Wimax Signal Peak To Average Power Ratio Suppression Techniques And Experimental Study,

Orthogonal Frequency Division Multiplexing (OFDM) technology, which can mitigate frequency-selective fading and own high frequency efficiency compared to single-carrier systems, has been chose as one of key physical layer technologies of standard 802.16d/e of Institute of Electrical and Electronics Engineers (IEEE) for wireless metropolitan access networks (WMAN). The technology specified in IEEE standard 802.16d is also called WiMAX (Worldwide Interoperability for Microwave Access), which has attracted a lot of interests in wireless communiation filed so far.However, high peak-to-average power ratio (PAPR) of WiMAX signals becomes one of the main barriers in its road to widespread applications, which means that the high PAPR of transmitted WiMAX signals require a quite stringent linearity requirement on the transmitter amplifier and the amplifier's power output back-off has to be large in order to reduce nonlinearity distortion and spectrum spreading. To sovle this problem, this thesis presented related research works in baseband signal processing point of view, including three type of new method, computer simulation verification, and measurement under a WiMAX testbed.First of all, this thesis introduces characteristics of OFDM and WiMAX signals, and review current researches on PAPR reduction, and summarizes problems needed to be resolved.Secondly, we propose a novel PAPR reduction method using null subcarriers for WiMAX system in the second chapter of thesis. According to WiMAX standard, data subcarriers are not allowed to be reserved, or for side information transmission. Therefore, Tone Reservation using Null Subcarriers method (TRNS) to reduce PAPR is proposed under WiMAX system. Through system simulation, the effects of TRNS method based on different number of null subcarriers and different predefined threshold are observed. Results show TRNS method is an effective method to reduce PAPR.Moreover, in order to reduce the complexity of TRNS method, we analyze the conditional probability of multiple peak amplitudes, and then, propose a new Low Complexity Tone Reservation using Null subcarriers method (LC-TRNS) and a new Peak Equivalent Tone Reservation method (PETR) in the third chapter of thesis. Simulation resuls also demonstrate both of them are effective for PAPR reduction, and with low complexity.Fourthly, the nonlinear effect by the high power amplifier (HPA) is analyzed under WiMAX system. Considering the two main solution for removing nonlinearity (predistortion and PAPR reduction methods), a new method is proposed through combining the predistortion and TRNS method. Simulation results show the new method can improve the total performance, especially, under low input back-off (IBO).Finally, we introduce developing works and measurement results based on a WiMAX testbed, which is implemented by RF Vector Signal Generator and RF Vector Signal Analyzer of National Instruments Company. After solving several important problems, such as synchronization, phase correction and power normalization, Error Vector Measurement and spectral leakage are measured.In the last chapter of thesis, we summarized whole thesis and pointed out further research directions in PAPR reduction for WiMAX systems.