Patent ID: 8406328

Claim:
A method for providing feedback for closed-loop transmitting with multiple transmit antennas and multiple receive antennas, the method comprising the steps of: providing a codebook containing sets of weightings for each data stream of the multiple transmit antennas with each set of weightings identified by an index known to a transmitter, wherein the same codebook is utilized for any number of data streams up to the number of transmit antennas; measuring a composite channel between the transmitter and receiver; determining at least one performance metric for each set of weightings in the codebook; selecting a preferred set of weightings for each data stream in response to the performance metrics; and sending to the transmitter an index of the preferred set of weightings in the codebook for use in subsequent transmissions of each data stream; wherein the codebook weightings include entries chosen from a finite alphabet consisting of 0 and powers of i, where i equals the square root of −1; wherein the determining step includes: calculating a rank 1 performance metric of a set of rank 1 weightings; and calculating a rank 2 performance metric of a set of rank 2 weightings, wherein a subset of the rank 2 weightings include the set of rank 1 weightings; and wherein the selecting step includes: deciding the rank of the transmission based on the rank 1 and rank 2 performance metrics; and selecting the index of the set of weightings of the rank decided in the deciding substep.