Research On Techniques For Peak-to-Average Power Ratio Reduction In Multicarrier Communication Systems

Multicarrier technology is an effective scheme of realizing high data rate transmission thanks to its intrinsic robustness to multipath fading, high frequency efficiency, simplification in channel equalization and flexibility of combing other technologies to bring new systems. Recently, multicarrier technology, especially orthogonal frequency division multiplexing (OFDM), is being successfully implemented in digital audio and video broadcasting systems, telephone-line based digital subscriber links, wireless access networks, satellite communication and power line communication, and it is being considered as one of the key technologies in the next generation wireless communication systems. However, the multicarrier communication system has the drawback of high peak-to-average power ratio (PAPR). High PAPR may cause signal distortion, spectrum spread and system performance degradation. The objective of this thesis is to research the techniques for reducing high PAPR in multicarrier communication systems.First of all, the thesis developed the theoretical foundations for analyzing the PAPR reduction problem. By deducing OFDM signal's envelope fluctuation, autocorrelation and instantaneous power properties, the cause of high PAPR was revealed. By proving the assumption that the complex OFDM signal converges in distribution to a stationary complex Gaussian random process, the statistical distribution functions of PAPR were investigated, and hereby the measures of PAPR reduction performance were provided. Based on the model of high power amplifier (HPA), the in-band distortion and out-of-band noise introduced by HPA nonlinearity were analyzed and the influences on the system performances by high PAPR were described.Secondly, the thesis investigated the scrambling technique for PAPR reduction. After summing up various methods of this technique, the pulse shaping and virtual subcarrier methods for PAPR reduction came into our sight. Thus the Nyquist pulse shaping and high frequency virtual subcarrier methods were proposed. The former consummated the explanation why the pulse shaping method could reduce PAPR, constructed practical pulse sets and related the PAPR reduction performance with the shaping pulses'capability of combating intersymbol interference (ISI). The later utilized the approach of minimizing the maximum average power of multiple subcarrier modulated optical signals, derived the lower bound for peak power of discrete multitone (DMT) signal and presented the algorithm for optimal high frequency virtual subcarrier signal.Thirdly, the thesis examined the coding technique for PAPR reduction. Considering the higher frequency efficiency of multilevel multicarrier modulation scheme in limited band, the PAPR reduction methods for M-ary multilevel quadrature amplitude modulated (MQAM) OFDM signal, namely Golay complementary sequence (GCS) mapping and trellis shaping methods were investigated. Approaches to create MQAM sequences with low PAPR using M-ary phase shift keying (MPSK) GCS were compared in detail. The partial trellis shaping method was presented. It decreased the computation complexity of trellis shaping method, could design shaping rule by applying the stack algorithm of sequential decoding and combine error control coding technique to adapt to communication systems with requirement for better bit-error-rate performance. In order to meet the requirements of wideband satellite communication system, the partial trellis shaping method based wideband OFDM satellite communication system model were presented and the BER performance in lognormal/Rican fading channel with additive white Gaussian noise (AWGN) were analyzed. The results contributed to the application of multicarrier technology in wideband satellite communication systems.At last, the thesis studied the spreading codes selection technique for PAPR reduction. This technique was specially used in multicarrier code division multiplexing access (MC-CDMA) system, which selected spreading codes that had better PAPR features. From the relationship of MC-CDMA signal's PAPR and spreading codes'characteristics, two measures were proposed to evaluate the PAPR reduction performances of spreading codes, and the upper bound for MC-CDMA signal's PAPR with orthogonal complementary codes were deduced. Three classes of orthogonal complementary codes that had good PAPR features were presented to apply in multiuser MC-CDMA system. The simulation results were explained by the aforementioned measures. To be continued, the polyphase pulse compression spreading codes making use of the polyphase codes in radar pulse compression phase coded signal were designed. Their characteristics were described and proved. The results showed that the polyphase pulse compression spreading codes were good choices for MC-CDMA systems.