| With the development of wireless communication, the anti-jamming performance of communication system has been increasingly attracting people’s attention, thus the spread spectrum technology was born and is widely used now. Synchronization of the signal in a spread spectrum communication system is a key problem in affecting the performance. Furthermore, the burst style of the communication in the WLAN makes the synchronization of spread spectrum network in the burst communication the focus of the research. Thus, we studied this type of synchronization problem in the paper.Firstly, we introduced the background of the two kinds of spread spectrum technologiesand the characteristics of burst communication. Then, we described the fundamentaprinciple of the two spread spectrum technologies and made a detailed presentation of thesynchronization methods of the spread spectrum PN code in the direct sequence spreadspectrum system. Analyzed the shortcoming when waiting synchronization method iused in military communication that the FH system is easy to be interfered accurately bythe enemy, we proposed a new synchronization scheme in network communicationnamely the discrete frequency synchronization method. Unlike the traditional waitingsynchronization scheme waiting at a single frequency, the new method estimates thestarting time of every frequency in the frequency hopping pictures respectively by thenetwork knowledge, which makes the dehopping discretely. If one frequency is nodetected, the receiver can start to detect the next frequency according to the expectedinformation. The whole synchronization in this new scheme will not be affected.To simulate the synchronization methods, we used MATLAB/Simulink to build three systems, namely the baseband direct sequence spread spectrum system, the expected frame detection system based on direct sequence spread spectrum and the frequency hopping communication system. We used a method based on the correlation of long sequences to realize the synchronization of the PN code, and the discrete frequency synchronization scheme to realize the synchronization of FH patterns. The first two systems were to research the anti-noise performance of the spread spectrum PN code synchronization method, and the anti-interference performance of this synchronization method under conditions that certain network knowledge was known respectively. The last FH system was to study the anti-noise, anti-single-frequency-interference, and antispecific-frequency-band-interference performance of the discrete frequency synchronization scheme.Finally, we gave the simulation results as follows. Using this spread spectrum PN code synchronization method, the accuracy rate of synchronization improves as the SNR increases, and at near 0d B, the accurate rate reaches to 90%. With the SIR increases, the probability of accurate detection namely the accurate synchronization probability rises. When the expected frame format changes, the corresponding synchronization performance changes. The anti-noise performance of the frequency hopping system is the same as that of the general non-spread-spectrum communication system. When taking discrete frequency synchronization scheme, the anti-single-frequency-interference performance of the FH system is stronger than taking the waiting synchronization method. For the specific band interference, when the SIR increases, the BER of the system reduces. The different interference factors correspond different BER performance curves, and for the FH system using new synchronization scheme, at proximately 13 d B, the BER is lower than 1e-3. |
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