On Research Of Transmitted Reference UWB Communication Systems With Time-hopping Multiple Access

Recently, ultra-wideband technology has emerged as a competitive solution for short range, low power consumption and high data rate wireless communication. Transmitted reference(TR) systems have become attractive in non-coherent ultra-wideband(UWB) communications because of their simple structures, no need for channel estimation, relaxed requirement for synchronization, and robustness against the pulse distortion due to channel propagation.In this thesis, we investigate TR-UWB systems and our research is focuses on multi-user issue. The main contributions of this dissertation are summarized as follows. Time-hopping(TH) is introduced to the TR-UWB system in which each frame within the transmitted signal for one symbol is divided into several non-overlapping time slots(or chips). Different users transmit dual-pulse in different time slots. Accordingly, to achieve multiple-access communications, a unique TH sequence is used for each user to determine which time slot within one frame is occupied by the transmitted dual-pulse. In order to guarantee reliable communications and mitigate multi-access interference, it is necessary to employ high-performance TH sequences. Therefore, m sequences, Gold sequences and permutation-sequences are respectively used in this paper as TH sequences for TH-TR-UWB systems. Moreover, the bit error rate(BER) performance is compared for the three investigated TH sequences over realistic UWB channel models. The transmitted pulses were changed in TR-UWB systems. On the basis of using TH to achieve multiple-access communications in this thesis, orthogonal Hermite pulse was applied to systems. Combining pulse shape modulation with TH in the transmitter can reduce multi-user interference and inter-symbol interference. In this system,different users use orthogonal Hermite pulses with different order. Even if the performance of TH sequence is not ideal and transmit at the same time, the orthogonality of the pulse sequence will not cause collision between the dual-pulse. Finally, the BER performance is analyzed.Theoretical analysis and computer simulation results indicate that the BER performance of the TH sequence based on permutation sequence is better than the other two sequences. And the BER performance of TH sequence based on Gold sequence is better than that of m sequence for its plentiful sequence number and excellent cross-correlation property. For the same TH sequence, the BER performance gets worse gradually with the increase of number of users. Furthermore, the BER performance can be improved by increasing the number of elements of TH sequences with the penalty in terms of effective transmission rate. The performance of system with orthogonal Hermite pulse is better than that of the system using traditional pulse. The orthogonality of the pulse can greatly eliminate the multi-user interference.