Serially Concatenated System Based On Continuous Phase Modulation

Continuous phase modulation (CPM) is a method for modulation of datacommonly used in wireless modems. It is used primarily because continuous phasemodulation has good spectral efficiency for a noncoherent modulation technique.Furthermore, CPM is typically implemented as a constant-envelope waveform, i.e. thetransmitted carrier power is constant. Therefore, CPM is attractive because the phasecontinuity yields high spectral efficiency, and the constant-envelope yields excellentpower efficiency. The primary drawback is the high implementation complexityrequired for an optimal receiver. With the development of hardware technology, anoptimal receiver for CPM is not difficult. As the OFDM technology, CPM is anattractive envelope of CPM signals transmission.In this thesis, we study the serially concatenated systems based on CPM (SCCPM).The outer codes can be convolutional codes or Low density parity check (LDPC) codes.We proposed two kinds of methods to improve the SCCPM system when the outer codeis convolutional codes. The first one is combine the TCM technology with CPM toimprove the error-correct ability of the inner coder, the other is to design"good"outercodes which have low convergence threshold.LDPC codes are well known for their near Shannon limit performance and theirparallel compute structure. More and more communication systems choose LDPC codesas their ECC schemes. In this thesis, we investigate a serial concatenation of LDPCcodes with minimum shift keying (MSK) when the receiver employs iterative decodingand demodulation. Since the recursive continuous phase encoder (CPE) of MSK can beexpressed in terms of a bipartite graph, the overall system can be viewed as aconcatenation of two Tanner graphs. Based on the analysis of the error correlation in therecursive CPE (RCPE) MSK demodulator and the overall loop in the joint Tanner graph,we show that the error correlation has a great impact on the performance of the iterativesystem when the LDPC codes are not designed carefully and interleavers are notemployed. To reduce the impact of the error correlation, we develop a new design rulewhich allows the serially concatenated system not to employ interleavers. Simulationresults show that the proposed design rule reduce the impact of the error correlation in asimple and effective way.In the end of this thesis, we introduce the hardware platform we developed forsatellite communications and a practical and flexible way of implementing CPM usingan adaptable Viterbi detector is presented.