| The combination of space-time block coding (STBC) and multi-carrier code divis-ion multiple access (MC-CDMA)(called STBC MC-CDMA) is one of the most promis-ing schemes for next generation wireless communication. MC-CDMA not only retainsmany advantages of CDMA and OFDM, it also make up for their deficiencies. Space-time coding technology of the main idea is to antenna transmit diversity of key techno-logy with the technique of channel coding and modulation technology are organicallycombined, can effectively improve the transmission performance in fading channels.STBC MC-CDMA can make a broadband MC-CDMA system obtain transmit diversity,and effectively solve the problem of channel fading and improving the reliability of thecommunication system.For transmission and receiver of STBC wireless communication systems, STBCsignal processing such as signal peak-to-average power ratio (PAPR) reduction, signalparamaters estimation, signal recognition are very important, speacially in the hightransmission rate, lowly signal-to-noise ratio (SNR) andabominable environment causes.But suffer from a serious drawback: the approximately Gaussian distributed outputsamples cause a high peak-to-average power ratio. The analog hardware at thetransmitter requires an expensive high power amplifier (HPA) to avoid clipping and orsoft threshold that causes nonlinear output. The power consumption of a HPA dependslargely on its peak power output rather than the average output power, and thus handlingoccasional large peaks leads to low power efficiency. Furthermore, it is necessary toknow that, which kind of STBC are used for decoding signal in the receiver. This paperhas done research on OSTBC MC-CDMA signal PAPR reduction and signal recognition.The paper is organized as follows:1. Introduced the basic theory of the OSTBC MC-CDM signal, describes OSTBCMC-CDMA baseband physical model system, the signal structure and matrix.2. The high PAPR is a one of main disadvantage of MC-CDMA signal, whichresults innonlinear distortion and deteriorative system performance. Acombinedadvantage active constellation extension (ACE) and particle swam optimization (PSO)algorithm is proposed. The algorithm first using improved ACE to process signal, thenusing the PSO algorithm to find the optimal cut peak threshold, which are be PAPR of each subcarrier, until meet the set of PAPR index.3. STBC and VBLAST signals had been used most widely in space-time coding.With STBC the transmitted signals are correlated in time, while with VBLAST schemethe transmitted signals do not have such correlation. So STBC signal has aspecific cyclic frequency in higher-order cycliccumulant, the VBLAST signal emittedfrom different antenna are uncorrelated. According to this property, the blindrecognition for STBC-VBLAST MC-CDMA signal based on fourth order cycliccumulant and DEM method is proposed in this paper. This algorithm first establishedthe correlation choosing criteria, then estimated fourth-order cyclic cumulints ofthese corresponding correlation functions. The cyclic statistics after that is estimated bycombined fourth-order cyclic cumulants with channel parameters, which are obtainedby using the DEM algorithm. Finally, the cyclic statistics is compared with detectionthreshold, which is obtained by givena probability of false alarms.4. Using sparse component analysis (SCA) applied in the blind recognitionOSTBC, the real OSTBC blind recognition based on robust competitive clusteringalgorithm (RCA) and SCA is proposed in this paper. The proposed algorithm first builtthe model of received signals and virtual channel matrix, due virtual channel matrix hasincluded information of space-time coding, so we can use it for recognition, then virtualchannel matrix is separated by using RCA algorithm. After that, according thecharacteristics of real OSTBC, two characteristic parameters of correlation matrix ofvirtual channel matrix such as sparsity and energy of ratio of non main and maindiagonal elements energy are obtained to recognize signals. |
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