Research On Electromagnetic Interference In Ultra Wideband Cognitive Radio System

Ultra wideband cognitive radio (UWB-CR) has become a current research focus as a new spectrum sharing wireless communication technology in recent years. Ultra wideband (UWB) wireless communication system coexists with the existing narrowband wireless communication systems in a spectrum underlay approach, on the other hand, cognitive radio (CR) need sense the spectrum holes in radio enverinment, and use its in an opportunistic manner, wherefore the electromagnetic interference causing by these two ways is evidently a key technique for researching into UWB-CR. This thesis is supported by the National Natural Science Foundation of China etc, and is quite significant to theoretic research and practical application.Based on the deep research on the principles of UWB and CR, this thesis mainly focuses on the electromagnetic interference of UWB-CR, and the following innovative results are achieved:For UWB coexisting with the exsiting narrowband communication systems in the spectrum underlay approach, an electromagnetic interference analysis method based on the physical layer model is proposed, furthermore, the effect of impulse-radio UWB (IR-UWB) and multiband-orthogonal frequency division multiplexing UWB (MB-OFDM-UWB) on some narrowband communication systems are analyzed. Depended on the requirements of bit error rate (BER) and the sensitivity of the receiver for narrowband communication systems, the theoretic reference values of the UWB emission limit are obtained by the simulation on the operating bands of narrowband communication systems. Comparied with the link budget interference anlysis method based on an interference to noise ratio (I/N) criteria, this method much more effectively reflects the actual circs of electromagnetic interference between the UWB systems and the narrowband communication systems, so the electromagnetic compatibility anlysis results are more persuasive.Aiming at the UWB-CR emission limit and the mathematical model of the interference temperature, a self-regulating transmission scheme for UWB-CR is proposed. Based on the relationship between the interference temperature and the brightness of the radio environment, and the interference temperature constraint, the dynamic power limit of UWB-CR can be obtained, i.e. the UWB-CR emission mask is set up dynamically. Finally, based on an indoor wireless personal area network composed by UWB-CR, the two-dimensional and three-dimensional working scenarios are given respectively, and are simulated and analyzed.For the narrowband interference suppression of UWB-CR based on IR-UWB, depended on the transform domain approach, a novel pulse suppressing the narrowband interference for UWB-CR is proposed. Firstly, to modify transform domain communication system(TDCS), then, a mask vector is generated based on the UWB mask, and replaces the scale factor of the modified TDCS, finally, utilizing multiple modified TDCS to sense the electromagnetic environment, this pulse using the interference free spectrum of the current electromagnetic environment is generated. This pulse can avoid interference to/from the existing narrowband wireless systems, and can be applied for an arbitrary UWB mask.Furthermore, in order to increase the index for the spectrum of the UWB-CR pulse matching the UWB mask, and eliminate the weakness of the mask vector, the another novel UWB-CR pulse using the compressed chirp waveforms and modified TDCS is proposed. Utilizing multiple modified TDCS to generate an adaptive notch filter, using the optimal combination of the compressed chirp waveforms to acquire a signal satisfied the UWB mask, this UWB-CR pulse can be obtained after this signal passes the adaptive notch filter.Finally, the content of the whole dissertation is summarized and some valuable research directions of UWB-CR are also discussed.