Performance of multitone and multicarrier DS-SS in the presence of imperfect phase synchronization

It is well known that accurate synchronization is more critical in multicarrier systems than in single carrier systems (Molisch (2001)). If all local receiver (and/or transmitter) subcarrier frequencies are generated from a common source, as is desirable in implementations, any frequency/phase inaccuracies can affect both individual subcarrier performance, and more seriously, introduce inter-subcarrier interference. Hence, study of non-ideal synchronization effects is well motivated We provide new analytical and computer simulation results for the performance of multitone (MT) and multicarrier (MC) direct-sequence spread spectrum (DS-SS) signaling in the presence of imperfect synchronization, manifested as phase noise. We investigate performance in phase noise as the number of subcarriers and the per-subcarrier processing gain vary, for a fixed data rate and fixed bandwidth. Long spreading codes are used, and we assume coherent detection with MPSK modulation. Comparisons between simulations and analysis show excellent agreement (Matolak (2001)). We provide comparative results for the three systems-conventional single-carrier DS-SS, and the MC and MT systems-in order to establish a relative ranking of these approaches in the presence of imperfect synchronization, and show that the SC and MC systems are the most robust to this impairment.