Contractive Interference Functions and Rates of Convergence of Distributed Power Control Laws

TL;DR

This paper introduces contractive interference functions that ensure fixed-point existence, uniqueness, and linear convergence in distributed power control, providing explicit convergence rate estimates and asynchronous convergence guarantees.

Contribution

It proposes a new class of contractive interference functions that improve convergence analysis and guarantees for distributed power control algorithms.

Findings

Many power control laws are contractive.

Derived analytical convergence rate estimates.

Proved convergence under asynchronous execution.

Abstract

The standard interference functions introduced by Yates have been very influential on the analysis and design of distributed power control laws. While powerful and versatile, the framework has some drawbacks: the existence of fixed-points has to be established separately, and no guarantees are given on the rate of convergence of the iterates. This paper introduces contractive interference functions, a slight reformulation of the standard interference functions that guarantees the existence and uniqueness of fixed-points along with linear convergence of iterates. We show that many power control laws from the literature are contractive and derive, sometimes for the first time, analytical convergence rate estimates for these algorithms. We also prove that contractive interference functions converge when executed totally asynchronously and, under the assumption that the communication delay is bounded, derive an explicit bound on the convergence time penalty due to increased delay. Finally, we demonstrate that although standard interference functions are, in general, not contractive, they are all para-contractions with respect to a certain metric. Similar results for two-sided scalable interference functions are also derived.