数字通信系统中的载波恢复技术初探

载波恢复在数字通信系统中具有补偿频偏损害、相位抖动等作用,是系统不可或缺的重要单元。本文立足于数字通信系统,简要介绍了该系统与载波恢复,从载波恢复思想与算法两方面出发对该技术进行了探析,希望对我国数字通信发展有所助益,为研究人员提供参考。     

QAM调制解调系统中载波恢复算法的研究

本文首先介绍了QAM调制解调系统的基本原理框图，就解调中载波恢复的几种实现算法进行了讨论，软件仿真实现了4QAM（QPSK）的整个调制解调系统，并重点就载波恢复的几种算法进行了仿真比较，得出了相关结论。     

基于RC-DD算法的QAM载波恢复方法设计

提出将扫频算法与简化星座图算法(RC-DD)相结合应用于QAM载波恢复中.介绍了新算法的基本原理、载波恢复方法的结构.仿真结果显示,该方法性能可靠,捕获速度快,稳定度好,精度高且捕获频偏可达符号速率级.可以在较宽的范围内快速、准确地恢复载波.     

软件接收机中DSB-SC信号载波同步的一种算法

本文提出了软件妆收机中抑制载波双边带调幅（DSB-SC）信号载波同步的一种算法，根据下变频后的基带信号估计出收发载波的频差，并经卡尔曼滤波后结合数字锁相环以达到载波捕获范围宽、跟踪速度快、环路噪声小的特点。文章最后给出了一个具体实例的仿真结果。     

相位处理载波恢复算法研究

针对数字信号传输同步接收机的数字化实现，提出一种载波同步新算法即相位处理载波恢复算法。它直接对接收信号的相角进行处理，完成载波频率的快速捕获和载波相位跟踪。理论分析和计算机仿真表明，该算法简单有效，运算量小，便于用DSP器件来实现，适用性强。     

基于扫频算法的QPSK载波恢复技术研究

针对欧洲DVB-S及DVB-S2协议标准均采用的QPSK调制解调方法,探讨一种有效的载波恢复技术。扫频算法具有强大的频偏捕获能力,在此基础上,本文结合判决自导方法,实现了很大范围内频偏的捕获与跟踪;改进了扫频门限的设定方法,使得该算法可适用信噪比大大降低;引入维特比译码反馈机制,自动调整系统参数,增强了同步系统的自适应能力。Matlab仿真结果表明,该方法性能可靠,稳定工作信噪比可至0.5 dB,频偏捕获范围甚至可达几倍符号率,适用于全数字高速数传QPSK接收系统,同时也可移植、推广至mPSK全数字雷达接收机中。     

基于QAM载波恢复算法的研究

针对高阶QAM调制解调系统对载波偏移的敏感性问题,采用一种基于导频、扫频环路和载波恢复环路的高阶QAM载波恢复方法。这里设计的扫频环路是由帧检测、扫频、频率校正三个模块组成,载波恢复环路由极性判决算法模块和判决导向模块组成。扫频和极性判决算法都具有较大的频偏捕获能力。两者联合用于载波频偏的捕获阶段,既克服了一般扫频算法残留频偏大的困难,也解决了极性算法可用角点少的问题。     

基于扫频算法的QAM载波恢复技术研究

针对QAM调制解调方案,探讨一种行而有效的载波恢复技术.扫频算法具有极大的频偏捕获能力,在扫频算法的基础上结合面向判决算法,实现了对载波大范围内频偏的捕捉和跟踪;改进了扫频门限的设定方法,使得在各种QAM制式下该算法都具有快速的频偏捕捉能力.Matlab仿真结果表明,该方法性能可靠,频偏捕捉范围可达5%符号率,适用于高...     

一种改进的DTMB单载波系统载波恢复算法

本文提出一种改进的DTMB单载波系统载波恢复算法。该算法在扫频阶段,通过选择合适的频点,对变步长扫频方法进行了改进。理论分析和软件仿真表明:在相同的接收条件下,使用改进的算法,扫频次数明显减少,由原来44次减少到20次,降低系统复杂度,但估计准确度不变。     

双导频载波恢复算法设计

针对国家地面数字电视标准GB 20600-2006,提出一种可应用于单载波模式的双导频载波恢复算法.该算法充分利用了单载波模式下双导频的特点,通过两个独立的锁频锁相环分别完成频偏估计,并采用环路加权求和的方式对抗多径干扰所导致的导频衰落.仿真证明,算法在多径信道条件下具有较好的性能.     

