【作者】 侯俊；

【导师】 葛建华；

【作者基本信息】 西安电子科技大学 ， 通信与信息系统， 2013， 博士

【摘要】 正交频分复用技术因其高频谱利用率及强抗多径衰落能力等优点,被广泛应用于IEEE802.11a/g与3GPP-LTE等标准。但该技术的一个主要缺陷就是传输信号具有较高的峰均功率比,这会导致发送端对功率放大器的线性度要求极高,从而降低了功放的效率。因此,本文就如何有效降低信号峰均功率比进行了研究,成果简述如下：1.在失真类技术中,首先利用压扩变换将原始信号幅值由瑞利分布转变为截尾分布,消除了瑞利长拖尾所引起的高幅值信号。并且通过分析表明,在某些给定条件下,即使接收端不对压扩信号进行处理也能准确恢复出原始信号；此外,通过放缩上述方案的功率限制条件,给出了一种峰值可调的压扩方案；其次,通过Bussgang定理对压扩信号扭曲噪声的分析,提出了一种基于梯形分布的压扩函数。通过调节梯形两腰来控制压扩噪声的大小,该方案能够在峰均比与误码率之间得到良好的折衷。最后,在峰值加窗技术中,提出了一种基于判定选择的加窗技术。通过调整相邻峰值间的窗长,该方案可以有效避免对相邻峰值加窗所引入的叠加失真；2.针对部分传输序列中高计算复杂度的问题,提出了一种基于免疫进化策略的部分传输序列方案。该方案通过对现行解适应度与差异度的分析,选取合适的量子门对免疫个体进行更新,直至找出具有最优解的个体。在保持可行解结构合理的前提下,该方案通过对局部特征信息的免疫处理,可以有效提高搜索效率,从而提升系统的整体性能；其次,提出了一种基于相关相位因子组的快速部分传输序列算法。该算法根据可选相位因子的汉明距离及相关性进行分组排序,从而简化计算相邻相位因子的信号峰均比复杂度；最后,提出了一种基于窗残留信号的载波预留技术。传统载波预留方案通常利用剪切滤波噪声来构建峰值消减信号,而本方案则利用窗函数平滑峰值时所产生的残留信号来构建消减信号。通过选择合适的步长因子最小化超出门限的信号功率,该方案能够以极小的代价获得令人满意的峰均比性能；3.在载波注入技术中,通过减少备选映射星座个数,提出了一种基于并行Tabu搜索的载波注入方案。此外,通过限制注入子载波的个数,该方案能够有效地改善系统发送功率；其次,提出了一种由剪切噪声确定等价星座位置的载波注入方案。该方案首先根据峰均比限制及原始信号分布确定可变星座点个数,然后通过计算剪切信号与等价星座点间的距离,挑选其中最优的等价星座点作为实际发送信号的星座。仿真表明,该方案能够有效降低系统峰均比。更多还原

【Abstract】 Orthogonal frequency division multiplexing (OFDM) has drawn explosive attention in a number of current and future standard systems including the IEEE802.11a/g wire-less standard and3GPP-LTE, owing to the advantages of high spectral efficiency and ro-bustness to frequency selective fading. Nevertheless, OFDM suffers from a high peak-to-average power ratio (PAPR). A large PAPR requires a linear high power amplifier (HPA), which, however, is inefficiently used. This thesis focuses mainly on the PAPR reduction of OFDM signals, which is organized as follows:1. For distortion PAPR reduction techniques, a novel scheme that transform the o-riginal OFDM signals into piecewise-distributed signals is proposed. In addition, analysis shows that under certain conditions, the proposed scheme without de-companding at the receiver can also offer a good BER performance. Besides, take power limitation into account, a constant average power adaptive companding scheme is also introduced. Then, through the Bussgang theorem and the distortion noise analysis, a trapezoidal-based companding scheme is presented. By properly choosing the parameters, it can achieve an effective tradeoff between PAPR reduc-tion and bit error rate (BER) performance, which gives OFDM system more design flexibility. Finally, by introducing a weighted coefficients with adaptive windowing length, a novel peak windowing method is proposed in order to avoid the adjacent windowing function overlap.2. A novel immune and evolutionary partial transmit sequences (PTS) scheme is in-troduced to reduce the complexity. Moreover, quantum gate is introduced to modify the fitness of the solution, so as to updating the qubit individuals. During the actu-al operation, the immune algorithm refrains degeneracy phenomena arising from the evolutionary process, thus making the fitness of population increase steadi-ly. Then, by utilizing the correlation and Hamming distance among the candidate signals generated in PTS, a new scheme is proposed to decrease the computa-tional complexity. Finally, an novel algorithm based on peak windowing residual noise, which is generated by windowing the signal samples that exceed the prede-termined threshold, is proposed. Filtering the residual noise to satisfy tone reser-vation constraints and scaling with a scaling factor determined to minimize the out-of-range power generates the peak-canceling signal. The proposed scheme achieves significant PAPR reduction while maintaining low complexity.3. In tone injection (TI), given that only constellations located on the outer ring can be shifted, a novel parallel tabu search algorithm is introduced for TI. In addition, a new parameter for further reduce the power increase is also put forth. Then, a new TI scheme that uses the clipping noise to find the optimal equivalent constellations is proposed. By minimizing the mean rounding error of the clipping noise and possible equivalent constellations, the proposed scheme can easily determine the size and position of the optimal equivalent constellations. Simulation results are provided to demonstrate the effectiveness of the proposed algorithm.更多还原