Fundamental Limits and Scaling Behavior of Cooperative Multicasting in Wireless Networks

TL;DR

This paper develops a framework to analyze the capacity and scaling behavior of cooperative multicasting in large wireless networks, introducing a new notion of capacity and a protocol that achieves it.

Contribution

It introduces a new capacity framework for cooperative wireless networks and a protocol that achieves this capacity, along with the concept of a network scaling exponent.

Findings

Capacity is the same for unicasting and multicasting.

Network size needed for target error probability differs between unicasting and multicasting.

The scaling exponent quantifies error probability decay with network size.

Abstract

A framework is developed for analyzing capacity gains from user cooperation in slow fading wireless networks when the number of nodes (network size) is large. The framework is illustrated for the case of a simple multipath-rich Rayleigh fading channel model. Both unicasting (one source and one destination) and multicasting (one source and several destinations) scenarios are considered. We introduce a meaningful notion of Shannon capacity for such systems, evaluate this capacity as a function of signal-to-noise ratio (SNR), and develop a simple two-phase cooperative network protocol that achieves it. We observe that the resulting capacity is the same for both unicasting and multicasting, but show that the network size required to achieve any target error probability is smaller for unicasting than for multicasting. Finally, we introduce the notion of a network ``scaling exponent'' to quantify the rate of decay of error probability with network size as a function of the targeted fraction of the capacity. This exponent provides additional insights to system designers by enabling a finer grain comparison of candidate cooperative transmission protocols in even moderately sized networks.