Theoretical Foundations of Waste Factor and Waste Figure with Applications to Fixed Wireless Access and Relay Systems

TL;DR

This paper develops a comprehensive theoretical framework for evaluating energy efficiency in wireless systems using the Waste Factor, integrating it into the Consumption Factor, and applies it to relay systems and fixed wireless access scenarios.

Contribution

It introduces the Waste Factor as a unifying metric for power waste, refines the energy-per-bit analysis, and extends the framework to FWA and relay architectures, including RIS considerations.

Findings

Closed-form energy-per-bit expressions for direct and relay links

Decision rule for energy-efficient communication path selection

Application of Waste Factor framework to FWA deployment strategies

Abstract

The exponential rise in energy consumption across wireless communication systems, particularly in anticipation of next-generation wireless systems, necessitates rigorous frameworks for evaluating and optimizing energy efficiency. This paper revisits and expands the concept of the Waste Factor (W), or Waste Figure (WF) in decibel scale, as a unifying metric that captures both utilized and wasted power in cascaded communication systems. Building upon its foundation in system-level power modeling, we integrate the Waste Factor into a refined formulation of the Consumption Factor (CF), the ratio of data rate to total consumed power, linking it directly to Shannon's theoretical limit on energy per bit. This analysis introduces additive energy waste into the classical energy-per-bit derivation through the Waste Factor term. We derive closed-form expressions for energy-per-bit expenditure in both direct and relay-assisted links and develop a decision rule to determine which communication path is more energy efficient under given conditions. While not modeled explicitly, Reflective Intelligent Surfaces (RIS) can be interpreted as a special case of relay-based architectures within this unified formulation, suggesting broader applicability of the Waste Factor framework to emerging 6G use cases. The framework is then extended to a Fixed Wireless Access (FWA) scenario, where uplink and downlink asymmetries, traffic directionality, and component inefficiencies are jointly considered to analyze energy-optimal deployment strategies.