Research On Synchronization Of Idma Systems

As a new multiple access technique, interleave-division-multiple-access (IDMA) has become a candidate for air interface of forth generation (4G) mobile communication systems due to its particular advantages. It has become one of the hot research areaes in recent years.Among the research topics about IDMA, the uplink synchronization is always the hard issue. Based on this circumstance, we take synchronization techniques of IDMA systems as our research topic in this thesis.At first, the effect of sample-timing error on the bit-error-rate (BER) performance of IDMA systems is studied in this paper. We construct an asynchronous IDMA system model to investigate the effect of sample-timing error caused by the asynchronous transmission from different user ends (UEs) on the BER performance in uplink. The theoretic analysis shows that sample-timing error can introduce both inter-symbol interference (ISI) and multiple access interference (MAI) into the traditional detection algorithm to degrade the system performance greatly. And the simulation results prove the same conclusion. At the same time, we evaluate the effect of different sample-timing error on system performance in order to get the performance requirements for the uplink synchronization schemes.For the uplink synchronization issue, we propose a non-data-aided timing acquisition scheme. Based on the theoretical analysis of SNR-variance technique, we apply this SNR-variance evolution in ZP-IDMA system for timing acquisition. In the base station (BS), we detect the average variance of the accessing user to estimate the corresponding timing offset and return it to its user transmitter for calibaration. However, we also find that this timing acquisition scheme is hard to apply in the high-speed-vehicle situations, which should be explored in the future works.In this thesis, we also study the PN-aided synchronization scheme which has been applied in IDMA. After modification about the timing acquisition and early-delay-gate, we still construct a feedback between base station and user ends for timing calibration, which performs well by simulation. However, the system capacity is sacrified due to the system resource allocated for the pilote signal, which is the compromise for system design.The synchronization of IDMA systems still is the difficult and important topic in this area, and we need devote more on this research.