A new pilot design for NC‐OFDM systems under power constraints

Abstract

ABSTRACTThe pilot design is one of the key issues that has to be solved in order to improve the performance of non‐continuous orthogonal frequency division multiplexing (NC‐OFDM) systems in cognitive radio context. Equally‐spaced and equally‐powered pilot tones that are the optimal pilot design for conventional OFDM systems cannot be applicable to NC‐OFDM systems with the non‐continuous(NC) spectrum. In NC‐OFDM systems, the secondary users(SUs) communicate to each other by spectrum mapping the primary users(PUs)’ band to protect the PUs from interference. So the SUs’ available subcarriers’ positions and power allocation will be changed with PUs’ active state and interference constraints. The NC available spectrum and power distribution bring new challenges on system design, which make the pattern of pilots in the frequency domain vulnerable. Several recent researches have studied the optimal or suboptimal pilot designs under equally‐powered assumption. In this paper, we only focus on the comb‐type pilot design under uneven power distribution hypothesis for the NC‐OFDM transmission. Firstly, based on maximising each available subcarrier’ power under PUs’ interference temperature constraints, the pilot power constraints have been discussed, then the formula between pilot positions and pilot powers have been derived by minimising the channel estimation mean square error; moreover, a suboptimal pilot design under the pilot power constraints is also presented. The proposed pilot design cannot only obtain better channel estimation performance compared with previous pilot designs, but also consider the PUs’ communication reliability. Simulation results demonstrate the effectiveness of the proposed method. Copyright © 2013 John Wiley & Sons, Ltd.