基于 PAM 分解面向判决的 Multi -h CPM 载波相位同步

多指数连续相位调制（Muhi—h CPM,Multi—h Continuous Phase Modulation）具有频谱效率高,抗误码性能好的特点,具有广泛的应用前景,但同步问题一直是Multi—hCPM接收机的难点之一。在已有单指数CPM载波相位同步算法的基础上,研究了一种基于PAM分解面向判决的Multi—hCPM信号载波相位同步算法,为了有效界定所提出算法的性能,推导出了Multi—hCPM载波相位估计的修正克劳美罗限（MCRB）。仿真结果表明,在较大多普勒频率及其变化率的环境下,该载波相位算法的估计性能良好且能逼近其MCRB。     

海事卫星BGAN载波恢复技术研究

载波恢复是实现信号相干解调的一个必不可少的部分。通过研究海事卫星全球宽带网（BGAN）信号帧中的独特字（UW）,采用数据辅助的频偏估计和面向判决的相偏估计算法,完成了对实际接收海事卫星BGAN信号的载波恢复,该方法捕获时间快,估计范围大,准确度高。结果表明该算法对BGAN信号的频偏、相偏均能正确收敛,恢复后星座图接近16QAM星座图,为信号解调提供保证。     

适用于机载卫星通信的低信噪比载波恢复算法

随着卫星通信技术的不断发展,对低信噪比下的解调技术提出了越来越高的要求,尤其是针对机载平台下的卫星通信系统,需要在极低信噪比条件下进行解调。采用了一种基于载波相位内插的低信噪比解调算法,利用FFT进行频偏估计,然后利用相邻2个帧头的相位估计结果进行内插,得到帧内各符号的载波相位信息,实现载波恢复。仿真和结果表明,帧头长度为32时可以获得较好的解调性能,解调门限附近载波恢复导致的解调损失小于0.3 dB。     

基于软件无线电的FM解调算法

软件无线电的基本思想是将宽带A/D及D/A尽可能靠近天线,将无线电台的各种功能在一个开放性、模块化的通用硬件平台上尽可能多的用软件来实现。软件无线电已成为移动通信中的关键技术之一。文中基于软件无线电采用软件实现通用硬件调制的目的,通过基带信号处理算法,结合软件无线电接收机中的相关理论对其中的调制方式识别和解调算法进行了仿真,说明了各个解调模块的功能,而且也验证了系统的科学性和可实现性。     

一种高速多模式载波同步方法

针对载波同步的两个关键问题———提高速度和适应多模式,研究了锁相环的鉴频辅助方法,构建了基于Costas鉴相和点积、差积鉴频算法的环路。仿真结果表明,所研究的载波同步方法适应BPSK、QPSK和8PSK等调制方式,同步速度约为传统方法的2倍。     

扩频通信中载波恢复的研究

介绍了在f0±150kHz(f0为中心频率)频率范围内,通过合理设置环路带宽,改进的平方环电路从20.14MHz的扩频BPSK信号恢复出的载波的相位噪声达-100dBc/Hz@1kHz,实现了±4kHz/s的跟踪速度。通过增加两级分频器,对f0±39.4kHz的杂散抑制大于65dB。     

Carrier Frequency Recovery Technique in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) systems are highly sensitive to carrier frequency errors. In this paper, a new method utilizing pilots to do frequency synchronization in frequency domain is proposed with large estimation range. It needs no such prerequisite assumption that a perfect symbol timing synchronization [IEEE Transactions on Communications 42 (1994) 2908; 45 (1997) 1613] has been done before performing integer carrier frequency synchronization. Also, a new adjusting model for fine carrier frequency is proposed. Simulation and performance analysis show that our overall frequency estimator has high accuracy. The corresponding FPGA circuit through test in high definition TV (HDTV) prototype in Team of Expert Engineering Group (TEEG) in China proves its availability and feasibility.Bo Ai (M2001) was born in Shannxi Province in China on February 7, 1974. He received a B.Sc. degree from Engineering Institute of Armed Police Force and a Master degree, a Ph.D degree from Xidian University in 1997, 2002 and 2004 in China respectively. He has once participated in the key research project on HDTV in TEEG (Team of Engineering Expert Group) of China, and has published over forty papers in his research area till now. He is senior member of Chinese Electronics Institute (CIE), an editorial commitee member of journal of Computer Simulations. His current interests are the research and applications of OFDM technique with emphasis on synchronization.Jian-hua Ge was born in September, 1961 in JiangSu Province in China. He received the B.Sc., Master and Ph.D. degree from Xidian University in 1982, 1985 and 1989 respectively. He is now the professor in both Xidian University in Xian and Shanghai Jiaotong University in Shanghai. He is the senior member of Chinese Electronics Institute. He has won lots of scientific and technical prizes in China and published many papers. His interests are transmission communications and web security.Yong Wang (M2003) was born in Shannxi Province in China in 1976. He received a B.Sc. and Master degree from Xidian University in China in 1997 and 2002 respectively, and is now working towards the Ph.D. degree on communications in the Key Laboratory of ISN in Xidian University. He has once participated in the key research project on HDTV in TEEG of China and his interests are broadband multimedia communications.Dian-fu Zhang was born in Shannxi Province in China in 1954. He received a B.Sc. degree from Xidian University in China in 1977. He is now working as a professor and the chairman of the telecommunication department in Engineering College of Armed Police Force. His interests are mobile communications.Jun Liu was born in Beijing in China in 1963. He received his B.Sc. degree from Nanjing University Of Aeronautics and Astronautics in China in 1984. He is now a professor in Engineering College Of Armed Police Force. His research interests include integrated circuit design and artificial intelligence.