Differential space-time modulation

We consider the design of space-time modulation techniques that do not require channel estimates at the transmitter or receiver. We propose a general approach to differential modulation for multiple transmit antennas based on group codes. This approach can be applied to any number of transmit antennas and any signal constellation. We also derive low-complexity differential receivers, error bounds, and modulator design criteria, which we use to design optimal modulators for two transmit antennas.