Adaptive Space-Time Trellis Codes Based on Convolutional Codes

Space-time trellis codes can significantly improve the error performance or the data rate of wireless communications systems with multiple transmit antennas. These codes are usually generated using a generator matrix with 2 columns and modulo 4 operations for QPSK modulation with two transmit antennas. They can also be implemented as Z₄ convolutional codes. Another way of representing them is to use a conventional binary convolutional code of rate 2/4. Such a representation is more flexible and allows an easy implementation of space-time encoders and decoders with different modulation schemes and numbers of transmit antennas. Only the rate of the convolutional code needs to be changed using the puncturing technique to accommodate these different schemes. Simulations results have shown that the new codes can achieve an error performance very close to that of the best usual space-time codes.