Iterative decision feedback equalizer with cyclic detection for DFT-S OFDM system

Abstract

One of the most challenging problems in high-data-rate wireless transmission is to reduce inter-symbol interference (ISI) resulted from the time dispersion caused by multi-path propagation. To solve this problem, equalization is introduced. Generally, efficient decision feedback equalizer (DFE) holds better performance than linear equalizer for the cancellation of ISI without noise enhancement. However, its inherent error propagation has some limitation for further improvement. In fact, as shown later in simulation results, conventional frequency domain DFE (FD-DFE) almost cannot be used in Discrete Fourier Transform-Spread Orthogonal Frequency Division Multiplex (DFT-S OFDM) system in Evolved-UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA) uplink transmission [3GPP, TR 25.814 V1.2.3. Physical layer aspects for evolved UTRA. May 2006 [release 7]]. Unique word (UW) is proposed in the literatures, as a known symbol sequence, can make error propagation beyond one FFT-block impossible since the last symbols of every block are always decided correctly. But the UW-based scheme is not appropriate for DFT-S OFDM, so it must be modified. This paper proposes a simple DFE-based equalization algorithm for DFT-S OFDM. Through cyclic detection and iteration, the new algorithm obtains a noticeable gain than conventional DFE, and is almost as effective as the modified UW-based methods but with much higher bandwidth efficiency. Furthermore, it does not need to change the frame structure of existing protocol.