Two-dimensional Signal Synchronization And Detection Technology

Multicarrier wireless communications have been widely investigated in the past decades. Recently, two-dimensional spread spectrum (2D-SS) system has drawn a lot of attention because of its full utilization of spreading characteristics in the frequency domain and time domain. Compared with multicarrier code division multiplex access (MC-CDMA), 2D-SS system can effectively mitigate multiple access interference (MAI) due to spreading in the time domain. While compared with direct sequence CDMA (DS-CDMA), 2D-SS system can significantly resist the fading due to frequency diversity resulting from spreading in the frequency domain. However, key issues of the 2D-SS system are not studied widely at present. Further research work should be done in this area.As for a communication system in practical, signal synchronization and detection are two critical techniques. Synchronization should be firstly done at the receiver, while the algorithms of signal detection deliver a direct effect on the system performance. As the differential detection enables the receiver to detect the data symbols without the knowledge of reference phase, it can be attractively applied to time-frequency selective fading environments. This thesis researched the time synchronization method for 2D-SS system, and deeply discussed the bit error rate (BER) performance of multicarrier domain spread spectrum chip-level differential detection (MC-SS-CLDD) in the presence of multi-user interference.We firstly introduced the research background and the characteristics of multicarrier wireless communications, and summarized the questions needed to be further researched.In the second part of this thesis, a method of time synchronization of 2D-SS system in multipath fading channels has been proposed. The detection probability and false-alarm probability were analyzed and also the numerical results on condition of different normalized thresholds were presented. Results showed that the serial acquisition needs no cyclic prefix and the spectral efficiency increases. Meanwhile, the synchronization algorithm in the DS-SS system can be used in 2D-SS system, and good synchronization performance can be obtained, with its algorithm simplified.The third part analyzed the BER performance of MC-SS-CLDD in the presence of multi-user interference in time-varying multipath fading channels. The theoretical results are evaluated by simulation. If the coherent bandwidth of channel doesn't exceed the occupied bandwidth of two chips, with the increase of delay spread of the channel, MC-SS-CLDD exhibits a better performance to make the system resistant to frequency-selective fading. Because of the simplicity of differential detection system, we could consider to apply it to the selective fading channels instead of coherent detection.In a word, synchronization issues of the 2DSS system are not studied in the open...