A Performance Study of Delta Modulation Systems for Voiceband Data Signals

In this paper the performance of delta modulation (DM) systems have been studied by computer simulation when the input signal to the DM coder is a voiceband data signal. First, the parameter values of three DM systems, linear DM (LDM), constant factor DM (CFDM), and continuously variable slope DM (CVSD) has been optimized for 4800 bits/s differential phase shift keying (DPSK) signal. Then, the performance of the three DM systems have been studied for ideal and noisy channels. It has been found that the peak signal-to-quantization-noise ratio (SQNR) is nearly the same regardless of coding scheme used, but CFDM yields the widest dynamic range. In a noisy channel, however, CFDM is very sensitive to channel bit errors. Considering the overall performance, CVSD appears to be the best among the three DM systems studied. Also, the performances of DM's have been compared with those of PCM and DPCM systems. In addition, we have studied the effect of DM quantization noise on modem bit error rate by the Monte Carlo simulation method. It is possible to transmit a 4800 bits/s DPSK signal at a bit error rate below 10^-5by CVSD with the rate of 32 kbits/s.     

A Delta Modulation Filter for Speech-Type Signals

This paper considers the realization of an all-digital system for direct filtering of a delta modulation (DM) encoded signal. We have shown [1] that this system can be realized fairly easily for any type of filter function when the signals are encoded with a linear DM. We now address the problem of digitally filtering an adaptive DM (ADM) encoded signal. We show that we can again realize any type of filter function and our system will operate directly on the ADM bit stream. In addition, we present a circuit realization that does not require complex digital hardware. Performance has been tested via simulation on a digital computer, using a variety of test signals; both temporal and spectral results are presented.     

Algorithms for Delayed Encoding in Delta Modulation with Speech-Like Signals

This concise paper is concerned with the problem of improved delta-coding by using delayed decision instead of bit-bit-by-bit decision. It is found that delayed encoding allows a fairly general predictor to be used without causing instability problems. Simulations indicate that considerable improvement can be achieved by matching the feedback filter to the input process. Delayed encoding requires a search algorithm for making the decisions. Some proposals of algorithms that are efficient from a computational point of view are presented. Particular interest is attached to a highly truncated version of the Viterbi algorithm, which seems very promising.     

Voice-Band Data Modem Performance Over Companded Delta Modulation Channels

This paper reports upon the results of tests of the transmission of data over single- and multiple-hop companded delta modulation (DM) systems. The DM coder-decoder (CODEC) was optimized for voice transmission. Modem bit error rate (BER) achievable over the range of 1200-9600 bits/s is presented. A comparison with the performance of pulse code modulation (PCM) is included. The comparison indicates that the two systems are comparable for error-free digital lines but favors the DM system for lines with errors.     

SNR Formula for Linear Delta Modulation with Band-Limited Flat and RC-Shaped Gaussian Signals

Easy to use simple equations of optimum slope loading factor and peak SNR are given for a linear delta modulator having Gaussian input signals with band-limitedRCspectra. The equations are accurate to within 1 dB over a wide range of normalized sampling frequency and forRCspectrum bandwidths of practical interest.     

一种CPM信号与PSK类信号的调制识别算法

提出了一种基于分形盒维数及二次方谱特征的方法,对由CPM与PSK类信号组成的信号集进行调制识别分类。首先提取信号集内各待识别信号的分形盒维数特征,将CPM和OQPSK识别出来;然后对信号集中剩余信号提取相应的二次方谱离散谱线特征依次区分出BPSK、UQPSK和QPSK;最后根据决策树原理设计分类器,实现信号集内信号的识别。仿真结果表明,该算法对信号集内的信号在信噪比达到3 d B以上条件下正确识别率可达到90%以上。     

通信信号调制方式识别方法综述

对通信信号调制方式的识别进行了深入研究,对通信信号常用的数字调制技术和调制识别预处理技术、理想高斯白噪声条件下基于决策论和基于统计模式的识别法、非理想信道条件下的调制识别法以及对共信道多信号调制方式的识别等进行了总结。在简要介绍各种方法的来源、理论基础和发展基础上讨论了各自的优缺点,并提出了调制识别研究领域的进一步发展方向。     

