Research On Key Technologies Of OFDM/OQAM System

Orthogonal frequency division multiplexing/offset quadrature amplitudemodulation (OFDM/OQAM) is a kind of generalized frequency division multiplexing(GFDM) technique. Compared to the traditional OFDM, OFDM/OQAM has someadvantages such as stronger immunity to inter-symbol interference (ISI) andinter-carrier interference (ICI), avoiding of cyclic prefix (CP) and lower out-of-bandradiation. OFDM/OQAM is a promising transmission technique and has been adoptedas an appropriate alternative for IEEE802.22wireless regional area network (WRAN),power line communication (PLC) and3rdgeneration partnership project long termevolution (3GPP LTE) technical standards. However, the advantages of OFDM/OQAMare acquired by relaxing of the orthogonality conditions from complex value to realvalue field. And pulse shapes with good time frequency localization (TFL)characteristics are introduced, leading to higher computational complexity and somekey techniques of traditional OFDM system can not be applied to OFDM/OQAMsystem directly. To solve these problems, based on the basic properties ofOFDM/OQAM system, this dissertation focuses on the key problems of systemrealization, channel estimation, channel equalization and peak to average power ratio(PAPR) reduction. And some novel solutions and improved methods are proposed forOFDM/OQAM system.Firstly, this dissertation researches on the system realization and performanceevaluation of OFDM/OQAM system. Through directly discretizing the transmittingsignal, a system realization method based on filters and discrete Fourier transform (DFT)is deduced. And then the popular filters used in OFDM/OQAM system are introducedand their time-frequency localization (TFL) characteristics are analyzed. Furthermore,this dissertation compares the performance between OFDM/OQAM system andtraditional OFDM system under the condition of typical application circumstances. Thesimulation results show that OFDM/OQAM system has some apparent advantages.Secondly, channel estimation of OFDM/OQAM system is addressed in thisdissertation. The problems of applicating the traditional channel estimation methoddirectly to the OFDM/OQAM system are presented. Based on the existing literatures, anovel channel estimation method based on iterative interference cancellation is proposed that it can acquire higher channel estimation precision while with lower pilotconsumption. At same time, since the estimated channel values among adjacentsubcarriers are correlative, a combining method is proposed to overcome the effect ofadditional white Gaussian noise (AWGN) channel and the channel estimation accuracyis improved. Besides, the joint estimation of carrier frequency offset (CFO) and channelis analysed. Furthermore, an effective preamble structure and a corresponding algorithmare proposed. The simulation results show that it can achieve high estimation accuracyand has strong robustness to time offset.Thirdly, this dissertation researches on the channel equalization of OFDM/OQAMsystem. Because of the performance floor when applicating simple zero forcing (ZF)equalization method for OFDM/OQAM system, an iterative interference cancellationmethod is proposed for both single-input single-output (SISO) and multi-inputmulti-output (MIMO) systems. Simulation results show that this method can improvethe system performance effectively. Furthermore, because the residual interference ofthe demodulated signal follows the Gaussian distribution, it can be treated as a part ofbackground noise for minimum mean square error (MMSE) equalization.Finally, this dissertation researches on the reduction of the peak-to-average powerratio (PAPR) in OFDM/OQAM system. According to the particularity ofOFDM/OQAM transmitting signal, an effective selective mapping (SLM) method isproposed with lower complexity. This dissertation also researches on the suppression ofclipping noise. The clipping noise is rebuilded in the receiver and then it is removedfrom the receiving signal to overcome its influence on system performance. Besides, theout-of-band radiation and the relation between clipping threshold and out-of-bandradiation are also addressed in this dissertation.The research achievements in this dissertation provide effective solutions andperformance improvements with respect to the primary problem of OFDM/OQAMsystem in different aspects. And these achievements can provide support for applicationof the OFDM/OQAM technique in popular system such as WRAN, advancedinternational mobile telecommunications (IMT-advanced) and future mobilecommunication systems.