Research On Key Techniques In Wireless Communication System Based On Fractional Fourier Transform

Wireless communication network brings convenient data transmission service topeople. However, the open channel property results in severe secure risks. Wirelesscommunications are vulnerable to eavesdropping, tampering and impersonation. Whilebroadband wireless communications provide higher rate, more convenience andflexibility, the requirements of transmission security become more and more stringent.With the rapid development of large scale intergrated circuit technology and thecomputational capabilities of chips, more complicated real-time computation can beimplemented in physical circuits. So, physical security techniques attract widespreadattention in recent years. One kind of the methods is using complex signal mappingoperation to increase the difficulty of the communication parameters estimation fornon-cooperators. Thus, the intercept and decipher of the communication signalsbecome very difficult.In this thesis, a multi-carrier communication system based on fractional Fouriertransform(FRFT) is studied. The synchronization and channel estimation algorithmsare discussed, and the physical security properties of this system are analyzed. FRFT isa general form of conventional Fourier transform (FT). The multicarrier modulatedoutput signals are generated by FRFT,as in FT-based OFDM system. The essentialdifference between FRFT-OFDM and FT-OFDM is FRFT-OFDM has more valuabletransform parameters. Without the accurate transform parameters, the demodulationperformance will degrade notably. Based on thess property, these following researchworks are completed.1. Based on the intensive study of the fractional Fourier transform theoryand itsdiscrete algorithm, a discrete fractional Fourier transform (DFRFT) algorithm withreversibility and fast calculation method is selected. A multi-carrier modulation systemmodel based on the selected DFRFT is given.2. The synchronization and channel estimation algorithms for given DFRFTOFDM are discussed, and the performance of these alogithms in multipath channelenvironment are analyzed and compared with the traditional FT-based OFDM system. Simulation results show that the FRFT-based OFDM system has stronger fadingresistibility than FT-based one.3. To selected DFRFT algorithm, the affections of transform parameter errors onthe receiving performance are discussed. The simulation results indicate that transformparameter errors have greatly influence on the demodulation performance. To achievean acceptable receiving performance, the transform parameter errors must beneglectable. This means that FRFT-based OFDM system has good interceptionresistance ability and wide perspective in security communications.