Analyzing the transitional region in low power wireless links

TLDR

Wireless sensor networks require realistic link‑layer models, and experiments reveal a transitional region of highly unreliable links that undermines idealized perfect‑reception models. The paper models low‑power wireless links with communication‑theory techniques to identify and quantify the causes of the transitional region, and proposes that spread‑spectrum and diversity can mitigate it. The authors derive packet‑reception‑rate expressions versus distance and transitional‑region width, incorporating path‑loss exponent, shadowing variance, modulation, and encoding parameters. They find that narrow‑band radios exhibit a transitional region caused by multi‑path fading, independent of radio non‑ideality.

Abstract

The wireless sensor networks community, has now an increased understanding of the need for realistic link layer models. Recent experimental studies have shown that real deployments have a "transitional region" with highly unreliable links, and that therefore the idealized perfect-reception-within-range models used in common network simulation tools can be very misleading. In this paper, we use mathematical techniques from communication theory to model and analyze the low power wireless links. The primary contribution of this work is the identification of the causes of the transitional region, and a quantification of their influence. Specifically, we derive expressions for the packet reception rate as a function of distance, and for the width of the transitional region. These expressions incorporate important channel and radio parameters such as the path loss exponent and shadowing variance of the channel; and the modulation and encoding of the radio. A key finding is that for radios using narrow-band modulation, the transitional region is not an artifact of the radio non-ideality, as it would exist even with perfect-threshold receivers because of multi-path fading. However, we hypothesize that radios with mechanisms to combat multi-path effects, such as spread-spectrum and diversity techniques, can reduce the transitional region.