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Estimation of the Feedback Reliability for IB-DFE Receivers

DOI: 10.5402/2011/980830

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single-carrier (SC) modulation with frequency-domain equalization (FDE) combined with iterative (turbo) FDE schemes has been shown to be suitable for cyclic-prefix (CP)-assisted block transmission within broadband wireless systems. Its excellent performance in severely time-dispersive channels, makes it a promising candidate for future broadband wireless systems. In this paper we investigated the impact of the correlation factor estimation in the performance of iterative block decision feedback equalization (IB-DFE) receivers. Since the correlation factor represents a key parameter to ensure the good performance of these receivers, reliable estimates of this factor are needed in the feedback loop. We present several methods to estimate the correlation coefficient. We also propose a technique to compensate the inaccuracy of the estimation. 1. Introduction Future wireless systems are required to support high quality of service at high data rates, for which we can have severely time-dispersion effects associated to the multipath propagation. It is known that block transmission techniques, with appropriate cyclic extensions and employing FDE techniques, are excellent candidates for severely time-dispersive channels [1, 2]. The most popular techniques based on this concept are orthogonal frequency division multiplexing (OFDM) and single-carrier with frequency-domain equalization (SC-FDE). However, the OFDM signals have high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR) leading to amplification difficulties. An alternative to OFDM modulations are SC modulations using FDE and CP-assisted block transmission techniques, especially for the uplink of broadband wireless systems [1, 2]. The performances and overall implementation complexities are similar to SC-FDE and OFDM [1, 2]. Typically the receiver for SC-FDE schemes is a linear FDE. However, it is known that nonlinear equalizers outperform linear equalizers [3]. iterative block decision feedback equalizer (IB-DFE) [4] is a promising iterative FDE technique for SC-FDE that was first proposed in [5] and extended to diversity scenarios [6] and layered space-time schemes [7]. IB-DFE receivers can be regarded as iterative DFE receivers with the feedforward and the feedback operations implemented in the frequency domain. Since the feedback loop takes into account not just the hard decisions for each block, but also the overall block reliability we have small error propagation. Consequently, the IB-DFE techniques offer much better performances than the noniterative methods, with


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