Simulation Research On Modulation And Spreading Technologies Of Wireless Communication Systems

Ultra Wideband (UWB) wireless communication technology has envolved into an attractive high-speed, short-range wireless communication technique because of its advantages such as low probability of detection, high processing gain, good multi-path resolvable ability, high transmission data rate, large spatial capacity, great penetrability and so on. Meanwhile, UWB technique exhibits in both military and civil areas including radar system, accurate locating and tracking system, wireless Ethernet network interface, intelligent wireless network, outdoor point to point network and sensor, orientation and identification network and so on. As one of the key technologies to implement the multiple user access, time-hopping technique plays an important role in UWB system. To ensure the reliable communications in ultra wideband impulse radio and suppress the multiple user interference, time-hopping sequences need to have good correlation properties.Based on the introduction to several traditional time-hopping sequences and their correlation properties, this thesis analyzes the contruction and correlation properties of the none or low hit zone (NHZ/FHZ) time-hopping sequences, the research of which has become very active recently. Further, on the basis of the UWB channel simulated in accordance with the UWB multipath channel model recommended by IEEE 802.15.3a workgroup, different time-hopping sequences are utilized to implement the multiple user access and the maximum radio combining technique are used to process the diversity signals collected by different fingers of RAKE receiver. The simulation results are presented, based on which, the effects on the system error performance exerted by the time-hopping sequences are analyzed to demonstrate the important role in multiple access of UWB system played by time-hopping sequences with good correlation properties.Emerged as another widely used technology in both military and civil applications, modulation classification develops rapidly in recent years. The objective of modulation classification is to offer the demodulation reference to receiver in the absence of any knowledge of given signal. Based on the comprehensive understanding and simulation implementation of physical layer processes involving data modulation and spreading in TD-SCDMA system, the method of modulation classification in TD-SCDMA system using fuzzy means clustering algorithm is studied in the thesis. The characters of on call signal in TD-SCDMA Signal Analyzer software are investigated and the satisfactory classification results are achieved with the flexible use of various clustering algorithms in this thesis.The foundational knowledge and process of modulation and spreading of physical layer in TD-SCDMA system are introduced comprehensively in this thesis, based on which, the implementation schemes of TD-SCDMA Signal Analyzer software are presented. Following the brief introduction to the demodulation flow of TD-SCDMA Signal Analyzer software, the bit error rate of TD-SCDMA system in the context of AWGN channel is simulated. For QPSK, 8PSK and 16QAM modulation schemes, the thesis implements the symbol partition through amplitude clustering, subtractive clustering and fuzzy C-means clustering after the signal pre-process and eventually determines the modulation scheme through cluster validity theorem. Simulation results presented indicate that the modulation classification algorithm adopted in the thesis can satisfy the requirement of modulation auto detection in TD-SCDMA Signal Analyzer.