Combined Transmitter Diversity and Multi-Level Modulation Techniques

Orthogonal transmitter diversity such as frequency diversity and time diversity is quite simple to implement and, with optimum signal combining, can take full advantage of fading multipath channels. However, such a scheme has a bandwidth efficiency that decreases inversely with the number of diversity branches making it less attractive in wireless communications applications. This paper considers combined orthogonal transmitter diversity and multi-level linear modulation techniques. The idea is to view the signal constellations of the modulation scheme in an augmented signal space formed by the modulation signal dimension and the number of branches of the transmitter diversity scheme. This augmented signal space provides a good spread for the modulation signal points and can be quite efficient for high-level linear modulation techniques. The obtained results show that this combined scheme, not only improves the system performance in both additive white Gaussian noise and fading multipath channels, but also improves the bandwidth efficiency of orthogonal transmitter diversity.