A Low Complexity Multi-Carrier System Over Doubly Selective Channels Using Virtual-Trajectories Receiver

Current communication standards are designed to operate under either frequency or time selectivity. However, the rising demand of higher data rates combined with the mobility of the transceivers has led to the necessity of transmitting under doubly selective channels. In these channels, both single-carrier and multi-carrier approaches find high interference conditions, where the performance in terms of spectral efficiency and bit error rate is low. The state-of-the-art solutions involve high complexity and/or low compatibility making them infeasible. In this paper, a modified orthogonal frequency-division multiplexing (OFDM) communication system based on the virtual decomposition of the channel is proposed. The system is fully compatible with the standard OFDM transmitters and maintains several blocks of the standard OFDM receivers. This novel system substantially surpasses the performance of current approaches while requiring low computational complexity.

I. Introduction

The requirement of transmitting high data rates over doubly selective channels (DSC) while maintaining reasonable spectral efficiency forces single carrier (SC) and orthogonal frequency division multiplexing (OFDM) systems to work under high interference conditions. In the case of SC wideband radio communications, the delay spread is so large that the inter-symbol interference (ISI) covers several symbols. In the case of OFDM based systems, Doppler spread introduces inter-carrier interference (ICI), which usually covers several carriers. Restricting the analysis to the case of block-type transmissions, either ICI in OFDM or ISI in SC become equivalent problems, so similar techniques have been developed in order to combat them. However, overall interference introduced by the DSC in the data symbols is commonly less severe in the OFDM system, as it exhibits rapid decay of interference contribution with respect to the symbol distance in SC systems; therefore, this work is focused on the operation of OFDM systems in DSC. In this context, there are two main approaches for dealing with transmission over DSC: a) Transmitting the traditional OFDM signals while increasing the complexity in the receiver (Rx) and b) Devising novel systems specifically designed to operate over DSC.