An uplink carrier frequency offset tracking method in Aeronautical Communications System

The L-band Digital Aeronautical Communications System 1 (L-DACS1) is working under the interference from the Distance Measuring Equipment (DME) system, which is also working at the L-band. Thus, considerable errors may be encountered in the carrier frequency offset (CFO) synchronization for L-DACS1. Note that continuous transmission mode is considered in the uplink for L-DACS1, which requires small CFO to provide a good bit error rate (BER) performance. Therefore, to improve the CFO accuracy in L-DACS1 under the interference from DME, in this paper, a closed-loop tracking scheme with a new adaptive feedback factor (AFF) algorithm is proposed. Pilots in uplink frames are utilized to estimate the residual CFO, while compensation frequency is updated in the tracking loop by the proposed approach. Moreover, using the AFF-based tracking method, both tracking speed and accuracy can be achieved in the aeronautical mobile channel. Through simulations, it is shown that rapid tracking convergence and accurate tracking compensation can be guaranteed by the proposed scheme, even in the case of large residual CFO under low signal-to-noise ratio (SNR).