We investigate the joint source-channel coding (JSCC) excess distortion exponentEJ(the exponent of the probability of exceeding a prescribed distortion level) for some memoryless communication systems with continuous alphabets. We first establish upper and lower bounds forEJfor systems consisting of a memoryless Gaussian source under the squared-error distortion fidelity criterion and a memoryless additive Gaussian noise channel with a quadratic power constraint at the channel input. A necessary and sufficient condition for which the two bounds coincide is provided, thus exactly determining the exponent. This condition is observed to hold for a wide range of source-channel parameters. As an application, we study the advantage in terms of the excess distortion exponent of JSCC over traditional tandem (separate) coding for Gaussian systems. A formula for the tandem exponent is derived in terms of the Gaussian source and Gaussian channel exponents, and numerical results show that JSCC often substantially outperforms tandem coding. The problem of transmitting memoryless Laplacian sources over the Gaussian channel under the magnitude-error distortion is also carried out. Finally, we establish a lower bound forEJfor a certain class of continuous source-channel pairs when the distortion measure is a metric.

We study the transmission of two discrete memoryless correlated sources, consisting of a common and a private source, over a discrete memoryless multiterminal channel with two transmitters and two receivers. At the transmitter side, the common source is observed by both encoders but the private source can only be accessed by one encoder. At the receiver side, both decoders need to reconstruct the common source, but only one decoder needs to reconstruct the private source. We hence refer to this system by the asymmetric two-user source-channel coding system. We derive a universally achievable lossless joint source-channel coding (JSCC) error exponent pair for the two-user system by using a technique which generalizes Csiszar's type-packing lemma (1980) for the point-to-point (single-user) discrete memoryless source-channel system. We next investigate the largest convergence rate of asymptotic exponential decay of the system (overall) probability of erroneous transmission, i.e., the system JSCC error exponent. We obtain lower and upper bounds for the exponent. As a consequence, we establish a JSCC theorem with single-letter characterization and we show that the separation principle holds for the asymmetric two-user scenario. By introducing common randomization, we also provide a formula for the tandem (separate) source-channel coding error exponent. Numerical examples show that for a large class of systems consisting of two correlated sources and an asymmetric multiple-access channel with additive noise, the JSCC error exponent considerably outperforms the corresponding tandem coding error exponent.

We establish random-coding lower bounds to the error exponent of discrete and Gaussian joint quantization and private watermarking systems. In the discrete system, both the covertext and the attack channel are memoryless and have finite alphabets. In the Gaussian system, the covertext is memoryless Gaussian and the attack channel has additive memoryless Gaussian noise. In both cases, our bounds on the error exponent are positive in the interior of the achievable quantization and watermarking rate region.

We consider a public multi-user information embedding (watermarking) system in which two messages (watermarks) are independently embedded into two correlated covertexts and are transmitted through a multiple-access attack channel. The tradeoff between the achievable embedding rates and the average distortions for the two embedders is studied. For given distortion levels, inner and outer bounds for the embedding capacity region are obtained in single-letter form. Tighter bounds are also given for independent covertexts.

Consider a multi-user private information-hiding scenario in which two information hiders separately embed correlated sources (S1, S2) into a common host source U (covertext). The i-th information hider embeds the secret source Siinto the covertext U subject to a distortion constraint Di(i = 1, 2). The outputs (stegotexts) are corrupted by a multiple access channel attack WY|X1X2. A sufficient condition (in single-letter form) under which (S1, S2) can be successfully embedded into U under WY|X1X2is established.

Consider transmitting two discrete memoryless correlated sources, consisting of a common and a private source, over a discrete memoryless multi-terminal channel with two transmitters and two receivers. At the transmitter side, the common source is observed by both encoders but the private source can only be accessed by one encoder. At the receiver side, both decoders need to reconstruct the common source, but only one decoder needs to reconstruct the private source. We hence refer to this system by the asymmetric 2-user source-channel system. In this work, we derive a universally achievable joint source-channel coding (JSCC) error exponent pair for the 2-user system by using a technique which generalizes Csiszar's method (1980) for the point- to-point (single-user) discrete memoryless source-channel system. We next investigate the largest convergence rate of asymptotic exponential decay of the system (overall) probability of erroneous transmission, i.e., the system JSCC error exponent. We obtain lower and upper bounds for the exponent. As a consequence, we establish the JSCC theorem with single letter characterization.

