Non-Data-Aided Timing Acquisition for Asynchronous IDMA Systems

Sample-timing error can cause significant performance degradation for the interleave-division multiple-access systems (Wang et al. 2009). In this paper, we propose a nondata-aided timing acquisition scheme tomitigate sample-timing error due to the asynchronous transmission of random allocated user ends (UEs) on the uplink. A closed-loop timing control scheme is constructed for the asynchronous IDMA system in this paper. We use the extrinsic information generated during the iterative detection algorithm with signal noise ratio evolution to estimate the timing offset for the asynchronous uplink in the base station (BS) receiver. The BS receiver returns the timing control bits, which is generated with estimated timing offsets, to the corresponding UE. And the UE uses the timing control bits to adjust local transmission time to guarantee the sampling performance at the BS receiver. The simulation results show that the proposed acquisition scheme based on feedback loop can provide high acquisition probability and low false alarm probability. The proposed scheme can overcome the bit-error-rate performance bottleneck, which is caused by the sample-timing error in BS receiver due to the asynchronous signals in the uplink.