Joint Source–Channel Coding Error Exponent for Discrete Communication Systems With Markovian Memory

We study the error exponent, $E_{J}$, for reliably transmitting a discrete stationary ergodic Markov (SEM) source ${mmb Q}$ over a discrete channel ${mmb W}$ with additive SEM noise via a joint source–channel (JSC) code. We first establish an upper bound for $E_{J}$ in terms of the RÉnyi entropy rates of the source and noise processes. We next investigate the analytical computation of $E_{J}$ by comparing our bound with Gallager's lower bound (1968) when the latter one is specialized to the SEM source–channel system. We also note that both bounds can be represented in CsiszÁr's form (1980), as the minimum of the sum of the source and channel error exponents. Our results provide us with the tools to systematically compare $E_{J}$ with the tandem (separate) coding exponent $E_{T}$. We show that as in the case of memoryless source–channel pairs $E_{J}leq 2E_{T}$ and we provide explicit conditions for which $E_{J}> E_{T}$. Numerical results indicate that $E_{J}thickapprox 2E_{T}$ for many SEM source–channel pairs, hence illustrating a substantial advantage of JSC coding over tandem coding for systems with Markovian memory.      

Lower Bounds for Finite Intersymbol Interference Error Rates

Some simple lower bounds for the probability of error for band-restricted digital communication are presented. The bounds revolve two values of the complementary error function, the system SNR, the peak value, second moment, and sometimes, the fourth moment of the intersymbol interference. Contrary to other available lower bounds, no parameter searches or infinite series computations are required. The bounds hold when the system "eye" is open and in some cases when the source symbols are correlated.     

Optimization of Branch Metric Exponent and Quantization Range in MLSE Receivers for Duobinary Systems

We analyze by simulation the performance of an optically amplified uncompensated duobinary system using a 64-state maximum-likelihood sequence estimation (MLSE) receiver (Rx) based on a Euclidean branch metric with variable postdetection nonlinear distortion exponent. We found that the optimum exponent depends on the accumulated dispersion, the Rx analog-to-digital converter (ADC) resolution, and signal clipping. On the other hand, we found performance to be weakly dependent on the exponent value. When using a finite number of ADC resolution bits, drastic signal clipping proved very beneficial in improving the performance of the MLSE processor. Assuming three resolution bits, with joint clipping and exponent optimization, uncompensated transmission at 10.7 Gb/s over 550 km of standard single-mode fiber could be achieved with essentially no penalty with respect to back-to-back.     

Error Rate Lower Bounds for Digital Communication with Multiple Interferences

This paper presents simple and general lower bounds for error rates in digital communication systems. The information bearing signal is taken to be impaired by additive interference and carrier phase jitter. The former is taken to be composed of two components; one component is peak-limited while the other is not. Intersymbol and cochannel interference are examples of peak-limited interference while additive thermal noise is an example of a nonpeak-limited interference. The novelty of the paper is in the generality of the results and in obtaining a simple error bound for transmission in the presence of cochannel interference and carrier phase jitter.     

Lower Bounds on Error Probability in the Presence of Large Intersymbol Interference

A lower bound on the symbol error probability achieved by any estimator of a digital pulse-amplitude-modulated sequence in the presence of white Gaussian noise and intersymbol interference is presented. The bound reduces to the well-known single-pulse error probability bound when intersymbol interference is small, but is tighter when interference is large. For example, on the singlepole (RC) channel, the effective signal-to-noise ratio for any estimator is shown to decrease by at least 3 dB for every doubling in pulse rate T^-1asT rightarrow 0and, on the double-pole channel, by at least 9 dB, thus disproving a recent conjecture [2] on the performance of nonlinear receivers.     

Cramer-Rao Lower Bounds for Semi-Blind ML Channel Estimation in UWB Systems

This paper derives a unified representation of the Cramer-Rao lower bounds (CRLBs) for semi-blind maximum-likelihood (ML) channel estimation in time-hopping (TH) ultra-wideband systems with pulse amplitude and position modulation, pulse amplitude modulation and pulse position modulation (PPM). These bounds subsume the existing results for both pilot-based and blind ML channel estimation in TH-PPM as special cases. A numerical example is used to illustrate the effects of different data modulation formats and system parameters on the CRLBs derived     

An Expression for the Average Quantization Error

The quantization error for MIMO (multiple-input multiple-output) downlink channels is known to be the minimum of independent and identically distributed beta random variables. In this note, an exact expression is derived for the average quantization error. Computational issues relating to its correctness, usage and approximations are discussed.

