Design And Research On Orthogonal Complementary Code Based UWB Communication System

Ultra Wide Band (UWB) technology which is the core technology of short distance and high speed wireless communications has been considered to be one of the most effective methods to realize high speed and reliable data transmission in wireless fading environment. The bandwidth allocated for UWB is7.5GHz, from3.1GHz to10.6GHz. And its power spectrum density is lower than-41.3dBm/MHz (1mW/MHz). The UWB technology has many characteristics, such as good resistance to severe multipath interference, high data rate, low power spectrum density, good secrecy and easy to implement, etc. Based on the merits of ultra-wideband technology, it gradually becomes the main possible candidates for the physical layer of wireless local area network (WLAN) and wireless personal area network (WPAN). Therefore, the research and improvement for UWB wireless communication system are of great significance to the development of wireless communication technology.The complex multipath interference (MI) and multiple access interference (MAI) inevitably exit in UWB communication system because of the typical indoor environment. Orthogonal complementary code (OCC) whose partial autocorrelation function (PAF) is zero for all shifts except for zero shift and whose partial cross-correlation function (PCF) for any pair is zero for all shifts is proposed in recent years. The system performance can be improved significantly if OCC is used as the spreading code of UWB system. The OCC based UWB system with offset stacking modulation can implement variable transmission rate. UWB system occupies large bandwidth to improve the transmission and inevitably interferences with the narrowband communication systems in the sharing spectrum. Nonlinear Chirp pulses can effectively suppress narrowband interference which exits in UWB system. We design nonlinear Chirp pulse based OCC UWB system so as to improve the performance of multi-user UWB system in multipath and narrowband environment.The basic theory of UWB technology is introduced in detail. The basic principles of UWB system is discussed as follows:firstly, we expatiate on the definition, advantages, key technologies and application prospect of UWB theology. At the same time, signal modulation and multi-access methods are carefully studied. Then, the time-frequency characteristics of UWB typical pulses are analyzed. Finally, we briefly describe the modeling of ultra-wideband IEEE802.15.3a wireless propagation channels and the fundamental of RAKE receiver.Then the correlation properties of spreading sequences and the definition of OCC are introduced. We investigate the performance of serial OCC based UWB system which adds zeros to distinguish different element codes. With the application of OCC in UWB system, we can offer MAI free operation in both synchronous and asynchronous transmissions over MAI-AWGN channel. Theoretical analysis illustrates that MI as well as MAI can be also mitigated over lognormal multipath fading channels in OCC based UWB system. Our simulation also shows the superiority of the OCC based UWB to unitary code based system. We also go into traditional Chirp waveforms and different narrowband interference (NBI) models. Simulation shows the improvement of nonlinear Chirp pulses based OCC UWB system in the suppression of MAI, MI and NBI.We also investigate the MAI and MI suppression principle and the RAKE receiver of OCC based UWB system with OS spreading modulation. Theoretical analysis and simulation results illustrate that the proposed UWB system can offer the elimination of MAI in both synchronous and asynchronous transmissions over AWGN channel. The shift intervals affect the performance of OS-UWB system in the multipath channel. We can find the superiority of the OCC based OS-UWB system to the serial OCC based UWB system by comparing to the simulation results. At last, the research work in this thesis which has been accomplished is summarized and the future work is prospected.