Information-Theoretic Methods in Distributed Learning

• 13:00: Keynote talk by Mohammad Ali Maddah-Ali (Nokia Bell Labs)
  
• Title: Coalition Through Coding: New Opportunities and Threats

Abstract

Information systems, running distributed algorithms and platforms, such as distributed learning, distributed storage, and distributed ledgers (blockchain), raise a wide range of challenges in terms of the security of the network, the privacy of the data, and the accuracy of the results. Working with coded data is known as an effective approach to alleviate those challenges. In this talk, we will review some of the coded solutions, and argue that while coding can help,  it can create some serious, but overlooked, inefficiencies and security threats. This is particularly the case where the computation is complicated (e.g., training deep neural networks), the system is multi-user (e.g., multi-user secret sharing), or the encoding has to be distributed (e.g., sharded blockchains). We will also show how to bound and mitigate the new threats and inefficiencies, and discuss open problems. 

• 14:00: Invited talk by Lifeng Lai (University of California Davis)
• Title: Distributed Statistical Inference with Compressed Data

Abstract

In the classic statistical inference problems, all data is available at a centralized location. With the explosion of the size of data sets, it is increasingly common that data is stored in multiple terminals connected by links with a limited communication capacity. In this scenario, terminals have to exchange compressed data and perform statistical inference using the compressed data. In this talk, we will discuss our recent work that addressed the following two questions: 1) Suppose we would like to achieve the same optimal inference as that of the centralized case, how much data compression can be performed?; and 2) Suppose we compress the data extremely (zero-rate compression), what is the optimal inference performance?

• 14:20: Invited talk by Songze Li (HKUST)
  
• Title: DeepPrivate: Scalable Distributed DNN Training with Data and Model Privacy

Abstract

A key friction in the information era is between the high utility of data and stringent privacy considerations. One possible resolution is to perform distributed learning with privacy guarantee. Consider N nodes, each of which stores locally some (function of) data from a set of clients, collaboratively train a model that is requested by a remote learner node, using data from all clients collectively. For this task, we develop DeepPrivate, a protocol that provides information-theoretic guarantees simultaneously for data and model privacy against any T < N colluding workers and data privacy against the curious learner. To achieve this, DeepPrivate partitions the entire dataset into K < N parts, and leverages secret sharing and compatible erasure coding to securely distribute the coded data partitions and intermediate computation results during the training process. As a result, DeepPrivate achieves a factor $K = \Theta(N)$ reduction in computation complexity compared with state-of-the-art private machine-learning frameworks. Furthermore, DeepPrivate improves the scalability and security via layer-by-layer training, which allows the workers to only compute polynomials of low degree during training, at a small cost on the model accuracy. 

• 14:40: Invited talk by Gauri Joshi (Carnegie Mellon University)
  
• Title: Adaptive Quantization of Model Updates for Communication-Efficient Federated Learning

Abstract

Communication of model updates between client nodes and the central aggregating server is a major bottleneck in federated learning, especially in bandwidth-limited settings and high-dimensional models. Gradient quantization is an effective way of reducing the number of bits required to communicate each model update, albeit at the cost of having a higher error floor due to the higher variance of the stochastic gradients. In this work, we propose an adaptive quantization strategy called AdaQuantFL that aims to achieve communication efficiency as well as a low error floor by changing the number of quantization levels during the course of training. Experiments on training deep neural networks show that our method can converge in much fewer communicated bits as compared to fixed quantization level setups, with little or no impact on training and test accuracy.

Joint Work with: Divyansh Jhunjhunwala, Advait Gadhikar, and Yonina Eldar.

