Study On Papr Reduction And Offset Qam In OFDM System

Orthogonal frequency division multiplexing (OFDM), which is robust to the frequency selective fading environment, becomes core radio transmission technologies for 3GPP LTE-Adavanced, wireless LAN (IEEE 802.11n) and wireless MAN (802.16e/m). However, OFDM system still has the two major drawbacks: High peak-to-average power ratio (PAPR) and inter-carrier interference (ICI). This dissertation focuses on PAPR reduction techniques and pulse shaping filter based OFDM/offset QAM system (OFDM/OQAM), which is robust to double selective fading channel.Firstly, although the tone reservation method could reduce PAPR by peak cancellation, the reserved subcarriers and side information of location will reduce the spectrum efficiency. According to the tranmission structure of WiMAX (World Interoperability for Microwave Access) system, a novel tone reservation PAPR reduction method utilizing null subcarriers (TRNS) is proposed. Furthermore, to reduce the complexity of TRNS method, the dissertation analyzes the properties of order statistics of WiMAX signals and low complexity TRNS method (LC-TRNS) is proposed. Finally, a joint nonlinearity reduction scheme by predistortion and TRNS method is proposed to further improve the high power amplifier (HPA) efficiency.Secondly, the channel estimation method for OFDM system with cyclic prefix can not be utilized for OFDM/OQAM system, since the multipath fading channel will destroy the real-field orthogonality constrain. The dissertation has proposed an improved ICI reduction channel estimation method of OFDM/OQAM system. Moreover, a joint channel estimation and detection method for OFDM/OQAM system to remove the residual ISI and ICI.Finally, since the extended Gaussian function (EGF) with different speading factor has the different time frequency localization, the dissertation proposed an adaptive OFDM/OQAM system with different EGF pulse shaping filter to optimize the system perforemance in different scenarios, such as using smaller speading factor for scenarios with strong ISI and using bigger speading factor for scenarios with strong ICI.The research results in this dissertation provide some improve techniques of orthogonal frequency division multiplex system to meet the physical layer technology needs in the next generation mobile communications system. Utilizing those novel techniques, they supply a feasible solution for high speed data transmissions in double-selective fading channel and can be applied in the IMT-Adavancd, IEEE 802.11, and IEEE 802.16 systems.