Successive Wyner-Ziv Research Articles

Two-Stage Successive Wyner-Ziv Lossy Forward Relaying for Lossy Communications: Rate-Distortion and Outage Probability Analyses

Two-Stage Successive Wyner-Ziv Lossy Forward Relaying for Lossy Communications: Rate-Distortion and Outage Probability Analyses

A Low-Complexity and Adaptive Distributed Source Coding Design for Model Aggregation in Distributed Learning

A major bottleneck in distributed learning is the communication overhead of exchanging intermediate model update parameters between the worker nodes and the parameter server. Recently, it is found that local gradients among different worker nodes are correlated. Therefore, distributed source coding (DSC) can be applied to increase communication efficiency by exploiting such correlation. However, it is highly non-trivial to exploite the gradient correlations in distributed learning due to the unknown and time-varying gradient correlation. In this paper, we first propose a DSC framework, named successive Wyner-Ziv coding, for distributed learning based on quantization and Slepian-Wolf (SW) coding. We prove that the proposed framework can achieve the theoretically minimum communication cost from an information theory perspective. We also propose a low-complexity and adaptive DSC for distributed learning, including a gradient statistics estimator, rate controller, and a log-likelihood ratio (LLR) computer. The gradient statistics estimator estimates the gradient statistics online based only on the quantized gradients at previous iterations, hence it does not introduce extra communication cost. The computation complexity of the rate controller and the LLR computer is reduced to a linear growth in the number of worker nodes by introducing a semi-analytical Monte Carlo simulation. Finally, we design a DSC-based distributed learning process and find that the extra delay introduced by DSC does not scale with the number of worker nodes.

Successive Wyner-Ziv Coding for the Binary CEO Problem Under Logarithmic Loss

The $L$-link binary Chief Executive Officer (CEO) problem under logarithmic loss is investigated in this paper. A quantization splitting technique is applied to convert the problem under consideration to a $(2L-1)$-step successive Wyner-Ziv (WZ) problem, for which a practical coding scheme is proposed. In the proposed scheme, low-density generator-matrix (LDGM) codes are used for binary quantization while low-density parity-check (LDPC) codes are used for syndrome generation; the decoder performs successive decoding based on the received syndromes and produces a soft reconstruction of the remote source. The simulation results indicate that the rate-distortion performance of the proposed scheme can approach the theoretical inner bound based on binary-symmetric test-channel models.

Successively Structured Gaussian Two-terminal Source Coding

Multiterminal source coding refers to separate encoding and joint decoding of multiple correlated sources. Joint decoding requires all the messages to be decoded simultaneously which is exponentially more complex than a sequence of single-message decodings. Inspired by previous work on successive coding, we apply the successive Wyner-Ziv coding, which is inherently a low complexity approach of obtaining a prescribed distortion, to the two-terminal source coding scheme. First, we consider 1-helper problem where one source provides partial side information to the decoder to help the reconstruction of the main source. Our results show that the successive coding strategy is an optimal strategy in the sense of achieving the rate-distortion function. By developing connections between source encoding and data fusion steps, it is shown that the whole rate-distortion region for the 2-terminal source coding problem is achievable using the successive coding strategy. Comparing the performance of the sequential coding with the performance of the successive coding, we show that there is no sum-rate loss when the side information is not available at the encoder. This result is of special interest in some applications such as video coding where there are processing and storage constraints at the encoder. Finally, we provide an achievable rate-distortion region for the m-terminal source coding.

Successive Wyner–Ziv Coding Scheme and Its Application to the Quadratic Gaussian CEO Problem

We introduce a distributed source coding scheme called successive Wyner-Ziv coding. We show that any point in the rate region of the quadratic Gaussian CEO problem can be achieved via the successive Wyner-Ziv coding. The concept of successive refinement in the single source coding is generalized to the distributed source coding scenario, which we refer to as distributed successive refinement. For the quadratic Gaussian CEO problem, we establish a necessary and sufficient condition for distributed successive refinement, where the successive Wyner-Ziv coding scheme plays an important role.

Layered Wyner Ziv Video Coding

Following recent theoretical works on successive Wyner-Ziv coding (WZC), we propose a practical layered Wyner-Ziv video coder using the DCT, nested scalar quantization, and irregular LDPC code based Slepian-Wolf coding (or lossless source coding with side information at the decoder). Our main novelty is to use the base layer of a standard scalable video coder (e.g., MPEG-4/H.26L FGS or H.263+) as the decoder side information and perform layered WZC for quality enhancement. Similar to FGS coding, there is no performance difference between layered and monolithic WZC when the enhancement bitstream is generated in our proposed coder. Using an H.26L coded version as the base layer, experiments indicate that WZC gives slightly worse performance than FGS coding when the channel (for both the base and enhancement layers) is noiseless. However, when the channel is noisy, extensive simulations of video transmission over wireless networks conforming to the CDMA2000 1X standard show that H.26L base layer coding plus Wyner-Ziv enhancement layer coding are more robust against channel errors than H.26L FGS coding. These results demonstrate that layered Wyner-Ziv video coding is a promising new technique for video streaming over wireless networks.