微分增益和微分相位的校正

在电视传输系统的指标测试中，微分增益（ＤＧ）、微分相位（ＤＰ）、亮度非线性失真往往互相影响。本文分析一速调管发射机的非线性校正环节，试寻求简便的调整方法，并就传输系统的特点讨论减少ＤＧ、ＤＰ的途径。     

微分增益的测量

当存在微分增益时,色饱和度对亮度电平的依从关系是没有保证的。在亮度电平高时,色饱和度的再现往往不准确。这种失真可用由叠加在不同亮度电平上的等幅色度信号组成的测试信号来测量。常用一种已调阶梯信号(见图1)。 阶梯测试信号由五个亮度梯级上的负     

微分相位和微分增益失真标准的建立

本文介绍一种供检定非线性失真(DG,DP)测试仪的基准失真标准的建立,并分析了基准失真的准确度。     

测量微分相位普遍存在的问题

正确测量微分相位失真对视频信号的产生、编辑和传输都非常重要。介绍了微分相位的一般测量方法,指出微分相位测量中普遍存在的问题,通过分析提出了使用仪器进行微分相位测量的正确方法。利用该方法,不仅能够给出对应于彩色图像质量的正确微分相位失真值,而且通过测量过程还能够了解被测网络相移特性的真实质量情况。     

高速ADC微分相位、微分增益的测试

本文采用数字处理技术对高速ADC的微分相位、微分增益的测试方法进行研究,给出了方程式,构建了数字测试系统,完成了高速ADC微分相位及微分增益的测试,该方法适用于大批量的ADC动态参数的测试.     

彩色信号的测量

FCC(美国联邦通信委员会)对有线电视运行指标在彩色信号测量方面有许多要求。其中,微分增益、微分相位和色度—亮度不均衡这三项相对说来是比较容易做到的,因为这些基带测量的必须遵守的期限是每三年进行一次。FCC的规定指出,这些测量至少必须在四个频道上进行(当频率上限超过100MHz时,每增加100MHz就要增测一个频道)。     

NI发布相位相干射频测量解决方案

美国国家仪器有限公司（NationalInstruments，简称NI）推出针对多通道多输人多输出（MIMO）射频设计和测试应用的NIPXIe-5663E6．6GHzRF矢量信号发生器和NIPXIe-5673E6．6GHzRF矢量信号分析仪，并有双通道、三通道和四通道三种版本供选择。     

GPS动态载波相位测量的航摄飞行试验及其分析

１９９４年４月下旬至５月上旬，在北京地区和太原航摄动态试验场，成功地进行了（飞）机载ＧＰＳ载波相位测量的航摄飞行试验，在三种不同的飞行高度上，三次飞行都取得了令人兴奋的试验成果；采用我们自己研究的ＤＤＫＩＮ动态数据处理软件，不仅精细地解算出每一个摄站三维坐标，而且算得了飞机的三维飞行速度及飞行轨迹，并用动态图形数据检验法评定了机载ＧＰＳ数据质量，而确认每一个摄站坐标的置信度。本文在论述所作机载ＧＰ     

HDTV未压缩信号的测量

经过多年的努力,高清晰度电视(HDTV)终于已实用化、商品化。事实上,该项技术是数字电视(DTV)的前奏,属于DTV的范畴。该技术的出现也要求设计出更多、更新的数字元件和子系统,解决测量问题也迫在眉捷。尽管本文主要是满足从事HDTV设计的工程人员的需要,然而对研究其它类型通信信号的技术人员也是十分有益的。     

Differential phase detection using recursively generated phasereferences

We show that decision-feedback differential phase detection (DFDPD) is equivalent to a technique which generates a phase reference by averaging several primitive phase references. We then modify the DFDPD into a differential phase detection (DPD) technique which generates the phase reference using a simple recursive form. The proposed technique can be easily implemented and has satisfactory error performance     

无相位去包裹的微分法三维形貌测量

提出了一种无需相位去包裹的微分算法,应用于 投影栅三维形貌测量。首先由计算机设计并生成 4幅四步相移正弦条纹图,利用DLP投影仪将其投影到待测物体上;然后由CCD相机采集受待 测物体面型调 制的变形光栅条纹图。再利用4幅四步相移变形条纹图,经数值运算求得沿水平和垂直方 向上待测物体 相位的偏导数,而相位偏导数的积分过程相当于求解泊松方程,于是利用离散余弦变换(DCT )求解泊松方程就可得 到待测物体三维形貌对应的相位数据,从而重构待测物体的三维形貌。测量结果表明,相位 解调的 标准差小于0.031rad,验证了本文方法的有 效性。     

Differential phase error in pulse-width-modulated TV transmission systems

A simple method is presented for prediction of the lower limit of differential phase error in TV transmission systems employing pulse width modulation (PWM). Comparison with measured data over a range of modulation indices demonstrates very close agreement.     

