Researches On Spectrum Spreading Code Design For Spectrum Spreading Communication

Spread Spectrum Communication (SSC) technology has the characteristic of high secrecy, robustness to noise and multipath influence, and it has been widly applied and developed in military and civilian communications, espcially in recent years. Its application in code division multiple addresses (CDMA) has attracted more and more interests. In direct sequence CDMA (DS-CDMA) system, the correlation characteristic of the spread spectrum codes and the number of the set of the spread codes affect the performance of the spread spectrum communication system and the volume of system greatly. Much work about the analysis of the spread spectrum sequence has been done and some typical spread spectrum sequences have been designed and studied, such as m sequence, Gold sequence and so on.In this thesis, based on the development of the spread spectrum technology and the newly proposed spread spectrum codes, complementary spread codes and chaotic spread codes, are investgated and the correlated characteristics of these two spread spectrum codes and their applications in the spread spectrum system are given. Moreover, the design criterion of those new spread spectrum sequence codes is discussed. For complementary spread codes, firstly we analyze the related design scheme and the evaluation of some typical paremeters, such as autocorrelation, crosscorrelation function and the balance characteristic. Then, combining with chaos map, we investgate the spread spectrum communication system based on chaotic spread sequences. Correlated choatic sequences with genetic algorithm are studied and its optimal design criterion is given. Following these analyses, the simulation results of the two new spread spectrum sequences are given in different channel environments. Finally, the conclusions are given.The contents of the paper are as follows. In chapter 1, the background, the motivation, the siginificance and also the organization of the work is given.In chapter 2, the principle of SSC and the DS-SSC system are studied. The properties and the performance of the spread spectrum codes are also provided, especially for M sequence and Gold sequence. In chapter 3 the definition and design of the complementary spectrum spread sequences are discussed. The correlation function and balance property of the complementary code sequences are also analyzed. In chapter 4, the author design a chaotic spectrum spread sequence based on chaotic mapping and the optimization schem based on genetic algorithm (GA) is also proposed. Under the condictions of synchronization and asynchronization Gaussian channel, the performance of m sequence, Gold sequence, complementary spread sequence and also the GA based chaotic spread sequence are provided. In chapter 5, the conclusions and future work are given.