  In communication systems, efficient use of the spectrum is an indispensable
concern. Recently the use of compressed sensing for the purpose of estimating
Orthogonal Frequency Division Multiplexing (OFDM) sparse multipath channels has
been proposed to decrease the transmitted overhead in form of the pilot
subcarriers which are essential for channel estimation. In this paper, we
investigate the problem of deterministic pilot allocation in OFDM systems. The
method is based on minimizing the coherence of the submatrix of the unitary
Discrete Fourier Transform (DFT) matrix associated with the pilot subcarriers.
Unlike the usual case of equidistant pilot subcarriers, we show that
non-uniform patterns based on cyclic difference sets are optimal. In cases
where there are no difference sets, we perform a greedy search method for
finding a suboptimal solution. We also investigate the performance of the
recovery methods such as Orthogonal Matching Pursuit (OMP) and Iterative Method
with Adaptive Thresholding (IMAT) for estimation of the channel taps.
