Partial FFT Demodulation: A Detection Method for Highly Doppler Distorted OFDM Systems

Abstract

Abstract-Employing Orthogonal Frequency Division Multiplexing (OFDM) signaling over time-varying channels results in inter-carrier interference (ICI) and degraded detection error probability due to the loss of orthogonality among the subcarriers. This problem is particularly exacerbated for systems operating in highly mobile scenarios such as underwater acoustic (UWA) communications, digital video broadcasting (DVB) for mobile devices and vehicle-to-vehicle (V2V) networks. To address the problem of data detection in such scenarios, we propose a novel demodulation strategy using several partial interval Fast Fourier Transforms (FFTs) instead of a conventional, single full interval FFT. Algorithms for computing the weights used to combine the outputs of the partial FFT are presented for three scenarios: full, partial and no knowledge of the time varying channel. Numerical simulations and an approximate theoretical analysis show that significant performance gains can be obtained over traditional equalizers at a very moderate complexity.

Multi-segmental OFDM signals equalization with piecewise linear channel model over rapidly time-varying channels

“…Additionally, the remaining terms except the first one corresponding to the time variations will become small with the large M, but these terms are not considered in [8]. In other words, the equalizer with a small M will be interfered with by the remaining terms.…”

“…Although the perfect CSI is used, the channel coefficients mismatch between the PLM and the perfect channel coefficients still exists and will be more significant with the increasing normalized Doppler frequency. However, the proposed model will be more accurate than the ones used in [8,20], which approximate the channels by the midpoint CIR with the slopes between two consecutive OFDM symbols rather than the two segments or only the midpoint CIR in one particular segment.…”

“…Note that the autocorrelation of the noise is defined as the same as [8]. The matrix form of the PLM with multi-segmental signals is expressed as…”

“…Additionally, some techniques in [4,5] exploit the sparsity of the banded matrix to design the OFDM block equalizers. Also, several pre-equalized methods have been proposed in [6][7][8][9][10] to reduce the time variations and obtain a quasi-diagonal channel matrix as convectional OFDM systems over the *Correspondence: huangyao@cuit.edu.cn Chengdu University of Information Technology, Sichuan, China slowly time-varying channels. Some decision feedback equalization techniques are also compatible with OFDM systems [11][12][13][14][15][16].…”

“…Unlike the methods in [3,4,15,16,18], the con-ventional banded channel matrix is not adopted for equalization. Motivated by [8,[19][20][21], a new form of multi-segmental OFDM signals equalizer with the PLM is derived for ICI suppression. Unlike the previous literature, we do not assume that the channels remain constant during each sample duration and neither exploit real oversampling benefits as in [19], in which more samples are obtained around each subcarrier.…”