基于SOPC实现扩频信号的捕获与跟踪

扩频信号的捕获与跟踪是扩频接收机进行定位解算的基础,提出了利用FPGA内的嵌入式软核Niosll在单片FPGA内实现扩频信号捕获与跟踪的设计方案.详细分析了该方案的匹配滤波器、相关器、载波跟踪环和码跟踪环设计和实现方法.给出了根据该设计对实时的GPS信号的捕获跟踪测试结果.结果表明,该设计能够实现对扩频信号的实时捕获与跟踪,相比利用FPGA+DSP方案实现扩频信号的捕获与跟踪,具有可重构性好,硬件开发难度低,接收机体积小等优点.     

扩频信号的捕获与跟踪

针对直接序列扩频信号,介绍了其发射和接收部分基本组成,给出了系统接收部分的具体设计框图。重点讨论了对扩频信号的捕获与跟踪的方法,其中包括扩频码的捕获与跟踪以及载波的捕获与跟踪。对各模块的性能进行了分析,提出了在高速信号处理板(以FPGA和DSP为基础)中对扩频信号的捕获与跟踪的实现方案。经工程验证,能够实现伪码同步和载波同步,解调出所需信号。     

GPS基带信号处理方法综述

全球定位系统(GPS)广泛应用于导航、测量、应急通讯等领域,近年来对GPS卫星基带信号捕获跟踪过程的研究日益深入,为此对捕获和跟踪算法进行系统的总结和对比.根据数字中频信号与本地信号混频后的处理方式将捕获算法主要分为相干捕获、非相干捕获和差分相干捕获等,根据跟踪环路功能将跟踪算法分为载波跟踪和码环路跟踪,分别对捕获和跟踪算法进行对比;归纳近几年捕获和跟踪的改进算法,分析其优缺点.最后展望捕获和跟踪算法的发展趋势.     

高动态下GPS信号的捕获和跟踪技术研究

为检测高动态GPS信号,需要设计码环及载波环的捕获和跟踪数字系统。如何快速捕获信号,并进行精确跟踪,是问题的关键。针对高动态环境下GPS信号的捕获和跟踪问题,分析了高动态环境对GPS信号的影响,提出了FFT码快速捕获算法,以及二阶FLL与三阶PLL混合载波跟踪方案,并对码环和载波环的结构和参数的设计方法进行了说明。仿真结果和分析表明该方案能在高动态环境下实现信号的快速捕获,且能较好地满足接收机动态性能和跟踪精度的要求。     

扩频通信中PN码序列的捕获

扩频信号的捕获与跟踪是扩频接收机进行定位解扩的基础,文中基于FPGA进行了扩频信号捕获与跟踪的设计实现。分析了该方案的匹配滤波器、载波跟踪环、码跟踪环的设计与实现方法。并通过BPSK调制,使用非相干扩频通信的PN码并行捕获算法实现信号的捕获。     

Turbo编码GMSK信号的多普勒频移捕获与跟踪

提出了Turbo编码GMSK信号的多普勒频移捕获和跟踪方案.该方案首先采用AR模型进行多普勒频移的初始捕获,其次采用基于FFT的联合帧同步和频偏估计算法捕获剩余频差,最后利用判决反馈PLL跟踪多普勒频移的变化.仿真结果表明:该算法在低信噪比时可快速捕获超过符号速率的多普勒频移,并能以很小的误差跟踪多普勒频移的变化,此时...     

高动态接收机的关键问题研究

为检测高动态GPS(Global Positioning System)信号,需要设计码环及载波环的捕获与跟踪数字系统.在高动态下,在GPS信号的码跟踪和载波捕获与跟踪问题中最关键的是要解决在高加速度下的载波跟踪问题.主要讨论了在高动态下,结合GEC公司的十二通道相关器GP2021,载波跟踪环路的特性并在此基础上提出了一个新的方法来改善载波跟踪环路的性能.     

