Patent ID: 7508808

Claim:
A frequency-division multiplexing system for use with M greater than or equal to two transmit antennas and N greater than or equal to two receive antennas, comprising: (a) a mapper modulator configured to map each of a plurality of incoming sets of message bits to a current M×M unitary symbol matrix; (b) a differential modulator configured to generate, in a sequence of repetitions, a sequence of consecutive differential M×M unitary space-frequency signal matrices by performing in each new repetition a differential action between said differential M×M unitary space-frequency signal matrix resulting from a last repetition and said current M×M unitary symbol matrix, thereby to generate a new differential M×M unitary space-frequency signal matrix, wherein said differential action is carried out such that said message bits mapped to said current M×M unitary symbol matrix are encoded as a differential between two consecutive differential M×M unitary space-frequency signal matrices, wherein said differential is substantially invariant to frequency-response conditions in a propagation channel between said transmit and receive antennas; and (c) a time-frequency transformer configured to accept each differential M×M unitary space-frequency signal matrix as a signal distributed over antennas and frequency sub-channels such that consecutive differential M×M unitary space-frequency signal matrices are distributed over consecutive frequency sub-channels, and further configured to transform each differential M×M unitary space-frequency signal matrix to a corresponding space-time transmit signal distributed over two or more antennas and time for transmission over a given time window.