Research On Key Techniques Of Ultra Wideband Localization And RAKE Receiver

Ultra Wideband (UWB) communication is a breakthrough for the traditional sinusoid carrier radio, which has attracted wide interests in wireless communications due to its unique property and novel applications. Owing to its large signal bandwidth, UWB has much better distance resolution than any other wireless systems, which results in desirable capabilities including accurate position locating and ranging. Meanwhile, UWB is usually working under the environment with complex multipaths, RAKE receiver can be used to improve the system performance by actively taking advantage of the energy of multipath components.This dissertation provides researches on UWB from two aspects, i.e. the relative issues about UWB localization as well as the analysis and design for RAKE receiver. The main contributions of the dissertation can be summarized as follows:(1) A joint localization scheme is proposed, which is based on the estimation algorithm of TOA (Time of Arrival) and AOA (Angle of Arrival) under UWB signaling. One reference node is enough for the proposed method to localize the unknown nodes, the synchronization of the network is not necessary, satisfying the low complexity requirement of the terminal. RTT (Round Trip Time) is used to estimate TOA, and the multi-path detection algorithm for TOA estimation is presented. TDOA is adopted to estimate AOA, avoiding the complicated antenna beam-forming for AOA. Two different localization technologies, TOA and AOA, are unified to realize the time delay estimation of UWB multipath components, so that the localization system is simplified.(2) NLOS localization, the difficult issue in UWB localization, is discussed. A localization scheme based on UWB suitable for NLOS is proposed. Due to the ingenious employment of the scatterer, we make the TOA and AOA still work in NLOS environment, even the direct path being blocked. The TOA estimation can be obtained based on the strongest path (SP) detection, avoiding the threshold search. The aforementioned scheme is also applicable for LOS situation. Unlike the regular localization algorithm, the proposed scheme can implement localization directly.(3) Since NLOS identification is capable of providing the significant prior information for UWB localization, the TOA estimation performance in IEEE 802.15.4a channel models is tested through simulations, and it is validated that the statistic property of UWB multipath components can be effectively used for NLOS identification. Then, through the statistic property of UWB localization error, the problem of LOS/NLOS status identification is resolved by means of the hypothesis test theory. The identification algorithm does not rely on the channel information. A closed-form expression for the probability density function of localization error under NLOS condition is derived, and the solution of the identification probability is obtained in terms of theoretical analysis.(4) A Reduced-Complexity Selective RAKE (RC-SRAKE) receiver scheme is proposed, which can be adopted in UWB multipath channel under NLOS environment. It determines finger parameters by sampling the output of the correlation of the received signal with reference waveform, while the matching template used for RAKE correlation receiving is determined according to the finger parameter. The proposed SRAKE has low complexity because it does not require channel information or channel estimation. A closed-form expression for symbol error probability of the proposed RC-SRAKE is derived in term of the combined fingers and noise. The error analysis and experimental results show that RC-SRAKE can achieve the performance approximate to the ideal SRAKE with a fewer fingers, and should be feasible in practical applications.