We study the two-user broadcast channel with degraded message sets and derive second-order achievability rate regions. Specifically, the channel noises are not necessarily Gaussian and we use spherical codebooks for both users. The weak user with worse channel quality applies nearest neighbor decoding by treating the signal of the other user as interference. For the strong user with better channel quality, we consider two decoding schemes: successive interference cancellation (SIC) decoding and joint nearest neighbor (JNN) decoding. We adopt two performance criteria: separate error probabilities (SEP) and joint error probability (JEP). Under our analysis, SIC and JNN decoding share the same second-order achievable rate region despite the fact that JNN decoding often yields better performance in other multiterminal problems. Furthermore, we generalize our results to the case with quasi-static fading and show that the asymptotic notion of outage capacity region is an accurate performance measure even at finite blocklengths.

We first study the two-user additive noise multiple access channel (MAC) where the noise distribution is arbitrary. For such a MAC, we use spherical codebooks and either joint nearest neighbor (JNN) or successive interference cancellation (SIC) decoding. Under both decoding methods, we derive second-order achievable rate regions and compare the finite blocklength performance between JNN and SIC decoding. Our results indicate that although the first-order rate regions of JNN and SIC decoding are identical, JNN decoding has better second-order asymptotic performance. When specialized to the Gaussian noise, we provide an alternative achievability proof to the result by MolavianJazi and Laneman (T-IT, 2015). Furthermore, we generalize our results to the random access channel (RAC) where neither the transmitters nor the receiver knows the user activity pattern. We use spherical-type codebooks and a rateless transmission scheme combining JNN/SIC decoding and derive second-order achievability bounds. Comparing second-order achievability results of JNN and SIC decoding in a RAC, we show that JNN decoding achieves a strictly larger first-order asymptotic rate. When specialized to Gaussian noise, our second-order asymptotic results recover the corresponding results of Yavas, Kostina, and Effros (T-IT, 2021) up to second-order.

We study the successive refinement setting of Shannon cipher system (SCS) under the maximal leakage secrecy metric for discrete memoryless sources under bounded distortion measures. Specifically, we generalize the threat model for the point-to-point rate-distortion setting of Issa, Wagner and Kamath (T-IT 2020) to the multiterminal successive refinement setting. Under mild conditions that correspond to partial secrecy, we characterize the asymptotically optimal normalized maximal leakage region for both the joint excess-distortion probability (JEP) and the expected distortion reliability constraints. Under JEP, in the achievability part, we propose a type-based coding scheme, analyze the reliability guarantee for JEP and bound the leakage of the information source through compressed messages. In the converse part, by analyzing a guessing scheme of the eavesdropper, we prove the optimality of our achievability result. Under expected distortion, the achievability part is established similarly to the JEP counterpart. The converse proof proceeds by generalizing the corresponding results for the rate-distortion setting of SCS by Schieler and Cuff (T-IT 2014) to the successive refinement setting. Somewhat surprisingly, the normalized maximal leakage regions under both JEP and expected distortion constraints are identical under certain conditions, although JEP appears to be a stronger reliability constraint.

We study the successive refinement problem of Shannon cipher system under maximal leakage for a discrete memoryless source with arbitrary bounded distortion measures. Specifically, we generalize the threat model described by Issa, Wagner and Kamath (T-IT, 2020) to the successive refinement setting and derive the optimal asymptotic normalized maximal leakage region under a joint excess-distortion probability constraint. In the achievability part, we propose a type-based coding scheme and derive the asymptotic achievable normalized maximal leakage region. In the converse part, by analyzing the guessing scheme of the eavesdropper, we manage to show the above normalized maximal leakage region is optimal. Our results reveal the fundamental tradeoff between reliability and secrecy. Furthermore, for a successively refinable source-distortion measure triplet, we find that our coding scheme satisfies the successive refinability under the maximal leakage metric.

