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In orthogonal frequency division multiplexing-based spectrum sharing networks, due to inefficient coordination or imperfect spectrum sensing, the signals from femtocells or secondary users appear as interference in a subset of subcarriers of the primary systems. For pilotbased doubly-selective channel estimation, the embedded pilots in pilot subcarriers would inevitably be harmed by the unpredictable interference. This unsolved issue is considered and proposed is a variational expectation maximisation-based method to iteratively learn the distribution of thermal noise plus interference, and refine doubly-selective channel estimates. Simulations demonstrated the superiority of the proposed approach over existing algorithms without considering interference mitigation.

Abstract-In this paper, equalization of multihop relaying orthogonal frequency division multiplexing (OFDM) signal is investigated under time-varying channel with unknown noise powers, channel orders and Doppler frequencies. An iterative algorithm is developed under variational expectation maximization (EM) framework. The proposed algorithm iteratively estimates the channel, learns the channel and noise statistical information, and recovers the unknown data, using only limited number of pilot subcarrier in one OFDM symbol. Simulation results show that, without any statistical information, the performance of the proposed algorithm is very close to that of the optimal channel estimation and data detection algorithm, which requires specific information on system structure, channel tap positions, channel lengths, Doppler shifts as well as noise powers.