【作者】 李为；

【导师】 尹浩； 魏急波；

【作者基本信息】 国防科学技术大学 ， 信息与通信工程， 2008， 硕士

【摘要】 正交频分复用技术(OFDM)是一种子载波相互重叠并保持正交的多载波传输技术,它可以有效的对抗多径衰落及符号间干扰(ISI),频谱利用率高,被认为是下一代宽带无线通信的关键技术之一。然而,OFDM技术存在着峰值平均功率比(PAPR)较高的缺点,高PAPR会导致信号失真和频谱扩展,从而降低系统性能。论文即围绕OFDM系统的降峰均功率比算法与实现展开研究,主要工作如下:1、论文详细分析了OFDM系统原理、关键技术及其优缺点,给出了峰均功率比的定义和分布,并结合功放模型分析了峰均比过高对系统的影响,并对目前国内外降低PAPR的各种方法进行了分析和总结。2、针对FPGA硬件设计的特点,提出了一种有效的分段线性压扩算法,其降峰均比效果与非线性压扩法基本相同,但算法的复杂度却大大降低。论文对该方案进行了硬件设计实现,将其应用到基于IEEE802.16d的OFDM系统中。实测效果和资源占用情况显示,该方案在OFDM系统中具有较高实用价值。3、对削波法降峰均比进行了FPGA设计实现。本设计对补0后的数据采用两倍IFFT运算进行过采样,然后再削波和滤波,这样有效的降低了带内噪声,同时也降低了后级插值的倍数,削弱了由插值导致峰值再升的影响,具有较好的降峰均比效果。4、提出一种新的降峰均比算法—星座映射优化法。该算法通过改变星座映射的幅度,采用全局优化方法来选择幅度变换因子,达到了最优的降峰均比效果。与传统降峰均比方法相比,该算法不需要传输边带信息,接收端无需任何变化即可解调;不会产生带内噪声和带外频谱泄漏;在大幅降低信号峰均比的情况下,对接收机误码率性能仅有很小的影响。更多还原

【Abstract】 Orthogonal Frequency Division Multiplexing (OFDM)is an effective transmission scheme to realizing high-rate data transmission thanks to its intrinsic robustness to multi-path fading, high spectral efficiency,and its characteristic of combating inter symbol interference(ISI). Recently OFDM is being considered as one of the key technologies in the next generation broadband wireless communication systems. However, the OFDM system has the drawback of high peak-to-average power ratio (PAPR).High PAPR may cause signal distortion, spectrum spread and system performance degradation. This dissertation explores the question of Peak-to-Average Power Ratio in OFDM systems primarily.Firstly, the principle of OFDM systems, its key techniques, advantages and disadvantages of OFDM technology are analyzed in this thesis .The definition and distribution of PAPR are introduced and the influences on the system performances by high PAPR were analyzed based on the model of high power amplifier. Various techniques on reducing the PAPR are researched. And the advantages and disadvantages of these techniques are analyzed and summarized.Secondly, a segmented linear companding transform method is proposed to fit the FPGA hardware implementation. Its performance is approached to the traditional no-linear companding transform but it greatly reduces the system’s complexity. Emulation and practical results shows the implementation scheme has a high practical value in OFDM system.Thirdly, clipping method to reduce the PAPR is implemented by FPGA hardware. We oversample each OFDM block by padding the original input with zeros and taking a twice longer IFFT. It reduces the band-in noise effectively. The practical result shows the implementation scheme has good effect.At last, a new method for reducing the PAPR of OFDM signal is proposed via constellation optimization. This method reduce the PAPR by changing the amplitude of constellation, choosing proper amplitude changing factor and adjusting the constellation position .The changing factor is acquired by solving an optimization problem. No change in receiver structure is required; no band-in noise and no spectrum spread; it can reduce the PAPR greatly with a little influence on the system bit error rate.更多还原