Timely Lossless Source Coding for Randomly Arriving Symbols

TL;DR

This paper develops optimal lossless coding schemes for real-time source streaming with randomly arriving symbols, aiming to minimize age of information in FIFO buffer systems, including practical empty-buffer signaling.

Contribution

It introduces a new optimal coding scheme for minimizing age of information in real-time streaming with FIFO buffers, considering both empty and non-empty buffer scenarios.

Findings

Optimal prefix-free coding minimizes average peak age when buffer can be empty.

Proposed encoding scheme effectively signals empty buffer states.

Analysis based on Geo/G/1 queue models.

Abstract

We consider a real-time streaming source coding system in which an encoder observes a sequence of randomly arriving symbols from an i.i.d. source, and feeds binary codewords to a FIFO buffer that outputs one bit per time unit to a decoder. Each source symbol represents a status update by the source, and the timeliness of the system is quantified by the age of information (AoI), defined as the time difference between the present time and the generation time of the most up-to-date symbol at the output of the decoder. When the FIFO buffer is allowed to be empty, we propose an optimal prefix-free lossless coding scheme that minimizes the average peak age based on the analysis of discrete-time Geo/G/1 queue. For more practical scenarios in which a special codeword is reserved for indicating an empty buffer, we propose an encoding scheme that assigns a codeword to the empty buffer state based on an estimate of the buffer idle time.