Timing Acquisition Technique With Distributed Antenna Cooperation

Relative to the centralized antenna systems (CAS), the higher spectral efficiency can be obtained in distributed antenna systems (DAS). As the key technology of the fourth generation (4G) wireless system, the DAS has been attracting worldwide research interests. It is a prospective research topic.However, the inaccuracies of timing acquisition degrade the performance of DAS. The existing methods of timing acquisition for DAS are mainly concentrated on independent timing acquisition (ITA), i.e., among the receive antennas, none of cooperative processing for timing acquisition is employed. A problem arises on whether the cooperation among the distributed receive antennas can be exploited for timing acquisition. As far as we know, there has been little concentration on this issue.Thus, we investigate the cooperative timing acquisition (CTA) for DAS in this thesis. To improve the acquisition performance (e.g., the probability of correct acquisition) for each distributed receive antenna, the cooperative processing among the multiple distributed receive antennas is applied in the timing acquisition of DAS.First, a maximum-likelihood (ML)-based CTA method is proposed by exploiting the location information of distributed receive antennas [A₁]. Moreover, we derive a lower bound for the probability of correct acquisition to evaluate the performance of the proposed CTA method. Compared to the ITA method, the analytical and simulation results show that the higher probability of correct acquisition for each distributed receive antenna can be obtained. When the received signal to noise ratios (SNR) of the two distributed receive antennas (i.e., RA₁ and RA₂ ) are 4dB and 8dB , respectively, the probability of correct acquisition for RA₁ is about 25% in ITA method while it can nearly increase to 95% with the cooperation of RA₂ .Second, we propose an ML-based CTA method by exploiting the coverage range of each distributed receive antennas [A₂]. Meanwhile, a lower bound of the probability of correct acquisition is derived to confirm the effectiveness of the proposed CTA method. Compared to the ITA method, the analysis and simulations indicate that the higher probability of correct acquisition for each distributed receive antenna can be obtained. When the received SNRs of the receive antennas RA₁ and RA₂ are 6dB and 14dB , respectively, the probability of correct acquisition for RA₁ is approximatively 62% in ITA method while it can nearly increase to 91% with the cooperation of RA₂ .Finally, a CTA method for the orthogonal frequency division multiplexing (OFDM)-based DAS is proposed by sensing the same transmitted signal with multiple distributed receive antennas [B1]. Compared to the ITA method, the analytical and simulation results show that the failure probability of timing acquisition for each distributed receive antenna is decreased, e.g., when the received SNR at one receive antenna is 6dB , the failure probability is nearly 2×10^-2 in ITA method, while it can decrease to 2×10^-3 with the cooperation of the other 5 distributed receive antennas.The research in this thesis explores the problem of cooperative timing acquisition for DAS, which extends the existing researches and has some theoretical and practical values. The research results can be applied for the distributed antennas-based 4G mobile communication systems.