Joint carrier synchronization and equalization algorithm for packet-based ofdm systems over the multipath fading channel

In this paper, a joint carrier synchronization and equalization algorithm is presented for orthogonal frequency-division multiplexing (OFDM) systems in the tracking stage. Based on the minimum mean-square-error (MMSE) criterion, the cost function of the joint algorithm is proposed to minimize the mean square error (MSE), namely, the uncoded bit error rate (BER), on each subchannel and to further lower the carrier frequency jitter concurrently. The carrier synchronization scheme with multirate processing is a dual-loop structure, which is composed of outer and inner loops. The outer loop is a frequency-tracking loop that deals with the phase offset, which is induced by the carrier frequency offset (CFO), in the time domain. The inner loop is a phase-tracking loop to cope with the phase distortions, which are caused by the carrier frequency error and the channel phase variation, on each subcarrier in the frequency domain. There is a gain equalization loop to compensate the magnitude distortion on each subchannel. Furthermore, the closed-loop stability of the carrier synchronization loop is particularly explored for the loop delay induced by hardware realization. Many simulations are done for the additive white Gaussian noise (AWGN) and the multipath frequency-selective fading channels to show that the joint algorithm not only accurately estimates and compensates the CFO and the channel impairment but also provides the cost-effective feature compared with the considered algorithms.