Vasuki Narasimha Swamy

Cooperative communication for high-reliability low-latency wireless control

The Internet of Things envisions not only sensing but also actuation of numerous wirelessly connected devices. Seamless control with humans in the loop requires latencies on the order of a millisecond with very high reliabilities, paralleling the requirements for high-performance industrial control. Todays practical wireless systems cannot meet these reliability and latency requirements, forcing the use of wired systems. This paper introduces a wireless communication protocol, dubbed “Occupy CoW,” based on cooperative communication among nodes in the network to build the diversity necessary for the target reliability. Simultaneous retransmission by many relays achieves this without significantly decreasing throughput or increasing latency. The protocol is analyzed using the communication theoretic delay-limited-capacity framework and compared to baseline schemes that primarily exploit frequency diversity. In particular, we develop a novel “diversity meter” designed to measure “effective diversity” in the non-asymptotic regime. For a scenario inspired by an industrial printing application with 30 nodes in the control loop, total information throughput of 4.8 Mb/s, and cycle time under 2 ms, the protocol can robustly achieve a system probability of error better than 10-9 with nominal SNR below 5 dB.

Network coding for high-reliability low-latency wireless control

The Internet of Things (IoT) envisions simultaneous sensing and actuation of numerous wirelessly connected devices. Emerging human-in-the-loop applications demand low-latency high-reliability communication protocols, paralleling the requirements for high-performance industrial control. This paper introduces a wireless communication protocol based on network coding that in conjunction with cooperative communication techniques builds the necessary diversity to achieve the target reliability. The proposed protocol, XOR-CoW, is analyzed by using a communication theoretic delay-limited-capacity framework and compared to different realizations of previously proposed protocols without network coding. The results show that as the network size or payload increases, XOR-CoW gains advantage in minimum SNR to achieve the target latency. For a scenario inspired by an industrial printing application with 30 nodes in the control loop, total information throughput of 4.8 Mb/s, 20MHz of bandwidth and cycle time under 2 ms, the protocol can robustly achieve a system probability of error better than 10−9 with a nominal SNR less than 2 dB with Rayleigh fading.

Low-Complexity Interactive Algorithms for Synchronization From Deletions, Insertions, and Substitutions

Consider two remote nodes having binary sequences X and Y, respectively. Y is an edited version of X, where the editing involves random deletions, insertions, and substitutions, possibly in bursts. The goal is for the node with Y to reconstruct X with minimal exchange of information over a noiseless link. The communication is measured in terms of both the total number of bits exchanged and the number of interactive rounds of communication. This paper focuses on the setting where the number of edits is o(n/log n), where n is the length of X. We first consider the case where the edits are a mixture of insertions and deletions (indels), and propose an interactive synchronization algorithm with near-optimal communication rate and average computational complexity of O(n) arithmetic operations. The algorithm uses interaction to efficiently split the source sequence into substrings containing exactly one deletion or insertion. Each of these substrings is then synchronized using an optimal one-way algorithm based on the single-deletion correcting channel codes of Varshamov and Tenengolts. We then build on this synchronization algorithm in three different ways. First, it is modified to work with a single round of interaction. The reduction in the number of rounds comes at the expense of higher communication, which is quantified. Next, we present an extension to the practically important case where the insertions and deletions may occur in (potentially large) bursts. Finally, we show how to synchronize the sources to within a target Hamming distance. This feature can be used to differentiate between substitution and indel edits. In addition to theoretical performance bounds, we provide several validating simulation results for the proposed algorithms.

An Asymptotically Optimal Push–Pull Method for Multicasting Over a Random Network

We consider all-cast and multicast flow problems where either all of the nodes or only a subset of the nodes may be in session. Traffic from each node in the session has to be sent to every other node in the session. If the session does not consist of all the nodes, the remaining nodes act as relays. The nodes are connected by undirected links whose capacities are independent and identically distributed random variables. We study the asymptotics of the capacity region (with network coding) in the limit of a large number of nodes, and show that the normalized sum rate converges to a constant almost surely. We then provide a decentralized push-pull algorithm that asymptotically achieves this normalized sum rate without network coding.

Finite block length coding for low-latency high-reliability wireless communication

This paper takes a step towards making practical cooperative protocols for wireless low-latency high-reliability communication. We consider the effect of finite block-length error correction codes and the main message is that the demands on the error-correcting code are different in different phases of a diversity-seeking cooperative protocol: In the first hop where messages must reach potential relays, the code only has to achieve a moderate probability of error. The final hop from relays to the destination is where the code must be ultrareliable. The results are illustrated in the context of a simple concatenated Hamming+Reed Solomon code.

Real-Time Cooperative Communication for Automation Over Wireless

High-performance industrial automation systems rely on tens of simultaneously active sensors and actuators and have stringent communication latency and reliability requirements. Current wireless technologies, such as Wi-Fi, Bluetooth, and LTE are unable to meet these requirements, forcing the use of wired communication in industrial control systems. This paper introduces a wireless communication protocol that capitalizes on multiuser diversity and cooperative communication to achieve the ultra-reliability with a low-latency constraint. Our protocol is analyzed using the communication-theoretic delay-limited-capacity framework and compared with baseline schemes that primarily exploit frequency diversity. For a scenario inspired by an industrial printing application with 30 nodes in the control loop, 20-B messages transmitted between pairs of nodes and a cycle time of 2 ms, an idealized protocol can achieve a cycle failure probability (probability that any packet in a cycle is not successfully delivered) lower than 10−9 with nominal SNR below 5 dB in a 20-MHz wide channel.

An asymptotically optimal push-pull method for multicasting over a random network

We consider all-cast and multicast flow problems where either all of the nodes or only a subset of the nodes may be in session. Traffic from each node in the session has to be sent to every other node in the session. If the session does not consist of all the nodes, the remaining nodes act as relays. The nodes are connected by undirected links whose capacities are independent and identically distributed random variables. We study the asymptotics of the capacity region (with network coding) in the limit of a large number of nodes, and show that the normalized sum rate converges to a constant almost surely. We then provide a decentralized push-pull algorithm that asymptotically achieves this normalized sum rate without network coding.