Noncoherent Multi-symbol Detection Of CPM Signals In Deep Space Communications

Due to channel features of deep space communications and the increasing amount ofcommunication data, continuous phase modulation is recommended in deep space communications bythe authoritative organizations, such as Consultative Committee for Space Data Systems and NationalAeronautics and Space Administration. The detection of CPM signals can be classified into coherentand noncoherent one. Because coherent detection requires complex phase synchronization, problemsassociated with a PLL circuit, such as loss of lock, phase ambiguity and so on, often occur in somebad communication environment. In many cases, coherent detection suffers high degradation fromphase estimation errors. Fast recovery from severe fading occurs in noncoherent detection. Thecomplexity of communication system is also reduced for eliminating the phase estimation. Formemory modulation schemes, multi-symbol detection usually achieves better performance thansymbol-by-symbol detection. CPM is typically a kind of memory modulation schemes. Thenoncoherent multi-symbol detection of CPM signals is examined in the paper with emphasis onimprovement of detection performance and simplification of the receiver structures. The detectionmethods with high reliability and simple receiver structures are provided for deep spacecommunication systems.The classical noncoherent multi-symbol detection algorithm is studied at first in the paper. Theclassical receiver structure is complex, although classical multi-symbol detection achieves obviouslybetter performance than symbol-by-symbol detection. To reduce the complexity, the maximumlikelihood block detection algorithm of full response CPM with simplified receiver structure isintroduced and then modified. The modified algorithm retains the advantages of the original one, butimproves the detection performance. At last, the maximum likelihood block detection algorithm ofpartial response case is examined to study whether the algorithm is suited for partial response CPM.Because maximum likelihood block detection achieves poor performance for CPM with longpartial response, independent overlapped noncoherent maximum likelihood sequence detection(IO-NMLSD), which utilizes overlapped observations to improve the detection performance, isintroduced in the paper. The linear decomposition of CPM signals in then applied to deduce thesimplified IO-NMLSD algorithm. The simplified algorithm effectively reduces the complexity ofIO-NMLSD receiver while the performance doesn’t get worse.Finally, FPGA implementation scheme of maximum likelihood block detection of CPM signals is proposed. The top-down approach is used in the FPGA design and the system is broken down intomultiple sub-modules. Each sub-module is accomplished and FPGA design scheme is verified by avariety of hardware simulation.