RTXP : A Localized Real-Time Mac-Routing Protocol for Wireless Sensor Networks

TL;DR

RTXP is a novel, decentralized real-time MAC and routing protocol for wireless sensor networks that guarantees deterministic delays using local information and cross-layer design, outperforming non-deterministic solutions especially under unreliable radio conditions.

Contribution

RTXP introduces the first decentralized, cross-layer real-time protocol for WSNs that guarantees end-to-end delay bounds using local information and a virtual coordinate system.

Findings

Theoretical delay bounds and capacity are established for RTXP.

Simulation results confirm RTXP's performance and delay guarantees.

RTXP outperforms non-deterministic solutions in unreliable radio environments.

Abstract

Protocols developed during the last years for Wireless Sensor Networks (WSNs) are mainly focused on energy efficiency and autonomous mechanisms (e.g. self-organization, self-configuration, etc). Nevertheless, with new WSN applications, appear new QoS requirements such as time constraints. Real-time applications require the packets to be delivered before a known time bound which depends on the application requirements. We particularly focus on applications which consist in alarms sent to the sink node. We propose Real-Time X-layer Protocol (RTXP), a real-time communication protocol. To the best of our knowledge, RTXP is the first MAC and routing real-time communication protocol that is not centralized, but instead relies only on local information. The solution is cross-layer (X-layer) because it allows to control the delays due to MAC and Routing layers interactions. RTXP uses a suited hop-count-based Virtual Coordinate System which allows deterministic medium access and forwarder selection. In this paper we describe the protocol mechanisms. We give theoretical bound on the end-to-end delay and the capacity of the protocol. Intensive simulation results confirm the theoretical predictions and allow to compare with a real-time centralized solution. RTXP is also simulated under harsh radio channel, in this case the radio link introduces probabilistic behavior. Nevertheless, we show that RTXP it performs better than a non-deterministic solution. It thus advocates for the usefulness of designing real-time (deterministic) protocols even for highly unreliable networks such as WSNs.