Research On CHIRP Spread Spectrum Techniques In Low-Rate Wireless Personal Area Network

The tremendous advancement in wireless communication and networking technologies has raised a significant number of major qualitative breakthroughs in improving the speed and scale of information dissemination, since the beginning of the 21st century. The fundamental goal of a communication system is to convey information smoothly without the constraints in time and space. Low-rate wireless personal area network(LR-WPAN) is an essential component of the future multi-domain heterogeneous wireless network. It can not only resolve the last mile access problem, but also can provide wireless connections to various services in personal operating space, which supports on-demand information transmission, coordination and processing. LR-WPAN requires the signaling techniques to adapt to the complicated indoor wireless environment, with robust performance in frequency selective fading channels, low power consumption, and low complexity. Chirp spread spectrum technique is equipped with good anti-interference ability and high bandwidth efficiency. Furthermore, it utilizes chirp signal matched filter and pulse compression features in spread spectrum communications, instead of using pseudo-random code as spreading code, without the requiremnent of frequency hopping pattern. Therefore, chirp spread spectrum technique is power efficient with low complexity, which makes it a very competitive candidate in LR-WPAN. Chirp spread spectrum in LR-WPAN has attraced a significant number of research attentions in recent years.As the background stands, this dissertation conducts an in-depth study on chirp spread spectrum technique for LR-WPAN communication:First, the chirp spread spectrum transmission model in LR-WPAN is investigated. According to the characteristics and transmission requirements of LR-WPAN, this work analyzes the properties of chirp signal in matched filtering and pulse compression characteristics. The dissertation also compares the performance of the BOK modulation shceme and the mixed modulation scheme in LR-WPAN, as well as the effects of chirp signal overlapping in time domain. Analysis indicates that although there is much to be desired, BOK modulation scheme is still the best choice for chirp spread spectrum in view of complexity, capacaity and system performance.Second, the M-ary chirp modulation scheme is studied based on the optimal chirp signal set. BOK modulation scheme fails to provide high link capacity for LR-WPAN, A new modulation scheme is proposed to improve the link capacity, where data is encoded by M-ray and transmitted by several chirp signals respectively. This work optimizes the design of chirp signal selection in order to improve the system BER performance degradation problem resulting from the cross correlation of multi-signal. The optimal signal set, constructed with liner chirp signal and combined chirp signal, can provide higher link capacity for LR-WPAN without significant increase in system complexity.Third, the chirp interference suppression method based on matched signal transform is sutided. Due to the coexistence of various wireless transmission system in 2.4G ISM band, interference is inevitable. Chirp interference has the most severe impact on chirp spread spectrum system, with no efficient and effective solution yet. This dissertation proposes a chirp inteference suppression method based on matched signal transfom. This method not only considers general case where the chirp rate of chirp interference signal is different from the useful one, but also provides solution for the special case where the interference and the useful signals share the same chirp rate. Theory analysis and simulation verification both prove that, by using this method, the system is not interfered by chirp interference.Last, this work studies the muti-access interference suppression methods for chirp spread system. A bivariate chirp method is proposed, which makes use of both chirp rate and intinal phase to construct the multi-access signal base. When the chirp rate differences are small, this method ensures the orthogonality of multi-user signals by distinguishing different initinal phases, so that more chirp signals can be contained in limited signal bandwidth. Meanwhile, a novel method is also proposed with non-linear chirp signal to enhance the multiple access capacity of a mixed chirp modulation communication system. This method makes use of the characteristics of sin chirp signal to suppress the multi-access interference. Both methods are easy to realize and have good performance to suppress multi-access interference. Although based on different modulation schemes, both methods have good performance for multi-access interference suppression and are suitable for expanding for mulit-user systems.