New design criteria of space-time codes for frequency-selective multipath wireless channels

In a single-input-single-output (SISO) system, signals are modulated to have a band-pass structure in the frequency domain in order to pass through a channel with a bandpass frequency response. Similarly, in a multiple-input-multiple-output (MIMO) system with multipath wireless channels, signals radiated from the multiple transmit antennas can be processed to form beams in order to have the spatial structure to pass through the wireless channel along the multipaths. Analogous to the frequency response, a natural angle response is formed by the multipath angles. In this paper, by jointly exploring the angle and the frequency structures of the space-time codes and of the space-time channels, novel space-time codes design criteria at moderate signals-to-noise ratios are proposed. New space-time trellis codes are identified through computer searches to justify the new criteria. Simulation results show that these codes have superior performance over the existing codes in the corresponding frequency-selective channels.