Receiver comparisons on an OFDM design for Doppler spread channels

Abstract

Abstract-Underwater acoustic channels induce large Doppler drifts that render intercarrier interference (ICI) for OFDM transmissions. Assuming that after proper Doppler compensation the residual ICI is limited to only direct neighbors, we propose an OFDM signal design that decouples channel estimation and data demodulation. We investigate eight receivers that are categorized into three groups: (i) three receivers that ignore the residual ICI, (ii) three receivers that are based on a basis expansion model (BEM) and pursue channel estimation independently along each basis, and (iii) two receivers that are based on discrete-path modeling. The receiver performance is compared based on data from the SPACE experiment conducted off the coast of Martha's Vineyard, Massachusetts, October 2008. The receiver based on the discrete-path modeling and a basis pursuit algorithm achieves the best performance while the receiver based on BEM and leastsquares channel estimation performs the worst. The performance differences among different receivers drastically increase as the channel's Doppler spread and the signal constellation size increase. Interestingly, the BEM based receivers are often inferior to the ICI-ignorant counterparts, implying that the ability of ICI compensation could be limited by the estimation accuracy of the much increased number of model parameters. I. INTRODUCTIONFast variation of underwater acoustic (UWA) channels introduces intercarrier interference (ICI) for underwater multicarrier transmissions. The receivers in [1], [2] are constructed assuming that all the propagation paths have a similar path variation rate and the residual ICI can be ignored after proper Doppler compensation. On the other hand, basis expansion models (BEM) have been used to approximate doubly (timeand frequency-) selective UWA channels in [3]- [5] so that the ICI is limited to within neighboring subcarriers.In this paper, we assume that the residual ICI of an orthogonal frequency division multiplexing (OFDM) system is limited to only direct neighbors after proper Doppler compensation. We then propose an OFDM signal design that decouples channel estimation and data demodulation. Specifically, pilot and data subcarriers are separated by at least two null subcarriers so that (presumably) they do not interfere with each other. For this system, we investigate eight receivers that are categorized into three groups:• Three receivers that ignore the residual ICI, where leastsquares (LS) as in [1], orthogonal matching pursuit

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A Novel Approach for the Estimation of Doubly Spread Acoustic Channels Based on Wavelet Transform

“…As observed in many experiments [6,7], signals from different paths will experience different Doppler scales, arrive at different time and have different energies. Therefore, the multi-scale multi-lag (MSML) channel, denoted in [8], can well model acoustic channel and has been adopted in many researches [7,9].…”

Effective mirror-mapping-based intercarrier interference cancellation for OFDM underwater acoustic communications

“…Orthogonal frequency-division multiplexing (OFDM) has recently attracted great interests from researchers in the field of underwater acoustic (UWA) communications due to its capability of combating inter-symbol interference (ISI) caused by large delay spread, which is quite common in UWA communications [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The key principle of OFDM is that the wideband time-invariant channel is converted into multiple orthogonal flat fading sub-channels, and modulated symbols transmitted over different subcarriers do not interfere with each other.…”

“…In the literature, there are mainly three categories of ICI suppression methods. In the first category, the basis expansion model (BEM) has been considered for ICI mitigation in some work [10][11][12]. However, the BEM coefficient estimation introduces additional computational burden at the receiver.…”