Study On Ultra Wideband Radio Technology

Due to its particular characteristics in frequency domain and time domain, the Ultra Wideband Radio (UWB-R) technology has found many potential applications in radar and communication communities. Now it has attracted increasing interests of a lot of researches and companies. As a revolutionary wireless technology, UWB-R has some advantages such as resistance to multipath fading and narrowband interference, high range resolution, low probability of intercept, strong penetration, high data rate and low complexity of system etc. It can improve the ability of target detection and make a best use of spectrum. However, UWB-R system works in a very different way with that of conventional narrow system in many aspects, such as transmitted waveform design, channel modeling and estimation, construction of receiver, space and time processing and so on. In this dissertation, a global analysis of the application of UWB-R system and a deep investigation for some key problems are obtained. The main work of the dissertation can be summarized as:1. For the requirement of the coexistence with other communication systems and the FCC spectrum mask, the waveform design of transmitted signal for UWB system is investigated. Base on the approximation with B-spline being basis function, a new method of UWB pulse design is proposed and a practical realization circuit is given. A communication system based on B-spline is analyzed in detail, and its feasibility is demonstrated. Taking B-spline being the basis can approximate an ideal pulse waveform with given spectrum shape, so the problem can be reduced to a constrained optimization problem. Genetic algorithm is then employed to get a series of approximately orthogonal UWB pulses that satisfying the FCC mask.2. The large-scale and small-scale UWB channel models are introduced and discussed. Simulation about IEEE 802.15.3a channel model is performed and the method to produce discrete channel response is expounded. The path-lost model of free space and the statistic of UWB multipath fading channel are analyzed, in which the revised Saleh-Valenzuela model are stressed. Then the link budget analysis of UWB system is performed. At last, some simulation experiments are performed for IEEE 802.15.3a channel based on S-V model. And the method to obtain the realistic discrete channel response based on interpolation is given. 3. The design methods of I-UWB receives are studied and a new hybrid RAKE/MUD adaptive UWB receiver is proposed. Started with optimal and sub-optimal receiver, the general design method and some problems are discussed. The structures of different RAKE receivers are given. The performance of RAKE receiver in the case of resolvable and non-resolvable paths is analyzed respectively. The structures and realistic realization scheme of TH-UWB RAKE and DS-UWB RAKE are studied with emphasis. To improve the ability of resistance to narrowband interference and multi-access interference, the adaptive MMSE and MUD detector are combined to get a new hybrid adaptive UWB RAKE/MUD receiver. And its update equations are deduced. At last we buildup a Simulink model to validate the performance of I-UWB with some simulations.4. A method of pulse detection and estimation of TOA for UWB signal based on analytic wavelet is proposed for UWB positioning system. First the channel estimation and direct path TOA estimation based on ML and GML are introduced. Then a new approach of analytic wavelet transform using the transmitted signal as wavelet basis is proposed to analyze received signal. By a threshold operation employing the cumulant of the coefficients of wavelet transform and the subsequent reconstruction, the received signal can de-nosing and we can get the intensity and time delay of the signal component accurately that is covered by intense noise. As a nonparametric method, it doesn't need to use the prior knowledge of signals. So it can overcome the disadvantages of match filter, and it works well even in the case of the distortion of signals.5. The space-time processing principle of antenna array for UWB pulse reception is studied. Aiming at the realization problem of highly accurate variable delay circuits (VDC), a combination of digital lines and fractional sample delay compensation filter (FDCF) for beamforming in time domain is proposed. The digital line can compensate the times delay of sample interval and FDCF is used to compensate the dispersed fractional delay. The available several approaches of fractional delay filter design are examined. As a result, the Lagrange interpolation method based on maximally flat criterion and Farrow structure based on Taylor expansion are found to be most suitable for compensating the fixed and adjustable continuous delay. For Farrow structure, a simple and distinct derivation based on Taylor expansion is taken and a FDCF scheme composing of first-order differentiator is given.In the simulation experiments, two kinds of directivity pattern of UWB pulse array are studied and compared with that of sinusoidal array. The effectiveness of the scheme presented is verified by the simulation results, which show that the VDC implementation by digital lines and FDCF can remarkably improve the performance of the directivity patterns of UWB pulse array especially when the system is with low sampling rate.6. A beamforming method for UWB pulse signal based on multirate filter bank is proposed. This method avoids the delay control in time domain, and at the same time realizing the frequency-invariant uniform array response in great wide band. Some structures of multirate filter realization are discussed, which has the merits of a simple implementation. And its computational cost dose not depend on the number of subbands. Also the feather of non-continuity of UWB pulses makes a simple interpolation possible for signal processing.7. Based on a realistic signal model, the dissertation presents a new method for the spatial time processing of UWB pulse array employing Radical Basis Function Neural Network (RBFNN). By the help of neural network able to approximate nonlinear function, the RBF network can realize the nonlinear delay system in multi channel for UWB pulse array processing and thereby obtains the satisfying beam steering. This method can focus the energy of signals on a desired direction by training samples and suppress the sidelobe gain to a great extent. It does not need to deal with every channel in separate way. So it is characterized by the accuracy and robustness.