基于科斯塔斯环法的载波提取的设计

介绍了平方变换法相干解调原理,从工程角度完善了载波提取的电路结构,消除了频移载波的误锁问题.提出用科斯塔斯环法来实现从2DPSK信号中提取相干载波,解决了提取的载波信号存在180度的相位含糊问题,为通信系统提高抗噪性能提供了条件.当载波频率很高时,工作频率较低的科斯塔斯环易于实现.并用Simulink设计出科斯塔斯环法提取载波的仿真电路图和进行相应的仿真实验.     

QPSK调制信号的同步载波提取

为了在QPSK数字调制系统中恢复QPSK的载波同步信号,以确保接收机能够接收到无失真的数据,在对QPSK调制理论阐述后提出基于DDS的平方环直接提取载波的方法,分析了电路中各个部分的作用和功能,用Matlab软件进行仿真实验,对锁相环提取的载波信号进行分析,在锁相环性能良好的前提下,实现了载波信号的提取。利用Verilog HDL语言对硬件电路进行行为级描述,综合出RTL级电路。     

一种用于高速QPSK解调的四次方环载波恢复电路

为解决高速QPSK信号全数字解调的技术瓶颈问题,采用模拟方案,研制了一种四次方环载波恢复电路,重点介绍了应用混频器上变频特性的宽带平方电路以及锁相环(PLL)载波提取电路的设计过程.测试结果表明,该载波恢复电路可以完成载频为720 MHz、码速率100 Mbit/s～1 Gbit/s范围的QPSK信号同步载波恢复,解决了高速信号相干解调中载波同步的关键技术问题.     

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。     

频率失谐时抑制载波跟踪环的特性

引言本文确定两种常用环路即平方环和科斯塔斯环的性能。它们在通讯工程中用于:1)解调双边带抑制载波模拟信号;2)在传输数字调制信号的相位相干接收机中提取载波或付载波参考信号。参考文献[1]确定了图1和图2所示两种电路,在环路滤波器增益为1,即一阶环路情况下的非线性特性。本文将这些结论推广到高阶参考     

相干解调器电路的研究

本文介绍了７０ＭＨＺ调相波解调器的设计方法。着重阐述了利用平方环电路撮相干载波的方法进行调相波的相干解调以及消除误码信号的大数判决电路的设计。     

用于QPSK载波恢复的宽带平方电路设计

介绍采用微波混频器的上变频特性实现宽带平方电路的设计方法与具体实现,主要用于高码速率QPSK信号的载波恢复。重点考虑了平方电路的宽带设计,进行了理论推导,并给出了测试结果。采用了功分器、混频器一体化的设计思路,将二者集成在同一基片上,实现了电路的轻小型化。经测试,该平方电路在输入频率为400~800 MHz,输出频率为800~1600 MHz的频带内变频损耗平坦度为±1 dB,能使码速率为300 Mbps的QPSK信号无失真的通过。     

一种用于FPGA的快速锁定全数字延时锁定环的设计实现

本文提出了一种用于FPGA中DDR SDRAM控制器的接口快速锁定的全数字延时锁定环。该电路对数据选择脉冲(DQS)实现90度的相位偏移。为了实现延时锁定环的快速锁定,同时解决了错误锁定的问题,本文提出了一种新颖的数字时间转换器的结构。在延时环路中设计了占空比纠正电路,实现50％的占空比输出。该延时锁定环电路采用0.13μm标准CMOS工艺设计制作。测试结果表明,工作频率范围为75MHz～350MHz,数字控制延时链(DCDL)的调节精度为15ps,并且电路的闭环特性能跟踪电压、温度等环境的变化。     

单频干扰对QPSK 载波同步影响的分析

本文分析了存四相相移键控(QPSK)信号载波中心频率附近出现的单频干扰对QPSK载波同步产生的影响.通过准线性法,分别得到了锁相环锁定在载波上时以及锁定在干扰上时,载波-干扰功率比与载波-干扰频率差的关系式,并定量评价了单频干扰对QPSK载波同步的影响.     

付载波跟踪方法和通信系统的设计

从功率考虑,采用抑制载波相干检波通信是有利的。本文分析了用于解调抑制载波信号的相关参考的两种产生方法,即平方环法和数学等效的科斯塔斯环法,某些地方包含了对压控振荡器噪声和初始频率失调的影响的分析。本文给出了稳态相位误差概率分布,也就是一阶环路首次失锁的予期时间。研究了利用平方环产生相干付载波参考的编码或非编码遥测系统的误差概率,以便于选择正确的系统参数。     

Intersymbol interference effects on BPSK and QPSK carrier trackingloops

The tracking performance of three conventional carrier tracking loops in the presence of intersymbol interference (ISI) is analyzed. The closed-form expressions for the squaring losses of BPSK (binary phase-shift-keyed) low-SNR (signal-to-noise ratio), BPSK high-SNR, and QPSK (quaternary phase-shift-keyed) low-SNR loops are derived. ISI is shown to affect the BPSK high-SNR loop as much as the I-Q loop despite the nonlinear effect of the hard-limiter. For the QPSK carrier tracking loop, the degradation is shown to be greater due to the modulation of both components of the carrier. In this case, ISI, in addition to modifying the coefficients in the squaring loss, adds a new term not present in wideband channels. In all cases, a unity squaring loss could not be achieved because of the irreducible error due to pattern noise. This noise is only present in band-limited channels and is dependent on the data model used     

Acquisition performance of various QPSK carrier tracking loops

The frequency and phase acquisition performance of three quadrature phase shift keying (QPSK) carrier tracking loops, the MAP estimation loop, the Costas crossover loop, and the generalized Costas loop, is described. Acquisition time and probability of acquisition as a function of both loop signal-to-noise ratio and frequency offset to loop bandwidth ratio are obtained via computer simulations for type II and III loops. It is shown that the MAP loop, which results in the smallest squaring loss for all signal-to-noise ratios, is sometimes outperformed by the other two loops in terms of acquisition time and acquisition probability     

