Method and apparatus for feedback in closed loop transmitting

An apparatus for providing feedback for closed-loop transmitting with multiple transmit antennas and multiple receive antennas, the apparatus comprising:

• 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;
• and
• a receiver that is operable to measure a composite channel between the transmitter and the receiver and determine at least one performance metric for each set of weightings in the codebook, the receiver also operable to select a preferred set of weightings for each data stream in response to the performance metrics, and send 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 only of 0 and powers of i, where i equals the square root of −1;
• and
• wherein the receiver is operable to 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 receiver is further operable to decide the rank of the transmission based on the rank 1 and rank 2 performance metrics and select the index of the set of weightings of the decided rank.