A suboptimal pilot design for NC-OFDM systems

Equispaced and equipowered pilot tones have been proved the optimal pilot design for conventional orthogonal frequency division multiplexing (OFDM) systems, but it does not hold true for non-contiguous OFDM (NC-OFDM) systems. In this paper, the optimal pilot design is derived for NC-OFDM systems with available but non-contiguously distributed spectrum fragments. Based on minimizing the average mean square error (MSE) of the least square (LS) estimate of the channel frequency response (CFR) over the data subcarriers, we provide the optimal pilot placement and its power allocation algorithm. A suboptimal pilot placement scheme is also presented for decreasing the computational complexity. Simulation results indicate that significant gain can be achieved by using the proposed approach.