高动态微弱信标信号载波捕获跟踪的设计与实现

为了研究高动态低信噪比下信标信号的载波捕获跟踪问题,采用两级二阶锁频环(FLL)和一级三阶锁相环(PLL)技术方案。FLL采用基于周期图的鉴频方法,实现极低信噪比下信号载波的捕获。PLL中的三阶锁相环通过对环路压控振荡器(VCO)的输入控制信号进行监测,自适应地调整环路滤波器的带宽,以满足高动态下信号载波频率动态范围大的要求。在基于FPGA构建的信号处理板上验证了上述实现方案,并给出实验结果。     

基于基带信号包络的数字AGC设计与实现

在卫星扩频通信系统中,通常采用自动增益控制(Automatic Gain Control,AGC)技术解决大动态的信号起伏和干扰,以实现扩频信号的快速捕获和跟踪.分析了扩频接收机基带信号数字采样门限,通过用信号包络功率值作为AGC控制信号,实现了接收基带信号大动态范围的信号处理,完成了数字AGC自适应控制.利用扩频信号进行完全捕获后的包络信号作为AGE信号可以有效防止信号捕获过程中多普勒频移等引起的失锁和误捕,实现扩频接收机RF(射频)信号大动态范围的信号控制.     

BOC(1,1)信号的自适应捕获

GPS现代化以及Galileo系统都将使用BOC调制信号,与单纯的扩频码相比,BOC信号有更小的跟踪抖动和更好的抗多径性能,但因为BOC信号自相关函数具有多峰性,使得捕获更具挑战性,跟踪时容易锁在假峰上.Julien提出的合成相关捕获算法完全删除了BOC(n,n)信号的边峰,保持主峰不变,因此不需要检查跟踪是否在主峰上.在此基础上推导了一种自适应捕获算法,在保证系统误捕率恒定的情况下,能根据接收卫星信号功率的不同自动的调整门限.     

A robust beam tracking scheme for millimeter wave HetNets

Millimeter Wave (mmWave) communication has been widely acknowledged as an attractive solution to address high-speed transmission of massive data in 5G and beyond 5G systems due to the promising spectrum availability. However, mmWave signals are highly susceptible to blockage and may suffer from rapidly changing channels. Thus, directional/beam tracking becomes imperative yet essential for robust mmWave communications. To address this challenge, we propose a robust beam tracking scheme for mmWave Heterogeneous Networks (HetNets) with multi-connectivity. Different from most existing schemes, the proposed beam tracking scheme is effective for outage events. We first discuss the μWave-assisted beam tracking procedure with and without candidate beams, and then analyze the inherent correlation between mmWave link quality and the operating beamwidth and occlusion range to derive the optimal beamwidth. Theoretical and numerical results show that the proposed beam tracking scheme can improve the robustness of mmWave communications while guaranteeing the rate performance.     

指针推进移动性管理策略中指针链长度的概率

为了降低移动通信网络中位置跟踪操作的代价,指针推进策略被提出.显然,指针链长度的确定对这一策略的有效应用是至为重要的.已有论文假定移动台在位置区的逗留时间服从指数分布的条件下,对指针链的长度进行研究,但指数分布的特殊性,限制了其研究结果的应用.本文推广了上述结果,研究了移动台在位置区的逗留时间服从一般概率分布的指针推进策略,通过构造向量马氏过程,利用密度演化方法,导出了指针链长度的概率公式,这个公式可用于对各种指针推进策略性能的评价.     

Research on the acquisition and tracking simulation system of light beacon in satellite-ground optical communications

The study on the acquisition and tracking simulation system in satellite-ground optical communications is presented here. By applying global positioning system (GPS) coordinate calculation, the time needed in initial acquisition of light beacon can be reduced largely. Smith predictor is applied to compensate the mechanical hysteresis of tracking system and to improve the dynamic performance of the system. Tracking experiments over a 16 km distance on the ground are conducted to verify the tracking of light beacon in satellite-ground optical communications. The standard deviation of horizontal coordinates is 35.3568 μrad and the maximum offset is 209.3675 μrad in stable tracking.     

Mathematical modeling and performance analysis for a two-stageacquisition scheme for direct-sequence spread-spectrum CDMA

Acquisition of synchronism is considered for DS/SS CDMA systems. For large systems with large timing uncertainties, it has been shown previously that acquisition in the presence of multiple-access interference may impose a significant limitation on capacity. This leads the authors to consider a system in which timing uncertainties are relatively small and to propose an acquisition scheme which exploits this to reduce complexity and acquisition overhead. The proposal may be appropriate for a microcellular environment for personal communications in which CDMA packet transmission is employed for both voice and data. Packetized transmission would imply that the overhead available for acquisition is small, and the large number of microcells would restrict the cost of the acquisition scheme used in the receiver in each microcell. The acquisition time required for a simple serial search scheme may therefore be unacceptably large. On the other hand, while acquisition using a passive matched filter is fast, the filter length required for reliable acquisition is liable to be excessive in terms of cost and complexity. Motivated by these considerations, the authors propose a two-stage acquisition scheme which employs a short programmable matched filter for initial detection, followed by a correlator for verification. Numerical results based on an approximate analysis of acquisition performance in the presence of multiple access interference are employed to compare the scheme with conventional acquisition schemes     

