Study On Some Issues Of Multi-carrier Modulation In Wireless Communication

Multicarrier modulation is one of the key technology of wireless communication. Recently, the multicarrier mudulation has attracted much interest for its advantages, and widely used in DAB,WLAN and so on. Furthermore, multicarrier mudulation will be the key technology of the 4th generation mobile communication system. Under such situation, some issues of multicarrier mudulation are studied and some achievements are acquired as follows.Based on the subblock envelop scaling scheme, one novel scheme of Peak-to-Average Power Ratio(PAPR) reduction for Orthogonal Frequency Division Multiplex(OFDM) is presented, named threshold presetted cycle optimization scheme. Under the precondition that system performance assured, the threshold is presetted and circulation shift optimization is done to reduce the PAPR of OFDM signal. In this way, the processing complexity can be greatly reduced. The proposed scheme can effectively reduce the PAPR of OFDM signal and have the advantage of low complexity, flexibility and no side information.One novel M-ary multi-carrier spread spectrum scheme based on wavelet packet is proposed, which can achieve higher bit transfer rate under bandwidth restricted condition. Good properties of wavelet packet functions ensure the new scheme has good performance of overcoming the influence of multi-path channel and multiuser interference. Based on Rayleigh slow fading channel model, the performance of the scheme is studied under different combining scheme and different M. The performance advantages of the new scheme over the M-ary multi-carrier spread spectrum scheme based on Discrete Fourier Transform (DFT) are demonstrated by both study and simulation.A novel wavelet packet M-ary multi-carrier spread spectrum scheme based on orthogonal cyclic codes is proposed. The scheme using one group of special codes as the M-ary spread spectrum codes, receiver can despread by using FFT and IFFT to take the place of correlation computation of all of the receiver correlation branches. Therefore, the complexity of wavelet packet M-ary spread spectrum system can be reduced efficiently when M is large.Different kind of antijamming schemes are studied, a new scheme of wavelet packet based multi-carrier spread spectrum receiver is proposed. Its complexity is very low since the process can cooperate with the despreading/demodulation of common wavelet packet based spread spectrum scheme. It has very strong ability to excise narrow bandjamming, where the system performance is efficiently improved by means of adaptively choosing optimizing parameters based on wavelet packet analysis. Its performance is much better than the DFT based multi-carrier spread spectrum scheme under the same working condition. Furthermore, the performance of M-ary multi-carrier spread spectrum system under narrowband jamming and transform domain based antijamming scheme are studied. Simulations are done and some conclusions are acquired.A new scheme for accurate estimation of single tone jamming parameters in multi-carrier spread spectrum system is presented. Base on the results computed by DFT in demodulation and dispreading, the scheme can estimate accurately the parameters such as frequency, amplitude and initial phase of single tone jamming by analyzing two spectra lines having higher energy than others. The scheme has low complexity and can overcome the shortcomings of common methods which adopt only single spectra line having maximum energy to estimate single tone jamming parameters. The simulation results show that the scheme has some advantages such as short computation time and high precision and can estimate all parameters. Based on jamming parameters' accurate estimation scheme, one novel single tone jamming elimination scheme is proposed. Compared with the "threshold exciser" scheme, the proposed scheme can eliminate more jamming energy on the whole frequency band with the minimum loss of useful signal energy. As shown in the research and simulation, the proposed scheme is much better than the "threshold exciser" scheme, especially in the c...