# On Multiple-Access in Queue-Length Sensitive Systems

## TL;DR

This paper analyzes the capacity of queue-length sensitive unreliable channels, especially in multiple-access systems, revealing how system behavior converges to single-user models under sparse conditions.

## Contribution

It characterizes the capacity of queue-length dependent channels for single and multiple users, and shows convergence to single-user capacity in large, sparse multiple-access systems.

## Key findings

- Capacity of single-user queue-length dependent channels determined.
- Optimal and worst dispatch and service processes characterized.
- Multiple-access capacity converges to single-user capacity with sparse arrivals.

## Abstract

We consider transmission of packets over queue-length sensitive unreliable links, where packets are randomly corrupted through a noisy channel whose transition probabilities are modulated by the queue-length. The goal is to characterize the capacity of this channel. We particularly consider multiple-access systems, where transmitters dispatch encoded symbols over a system that is a superposition of continuous-time $GI_k/GI/1$ queues. A server receives and processes symbols in order of arrivals with queue-length dependent noise. We first determine the capacity of single-user queue-length dependent channels. Further, we characterize the best and worst dispatch processes for $GI/M/1$ queues and the best and worst service processes for $M/GI/1$ queues. Then, the multiple-access channel capacity is obtained using point processes. When the number of transmitters is large and each arrival process is sparse, the superposition of arrivals approaches a Poisson point process. In characterizing the Poisson approximation, we show that the capacity of the multiple-access system converges to that of a single-user $M/GI/1$ queue-length dependent system, and an upper bound on the convergence rate is obtained. This implies that the best and worst server behaviors of single-user $M/GI/1$ queues are preserved in the sparse multiple-access case.