Improving data rates for two-user wireless channels with power strategies
Second-Order Asymptotics for the Gaussian MAC on the Relative Interior of the Sum-Rate Face
Information Theory
Summary
Communicating efficiently over wireless channels when two users share the same space is tricky. The authors found that splitting signal power between users in a mixed way can improve data transmission beyond what usual fixed splits achieve. They mathematically proved just how much better this method is for transmitting data reliably at high rates. This offers a more precise understanding of communication limits when many devices share the same network space.
What this means in practice
- •For wireless network engineers: Design transmission schemes for multiple devices sharing a wireless channel to maximize reliable data rates by optimizing power allocation between users.
- •For communication system designers: Develop improved coding strategies ensuring better error performance in multi-user communication systems by employing variable power splits.
Authors
Vincent Y. F. Tan
Abstract
We completely characterize the second-order coding rate region of the two-user Gaussian multiple-access channel at points in the relative interior of the sum-rate face, under maximal per-codeword power constraints. For any fixed average error probability $0 < \varepsilon < 1/2$, a nontrivial mixture of power splits reduces the sum-rate dispersion and strictly improves upon standard inner bounds based on a constant power split. Thus, a constant power split, although sufficient to attain the first-order capacity region, is insufficient for second-order optimality in this regime. Our achievability proof builds on the constant composition and coded time-sharing framework of Scarlett, Martinez, and Guillén i Fàbregas, with an optimization over admissible power splits. A matching second-order converse establishes the optimality of the resulting coded time-sharing strategy.