基于视觉特性的多比特量化水印方案

基于人类视觉特性(VHS),提出了一种新的量化水印方案。水印信息以量化方式嵌入在二层变换系数上,这些二层变换系数是由小波系数乘以不同权重、混洗后再进行离散余弦变换生成的。其中权值根据视觉特性确定,使得水印信号在高、低频部分的能量合理分配以保证较小的视觉失真。这种方法在无视觉失真的条件下可以保证较好的嵌入量和稳键性。定量地分析了信息量、隐蔽性和稳健性三者的关系,并用模拟实验验证了这些结果。     

Error Exponent Regions for Gaussian Broadcast and Multiple-Access Channels

In modern communication systems, different users have different requirements for quality of service (QoS). In this work, QoS refers to the average codeword error probability experienced by the users in the network. Although several practical schemes (collectively referred to as unequal error protection schemes) have been studied in the literature and are implemented in existing systems, the corresponding performance limits have not been studied in an information-theoretic framework. In this paper, an information-theoretic framework is considered to study communication systems which provide heterogeneous reliabilities for the users. This is done by defining individual probabilities of error for the users in the network and obtaining the fundamental tradeoffs of the corresponding error exponents. In particular, we quantify the reliability tradeoff by introducing the notion of error exponent region (EER), which specifies the set of error exponent vectors that are simultaneously achievable by the users for a fixed vector of users' rates. We show the existence of a tradeoff among the users' error exponents by deriving inner and outer bounds for the EER. Using this framework, a system can be realized, which can provide a tradeoff of reliabilities among the users for a fixed vector of users' rates. This adds a completely new dimension to the performance tradeoff in such networks, which is unique to multiterminal communication systems, and is beyond what is given by the conventional performance-versus-rate tradeoff in single-user systems. Although this is a very general concept and can be applied to any multiterminal communication system, in this paper we consider Gaussian broadcast and multiple-access channels (MACs).     

Error Rate Bounds for Differential PSK

Differential phase-shift keying (DPSK) and coherent phase-shift keying (CPSK) are two of the techniques widely used in digital communications over channels such as satellite, terrestrial radio, and voiceband telephone. Because of the linear nature of the demodulation process in CPSK, the error performance of CPSK with various sources of impairments has been exhaustively treated, but even with additive Gaussian noise, only asymptotic approximations are available to determine the detection performance ofM-ary DPSK,M> 2. In this note, the error performance of nonbinary DPSK in additive Gaussian noise channels has been bounded in terms of tabulated functions and various approximations are then derived.     

Lower Bounds for Constant Multiplication Problems

Lower bounds for problems related to realizing multiplication by constants with shifts, adders, and subtracters are presented. These lower bounds are straightforwardly calculated and have applications in proving the optimality of solutions obtained by heuristics.     

基于量化和关系的图像水印算法

提出了一种基于量化和关系的奇异值分解水印算法。算法先对载体图像进行互不重叠的8×8分块;其次对选取的分块进行1级离散小波变换和分别对生成的低频子带和高频子带进行奇异值分解;最后对低频和高频子带奇异值分解后的最大奇异值分别采用量化和关系的嵌入方法嵌入预处理后的水印。实验表明,该算法具有较好的透明性和鲁棒性。与其他算法相比,对于大多数的攻击,该算法具有更好的性能。     

Asymptotics and Error Rate Bounds for M-ary DPSK

The symbol error probabilityP_{E}(M)forM-ary DPSK is shown to be bounded in terms of a recent asymptotic approximationP_{asym}(M)by the inequalitiesP_{asym}(M) < P_{E}(M) < 1.03P_{asym}(M);M geq 4, E_{b}/N_{0} geq 1whereE_{b}/N_{0}is the bit energy-to-noise spectral density ratio. Aside from the wide range of validity and the closeness of the lower and upper bounds, this result is striking in light of the often held view that such asymptotic approximations are primarily of value only in the limitE_{b}/N_{0} rightarrow infty; thus, one of the goals of this note is to demonstrate that asymptotic methods can lead to extremely good error rate approximations in lieu of the more traditional and more widely used bounding techniques. The results are also noted to be applicable in other similar situations which commonly occur.     

