Techniques for noncoherent space-time communications

Space-time (ST) systems have the potential to greatly improve the performance of wireless communications, by providing diversity via coordinated use of many propagation channels. Owing to the potentially large number of channels, it is often desirable to avoid the transmission overhead and the receiver processing associated with coherent detection. Hence, this research adopts a noncoherent approach, where channel state information is unavailable at both communication endpoints. This dissertation is comprised of three investigations; the goal is to realize the significant performance gains promised by diversity systems, while maintaining low complexity noncoherent system structures. The first investigation considers a differential ST modulation with pi/2-shifted BPSK. A novel transformation is performed on the received signal, showing that this second order transmit diversity pi/2-shifted BPSK is equivalent to second order receive diversity with QPSK. This equivalent representation allows selection diversity and scalar multiple symbol differential detection (MSDD) to be applied. Furthermore, receiver performance is enhanced by applying iterative joint channel estimation and sequence detection. Employing a more general modulation format, the second investigation introduces an eigen-assisted (EA) transmitter/receiver system. The EA system performs within a fraction of a dB of the coherent detection lower bound, using scalar differential encoding of M-ary PSK in a dual transmit antenna format and scalar MSDD at the receiver. Additional benefits of the EA system include the avoidance of the constel lation expansion observed with conventional ST differential en coding and a receiver complexity comparable to that of a symbol-by-symbol conventional differential detector. The final ST investigation considers M-ary CPFSK, a specific continuous phase modulation (CPM), rather than the linear modulations previously considered. An encoding scheme is proposed for a general number of transmit antennas, in which each transmitted signal exhibits characteristics expected of single channel M-ary CPFSK. However, when sampled at the symbol rate, the transmissions also fall into the class of unitary ST block codes. Consequently, a diversity order equal to the number of transmit antennas is guaranteed, provided that a pre-processed subset of the received samples are used to detect the underlying differential code.