Performance analysis for an adaptive filter code-tracking techniquein direct-sequence spread-spectrum systems

This paper investigates tracking of direct-sequence spread-spectrum (DS/SS) signals based on an adaptive filtering technique. It is shown that a previously proposed hardware for code acquisition is also capable of code-tracking, and, hence, by performing both acquisition and tracking with the same circuitry, a significant simplification in the overall DS/SS receiver structure is gained. Analytical results show that the proposed scheme has a good tracking performance, as measured by the hold-in time and the false alarm penalty time, and is less sensitive to variations in the signal-to-noise ratio (SNR) compared to conventional delay-locked loops (DLLs). Moreover, simulation results show that the proposed adaptive filter tracking scheme has a smaller residual tracking error than that produced by a conventional maximum-likelihood estimator (MLE)     

Parallel acquisition in mobile DS-CDMA systems

This paper presents the performance of a direct sequence spread spectrum acquisition scheme in a mobile terrestrial communications system. The effects of fading, multipath, power control, shadowing, multiple access interference, out-of-cell interference, vehicle speed, voice activity, and sectorization are examined. The acquisition scheme uses noncoherent detection and a parallel search strategy. The analysis is done for the reverse link of a mobile code-division multiple-access (CDMA) system. The purpose of this paper is to derive the acquisition performance of a mobile communications system under practical assumptions, and give realistic capacity estimates based on acquisition performance criteria     

PN code acquisition for DS-CDMA systems employing smart antennas .II

For pt. I see IEEE Trans. Veh. Technol. A smart antenna, i.e., a blind adaptive antenna array, has attracted much attention to improve the capacity of a future code-division multiple-access wireless communications system. It has been demonstrated that there is significant improvement in data demodulation through lab simulations and field experiments by employing a smart antenna of multiple elements. However, only one element is used for the pseudonoise (PN) code acquisition process, which is a coarse PN code synchronization prior to data demodulation. This paper proposes a simple and practical PN code acquisition scheme, which employs all elements in the smart antenna. Also, this paper uses an adaptive threshold for the PN code acquisition. Simulation results demonstrate that the proposed scheme can significantly improve the PN code acquisition performance, e.g., the PN code acquisition time will be half as long by employing five elements rather than the single element at a given bit-energy-to-interference power spectral density ratio.     

自由空间量子通信动态偏振补偿研究(英文)

In polarization-encoded free-space quantum communications, a transmitter on a satellite and a receiver in a ground station each have a respective polarization zero direction, by which they encode and decode every polarization quantum bit required for a quantum communication protocol. In order to complete the protocol, the ground-based receiver needs to track and compensate for the polarization zero direction of the satellite-based transmitter. Expressions satisfied by amplitudes of the s-polarization component and the p-polarization component are derived based on a two-mirror model, and a condition satisfied by the reflection coefficients of the two mirrors is given. A polarization tracking principle is analyzed for satellite-to-ground quantum communications, and quantum key encoding and decoding principles based on polarization tracking are given. A half-wave-plate-based dynamic polarization-basis compensation scheme is proposed in this paper, and this scheme is proved to be suitable for satellite-to-ground and intersatellite quantum communications.     

星间光通信中跟踪控制技术及发展

星间光通信具有巨大的潜在应用价值,国际上已实现高码率、小型化、轻量化和低功耗激光通信终端,其中光学ATP系统的设计是关键技术之一。对ATP系统的特点进行了讨论,介绍了ATP系统中的跟瞄过程,综述了国内外在星间光通信ATP跟踪系统中所采用的控制算法,指出研究新的控制算法或新的PID参数整定方法,是提高ATP跟踪系统精度的发展方向。     

基于ML和相关器的超宽带系统同步捕获的实现

超宽带(UWB)以其传榆速率高、抗多径和抗干扰能力强等优点,在短距多址无线通信中良好的应用前景而引起广泛研究.文章提出了一种基于ML的UWB同步接收方案,采用相关器与ML估计准则结合在一起实现同步.仿真结果表明:捕获的导频序列M越长和估计的支路数越多,误码率就越低.