The performance of suppressed carrier tracking loops in the presence of frequency detuning

The extraction of a coherent reference for purposes of demodulating double-sideband suppressed carrier (DSB-SC) signals can be accomplished using either a squaring loop or a Costas loop. By means of the Fokker-Planck equation, this paper establishes the tracking performance of these two circuits in the presence of frequency detuning, and then applies the results in evaluating the performance of coherent demodulators of digital (coded or uncoded) data. The results are sufficiently general to assess the effects of a broad class of prefiltering characteristics on tracking performance, as well as the effects due to various loop filter mechanizations. An expression for the moments of the time to first loss of synchronization is also given.     

Analysis of two loops for carrier recovery in CPM with index 1/2

An examination is made of the performance of a squaring loop and a fourth-power loop used for tracking the received carrier phase of binary continuous-phase modulated (CPM) signals with index 1/2. Noise-free analysis is performed first and a simple relationship between the phase error and the control voltage is obtained for each case, with the premodulation filter response as a parameter. Linearized analysis of the phase error variance is then conducted in the presence of additive white Gaussian noise. It is shown that the phase variance in both cases contains a self-noise component that sets a lower bound on the synchronizer's performance at very high signal-to-noise ratios. Numerical results are presented for a number of popular CPM signals. It is found that the squaring loop performs best with MSK (minimum shift keying), while the fourth-power loop performs best with duobinary MSK     

Novel p.s.k. tanlock loop

A new loop for coherent demodulation of suppressed carrier phase-shift-keyed (p.s.k.) signals is presented. The p.s.k. tanlock loop (p.s.k.-t.l.l.) has a wider tracking range and faster phase acquisition than the Costas or squaring loops usually used for p.s.k. suppressed carrier tracking, but it has a greater tendency to false lock.     

On the Calculation of Squaring Loss in Costas Loops with Arbitrary Arm Filters

The calculation of the optimum performance of suppressed carrier receivers with Costas loop tracking is directly related to evaluating the loop's so-called squaring loss. Recent work by the author and others presented specific numerical results for this loss when the input data were biphase-L(Manchester coded) and the Costas loop arm filters were of then-pole Butterworth type. These results were largely obtained by numerical integration on a digital computer. This paper presents a partial fraction expansion technique for arriving at closed form expressions for squaring loss for Costas loops with arbitary arm filters and NRZ as well as Manchester coded data. Specific closed form results are given for one and two pole Butterworth filters as examples.     

On the Optimality of the MAP Estimation Loop for Carrier Phase Tracking BPSK and QPSK Signals

Starting with MAP estimation theory as a basis for optimally estimating carrier phase of BPSK and QPSK modulations, it is shown in this paper that the closed loop phase trackers, which are motivated by this approach, are indeed closed loop optimum in the minimum mean-square phase tracking jitter sense. The corresponding squaring loss performance of these so-called MAP estimation loops is compared with that of more practical implementations wherein the hyperbolic tangent nonlinearity is approximated by simpler functions.     

The effects of multipath delay spread on timing recovery

Equations for the recovered timing for a squaring timing recovery circuit under multipath radio propagation are derived. Both coherent and differential detections are studied. If delay spread is much smaller than the symbol duration, the recovered timing can be approximated by the centroid of the power delay profile, p(t). Two cases of timing loop bandwidth are considered. If the fading frequency is much lower than the bandwidth of the timing loop, the instantaneous sample of p(t) is used to generate the timing clock. If the fading frequency is much higher than the loop bandwidth, the ensemble average of p(t) over fading samples is used to recover the timing. A computer simulation is performed for a system operating in a frequency-selective, slowly fading environment. It is found that for root mean square (rms) delay spread less than or equal to 0.1 of the symbol duration, a squaring timing loop with either narrow or wide bandwidth can properly determine the timing detection. The main mechanism of the "irreducible bit error rate" in this case is the closure of the eye-pattern instead of timing error.     

Tracking Performance of Costas Loops with Hard-Limited In-Phase Channel

It is becoming increasingly popular in the design of suppressed carrier receivers, which employ Costas loops for earrier reconstruction, to hard-limit the output of the in-phase channel. Doing so allows replacement of the analog multiplier, which forms the loop error signal, with a chopper-type device which typically exhibits much less dc offset. The false lock behavior of such a hard-limited loop was recently investigated and shown to be quite different from that of the conventional Costas loop without the hard limiter. This paper presents the companion, analysis of the tracking performance of the hard-limited loop and assesses the penalty, if indeed it is a penalty rather than an improvement, in this performance relative to the conventional Costas loop with an analog third multiplier. In particular, for the case ofRCarm filters and NRZ data, the squaring loss (or equivalently the linear loop tracking jitter) is evaluated and illustrated as a function of the ratio of arm filter bandwidth to data rate and data signal-to-noise ratio. Superimposed on these numerical results will be the corresponding ones for the conventional Costas loop. As a finale, the equivalence in operation of the Costas loop with hard-limited in-phase channel and a baseband modulation carrier reconstruction loop referred to as a demod/ remod loop is discussed.     

一种符号定时算法的研究与仿真

在数字通信系统中,符号同步是正确接收发送信号的先决条件之一,对于单载波而言,需要正确地寻找到最佳的采样点,因为一点偏移都会造成星座图的发散。文中对数字滤波和平方的符号定时算法进行了研究,并以此算法为基础,结合F．M．Gardner提出的插值滤波器构成锁相环路,对环路的各个模块进行了详细描述,并给出了64QAM信号仿真的结果。