Factor-Graph-Based Detection Algorithms for Coded OFDM over Time-Varying Channels
Sprache des Vortragstitels:
Englisch
Original Tagungtitel:
Proc. of the JNCW 2011 - NEWCOM++/COST 2100 joint Workshop
Sprache des Tagungstitel:
Englisch
Original Kurzfassung:
In this paper we consider a coded orthogonal frequency
division multiplexing (OFDM) system over time-varying
channels. We propose soft-input soft-output detection algorithms
based on a cyclic factor graph representation of the a posteriori
distribution of the transmitted symbol sequence. By applying
the sum-product algorithm (SPA) to this graph we compute
the a posteriori probabilities of each transmitted symbol, where
the message schedule for the SPA determines the performance
of the detection algorithms. Therefore we present on the one
hand a serial schedule which provides a good bit error rate
(BER) performance at the initial iteration but has a high latency
and on the other hand a parallel schedule with low latency
but a poor initial performance. Moreover we introduce a novel
hybrid message schedule which provides a tradeoff between
the aforementioned message schedules. The proposed detection
algorithms provide a remarkable complexity reduction compared
to the optimal forward-backward algorithm (FBA). By computer
simulations of an OFDM-LTE downlink system with turbo
equalization we demonstrate the effectiveness of the proposed
algorithms, for instance we show that after 3 iterations the BER
performance of the proposed algorithms is similar to that of the
FBA.
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