On the design of algebraic space-time overlays

We consider the design of space-time overlays to upgrade single antenna wireless communication systems to efficiently accommodate multiple transmit antennas. We define the overlay constraint such that the signal transmitted from the first antenna in the upgraded system is the same as that in the single antenna system. The signals transmitted from the remaining antennas are designed according to space-time coding principles to achieve full spatial diversity in quasi-static flat fading channels. For both BPSK and QPSK modulated systems, we develop an algebraic design framework that exploits the structure of existing single dimensional convolutional codes in designing overlays that achieve full spatial diversity with minimum additional decoding complexity at the receiver. We also investigate a concatenated coding approach for BPSK overlay design in which the inner code is an orthogonal block code. This approach is shown to yield near optimal asymptotic performance for quasi-static fading channels.