We study the mismatched successive refinement problem where one uses Gaussian codebooks to compress an arbitrary memoryless source with successive minimum Euclidean distance encoding under the quadratic distortion measure. Specifically, we derive achievable refined asymptotics under both the joint excess-distortion probability (JEP) and the separate excess-distortion probabilities (SEP) criteria. For both second-order and moderate deviations asymptotics, we consider two types of codebooks: the spherical codebook where each codeword is drawn independently and uniformly from the surface of a sphere and the i.i.d. Gaussian codebook where each component of each codeword is drawn independently from a Gaussian distribution. We establish the achievable second-order rate-region under JEP and we show that under SEP any memoryless source satisfying mild moment conditions is strongly successively refinable. When specialized to a Gaussian memoryless source (GMS), our results provide an alternative achievability proof with specific code design. We show that under JEP and SEP, the same moderate deviations constant is achievable. For large deviations asymptotics, we only consider the i.i.d. Gaussian codebook since the i.i.d. Gaussian codebook has better performance than the spherical codebook in this regime for the one layer mismatched rate-distortion problem (Zhou et al., 2019). We derive achievable exponents of both JEP and SEP and specialize our results to a GMS, which appears to be a novel result of independent interest.

This paper is eligible for the Jack Keil Wolf ISIT Student Paper Award. We derive achievability results on large deviations for mismatched successive refinement where one uses random i.i.d. Gaussian codebooks and minimum Euclidean distance encoding to compress an arbitrary memoryless source. Specifically, we consider both separate and joint excess-distortion criterion and derive achievable error exponents for both cases. Under the mismatched coding scheme, we show that the exponent of the joint excess-distortion probability equals the exponent of one of the separate excess-distortion probabilities, depending on the compression rate of the second encoder only. When specialized to a Gaussian memoryless source (GMS), we obtain the first achievable error exponent region. However, in contrast to the second-order asymptotics and to the large deviations for mismatched rate-distortion, the specialized result for GMS is not optimal. Further investigations are required to close the gap.

We study the mismatched successive refinement problem where one uses a fixed code to compress an arbitrary source with random Gaussian codebooks and minimum Euclidean distance encoding in a successive manner. Specifically, we generalize the mismatched rate-distortion framework by Lapidoth (T-IT, 1997) to the successive refinement setting and derive the achievable second-order asymptotics. Our result implies that any source that satisfies a mild moment constraint is successive refinable under our code. Furthermore, our proof, when specialized to a Gaussian memoryless source, provides an alternative achievability proof with structured codebooks for the successive refinement problem, which was studied by Zhou, Tan, Motani (T-IT, 2018) where a covering lemma without specifying the locations of codewords was used.

This paper describes a low complexity video codec with high coding efficiency. It was proposed to the High Efficiency Video Coding (HEVC) standardization effort of MPEG and VCEG, and has been partially adopted into the initial HEVC Test Model under Consideration design. The proposal utilizes a quad-tree structure with a support of large macroblocks of size 64×64 and 32×32, in addition to macroblocks of size 16×16. The entropy coding is done using a low complexity variable length coding based scheme with improved context adaptation over the H.264/AVC design. In addition, the proposal includes improved interpolation and deblocking filters, giving better coding efficiency while having low complexity. Finally, an improved intra coding method is presented. The subjective quality of the proposal is evaluated extensively and the results show that the proposed method achieves similar visual quality as H.264/AVC High Profile anchors with around 50% and 35% bit rate reduction for low delay and random-access experiments respectively at high definition sequences. This is achieved with less complexity than H.264/AVC Baseline Profile, making the proposal especially suitable for resource constrained environments.

This paper describes a low complexity video codec with high coding efficiency. It was proposed to the high efficiency video coding (HEVC) standardization effort of moving picture experts group and video coding experts group, and has been partially adopted into the initial HEVC test model under consideration design. The proposal utilizes a quadtree-based coding structure with support for macroblocks of size 64$\,\times\,$64, 32$\,\times\,$32, and 16$\,\times\,$16 pixels. Entropy coding is performed using a low complexity variable length coding scheme with improved context adaptation compared to the context adaptive variable length coding design in H.264/AVC. The proposal's interpolation and deblocking filter designs improve coding efficiency, yet have low complexity. Finally, intra-picture coding methods have been improved to provide better subjective quality than H.264/AVC. The subjective quality of the proposed codec has been evaluated extensively within the HEVC project, with results indicating that similar visual quality to H.264/AVC High Profile anchors is achieved, measured by mean opinion score, using significantly fewer bits. Coding efficiency improvements are achieved with lower complexity than the H.264/AVC Baseline Profile, particularly suiting the proposal for high resolution, high quality applications in resource-constrained environments.