Adaptive MAP Detection via the EM Algorithm for LDPC-Coded MIMO-OFDM Mobile Communications

Tsuyoshi KASHIMA
Kazuhiko FUKAWA
Hiroshi SUZUKI

IEICE TRANSACTIONS on Communications   Vol.E90-B    No.2    pp.312-322
Publication Date: 2007/02/01
Online ISSN: 1745-1345
DOI: 10.1093/ietcom/e90-b.2.312
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Wireless Communication Technologies
mobile communication,  MIMO,  OFDM,  LDPC,  MAP,  EM algorithm,  channel estimation,  

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This paper proposes an iterative maximum a posteriori probability (MAP) receiver for multiple-input-multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM) mobile communications. For exploiting the space, time, and frequency diversity, the low-density parity-check code (LDPC) is used as a channel coding with a built-in interleaver. The receiver employs the expectation maximization (EM) algorithm so as to perform the MAP symbol detection with reasonable computational complexity. The minimum mean square error (MMSE), recursive least squares (RLS), and least mean square (LMS) algorithms are theoretically derived for the channel estimation within this framework. Furthermore, the proposed receiver performs a new scheme called backward symbol detection (BSD), in which the signal detection uses the channel impulse response that is estimated one OFDM symbol later. The advantage of BSD, which is explained from the viewpoint of the message passing algorithm, is that BSD can exploit information on the both precedent and subsequent OFDM symbols, similarly to RLS with smoothing and removing (SR-RLS) [25]. In comparison with SR-RLS, BSD reduces the complexity at the cost of packet error rate (PER) performance. Computer simulations show that the receiver employing RLS for the channel estimation outperforms the ones employing MMSE or LMS, and that BSD can improve the PER performance of the ones employing RLS or LMS.