脉内调制信号的分析

通过对几种脉冲调制算法的比较，分析了各种算法的优缺点和适用范围，并在原算法基础上加以改进，提出了一种新的脉冲信号调制分析方案：针对不同的信号采用不同的算法。计算机仿真结果表明：此方案识别信号能力强，在较低的信噪比下具有很好的效果。     

角度调制信号调制指数盲估计研究

 调制指数估计在角度调制信号的解调、FM／PM识别等应用中具有十分重要的意义。分析了基带为单音、PSK、FSK等信号时角度调制信号的时频结构,进而建立了信号的统一数学表达式,由此推导并提出了一种无需任何先验信息的调制指数估计方法。仿真实验表明：该方法能有效估计上述基带调制时的角度调制指数。     

Hybrid Companding Delta Modulation

We present a reasonably complete account of an improved adaptive delta modulation (ADM) system called hybrid companding delta modulation (HCDM). The HCDM system that is far superior to continuously variable slope DM (CVSD) or constant factor DM (CFDM) is advantageous, particularly for speech coding. It employs both syllabic and instantaneous companding schemes. Performance analysis of the system has been done and verified by computer simulation. In getting the mathematical formula for HCDM granular noise, a new method based on amplitude distribution is proposed. Optimization of the system parameter values by simulation is also discussed. In addition, an efficient method of hardware implementation is considered.     

GLSFBC-OFDM信号调制识别算法

提出了频率选择性衰落信道条件下区分GLSFBC结构的多载波信号(OFDM)和单载波信号(MFSK、MPSK、MQAM)的调制识别算法.该算法基于接收信号的高阶累积量,只需直接对接收的中频信号进行识别处理,不需要发射信号和信道的先验知识.仿真结果表明,在SNR高于7 dB时识别率可以达到90％.     

基于小波变换的信号调制方式的识别研究

根据小波理论,利用小波变换的尺度分解和局部放大的能力,对调制信号进行小波变换和分解,挖掘调制信号在间断点的瞬态特性,成功建立了不同调制方式和其调制特征间的对应关系。在不需要同步和符号速率等先验知识的情况下,实现了对MASK、MFSK、MPSK、MQAM等数字调制方式的完全识别。通过理论分析和计算机仿真验证了所提方法的有效性和实用性,具有很高的应用价值。     

Continuous Phase Modulation of F-QPSK-B Signals

A continuous phase modulation (CPM) implementation alternative of a recently standardized class of Feher-patented quadrature phase-shift keying (F-QPSK-B) modulation is proposed. Based on the fact that the F-QPSK-B signal has a quasi-constant envelope and continuous phase characteristics, it is shown that it can indeed be generated by the CPM scheme. For example, an F-QPSK-B signal can be fully generated using an existing FM-based transmitter with a modulation index of 0.5. Furthermore, a premodulation filter and an alternating change monitor differential encoder for the continuous-phase-modulated F-QPSK-B signal to be fully compatible with the I/Q modulated F-QPSK-B signal are proposed, allowing direct symbol-by-symbol coherent detection without the use of any special decoding schemes inherent in all CPM schemes. It is shown that the power spectral density and eye diagram of the continuous-phase-modulated F-QPSK-B signal are practically the same as those of the I/Q modulated F-QPSK-B signal. By utilizing CPM characteristics, an optimum maximum-likelihood (ML) coherent receiver for the F-QPSK-B signal is proposed. It is shown that the bit-error-rate performances of the optimum ML coherent detection, symbol-by-symbol coherent detection, and noncoherent detection of the continuous-phase-modulated F-QPSK-B signal are almost the same as those of the I/Q modulated F-QPSK-B signal     

多分量相移键控信号调制识别技术

为解决单通道接收机在多信号环境下的调制识别问题,提出了一种不经信号分离直接提取各信号分量的特征不变量以实现多个相移键控信号的调制识别算法.首先给出了多信号特征不变量提取原则,进而提出了融合二、四阶循环累积量的特征不变量提取方法,推导了所提特征不变量的理论值,最后设计了适合于这里模型的分类器.仿真实验表明:该算法能不受干扰地提取各分量的特征不变量,进而分类器能有效地识别调制组合内任意的双分量相移键控信号.同等实验条件下,所提算法的识别性能优于现有的基于四阶循环累积量的算法.     

