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Iterative frequency-domain equalization for WFRFT and EST based modulation schemes over doubly selective wireless fading channels

Recently, two fire-new modulation schemes: the so-called hybrid carrier (HC) modulation based on weighted-type fractional Fourier transform (WFRFT) and the modulation based on energy spreading transform (EST), have emerged as promising solutions to repress the inter-sample and inter-carrier interference caused by doubly selective channels. In this paper, we propose an iterative frequency domain minimum mean-square-error (MMSE) equalization scheme for systems with WFRFT and EST precoders in order to achieve a better tradeoff between the interference-repression performance and complexity. During the process of the proposed iterative equalization, priors-aided linear MMSE estimations (LME) are performed iteratively in the frequency domain, and the priors are updated in precoding domains. During the iterations, the prior information is estimated more accurately in WFRFT and EST based modulation systems than those in conventional orthogonal frequency division multiplexing (OFDM) and single carrier (SC) systems. Simulation results manifest that the proposed iterative frequency domain MMSE equalization (IFME) scheme outperforms existing iterative MMSE equalization schemes proposed for OFDM and SC architectures in terms of bit-error-ratio.