Iterative Channel and Symbol Estimation for OFDM and for SIMO Diversity

摘要

This paper proposes a new approach of Iterative Channel and Symbol Estimation (ICSE) with applications in Orthogonal Frequency Division Multiplexing (OFDM) and Single Input Multiple Output (SIMO) diversity systems. Our method extends the traditional approaches of Pilot Symbol Assisted Method (PSAM) and Decision Directed Method (DDM) for symbol detection. This paper describes the key mathematical methods for (i) estimating the log likelihood ratio of the unknown information bearing symbol given an uncertain estimate of the channel (derived using sparsely-transmitted pilot symbols), and (ii) subsequently re-estimating the channel coefficients using this log likelihood ratio. Formulations in this paper, thus, establish the underlying methods that enable the ICSE. The main contributions of this paper are to (i) provide a specific method of estimating the channel coefficients using uncertain symbol/bit estimates, (ii) show mathematical equivalence of this method with the method of deriving the symbol log likelihood ratio, and (iii) describe the applicability of the proposed ICSE scheme to the OFDM receiver and the SIMO receiver. A simulation and analytical (Cramer Rao Bound) evaluation of the proposed method provides demonstration of the potential performance benefit of the proposed approach.