Optimal Discrete-Time Delta Modulation System

Delta modulation communication systems are a popular and effective approach for transmitting analog signals over a binary channel. The performance of a discrete-time linear and leaky delta modulator is compared to the performance of the optimal delta modulator for a firstorder Gauss-Markov source.     

Decimation for Sigma Delta Modulation

Decimation is an important component of oversampled analog-to-digital conversion. It transforms the digitally modulated signal from short words occurring at high sampling rate to longer words at the Nyquist rate. Here we are concerned with the initial stage of decimation, where the word rate decreases to about four times the Nyquist rate. We show that digital filters comprising cascades of integrate-and-dump functions can match the structure of the noise from sigma delta modulation to provide decimation with negligible loss of signal-to-noise ratio. Explicit formulas evaluate particular tradeoffs between modulation rate, signal-to-noise ratio, length of digital words, and complexity of the modulating and decimating functions.     

卫星通信信号调制识别技术研究

通信信号的调制方式识别是非协作通信领域的一个研究热点,它需要在没有任何先验条件,且环境复杂有噪声的条件下,不依赖于其它的先验知识,确定目标信号的调制方式。然后就可提取载频、码速率、滚降系数等参数,为信号的进一步深入研究提供依据。分析了几种经常用于卫星通信的MPSK调制信号和高阶调制信号16APSK,提出了一种基于高阶累积量与频谱特征的识别算法。在特定的数据长度和信噪比条件下,理论分析与仿真验证均验证了该算法易于实现、识别率高（≥95％）。     

Time-Frequency Coherent Modulation Filtering of Nonstationary Signals

Modulation filtering is a class of techniques for filtering slowly-varying modulation envelopes of frequency subbands of a signal, ideally without affecting the subband signal's temporal fine-structure. Coherent modulation filtering is a potentially more effective type of such techniques where, via an explicit product model, subband envelopes are determined from demodulation of the subband signal with a coherently detected subband carrier. In this paper we propose a coherent modulation filtering technique based on detecting the instantaneous frequency of a subband from its time-frequency representation. We devise theory to show that coherent modulation filtering imposes a new bandlimiting constraint on the product of the modulator and carrier as well as the ability to recover arbitrarily chosen envelopes and carriers from their modulation product. We then formally show that a carrier estimate based on the time-varying spectral center-of-gravity satisfies the bandlimiting condition. This bandwidth constraint leads to effective and artifact-free modulation filters, offering new approaches for potential signal modification. However, the spectral center-of-gravity does not, in general, satisfy the condition of arbitrary carrier recovery. Finally, the results from modulation-filtering a speech signal are then used to validate the theory.     

调制信号小波变换的尺度特征

本文根据小波变换的定义和通信调制信号的一般表示形式,分析了典型调制信号的小波系数在时间-尺度平面上的特征,详细推导了小波系数达到最大时所对应的最佳尺度因子与调制类型的关系,并给出了仿真结果.理论分析和实验结果均表明,不同调制信号的小波系数有着不同特征,最佳尺度因子的变化规律与调制类型一一对应,并且与被调制的基带信号存在确定关系.最佳尺度因子的这种特征可用来构造基于小波变换的调制信号分类器和解调器.     

Delta Modulation of the Wiener Process

The analysis of the performance of a delta modulator with a Wiener process input is considered. The mean and the variance of the steady-state squared error are derived. In addition, the mean of the steady-state error of order four is calculated. It is shown that the behavior of all these moments as functions of the step size Δ and the sampling intervalTis similar: for each fixed Δ, the moments are monotonically increasing inT. More important, for each fixedT, there exists an optimal step size Δoptwhich minimizes each of these moments. It is shown that Δoptis a multiple ofT^{1/2}and that the corresponding minimum value of the moments is a multiple of eitherTor T², depending on the order of the moment.