Iterative Carrier Frequency Offset and Channel Estimation for Underwater Acoustic OFDM Systems

Kang, Tae Gon; Iltis, R.A.

doi:10.1109/jsac.2008.081205

Cited by 117 publications

(43 citation statements)

References 53 publications

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“…An OMP receiver can iteratively reconstruct the channel paths. OMP has been used to estimate sparse UWA channels in [11] for single carrier and in [6] for multicarrier systems.…”

Section: A Ici-ignorant Receiversmentioning

confidence: 99%

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Receiver comparisons on an OFDM design for Doppler spread channels

et al. 2009

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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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“…An OMP receiver can iteratively reconstruct the channel paths. OMP has been used to estimate sparse UWA channels in [11] for single carrier and in [6] for multicarrier systems.…”

Section: A Ici-ignorant Receiversmentioning

confidence: 99%

“…(OMP) as in [6], and basis pursuit (BP) algorithms as in [7] are used for channel estimation based only on measurements on pilot subcarriers. The LS channel estimator assumes the channel to be non-sparse while OMP and BP are compressive sensing algorithms [8], which are suitable for sparse channel estimation [7].…”

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confidence: 99%

Receiver comparisons on an OFDM design for Doppler spread channels

et al. 2009

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“…While the large delay spread motivates multicarrier transmission schemes that can use efficient frequency domain equalization (see, e.g., [1]- [3]), the significant Doppler spread will lead to loss of orthogonality between the subcarriers. Early multicarrier receiver designs ignored that the loss of orthogonality between the subcarriers would lead to intercarrier interference (ICI) [1]- [3], but now it is largely agreed that estimating and equalizing the ICI (or at least some of it) leads to significant performance improvement [4]- [7]. Unfortunately to estimate the ICI, e.g., using a basis expansion model (BEM) [6], [8], the number of unknown parameters explodes.…”

Section: Introductionmentioning

confidence: 99%

“…Although it has been recognized for a long time that UWA channels are sparse [9], so far most work to take advantage of this fact has focused only on reconstructing channels in the delay domain [3], [10]- [12]. It turns out that estimating the channel both in delay and Doppler dimension with sufficient accuracy is challenging even when using known transmitted signals [13], or needs increased pilot overhead [4].…”

Section: Introductionmentioning

confidence: 99%

Study of pilot designs for cyclic-prefix OFDM on time-varying and sparse underwater acoustic channels

Berger

Gomes

Moura

2011

OCEANS 2011 IEEE - Spain

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Abstract-Estimation of time-varying and sparse channels is a topic that has attracted considerable interest lately, especially for underwater acoustic communication. In the context of multicarrier transmission, several important questions remain unanswered: i) should pilots be placed in clusters as for timevarying, non-sparse channels, or randomly dispersed between the data as common in the Compressive Sensing literature; ii) as pilot and data subcarriers cannot be perfectly separated at the receiver due to intercarrier interference (ICI) should channel estimation be based on observations corresponding to pilot subcarriers only, or can the data subcarriers be used to practically extract additional information about the channel; and iii) how does the performance vary with the number of pilot symbols? We use data recorded at the recent CalCom'10 experiment to investigate these questions. We find that a sufficient number of adjacent observations is required to estimate the ICI, which can either be achieved by a pilot design that uses clustered pilots, or by using data subcarriers as additional observations. When using data subcarriers as observations, the effect of the unknown data should be modeled as increased noise. Finally, by varying the number of pilot subcarriers, we can trade off error performance for data rate.

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“…However, it is known that OFDM is sensitive to Doppler effects, since Doppler introduces a carrier frequency offset (CFO) and destroys orthogonality of the subchannels. 1 Examples of OFDM applications to UAC for both fixed and moving platforms are available [2][3][4][5] while the OFDM algorithm itself is well documented in the wireless literature. 1 Nevertheless, typical experimental demonstrations of the OFDM approach in UAC are limited in terms of range (less than 2.5 km in very shallow water), data rate, frequency band, and environment.…”

Section: Introductionmentioning

confidence: 99%

Long-range multi-carrier acoustic communications in shallow water based on iterative sparse channel estimation

Kang¹,

Song²,

Hodgkiss³

et al. 2010

The Journal of the Acoustical Society of America

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Long-range orthogonal frequency division multiplexing (OFDM) acoustic communications is demonstrated using data from the Kauai Acomms MURI 2008 (KAM08) experiment carried out in about 106 m deep shallow water west of Kauai, HI, in June 2008. The source bandwidth was 8 kHz (12–20 kHz), and the data were received by a 16-element vertical array at a distance of 8 km. Iterative sparse channel estimation is applied in conjunction with low-density parity-check decoding. In addition, the impact of diversity combining in a highly inhomogeneous underwater environment is investigated. Error-free transmission using 16-quadtrative amplitude modulation is achieved at a data rate of 10 kb/s.

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Iterative Carrier Frequency Offset and Channel Estimation for Underwater Acoustic OFDM Systems

Cited by 117 publications

References 53 publications

Receiver comparisons on an OFDM design for Doppler spread channels

Receiver comparisons on an OFDM design for Doppler spread channels

Study of pilot designs for cyclic-prefix OFDM on time-varying and sparse underwater acoustic channels

Long-range multi-carrier acoustic communications in shallow water based on iterative sparse channel estimation

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