Research On The Synchronization Acquisition Technique For Impulse Radio Ultra Wideband Communications

Ultra-wideband (UWB) wireless communication is a revolutionary technology for transmitting large amounts of digital data over a wide spectrum of frequency bands. UWB technology has made it a promising technology for wireless personal area networks (WPAN), In-Home Network and Sensor Network, owing to its ultra-wideband nature, which include high data rate, large capacity, low transmit power, and availability of low-cost transceivers, and so on. At present, two opposing groups of UWB developers are battling over the IEEE standard. The two competing technologies are conventional "carrier wave" and impulse radio. Conventional "carrier wave" is multiband orthogonal frequency division multiplexing (MB-OFDM) candidate. The other candidate is Impulse Radio Ultra-wideband (IR-UWB) which is proposed in the original. This type of UWB technology is fundamentally different from conventional forms of RF technology. UWB employs a "carrier free" architecture, which does not require the use of high frequency carrier generation hardware, carrier modulation hardware, and has recently received great attention in both academia and industry.In this paper, with the unique features of UWB impulse radios and the effects caused by dense multipath channel, we studied the synchronization acquisition technique for IR-UWB communications, and discussed the complexity, the acquisition speed and the timing accuracy of these acquisition algorithms.Firstly, starting from the channel model which is used to help evaluate Physical Layer (PHY) submissions to IEEE 802.15.3a, we analyze several important parameters to be included in this model, such as mean excess delay, RMS delay spread, number of multipath components and so on. The Power decay and the Inter Symbol Interference (ISI) caused by the multipath channel are also analyzed. After depth analysis of this channel model, we summarize three principles of the acquisition technique of IR-UWB communications-the acquisition speed, the timing accuracy and the complexity, and discuss the impact factors of the three indicators. The assessment of the various different acquisition algorithms is summarized.Secondly, a rapid timing acquisition algorithm based on Least Square Estimation (LSE) is presented. Using the autocorrelation of the Barker code, a novel training sequence is judiciously designed. Based on a symbol-by-symbol sliding correlator, the algorithm is proposed that exploit the geometrical interpretations for the linear LS approach to estimate the start of the individual frame with respect to the receiver's clock (frame timing) in data-aided(DA) mode, which focus on the UWB transmitted signals with pulse amplitude modulation (PAM) and time hopping (TH). Based on the unique features, we explore training sequence design, the acquisition ambiguity within a frame and comparison of the complexity and the acquisition speed with the conventional synchronization techniques. Simulations are presented under various operating environments to demonstrate their mean-square timing estimation errors and their system-level impact on bit error rate (BER) performance. The results show that the scheme can achieves rapid acquisition with a high synchronization performance, and compared to the conventional algorithm, the algorithm reduces considerably implementation complexity and acquisition time.Thirdly, a timing algorithm for PPM-UWB signals in data-aided mode based on generalized likelihood ratio test (GLRT) is proposed. Most existing timing algorithms are not applicable to nonlinearly modulated PPM-UWB signals with nonzero mean. Based on a novel correlation template, the algorithm capitalizes on the output of a symbol-rate sliding correlator to detect the received UWB signal and identify the symbol-level timing-offset parameter which employ generalized likelihood ratio tests (GLRT), and estimate the frame-level timing-offset parameter which employ likelihood ratio function, exploiting the training sequence pattern and transforming nonlinear parameter to linear parameter. The performance of the scheme is assessed by simulating in dense multipath channel, and simulations confirm that the algorithm ensures rapid acquisition of the PPM-UWB system with lower complexity and without high sample rate.Finally, three timing acquisition algorithms are presented based on serial search techniques. The first algorithm is a novel symbol and frame synchronization algorithm based on the maximum-likelihood criterion. Unlike the two algorithms proposed in first two chapters, the first algorithm is developed with high sample rate and serial search. As a result, the algorithm can improve the timing accuracy with higher complexity. The second algorithm is a parallel search and maximum-selected and threshold crossing (MAX/TC) scheme. In this case, the uncertainty region is divided into several sectors with several cells each, and in a sector a cell is selected; the test variables in each sector are compared to a threshold. This parallel search based on MAX/TC criterion can effectively reduce the mean acquisition time, while keeping a high timing accuracy for acquisition and performing detection with less sensitive to the detection threshold and low complexity. The third algorithm is a synchronizer with flexible search step sizes in a correlator in chapter 3. This algorithm remains operational in both data-aided (DA) and nondata-aided (NDA) modes.It can be summarized that, this paper discusses the synchronization acquisition technique for IR-UWB communications. Many analysis methods and solutions are proposed. Besides the theoretical analysis many simulations are carried out to support the effectiveness of our methods.