Low Complexity Carrier Frequency Offset and Channel Estimation for Multiuser OFDMA Networks

Multiple carrier frequency offsets exist in the orthogonal frequency-division multiple access (OFDMA) uplink receivers, and consequently induce inter-carrier interference and multiple-access interferences simultaneously. We therefore propose a joint carrier frequency offset (CFO) and channel estimation scheme by leveraging the characteristic of transmission signals in the OFDMA uplink systems. A fully loaded assignment of subcarriers to active users is also supported by the proposed method. By modeling the system in a Hadamard product form, we develop an iterative algorithm wherein a closed-form estimate of CFO and channel is applied in each updating iteration. Different from the traditional expectation-maximization type methods, which update only a single CFO and channel of one user while keeping the other users’ CFOs and channels constant in each iteration, our proposed scheme updates the CFOs and channels of all active users simultaneously. Therefore, the proposed CFO and channel estimator enjoys faster convergence and lower complexity. Through numerical results, the proposed scheme is demonstrated to be robust to large CFOs and perform comparably well to the conventional approaches.