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

Abstract

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.

Recent trends in multicarrier underwater acoustic communications

“…At the same time compressed sensing algorithms uniformly outperformed the LS and subspace methods and could handle channels with significant Doppler spread. In [58] the same authors discussed sparse channel estimation for time-varying UWA channels using MC transmission. In case when pilots and data symbols were not separated at the receiver, it was shown that subcarriers corresponding to data symbols could be used to observe the ICI caused by the neighbouring pilot subcarriers.…”

Review Article: Multicarrier Communication for Underwater Acoustic Channel

“…Transmission The challenges in pilot design for multicarrier transmission over underwater acoustic time-varying channels are two-fold [40,41]: 1) Sets of adjacent observations are needed to estimate the inter-carrier interference (ICI) coefficients; 2) Keeping pilot and data symbols orthogonal at the receiver is challenging due to the ICI. Generally there are three types of pilot insertion methods for OFDM system, comb-type; block-type; hexagonal gridtype, etc.…”

Greedy Deterministic Pilot Pattern Algorithms for OFDM Sparse Channel Estimation

“…For underwater acoustic (UWA) channel estimation, a clustered pilot design has been proposed [12]. A random pilot allocation algorithm based on UWA channel is proposed to look for the optimized pilot arrangements at the transmitter, which requires a large amount of memory [13].…”