SQRT Chirp Function Waveform Based UWB System Design With Multiple Interferences Suppression

For its inherent many characteristics, Ultra wideband (UWB) technology has been considered as one of the most effective methods to realize reliable and high-speed data transmission in indoor short range wireless communications after its proposition, which inspires more and more attention of the academic experts and scholars. UWB technology has very broad application prospects, such as radar, accurate positioning, family multimedia network, etc. Therefore, the research and application of UWB technology is meaningful and important, especially for 5G indoor wireless communications.With the occupied spectrum band from 3.1 GHz to 10.6GHz, the huge bandwidth of UWB signals makes the UWB system inevitably be affected by the existed narrowband systems within the shared spectrum. In general, the interference caused by the narrowband system can not be ignored since the power spectral density (PSD) of narrowband signals is much larger than that of UWB signals. But for UWB system, it has very low PSD and the influence to the narrowband signals system caused by UWB systems can be regarded as background noise. Therefore, how to efficiently suppress the influence of the narrowband systems to UWB system is our main consideration in this thesis. At the same time, the actually existed multipath interference (MPI) and multi-user interference (MUI) in the UWB dense multipath environment should be considered in order to make UWB system more suitable to the practical wireless communication environment. The first work of this thesis is to design the UWB waveform based on sqrt Chirp function that can suppress narrowband interference (NBI) effectively; Then combine it with offset stacking-orthogonal complementary code (OS-OCC) that has good ability in the suppression of MPI and MUI to resist the typical NBI, MPI, and MUI in UWB communication; At last, we use the multiband scheme for the proposed OS-OCC UWB system to improve the spectrum utilization efficiency and data transmission rate. For the typical interference problems to be solved, the main work of this thesis can be divided into three parts as follows:Firstly, it proposes a kind of modified nonlinear sqrt Chirp waveforms that can effectively suppress NBI based on the good time-frequency mapping relation of Chirp functions. The influence of the NBI can be reduced by setting the Chirp rate of the sqrt Chirp function achieving infinity at NBI band. So, the Chirp function waveform quickly passes through the narrowband spectra. In order to highlight the NBI suppression ability of the nonlinear sqrt Chirp function waveform, we also compare it with the typical inverse trigonometric function waveform. Furthermore, the design of the nonlinear sqrt Chirp waveform with the ability of multiple NBIs suppression is provided, and the design method can be obtained through time domain processing, which is flexible and simple. Simulation results show that the nonlinear sqrt Chirp waveform can suppress NBI more efficiently.Secondly, to further overcome the MUI and MPI in the practical UWB environment, OCC with ideal autocorrelation and cross-correlation properties has been employed as the spreading code. To improve the data transmission rate, OS modulation with variable transmission rate design is considered. Combining the nonlinear sqrt Chirp waveform with the OS-OCC, this thesis presents a nonlinear sqrt Chirp waveform based OS-OCC UWB system to suppress the typical interferences in UWB communications and achieve high and flexible data transmission rate. Theoretical analysis and simulation results show that the nonlinear sqrt Chirp waveform based OS-OCC UWB system achieves lower bit error rate and better performance in the suppression of NBI, MUI, and MPI under multi-user and multipath channel environment.Finally, this thesis designs a nonlinear sqrt Chirp function based multiband OS-OCC UWB system to improve the spectrum utilization efficiency and improve the transmission rate effectively. The presented multiband OS-OCC UWB scheme divides the system bandwidth into sub-bands with NBI contained and sub-bands with NBI excluded. The sub-bands that contain NBI adopt nonlinear sqrt Chirp function, while the other sub-bands adopt traditional linear Chirp function. The scheme can achieve data transmission through multiband at the same time, and improve the spectrum utilization and the data transmission rate, meanwhile achieve the suppression of multiple NBIs. Simulation results show that the designed multiband OS-OCC UWB system has good performance in the suppression of multiple NBIs, MUI and MPI, and improves the spectrum utilization and data transmission rate.