Timely updates over an erasure channel (original) (raw)

A Systematic Approach to Incremental Redundancy over Erasure Channels

2018 IEEE International Symposium on Information Theory (ISIT), 2018

As sensing and instrumentation play an increasingly important role in systems controlled over wired and wireless networks, the need to better understand delay-sensitive communication becomes a prime issue. Along these lines, this article studies the operation of data links that employ incremental redundancy as a practical means to protect information from the effects of unreliable channels. Specifically, this work extends a powerful methodology termed sequential differential optimization to choose near-optimal block sizes for hybrid ARQ over erasure channels. In doing so, an interesting connection between random coding and well-known constants in number theory is established. Furthermore, results show that the impact of the coding strategy adopted and the propensity of the channel to erase symbols naturally decouple when analyzing throughput. Overall, block size selection is motivated by normal approximations on the probability of decoding success at every stage of the incremental transmission process. This novel perspective, which rigorously bridges hybrid ARQ and coding, offers a pragmatic means to select code rates and blocklengths for incremental redundancy.

A Systematic Approach to Incremental Redundancy With Application to Erasure Channels

IEEE Transactions on Communications

This paper focuses on the design and evaluation of pragmatic schemes for delay-sensitive communication. Specifically, this contribution studies the operation of data links that employ incremental redundancy as a means to shield information bits from the degradation associated with unreliable channels. While this inquiry puts forth a general methodology, exposition centers around erasure channels because they are well suited for analysis. Nevertheless, the goal is to identify both structural properties and design guidelines that are broadly applicable. Conceptually, this paper leverages a methodology, termed sequential differential optimization, aimed at identifying near-optimal block sizes for hybrid ARQ. This technique is applied to erasure channels and it is extended to scenarios where throughput is maximized subject to a constraint on the feedback rate. The analysis shows that the impact of the coding strategy adopted and the propensity of the channel to erase symbols naturally decouple when maximizing throughput. Ultimately, block size selection is informed by approximate distributions on the probability of decoding success at every stage of the incremental transmission process. This novel perspective, which rigorously bridges hybrid automatic repeat request and coding, offers a computationally efficient framework to select code rates and blocklengths for incremental redundancy. These findings are supported through numerical results.

Optimal Selective Encoding for Timely Updates with Empty Symbol

2020 IEEE International Symposium on Information Theory (ISIT), 2020

An information source generates independent and identically distributed status update messages from an observed random phenomenon which takes n distinct values based on a given pmf. These update packets are encoded at the transmitter to be sent to a receiver which wants to track the observed random variable with as little age as possible. The transmitter implements a selective k encoding policy such that rather than encoding all possible n realizations, the transmitter encodes the most probable k realizations and sends a designated empty symbol when one of the remaining n−k realizations occurs. We consider two scenarios: when the empty symbol does not reset the age and when the empty symbol resets the age. We find the time average age of information and the age-optimal real codeword lengths, including the codeword length for the empty symbol, for both of these scenarios. Through numerical evaluations for arbitrary pmfs, we show that this selective encoding policy yields a lower age ...

On Minimizing the Maximum Age-of-Information For Wireless Erasure Channels

2019 International Symposium on Modeling and Optimization in Mobile, Ad Hoc, and Wireless Networks (WiOPT), 2019

Age-of-Information (AoI) is a recently proposed metric for quantifying the freshness of information from the UE's perspective in a communication network. Recently, Kadota et al. [1] have proposed an index-type approximately optimal scheduling policy for minimizing the average-AoI metric for a downlink transmission problem. For delay-sensitive applications, including real-time control of a cyber-physical system, or scheduling URLLC traffic in 5G, it is essential to have a more stringent uniform control on AoI across all users. In this paper, we derive an exactly optimal scheduling policy for this problem in a downlink cellular system with erasure channels. Our proof of optimality involves an explicit solution to the associated average-cost Bellman Equation, which might be of independent theoretical interest. We also establish that the resulting Ageprocess is positive recurrent under the optimal policy, and has an exponentially light tail, with the optimal large-deviation exponent. Finally, motivated by typical applications in smallcell residential networks, we consider the problem of minimizing the peak-AoI with throughput constraints to specific UEs, and derive a heuristic policy for this problem. Extensive numerical simulations have been carried out to compare the efficacy of the proposed policies with other well-known scheduling policies, such as Randomized scheduling and Proportional Fair.

