【作者】 黄忠虎；

【导师】 沈连丰；

【作者基本信息】 东南大学 ， 通信与信息系统， 2006， 博士

【摘要】 短距离无线通信,如无线局域网(WLAN,Wireless Local Area Network)、无线个域网(WPAN,Wireless Personal Area Network)、蓝牙(Bluetooth)、Zigbee、射频识别(RFID,Radio Frequency Identification)、无线传感器网络(WSN,Wireless Sensor Network)等,是目前无线通信领域研究和应用的热点。本学位论文围绕短距离无线通信网络低信噪比接收算法展开研究,重点研究低信噪比条件下无线接收机的载波频率同步、载波相位同步、定时同步、差错控制和低密度校验码(LDPC,Low-Density Parity-Check)的迭代随机构造等。首先,论文提出一个基于最大后验概率(MAP,Maximum a Posterrior Probability)准则的联合载波频偏估计与信道译码因子图,并根据该因子图提出了联合载波频偏估计与信道译码算法。由于原始联合载波频偏估计与信道译码算法的复杂度高,本文采用载波频偏离散化和长帧数据分为多个短子帧两个近似方法,推导了该算法的近似形式,降低了该算法的运算复杂度,扩大了它的应用范围。仿真结果表明该算法有效地提高了低信噪比条件下载波频率同步性能。然后,针对低信噪比条件下接收机的载波相位估计问题,提出了一种新的自适应迭代相位估计算法。在该算法中,相位估计和信道译码是独立进行的。相位估计器把从信道译码得到的软判决信息当作训练序列,把每个发送比特当作一个随机变量,采用最大似然准则(ML,Maximum Likelihood)完成相位估计。由于该自适应迭代相位估计算法相位估计范围不足,论文在该算法启动之前,先采用基于ML的相位估计算法来估计接收信号的相位,然后消除大相位误差对接收信号的干扰。仿真结果表明,数据辅助自适应迭代相位估计算法能消除各种相位误差,并且加快了自适应迭代相位估计算法的收敛速度。然后,论文通过仿真发现了降低常用定时同步算法性能的两个原因:区域效应和临界效应。针对这两个效应,提出了相对应的修正算法,并将该修正算法应用于Lee、平方环、对数、绝对值等定时同步算法中。仿真结果表明,改进区域效应和边界效应算法的性能优于传统定时同步算法。其次,提出一种基于线性预测的自适应可变冗余混合ARQ(VR-HARQ,Variable Redundancy Hybrid Automatic Repeat Request)方案。根据信道信噪比,时变信道被等效为有限状态的Markov过程。在推导每个Markov状态的最佳编码方案的基础上,系统采用自适应线性预测算法,根据当前L个时段的信道状态估计下一个时段信道的所对应的Markov状态,最后根据吞吐率最大原则选择合适的纠错编码方案。仿真结果表明:自适应VR-HARQ方案的性能比传统纠错编码方案提高了2dB。更多还原

【Abstract】 The study for the small area wireless communication networks is one of the hot points in the research and application of the wireless communication, which include Wireless Local Area Network (WLAN), Wireless Personal Area Network (WPAN), Bluetooth, Zigbee, Radio Frequency Identification (RFID), Wireless Sensor Network (WSN) and so on. Surrounding the key technologies of the small area wireless communication networks, the receiving algorithms in low Signal Noise Ratio (SNR) are studied deep in this dissertation. The emphases have been focused on the random construction for Low-Density Parity-Check (LDPC) codes, the synchronizations of carrier frequency, carrier phase and symbol timing.Firstly, based the MAP criterion, the factor graph is constructed for the joint channel decoding and the carrier frequency offset estimating. The corresponding joint algorithm of channel decoding and the carrier frequency offset estimating is proposed. Due to the high complexity of the joint algorithm of channel decoding and the carrier frequency offset estimating, the approximate realization of the joint algorithm is presented, where the long frame is divided to many short frames and the carrier frequency offset is quantified. So the application fields are enlarged. The simulation results show that the performance of the carrier frequency offset estimating is improved greatly by using the joint algorithm of channel decoding and the carrier frequency offset estimating.Secondly, a new adaptive iterative phase tracking algorithm is proposed for the carrier phase estimating of the receiver in low SNR. In this new approach, the phase tracking and the channel decoding are performed separately. The maximum- likelihood (ML) carrier phase estimator is completed, which the transmitted bits are considered as random variables. Due to the small scope of this adaptive iterative phase tracking, the data-aided carrier phase estimating is used before the adaptive iterative phase tracking and the large carrier phase error is eliminated. Simulation results show that this method not only eliminates the carrier phase error, but also improves the convergence rate of iterative carrier phase tracking.Thirdly,region effect and boundary effect are found in the simulation results, which worsen the timing synchronization algorithms. To eliminate them, two modified algorithm are proposed. And the modified algorithms are applied in the Lee, square, logarithm, and absolute timing synchronization algorithms. The simulation shows that the modified algorithms can greatly improve the performance of normal timing synchronization algorithms.And then, a new VR-HARQ (Variable Redundancy Hybrid-Automatic Repeat Request) scheme proposed. The channel is equivalent to a finite-markov process,更多还原