Performance Analysis Of Anti-interference For Wireless Commnunication Systems

Fading and interference are the main factors restricting the performance of wirelesscommunication systems. In the past15years, there are so many studies in fadingresearching area. Therefore, in recent years, the interference and interference rejectiontechniques have gradually become a hot topic in the field of wireless communications.Especially, anti-interference technology research has important practical significanceand engineering value for weak signal detection in extreme communicationenvironments.Considering the extreme environments, the thesis attempts to analyze theperformance bound of the two-dimensional spread spectrum technique under multipathfading condition. Meanwhile, a co-channel interference suppression algorithm of theanti-interference techniques is proposed for third generation mobile communicationLong Term Evolution (LTE) uplink. Finally, a performance verification method foranti-interference algorithm is proposed with the bit error rate (BER) tester.First, using the joint algorithm of coherent detection and non-coherent detection,the upper processing gain bound of the spreading signal, which is two-dimensionalspread spectrum signal relative to BPSK and transmitted in rich scattering multipathfading channel, is sought. Firstly, the expression of the processing gain of the spreadingsignal is calculated. Secondly, with increasing signal bandwidth or symbol periodunlimitedly, the processing gain is bounded. At last, it is obtained that the upperprocessing gain bound is determined by the channel parameters and signal noise ratio.By analysis and simulation, the processing gain of the spreading signal, relative toBPSK and transmitted in rich scattering multipath fading channel, is not more than30dB, when the signal noise ratio is20dB, the maximum Doppler shift is100Hz, andthe negative exponential factor is5×10-6.Second, considering the WiFi co-channel interference in LTE uplink withmulti-received antennas, a new combining approach named Interference ReconstructionRejection Combining (IRRC) is proposed. Firstly, as the covariance matrixapproximation of the interference, the covariance matrix of the received signal isestimated. Secondly, the desired signal is reconstructed by Interference RejectionCombining. Then, the interference is reconstructed by removing the desired signal. Atlast, the covariance matrix of the interference is estimated again for InterferenceRejection Combining. Simulation results over multipath fading channels show that theIRRC approach based on the minimum mean square error outperforms the conventionalIRC approach about2dB when the signal in LTE uplink is modulated by QPSK with1transmit antenna and2receive antennas, and the jam to signal ratio is0dB. Third, considering scrambling and descrambling in high-speed wireless signalprocessing with multicore processors, a parallel scrambling method based on sparsematrix in multicore processors is proposed. By analysis of the calculated amount, usinggenerating polynomial of scrambler in IEEE802.11n, compared with parallelscrambling method based on common matrix multiplication in multicore processors, thecalculated amount of the parallel scrambling method based on sparse matrix inmulticore processors decreases one order of magnitude.Finally, a new type of BER tester to measure the anti-interference performance ofwireless communication is proposed. In order to obtain the performance of the deviceunder test, we design a BER tester based on FPGA, which can simulate one-pathRayleigh fading channel with look-up table Sum-of-Sinusoid (SoS) method. Byhypothesis testing method, processed data show the envelope of BPSK signal followsRayleigh distribution at0.95confidence level. With BER of10-3and4×106samplingdata, the0.99confidence interval of BER tester is within±5%of theoretical BER,which satisfies the BER testing for wireless communication systems in one-pathRayleigh fading channel and cut down the testing cost efficiently.In this thesis, the performance bound of the two-dimensional spread spectrumtechnique under multipath fading condition is analyzed. Considering extremecommunication environments, a co-channel interference suppression algorithm isproposed. And a performance verification method for anti-interference techniques isdesigned. The research in this thesis extends the existing researches and has theoreticaland practical significance. The results can be applied to satellite navigation, militarysecure communications and the next generation mobile communication systems.