The Age of Information of Short-Packet Communications: Joint or Distributed Encoding?

ICC 2022 - IEEE International Conference on Communications

In this paper, we analyze the impact of different encoding schemes on the age of information (AoI) performance in a point-to-point system, where a source generates packets based on the status updates collected from multiple sensors and transmits the packets to a destination. In this system, we consider two encoding schemes, namely, the joint encoding scheme and the distributed encoding scheme. In the joint encoding scheme, the status updates from all the sensors are jointly encoded into a packet for transmission. In the distributed encoding scheme, the status update from each sensor is encoded individually and the sensors' packets are transmitted following the round robin policy. To ensure the freshness of packets, the zero-wait policy is adopted in both schemes, where a new packet is immediately generated once the source finishes the transmission of the current packet. We derive closed-form expressions for the average AoI achieved by these two encoding schemes and compare their performances. Simulation results show that the distributed encoding scheme is more appropriate for systems with a relatively large number of sensors, compared with the joint encoding scheme. Index Terms-Age of information, short packet communications, low latency communications, encoding scheme.

On coding for real-time streaming under packet erasures

2013 IEEE International Symposium on Information Theory, 2013

We consider a real-time streaming system where messages created at regular time intervals at a source are encoded for transmission to a receiver over a packet erasure link; the receiver must subsequently decode each message within a given delay from its creation time. We study a bursty erasure model in which all erasure patterns containing erasure bursts of a limited length are admissible. For certain classes of parameter values, we provide code constructions that asymptotically achieve the maximum message size among all codes that allow decoding under all admissible erasure patterns. We also study an i.i.d. erasure model in which each transmitted packet is erased independently with the same probability; the objective is to maximize the decoding probability for a given message size. We derive an upper bound on the decoding probability for any time-invariant code, and show that the gap between this bound and the performance of a family of time-invariant intrasession codes is small in the high reliability regime.

Optimal Selective Encoding for Timely Updates

2020

We consider a system in which an information source generates independent and identically distributed status update packets from an observed phenomenon that takes n possible values based on a given pmf. These update packets are encoded at the transmitter node to be sent to the receiver node. Instead of encoding all n possible realizations, the transmitter node only encodes the most probable k realizations and disregards whenever a realization from the remaining n−k values occurs. We find the average age and determine the age-optimal real codeword lengths such that the average age at the receiver node is minimized. Through numerical evaluations for arbitrary pmfs, we show that this selective encoding policy results in a lower average age than encoding every realization and find the age-optimal k. We also analyze a randomized selective encoding policy in which the remaining n−k realizations are encoded and sent with a certain probability to further inform the receiver at the expense o...

Code rate, queueing behavior and the correlated erasure channel

IEEE Information Theory Workshop 2010 (ITW 2010), 2010

This paper considers the relationship between coderate selection and queueing performance for communication systems with time-varying parameters. While error-correcting codes offer protection against channel unreliability, there is a tradeoff between the enhanced protection of low-rate codes and the increased information transfer of high-rate codes. Hence, there exists a natural compromise between packet-level error protection and information rate. In the limiting regime where codewords are asymptotically long, this tradeoff is well-understood and characterized by the Shannon capacity. However, for delaysensitive communication systems and finite code-lengths, a complete characterization of this tradeoff is still not fully developed. This paper offers a new perspective on the queueing performance of communication systems with finite block-lengths operating over correlated erasure channels. A rigorous framework that links code rate to overall system performance for random codes is presented. Guidelines for code rate selection in delay-sensitive systems are identified.