Research On Time-Hopping Sequences In UWB Communication System

Ultra-Wideband (UWB) pulse communication is a very different communication technique from other wireless communication. It has characteristics of low power spectral densities, high system capacity, exceptional multiple-path immunity, simple structure, high process gain and good confidentiality. The UWB pulse communication is new exploration of radio spectrum and it is the strong support for wireless communication. So far it has been widely used for wireless multimedia family area network, personal area network, radar positioning, intelligent transportation systems, and military communications, medical detector etc. fields. Therefore, it is necessary to study and grasp the new technology.At present, the realization methods of UWB are three: time-hopping UWB, direction sequence UWB and multiple-band OFDM UWB. The paper introduces the most frequently-used and the most traditional method: transmitting the very short pulse in time domain, the transmission technology is also called"pulse radio". For forming the spectrum, we not only modulate the pulse, but also encode the data symbols by utilizing pseudo-random code. This is the time-hopping ultra wide-band communication system. A lot of analysis and study about time-hopping code are carried out in the paper.The major contribution of this paper is summarized as follows:1. In the paper, the principle of wireless communication technology and the development status quo of ultra wide-band system are analyzed systematically. The modulation methods and multi-Access of ultra wide-band system are studied and the priority research is the system models using pulse position modulation and pulse amplitude modulation. The channel models and receiver of ultra wide-band are analyzed, and the importance and necessity of time-hopping code are elaborated.2. The paper discussed the generating mechanism of balance Gold code and shortened balance Gold code and studied the auto-correlation and cross-correlation of the two codes. And the paper compared the correlation performance between the aforementioned two codes with m sequence. Using balance Gold code and shortened balance Gold code for the time-hopping technology of UWB are presented in the paper. And the technology solves the commands of numbers and balance for multi-access codes. At last, the paper simulates the bit error ratio of multi-path and mutli-access in two channels. The simulation results specify that the present time-hopping codes have high error probability performance over traditional pseudo-random code.3. On the basis of the study of the pseudo-chaotic sequence generated through Tent and Logistic mapping in the other literatures, the paper discussed the mathematics mechanism of Hybrid mapping and studied the auto-correlation and cross-correlation of the pseudo-chaotic sequence generated by Tent mapping. And the paper compared the correlation performance between the aforementioned codes with the pseudo-chaotic sequence generated by Logistic mapping. The criterion of selective preference of Hybrid mapping is analyzed in the paper. Utilizing the pseudo-chaotic (PC) code which is generated by Hybrid mapping in the time-hopping technology of UWB is presented in the paper. The key problems of codes'numbers and system's confidentiality and security are solved. Hybrid mapping not only inherits the characteristics of easy generation of Logistic mapping and Tent mapping, but also the output sequence is more random and unpredictable. And the number of the sequence is very much and this increases the system's confidentiality and the pseudo-chaotic system's security. Simulation results also indicate all features of the pseudo-chaotic sequence need the requirements of pseudo-random sequence and have high confidentiality and security. It is a promising pseudo-random time-hopping sequence. Simulation results indicate the pseudo-chaotic sequence has the higher performance than traditional pseudo-random code in time-hopping ultra wide band system.4. On the basis of the elaboration of the RS codes'fundamental theory, the paper studied the auto-correlation and cross-correlation of RS codes and discussed its mechanism of using for frequency-hopping code. The transposing relationship from frequency-hopping to time-hopping is analyzed in the paper. Introducing time reverse technology, and using the RS code in the time-hopping technology of UWB is presented in the paper. The problem which RS can be used for time-hopping code is solved. Simulation results verify that using Reed-Solomon code for time-hopping code in UWB system is a good choice. Simulation results verify the correctness of the theory.