Working Out The Key Technologies Of Ultra-Wideband Wireless Communications

Ultra-Wideband (UWB) wireless communications technique has outstanding characteristics of high data rates, low power consumption, low equipment cost, low probability of detection and high positioning accuracy. It displays extensive potential applications in digital home network, wireless personal area networks (WPAN), intelligent vehicular systems, radar detection and imaging systems. Consequently, UWB is rapidly becoming one of the hot issues researched by academic community, business developer and related standardization organizations.At the present time, though some UWB wireless communication products have come into the market, there still exist many technical difficulties to be solved as to the UWB future practical applications. This dissertation focused on the key technologies for the physical layer of UWB wireless communications systems. The novel works are as follows:1．A new method based on the Chirp Signals compression is proposed for the design of the Impulse Radio (IR) UWB pulse waveform. Based on the compressibility of the chirp signals passed matched filter and the linearity of the Fourier transform, a new UWB pulse is obtained by superposition of the compressed pulses from different central frequency Chirp signals. It satisfies the outdoor FCC spectral mask and can achieve 83．33% spectrum utilization. By selecting the proper central frequency of Chirp signals, the obtained UWB pulse can suppress the coexistence interference between the UWB systems and WLAN 802．11a systems, while its spectrum utilization is 73．30%. This method can be applied to different countries' UWB frequency spectrum programming for its flexible control of pulse frequency and bandwidth.2．An improvement is made to the multi-user Prolate Spheroidal Wave Functions (PSWF) IR UWB orthogonal pulse waveforms design. By the superposition of the selected multi-frequency PSWF waveforms, the UWB pulses that can suppress the coexistence interference between the UWB systems and the narrowband systems are obtained. The orthogonality of the multi-user pulses is ensured by the Gram-Schmidt orthogonal process, while the spectrum utilization of the pulse is increased from 39% to 43．51%.3．Based on the Chirp Spread Spectrum (CSS) technique, the design schemes of CSS-BOK-UWB and CSS-π/4-DQPSK-UWB high-speed wireless communications systems are proposed for the first time. The transmitter gets its spread gain through the Ultra-Wideband Chirp signals, and the receiver achieves the MRC S-Rake through several Surface Acoustic Wave(SAW) filters. The theoretical analysis and computer simulation results demonstrate that the proposed CSS UWB wireless communication system is highly robust against multipath effects for the excellent autocorrelation and matched filtering property of Chirp signals. Moreover, it is low power, and low complexity for the using of analog passive SAW filters.4．In the conventional MB-OFDM UWB receiver, the FFT algorithm is realized by using the costly and high power consumption Digital Signal Processing (DSP) chips. In chapter 4, the lower power consumption, lower cost and lower complexity real-time analog SAW Chirp-Fourier transform devices are adopted to replace the DSP part. According to the parameters of the MB-OFDM UWB system, a MB-OFDM UWB receiver scheme based on the 100% duty cycle M-C-M SAW Chirp-Fourier transform is proposed and the step of signal transformation from input signals is also depicted. The simulation results show that the proposed receiver provides similar bit error performance compared to the fully digital receiver when running in the indoor UWB channel model suggested by the IEEE 802．15SG3a.