Detection-based Synchronization Algorithm For Ultra-wideband System

Short pulses and low power spectral density signaling employed in UWB systems place stringent timing requirements at the receiver for demodulation. The short pulses and low duty cycle generate wide bandwidths, which results in a fine resolution of the timing uncertainty region, thereby imposing a large search space for the acquisition system. Moreover, the relatively low transmission power of UWB systems requires the receiver to process the received signal for long periods in order to obtain a reliable estimation of the timing information. And the effect of noise and interference make it difficult to reach high acquisition probability. Even a small synchronization error could cause remarkable performance degradation which would be a serious challenge to synchronization in UWB systems. Consequently, synchronization is very important in UWB systems.At present, acquisition schemes for UWB systems in the literature can be broadly classified into those which follow detection-based approaches, and those which rely on estimation-theoretic strategies. In this dissertation, all the algorithms are detection-based approaches, the research work contains two main parts as follow: firstly, considering the UWB channel is a dense multipath channel without significant fading, the EGC acquisition approach is discussed in the paper and its improved approach is analyzed and simulated; secondly, DS-UWB systems require large acquisition time, and a two-stage acquisition strategy can reduce the acquisition time effectively, therefore, a two-stage acquisition strategy in [11] is discussed and an improved approach based on this acquisition strategy is researched and analyzed.In a dense multipath environment, there will be a considerable amount of energy available in the multipath components (MPCs). It seems reasonable to expect that an acquisition scheme which collects the energy in the MPCs would perform better than one which does not. The equal-gain combining (EGC) approach is performed to exploit the rich path diversity present in UWB channels, it combines the energy in the MPCs. It is a detection-based approach. The receiver template signal is composed of several multipath components which have the same amplification, and a particular phaseτ? in the search space is checked by correlating the received signal with a locally generated template signal with fixed delayτ? . The measure of correlation is then compared to a threshold which is set before in order to make a decision. If the integrator output exceeds the threshold, the phaseτ? is declared to be a coarse estimation of the true phase in the received signal. If the threshold is not exceeded, the search control updates the phase to be checked,this process continues until the threshold is exceeded.In this paper, the acquisition probabilities and acquisition time of the EGC acquisition is analyzed firstly. Then, an improved acquisition approach is researched based on the EGC scheme, which considers the amplifications and their related time delay in multipath, and puts these parameters into template signal. From the simulation, it can be seen that this new approach can improve acquisition probabilities compared with those of the EGC scheme, but it increased acquisition time.DS-UWB systems employ long spreading sequences in order to remove multiple symbol intervals and spectral lines resulting from the pulse repetition present in the transmitted signal. In the absence of any information regarding the timing of received signal, the receiver needs to search through a large number of phases at the acquisition stage. This results in a large acquisition time if the acquisition system evaluates phases in a serial manner. Furthermore,the wide bandwidths of DS-UWB signal impose a larger search space for the acquisition system compared with traditional spread spectrum communication systems. Decreasing the search space can reduce acquisition time. Some acquisition schemes attempt to solve the large search space problem by employing a two-stage acquisition strategy.A two-stage acquisition strategy which employed two adaptive templates in [11] is discussed first. This scheme is composed of two stages, the first stage is called coarse search, and the second stage is the fine search. In the coarse acquisition stage, two adaptive templates are constructed, these two templates squares first and then integrates with the squared receive signal respectively. This can get different energy, is reserved. This stage leads to a smaller subset of the search space. After several times comparisons, the acquisition space is confirmed in a subset which can get the largest energy. The second stage then proceeds to search in this smaller subset and identifies the true phase in a serial search strategy.This acquisition approach needs to set the frame time to be 2N multiples of a single pulse period. An improved scheme can make the frame time be any multiples of a singular pulse persisting time. Larger multiples between frame time and a single pulse period can cause higher duty cycle, which could cause larger acquisition space. In order to achieve similar performance, it has no use for setting the multiples to be 2N , the improved scheme can decrease the multiples, and consequently, reduce acquisition time in [11].