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UBC Theses and Dissertations

Space-time continuous phase modulation Silvester, Anna-Marie


The combination of Space-Time (ST) coding and Continuous-Phase Modulation (CPM) produces a low power, energy efficient communication scheme suitable for wireless transmission. Space-time coding increases the reliability of transmission, and continuous-phase modulation (CPM) has the potential to provide considerable energy savings. CPM is a modulation technique that involves the transmission of a signal with continuous-phase and a constant envelope, where the continuous-phase property produces a very bandwidth efficient signal, and the constant-envelope property enables non linear (and thus energy efficient) signal amplification. The ST-CPM code is of special interest for wireless sensors because in the wireless sensor network environment energy consumption is highly constrained. The combination of ST codes and CPM is non-trivial and thus ST-CPM codes based upon block-based orthogonal and diagonal signal matrices are presented. These codes are forms the basis of a distributed ST-CPM code. The distributed ST codes are designed to operate in wireless networks containing a large set of nodes, of which only a small a priori unknown subset will be active at any time. The devised distributed ST-CPM scheme combines the ST-CPM code with a diagonal signaling matrix, (commonly assigned to all relay nodes) with signature vectors(uniquely assigned to nodes). The energy consumption of the proposed distributed ST-CPM scheme is compared with that of a distributed ST linear modulation (LM) scheme. The distributed ST-CPM scheme is shown to outperform the distributed ST-LM scheme for all but short-range transmission. Finally, a serially concatenated code for ST-CPM is proposed. The concatenated code consists of the diagonal signalling matrix as the inner code, and a class of double parity check (DPC) codes as the outer code. The resulting concatenated codes that are formed from the ST-CPM code and a DPC code are shown to provide performance close to capacity, and to provide performance superior to that provided by the more common combination of CPM, or ST-CPM schemes with convolutional codes.

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