We study the error exponent, EJ, for reliably transmitting a discrete stationary ergodic Markov (SEM) source Q over a discrete channel W with additive SEM noise via a joint source-channel (JSC) code. We first establish an upper bound for EJin terms of the Renyi entropy rates of the source and noise processes. We next investigate the analytical computation of EJby 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 Csiszar'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 EJwith the tandem (separate) coding exponent EJ. We show that as in the case of memoryless source-channel pairs EJles 2Erand we provide explicit conditions for which EJ> ET. Numerical results indicate that EJap 2ETfor many SEM source-channel pairs, hence illustrating a substantial advantage of JSC coding over tandem coding for systems with Markovian memory.

For a memoryless Gaussian source under the squared-error distortion fidelity criterion and a memoryless additive Gaussian noise channel with a quadratic power constraint at the channel input, upper and lower bounds for the joint source-channel coding excess distortion exponent (which is the exponent of the probability of excess distortion) are established. A necessary and sufficient condition for which the two bounds coincide is provided, thus exactly determining the exponent. This condition is observed to hold for a wide range of source-channel parameters

We investigate the computation of Csisza/spl acute/r's bounds for the joint source-channel coding (JSCC) error exponent E/sub J/ of a communication system consisting of a discrete memoryless source and a discrete memoryless channel. We provide equivalent expressions for these bounds and derive explicit formulas for the rates where the bounds are attained. These equivalent representations can be readily computed for arbitrary source-channel pairs via Arimoto's algorithm. When the channel's distribution satisfies a symmetry property, the bounds admit closed-form parametric expressions. We then use our results to provide a systematic comparison between the JSCC error exponent E/sub J/ and the tandem coding error exponent E/sub T/, which applies if the source and channel are separately coded. It is shown that E/sub T//spl les/E/sub J//spl les/2E/sub T/. We establish conditions for which E/sub J/>E/sub T/ and for which E/sub J/=2E/sub T/. Numerical examples indicate that E/sub J/ is close to 2E/sub T/ for many source-channel pairs. This gain translates into a power saving larger than 2 dB for a binary source transmitted over additive white Gaussian noise (AWGN) channels and Rayleigh-fading channels with finite output quantization. Finally, we study the computation of the lossy JSCC error exponent under the Hamming distortion measure.

We establish an upper bound for the joint source-channel coding (JSCC) error exponent E/sub J/(Q, W) for a discrete stationary ergodic Markov (SEM) source Q and a discrete channel W with additive SEM noise. This bound, which is expressed in terms of the Renyi entropy rates of the source and noise processes, admits an identical form to Csiszar's sphere-packing upper bound for the JSCC error exponent for memoryless systems (I. Csiszar, Nov. 1982). In this regard, our result is a natural extension of Csiszar's upper bound of the JSCC error exponent from the case of memoryless systems to the case of SEM systems. We also investigate the analytical computation of E/sub J/(Q,W) by comparing our bound with Gallager's random-coding lower bound (R. G. Gallager, 1968), when the latter one is specialized to the SEM source-channel system.

We study the analytical computation of Csiszar's [1980] random-coding lower bound and sphere-packing upper bound for the lossless joint source-channel (JSC) error exponent, E/sub J/(Q, W), for a discrete memoryless source (DMS) Q and a discrete memoryless channel (DMC) W. We provide equivalent expressions for these bounds, which can be readily calculated for arbitrary (Q,W) pairs. We also establish explicit conditions under which the bounds coincide, thereby exactly determining E/sub J/(Q,W).