Application of randomization techniques to space-time convolutional codes

In this paper, we demonstrate that a system employing a space time convolutional code (STCC) can be implemented with only a single transmit antenna when there are multiple receive antennas. The idea is to transmit more than one symbol from a single transmit antenna during a symbol period by superimposing the encoded symbols on top of each other. This objective is achieved by inducing randomness into the system, that creates additional channel paths, called virtual paths. The design of such an approach is studied for slow Rayleigh fading channels. One immediate application of this approach is to model an n × m multiple-input multiple-output (MIMO) system as an equivalent group of n distinct 1 × m systems. Consequently, we demonstrate that STCCs with high spectral efficiencies can be designed utilizing QPSK STCCs as component codes for each 1 × m system. Simulation results evaluate the performance of this technique for the case of two transmit antennas and several different number of receive antennas, a spectral efficiency of 4 bits/s/Hz. and slow Rayleigh fading channels.