• 15:00: Invited talk by Martin Jaggi (EPFL)
  
• Title: Communication-Efficient Distributed Deep Learning

Abstract

We discuss gradient compression methods for communication-efficient distributed training, in centrally-coordinated as well as fully decentralized scenarios.
In particular, we demonstrate that low-rank linear compressors applied on model differences can lead to fast encoding and decoding, as well as efficient aggregation between workers, while maintaining training and test accuracy. The key building blocks used are the linearity of the power iteration, applied to the fast-evolving matrix of gradients, paired with error-feedback.
We present empirical results on reduced training times for many neural network architectures with our open-source code, as well as theoretical convergence rates of the methods, applicable also for heterogeneous data, and asymptotically independent of the network topology and compression ratio.

Based on joint work with Sai Praneeth Karimireddy & Thijs Vogels.

• 15:30-16:00: Break

16:00: Invited Session on Post-Shannon Communications

Organized by Marios Kountouris (EURECOM)

• 16:00: Invited talk by Yonina Eldar (Weizmann Institute of Science, Israel)
  
• Title: Task-Based Sampling and Quantization
  

Abstract

We consider sampling and quantization systems that can operate at sampling and bit rates far lower than traditionally required, by representing a specific desired function of the signal rather than the signal itself. The proposed systems employ analog pre-filtering, uniform low rate sampling, and scalar uniform quantization of the input before subsequently recovering the task using a digital recovery filter. We optimize the analog and digital filters for the specific task and show that in certain cases even one-bit quantization is possible while still approaching the optimal performance of high rate samplers.

• 16:20: Invited talk by Holger Boche (Technische Universität München, Germany) 
  
• Title: Post Shannon Theory; Deterministic Identification with and without Feedback
  

Abstract

Deterministic identification (DI) is addressed for Gaussian channels with fast and slow fading, where channel side information is available at the decoder. In particular, it is established that the number of messages scales as 2^nlog(n)R , where n is the block length and R is the coding rate. Lower and upper bounds on the DI capacity are developed in this scale for fast and slow fading. Consequently, the DI capacity is infinite in the exponential scale and zero in the double-exponential scale, regardless of the channel noise. In the second part of the talk we analyze deterministic message identification via Gaussian channels with noiseless feedback under average power and peak power constraints, which is part of the Post Shannon theory. The consideration of communication systems beyond Shannon’s approach is useful in order to increase the efficiency of information transmission for certain applications. We considerthe Gaussian channel with feedback. If the noise variance ispositive, we propose a coding scheme that generates infinite common randomness between the sender and the receiver and show that any rate for deterministic identification via the Gaussian channelwith noiseless feedback can be achieved.

• 16:40: Invited talk by Mari Kobayashi (Technische Universität München, Germany) 
  
• Title: Scalable Information Extraction for Semantic Communications
  

Abstract

We consider a scenario where the encoder observes the source remotely and wishes to extract multiple descriptions in a scalable manner depending on the allowed levels of complexity. By focusing on the successive refinement encoding and degraded side information at the decoders, we characterize the relevance-complexity complexity region for Gaussian sources. Then, we derive a variational inference type algorithm to deal with general sources under unknown distributions and provide experimental results on the popular dataset. Finally, we discuss a possible application in the context of semantic communications, where each node equipped with on-board sensors wishes to send a message that conveys only the most relevant piece of information depending on the required tasks. This is a joint work with Abdellatif Zaidi and Mohammad Mahdi Mahvari.  

• 17:00: Invited talk by Victoria Kostina (Caltech, USA)
  
• Title: The value of timing information in coding and control

Abstract

We consider a scenario where the encoder observes a stochastic process in real time and decides when and what to transmit about it, while the decoder estimates the process in real time using the codewords it has received by then. For a class of stochastic processes, we determine the optimal tradeoff between the expected instantaneous distortion incurred at the decoder and the expected bit rate, and we show that a simple two-threshold coding policy that transmits a single bit once the process innovation passes one of the two thresholds achieves it. Surprisingly, the achievable distortion-rate tradeoff is better than the distortion-rate tradeoff achieved in the limit of infinite delay by the best block code. This is because our event-triggered coding policy exploits the free timing information supplied by the zero-delay channel between the encoder and the decoder. The results are extended to channels with delay and to control. This is joint work with Nian Guo.