Optimization And Metric Of Performance Of Impulsed-Radio UWB Energy Detection System

With the wide and profound influence on society, wireless network of high speed and super quality become important approach to access information. As one technology of carrierless and huge bandwidth, Impulsed radio Ultra-Wide Bandwidth (IR-UWB) presents most potential competence for short-distance data transimission, such as wireless personal area network (WPAN), due to its large capacity and good electromagnetic compatibility.The typical application of WPAN is short distance communication indoor. Contrasted to outdoor system and traditional carrier system, UWB system indoor experience compicated environment where dense multipath components lead to large delay spread. This makes the system design difficult, especially in coherent system of RAKE receiver and in noncoherent Transmitted Reference (TR) system. However, energy detection (ED) system suffers less for its principle and simple structure. Considering the basic characteristics of multipath fading channel (MFC) indoor, this dissertation focuses on two problems of UWB ED system, averaged criterion of system performance and performance optimization. By describing the stastics characteristic of signal power to noise ratio (SNR) in detection window of receiver, we derive the closed form of averaged bit error probability and the criterion of acquisition performance of sytem. Moreover, the packet acquisition performance of UWB packet transmission system is evaluated by the criterion proposed here with a complete analytical framework of UWB ED system performance in MFC. Besides, to improve the UWB system performance, the optimization design of receiver scheme, including selection on detection window, determination on threshold of decision and signal acquisition algorithm, is investigated for the engineering implements of UWB ED system. The main content consist of :I. The ED system and channel model. Different with the sine carrier system, IR-UWB system employs the short pulse to carry information. Therefore a lot of components of receiver, such as phase-locking loop and medium-frequency, are not necessary. Moreover, for ED system, the receiver has not correlator which is indispensable in RAKE and TR system and thus has more simple structure. And two modulations corresponding to the pulse format are introduced followed by the channel model indoor.II. The investigation on the averaged criterion of BEP (Bit Error Probability) of UWB ED system. Since many MPCs arrive the detection window of receiver randomly, the statistic of SNR of window is difficult to describe which is critical for the derivation on averaged BEP. In this dissertation, the averaged BEPs are derived in closed form based on the channel model described by clustered point process, respectively on two conditions of low data rate (without Inter symbol Interference, ISI ) and high data rate (with ISI). In addition, the qualitative relation between data rate and BEP is given and the averaged BEP bounds are demonstrated by simulation in term of optimization on threshold and integral length.III. The investigation on the averaged criterion of acquisition performance of UWB ED system. Due to the dense MPCs and huge search space, the objects, approachs and evaluations of the signal acquisition in UWB ED system are different from traditional sine system. This embodies the three terms of derivation on HIT set, design of search strategy and averaged criterion of acquisition performance. Based on the averaged BEP given, the HIT set is obtained in closed form and subsequently the expressions of mean acquisition time and the acquisition probability in certain interval are derived with serial search strategy via the model of Markov process. Moreover, the probability of packet acquisition of UWB packet transmission system is defined and given in closed form for the UWB applications in the future.IV. The approaches of optimization on UWB ED receiver scheme. First, the optimal length of detection window and the optimal threshold of data detection are investigated and designed. Gaussian distribution is employed for approximation since chi-square distribution of statistic of decision variable is hardly expressed in closed form. Based on this approximation, the polynomial fitting of least square is used for the solution of optimal threshold of decision, which does not improve the complex of engineering of system implements. Moreover, considering the feature of two-dimension search on parameters of signal acquisition, the acquisition scheme based on genetic algorithm combined with SNR estimation is proposed for signal acquisition. The results show that the proposed algorithm performs better than general search strategy.