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Design of Detector for SEFDM Signals

Heydari Khormizi, Javad | 2012

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 43991 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Marvasti, Farokh
  7. Abstract:
  8. This thesis considers theoretical, analytical and engineering design issues relating to non-orthogonal Spectrally Efficient Frequency Division Multiplexing (SEFDM) communication systems that exhibit significant spectral merits when compared to Orthogonal FDM (OFDM) schemes. Alas, the practical implementation of such systems raises significant challenges, with the receivers being the bottleneck.
    This research explores detection of SEFDM signals. The mathematical foundations of such signals lead to proposals of different orthonormalisation techniques as required at the receivers of non-orthogonal FDM systems. To address SEFDM detection, two approaches are considered: either attempt to solve the problem optimally by taking advantage of special cases properties or to apply sub optimal techniques that offer reduced complexities at the expense of error rates degradation
    Initially, the application of sub-optimal linear detection techniques, such as Zero Forcing (ZF) and Minimum Mean Squared Error (MMSE), is examined analytically and by detailed modelling. To improve error performance a heuristic algorithm, based on a local search around an MMSE estimate, is designed by combining MMSE with Maximum Likelihood (ML) detection. Yet, this new method appears to be efficient for BPSK signals only. Hence, various variants of the sphere decoder (SD) are investigated. Detailed modelling shows the SD detector to be well suited to the SEFDM detection, however, with complexity increasing with system interference and noise. Standard reformulation techniques are used to relax the original optimal detection problem to a convex Semi-Definite Program (SDP) that can be solved in polynomial time. Although SDP performs better than other linear relaxations, such as ZF and MMSE, its deviation from optimality also increases with the deterioration of the system inherent interference. To improve its performance a heuristic algorithm based on a local search around the SDP estimate is further proposed. Finally, a modified SD is designed to implement faster than the local search SDP concept.
    In this thesis, two new methods were proposed for detection of SEFDM signal which both of them use an iterative approach. In the first one, we combined the classic Iterative method, which first was proposed by Marvasti to compensate the distortion caused by interpolation, with the idea of soft decision at the end of each iteration block to gain an appropriate detection. The second method uses the idea of DAR technique; a method used for PAPR reduction, and tries to reconstruct an assumed discarded part to convert the problem of SEFDM detection to a more convenient one in OFDM detection. Both methods show great complexity reduction relative to previously found methods and achieve the same Bit Error Performance as optimum detector in some special cases
  9. Keywords:
  10. Optimum Receiver ; Iteration Method ; Frequency Division Multiplex (FDM) ; Intercarrier Interference ; Spectral Efficiency ; Hard and Soft Decision

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