1
• M
• 
• DPA
• ,
• where
• M is the number of transmit antennas,
• D is a diagonal unitary matrix of the form D=diag (1, exp(jφ1), exp(jφ2), . . . exp(jφM-1)),
• P is a permutation matrix interchanging only the last M−1 rows, and
• A is a general Hadamard matrix;
• and
• a transmitter operative to transmit the precoded data, and a representation of D, P and A, to the UEs.

User Equipment (UE) operative in a Multi-User-Multiple Input, Multiple Output (MU-MIMO) communication system and operative to receive, from a base station, data precoded in accordance with a beamforming matrix, the UE comprising:

• a channel estimator operative to generate channel estimates;
• a transmitter operative to transmit the channel estimates to the base station;
• a receiver operative to receive, from the base station, precoded data and at least a first and a second index representative of a beamforming precoding utilized by the base station for beamforming the transmitted data;
• and
• a controller operative to
• retrieve a quantized vector from a look-up table in response to the indexes,
• compute, from the quantized vector,
• a diagonal unitary matrix of the form D=diag (1, exp(jφ1), exp(jφ2), . . . exp(jφM-1)),
• a permutation matrix P interchanging only the last M−1 rows,
• a Hadamard matrix A, and
• a precoding matrix Vcu according to the equation
• V
• CU
• =
• 1
• M
• 
• DPA
• ,
• where M is the number of transmit antennas;
• and
• apply the precoding matrix to process the received, precoded data.