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Turbo Coded OFDM Receiver Using Joint Synchronization, Channel Estimation and Decoding | IEEE Conference Publication | IEEE Xplore

Turbo Coded OFDM Receiver Using Joint Synchronization, Channel Estimation and Decoding


Abstract:

This paper presents a turbo coded OFDM receiver structure using joint synchronization, channel estimation and decoding. In this proposed scheme, the estimator uses soft-d...Show More

Abstract:

This paper presents a turbo coded OFDM receiver structure using joint synchronization, channel estimation and decoding. In this proposed scheme, the estimator uses soft-decision information from the previous soft-input soft-output (SISO) decoder to produce better estimates of the unknown parameters, which will in turn help the decoder to make more reliable decision. The whole process will be performed in an iterative manner and good system performance can be achieved with only a few iterations for moderate initial synchronization errors.
Date of Conference: 11-15 March 2007
Date Added to IEEE Xplore: 04 June 2007
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Conference Location: Hong Kong, China

I. INTRODUCTION

By considering the soft information from a soft-input soft-output (SISO) decoder in an iterative estimation of synchronization parameters, various turbo synchronization algorithms have been proposed. It is shown in [1] that maximum-likelihood (ML) synchronization can be implemented by expectation maximization (EM) algorithms. Furthermore, in a turbo coded system, it can be naturally integrated with the iterative decoding process since a posteriori probability provided by maximum a posteriori (MAP) decoder is exactly what EM algorithms require for estimation. In [2], EM-based timing technique is proposed, which is then generalized to the multi-user case in [3]. Timing recovery in inter-symbol interference (ISI) channel is performed, again, by EM algorithm in [4], assuming constant timing offset within one packet. In [5] [6], timing recovery using iterative execution of equalization, synchronization and decoding to achieve sub-optimal solutions is considered for ISI channels suffering from time-varying timing offsets. In the proposed receiver structures, soft information provided by the turbo equalizer is fed back to the phase-locked loop (PLL)-based timing recovery block to improve the timing estimates, which are consequently used to refine the samples being fed back to the turbo equalizer for further iterations. With a moderate random walk timing offset, a good gains of 3.5dB at BER of 10−3 can be achieved, as compared to conventional system with separate timing recovery and turbo equalization. Since the new timing recovery block is actually embedded inside the turbo equalizer, the overall scheme is slightly more complex than a turbo equalizer.

References

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