The Chirp Ultra-broadband Communications, Modulation And Time Synchronization Technology Research

Recently, ultra wideband (UWB) radio which can achieve high speed communications is widely researched in wireless communication field. Furthermore, the UWB communication systems based on chirp spread spectrum technology have many merits, including low probability of intercept, insensitivity to frequency offset, good anti-multipath performance and low power. So Chirp UWB will have a broad application prospect. In 2007, chirp spread spectrum technology approved into IEEE 802.15.4a Physical Layer Standard proves its development potential.We deeply investigate Chirp UWB communication technology, especially modulation schemes and timing synchronization schemes. The research includes the following topics:We firstly survey the concept of UWB, the history, the application and the researeh status of Chirp UWB. Some concentrated problems in the research of Chirp UWB are listed. And our main research contents are pointed out. Then we introduce the chirp spread spectrum technology which is the core of Chirp UWB and the UWB channel model proposed by IEEE 802.15.4a Task Group.We study the modulation schemes of Chirp UWB, including binary orthogonal keying (BOK) and direct modulation (DM). The power spectrum density of these two schemes are derived and verified, and their bit error rates are also studyed. The correlation coefficients of BOK are analyzed. Compared to DM, the demodulation of BOK doesn't need the channel estimation, but its rate of information transmission is low. So we propose a new modulation scheme and its differential coding mode, Quaternary Bi-Orthogonal Keying (QBOK) and Differential Quaternary Bi-Orthogonal Keying (DQBOK). The power spectrum density and symbol error rate of QBOK is analyzed. And the bit error rate of DQBOK in the UWB channel is investigated by simulations.We analyzed the impact of synchronization offset on system performance. And then the common timing synchronization scheme is introduced, which is approved to be the approximate maximum likelihood estimation of channel delay in the condition of low signal to noise radio (SNR). Because the common scheme is very sensitive to noise, an improved timing synchronization scheme based on interference mitigation mechanism is present. The simulations show that the improved scheme improves the system performance. At last, for estimating channel in higher-order modulation, a joint channel and timing estimation scheme based on the transmitted reference technology is proposed. The performance of joint estimation scheme is investigated by simulations.We design the digital circuit architectures for Chirp UWB systems using three different modulation schemes. Due to big resources consumption of the digital matched filter, one-bit quantification of its coefficients is chose to reduce its resources consumption. We test the hardware implementations of these systems on the circuit board. And the test results agree with theoretical analysis.