The Research On Spectrum Suppression In Cognitive Ultra Wideband Systems

With the rapid development of wireless communication technologies and the growing demands of broadband communication, the shortage of spectrum is becoming a significant problem. On the one hand, the confliction between spectrum supply and demand is increasing. On the other hand, according to the survey results of related organizations the utilization of licensed of spectrums is very low under the present static spectrum management mode. Under the above background, the Cognitive Ultra Wideband technology is proposed, which can take advantages of Ultra Wideband such as high data rate, high security, low power consumption, low costs and intelligent spectrum management of Cognitive Radio. The technology that solves the difficulties of Cognitive Radio and Ultra Wideband can provides a reliable high rate communication for future wireless communication and improves spectral efficiency.UWB occupy an extremely large bandwidth spanning from 3.1 to 10.6 GHz, portions of the UWB spectrum are shared with existing licensed narrowband systems. Consequently, UWB system will have to dynamically detect the presence of narrowband radio transmissions and reduce the emission power to avoid interference introduced to the existing system. Clearly, one can exploit the flexibility of OFDM by simply turning off those subcarriers that fall over the transmission band of the victim radio system, which can reduce the emission power to avoid to interference the narrowband system.An extension of sub-carrier grouping coded modulation is proposed by introducing Polynomial Cancellation Coding (PCC) to Ultra Wideband cognitive radio system. In PCC-OFDM system, independent dates to be transmitted are mapped onto a group of subcarriers instead of individual subcarrier. In the general case for groups of m subcarriers the relative weightings are given by the coefficients of the polynomial, (1-x)m-1.Simulation results shows that powe spectrum of an OFDM signal flatten out quickly by applying PCC technology Consequently, the notch achieved by simply turning off the subcarriers is deep enough to avoid interference the victim radio system. Compared with ordinar OFDM, PCC-OFDM has largely reduced sensitivity to frequency offset and Doppler spread, reduced intersymbol interference and elimination of a cycli(?) prefix compensating some of spectral efficiencyTo solve the problem of large OOB leakage, high PAPR, low spectra efficiency in OFDM UWB system, a scheme for cognitive UWB system base(?) on Filtered Multitone Modulation (FMT) is proposed. In FMT system, the spectrum of subcarrier is strictly restrained by using filters, the main lobe o subcarriers is not crossed and the side lobe can be reduced by filtering. Thi: method can simply turning off those subcarriers that fall over the transmissioi band of the victim radio system to avoid to interference the narrowband system Simulation results demonstrate that FMT system has much more advantage: than MB-OFDM system in spectrum control and spectral efficiency.This article divides into five chapters:The first chapter introduces the basie principle and the present development situation of cognitive ultra-widebam system. The second chapter first introduces OFDM technology and the CR-UWB system based on OFDM technology, and then introduces the presen methods about spectrum suppression. The third chapter introduces CR-UWE system based on Polynomial Cancellation Coding. The forth chapter introduces CR-UWB system based on Filtered Multitone Modulation technology. At last the whole thesis is summarized and the future researches are outlined.