Influence of Cyclic Strain-Hardening Exponent on Fatigue Ductility Exponent for a Sn-Ag-Cu Micro-Solder Joint

The fatigue ductility exponent in the Coffin–Manson law for a Sn-Ag-Cu micro-solder joint was investigated in terms of the cyclic strain-hardening property and the inelastic strain energy in fracture for isothermal fatigue. The fatigue ductility exponent was found to increase with temperature and holding time under strain at high temperature. This exponent is closely related to the cyclic strain-hardening exponent, which displays the opposite behavior in that it decreases with increasing temperature and with coarsening of intermetallic compound particles while holding under strain at high temperature. This result differs from the creep damage mechanism (grain boundary fracture), which is a primary reason for the significant reduction in fatigue life for all strain ranges for large-size specimens.     

Quantization Index Modulation Methods for Digital Watermarking and Information Embedding of Multimedia

Copyright notification and enforcement, authentication, covert communication, and hybrid transmission applications such as digital audio broadcasting are examples of emerging multimedia applications for digital watermarking and information embedding methods, methods for embedding one signal (e.g., the digital watermark) within another host signal to form a third, composite signal. The embedding is designed to achieve efficient trade-offs among the three conflicting goals of maximizing information-embedding rate, minimizing distortion between the host signal and composite signal, and maximizing the robustness of the embedding.We present a class of embedding methods called quantization index modulation (QIM) that achieve provably good rate-distortion-robustness performance. These methods, and low-complexity realizations of them called dither modulation, are provably better than both previously proposed linear methods of spread spectrum and nonlinear methods of low-bit(s) modulation against square-error distortion-constrained intentional attacks. We also derive information-embedding capacities for the case of a colored Gaussian host signal and additive colored Gaussian noise attacks. These results imply an information embedding capacity of about 1/3 b/s of embedded digital rate for every Hertz of host signal bandwidth and every dB drop in received host signal quality.We show that QIM methods achieve performance within 1.6 dB of capacity, and we introduce a form of postprocessing we refer to as distortion compensation that, when combined with QIM, allows capacity to be achieved. In addition, we show that distortion-compensated QIM is an optimal embedding strategy against some important classes of intentional attacks as well. Finally, we report simulation results that demonstrate the performance of dither modulation realizations that can be implemented with only a few adders and scalar quantizers.     

Low-Resolution Scalar Quantization for Gaussian Sources and Absolute Error

This correspondence considers low-resolution scalar quantization for a memoryless Gaussian source with respect to absolute error distortion. It shows that slope of the operational rate-distortion function of scalar quantization is infinite at the point D_max where the rate becomes zero. Thus, unlike the situation for squared error distortion, or for Laplacian and exponential sources with squared or absolute error distortion, for a Gaussian source and absolute error, scalar quantization at low rates is far from the Shannon rate-distortion function, i.e., far from the performance of the best lossy coding technique     

Joint Estimation of Time Delay and Clock Error in the Incoherent Reception Systems

The assumption that observed signals are ideally received is commonly used in the literature on time-delay estimation. However, for practical digital receivers, the received radio-frequency signals are usually downconverted to the baseband and digitized by analog-to-digital converters. Because inaccurate and unstable system clocks are used, frequency and phase offsets are usually induced by the frequency-mixing procedure, whereas a time stretch may ensue from the sampling procedure. The aforementioned problems are almost inevitable for incoherent reception systems. Therefore, the neglect of imperfect reception for incoherent systems may reduce the performance of conventional time-delay estimation methods. In this paper, employing refined signal models developed specifically for incoherent time-delay estimation in active and passive systems, the corresponding joint maximum likelihood estimates of time delay and system-clock frequency error are proposed. The Cramér–Rao lower bounds (CRLBs) on time-delay and clock frequency error estimations are also derived. The performance of the proposed time-delay estimators can be improved for frequency/phase offsets and time stretches, approaching the performance of the CRLBs in scenarios of moderate and high signal-to-noise ratios. Furthermore, both CRLBs analysis and simulation results verify that the accuracy of the proposed time-delay estimator is unaffected by the performance of the system clock in moderate scenarios.     

基于卷积码和量化的盲数字水印算法

根据水印系统与通信系统的相似性,将通信信道编码中的卷积编码和交织技术应用到图像数字水印算法中.水印在嵌入前进行Toral自同构运算、卷积编码和交织,以提高水印的安全性和鲁棒性.根据水印信息对DCT后的直流系数进行量化,以实现盲检.实验表明,该算法对椒盐噪声、高斯噪声、压缩、滤波和剪切等具有良好的鲁棒性.