A joint pilot assisted and despread soft-output carrier synchronization for burst DSSS system

摘要

Current carrier synchronization algorithms at extremely low signal to noise ratios (SNRs) for burst direct sequence spread spectrum (DSSS) communication systems are not very well at achieving high estimation precision and wide estimation range at the same time. An averaging periodogram (AP) and maximum mean square despread soft-output (M²SDSO) based joint pilot assisted and despread soft-output carrier synchronization algorithm (AP-M²SDSO) is proposed in this paper. In this algorithm, a frame structure in which pilot bits and data are arranged alternately is employed. First, with the help of pilot bits, a coarse frequency offset estimation is performed based on the AP method, and a coarse phase offset estimation is obtained with the maximum likelihood (ML) algorithm, then the phase of the received signals is compensated for each pair of pilot and data. Next, using despread soft-output, a fine frequency offset estimation is carried out based on the M²SDSO algorithm; then, the fine phase offset estimation is obtained. Simulation results show that at extremely low SNRs the performance of AP-M²SDSO algorithm is near the modified Cramer-Rao bound (MCRB) with high frequency offset estimation precision and wide frequency offset and phase offset estimation ranges. The bit error rate of the AP-M²SDSO algorithm is near the BER performance of ideal synchronization.