Differential detection of quadrature frequency/phase modulatedsignals

This paper proposes a pilot-symbol-assisted (PSA) signaling format that enables the differential detection of the differentially phase-encoded quadrature frequency/phase modulated (NDQFPM) signal using N orthogonal frequencies. The PSA-NDQFPM signal is transmitted on a frame-by-frame structure. The channel considered is an additive white Gaussian noise channel where the channel phase varies so slowly that it is assumed constant over one frame duration. Each frame consists of J NQFPM pilot symbols and I data blocks, each containing L NDQFPM symbols, with the first symbol differentially phase encoded with respect to pilot symbols. Based on the maximum-likelihood sequence estimation principle, the maximum-likelihood differential-detection (ML-DD) algorithm is developed to detect the PSA-NDQFPM signal on a block-by-block basis. Tight upper and asymptotic bounds are derived and verified by simulation to evaluate the bit error performance of the ML-DD algorithm. Both bandwidth and power efficiencies of PSA-NDQFPM with ML-DD are compared to NQFPM with coherent detection, constant-envelope NQFPM with coherent detection, constant-envelope NDQFPM (also known as NFSK/4DPSK) with ML-DD, and conventional 2DQFPM (also known as DQ²PSK) with ML-DD. It is analytically shown that PSA-NDQFPM with ML-DD has lower power efficiency than NQFPM with coherent detection and NFSK/4DPSK with ML-DD, but still can provide noticeably higher power efficiency than DQ ²PSK with ML-DD when a medium frame length is used. Due to the use of pilot symbols, PSA-NDQFPM with a medium frame length has marginally lower bandwidth efficiency than its coherent counterpart NQFPM, but still yields significantly higher bandwidth efficiency than constant-envelope NQFPM and NFSK/4DPSK     

Differential phase contrast acoustic microscopy using tilted transducers

A differential phase contrast reflection acoustic microscope is reported. In this system the lens is illuminated by two beams, tilted with respect to the lens axis. This leads to two adjacent off-axis foci at the focal plane of the lens. The phase difference between the signals received from these two foci provides the image contrast. Experiments at 10MHz are described and illustrated by preliminary results.     

Differential phase shift-quantum key distribution - [ITU-T kaleidoscope]

Quantum-key distribution has been studied as an ultimate method for secure communications, and now it is emerging as a technology that can be deployed in real fiber networks. Here, we present our QKD experiments based on the differential- phase-shift QKD protocol. A DPSQKD system has a simple configuration that is easy to implement with conventional optical communication components, and it is suitable for a high-clock rate system. Moreover, although the DPS-QKD system is implemented with an attenuated laser source, it is inherently secure against strong eavesdropping attacks called photon number-splitting attacks, which pose a serious threat to conventional QKD systems with attenuated laser sources. We also describe three types of single-photon detectors that are suitable for high-speed, long-distance QKD: an up-conversion detector, a superconducting single-photon detector, and a sinusoidally gated InGaAs avalanche photodiode. We present our recordsetting QKD experiments that employed those detectors.     

Differential phase shift keying in two-path Rayleigh channel withadjacent channel interference

A formula is derived for the error probability of M-ary differential phase-shift keying with differential phase detection in a two-path Rayleigh fading channel taking into account adjacent channel interference (ACI), cochannel interference (CCI), intersymbol interference (ISI), and Doppler frequency shift. Square-root Nyquist filters are used with roll-off, β, the transmitter and receiver as in the proposed US digital mobile radio system. The presence of the second path has a profound effect on increasing the bit error probability (BEP) because it causes ISI. In the absence of ISI, ACI has a smaller effect on BEP than CCI. In the presence of ISI their effect is essentially the same. For a given bit energy-to-noise ratio, the binary system has the lowest BEP; however, the bit rate is also the lowest for a given bandwidth. When the main interference is ACI or CCI, a quaternary system has a lower BEP than the octal system. When the main interference is ISI, this is reversed     

Differential phase noise distribution of Rayleigh faded DPSK signal with selection diversity

Closed-form expressions for the distribution of differential phase noise due to additive white Gaussian noise (AWGN) are derived for predetection selection diversity with independent, equal power very slow Rayleigh fading signals. Also investigated are the effects of fading correlation and unequal powers between diversity antennas on practical two-branch diversity reception. The derived phase distribution is used to calculate the average symbol error rate of 8 DPSK as an example.<>     

Differential detection in quadrature-quadrature phase shift keying(Q2PSK) systems

A generalized quadrature-quadrature phase shift keying (Q² PSK) signaling format is considered for differential encoding and differential detection. Performance in the presence of additive white Gaussian noise (AWGN) is analyzed. Symbol error rate is found to be approximately twice the symbol error rate in a quaternary DPSK system operating at the same E_b/N₀. However, the bandwidth efficiency of differential Q²PSK is substantially higher than that of quaternary DPSK. In differential detection, it is quite reasonable to suspect that errors tend to occur in pairs. It is shown that when the error is due to AWGN, the ratio of double error rate to single error rate can be very high, and the ratio may approach zero at high signal-to-noise ratio. In an attempt to improve the error rate performance, differential detection through maximum-likelihood decoding based on multiple or N symbol observations is considered     

Differential phase tracking applied to Bragg gratings in multi-core fibre for high accuracy curvature measurement

High resolution quasi-static and dynamic curvature measurements are made by differential interferometric phase measurement of fibre Bragg gratings in separate cores of a multi-core fibre. A DC curvature stability of 1/spl times/10/sup -3/m/sup -1/ and an AC curvature resolution of 1/spl times/10/sup -4/ m/sup -1//Hz/sup 1/2/ are reported.