Design And Researches On The Interference Suppression Of The UWB System Based On Chirp Function

Ultra-wideband (UWB) has attracted more and more attention in recent years after it was opened to civilian use by FCC in 2002. The characteristics, such as low power, low cost, interference and multipath immunity, etc, lead UWB technology an excellent candidate for indoor high data rate wireless communications. Historically, NBI mitigation techniques has been a hot research point in UWB technology field, so we mainly focus on the features of UWB system, Chirp function and Orthogonal complementary codes (OCC) in this paper. We design Chirp cognitive radio UWB system based on OCC in this thesis, so as to improve the performance of multi-user UWB system in narrowband environment.Most of the theoretical analysis and simulation results centered on direct sequence spread spectrum UWB system. The basic principles of UWB systems are discussed as follows:firstly, we expatiate on the definition, features and application values of UWB theology. At the same time, the impacts of different pulse factors on the time frequency character of Gaussian pulses are also analyzed. Then, signal modulation and multi-access methods are carefully studied, and BER of multi-user DS-UWB system is also deduced carefully. Finally, we briefly describe the modeling of ultra-wideband indoor wireless propagation channels and standard channel model provided by IEEE.The huge bandwidth of UWB signals forces UWB to coexist with some existed narrowband systems. We go into traditional Chirp waveforms and different NBI models depending on its types. And then, in order to alleviate narrowband interference to UWB systems, design two novel non-linear Chirp functions, arc trigonometric function and arc hyperbolic function, to construct ultra wideband pulses and alleviate narrowband interference (NBI). Simulation results demonstrate that UWB systems composed of the new pulses have significant performance in suppressing the NBI. The adaptive Chirp waveforms generator has to first get the spectra parameters of NBI through spectrum sensing technologies in cognitive radio, so as to get their expression in time domain. Both of them require only time domain processing for the inherent characteristics of these Chirp waveforms.Besides the NBIs, multipath interference (MI) and multiple-access interference (MAI) also limits the capacity and the spectrum efficiency of the system. We first define the complementary code, complete complementary code and orthogonal complementary code according to the difference on the correlation function of the sequence. And then, the specific implementation scheme of spreading and dispreading in serial OCC multi-user system are investigated in detail. In traditional CDMA systems, the excellent multipath and MAI suppression performance of the proposed OCC scheme is confirmed. At last, we further study the cognitive Chirp UWB system based on orthogonal complementary code and attempt to suppress NBIs and MAI simultaneously. Simulation results are given to verify that under ideal condition, MAI and NBIs will not be a problem if we use an orthogonal complementary code set in the proposed cognitive Chirp UWB system. In the final chapter, the research work in this thesis which has been accomplished is summarized and the future work is prospected.