A multi-channel multiple access scheme using frequency offsets — Modelling and analysis

A system using frequency offset based transmit- reference (TR) modulation allows multiple nodes to transmit simultaneously and asynchronously without any mutual timing coordination. Thus, such a system provides inherent capabilities for a multiple access in the medium access control (MAC) layer to coordinate the shared use of the common wireless medium among the nodes of the wireless sensor network (WSN). However, certain characteristics of a frequency offset based system limits its performance, for example, the number of available frequency offsets is limited as it depends on several system parameters, and the number of simultaneous communications using different frequency offsets is limited due to inter-user interference. In this paper, we introduce an extended version of the performance model of a basic slotted- Aloha system, that captures the basic phenomena of a multi- channel system with a limited set of channels and a limit to the number of simultaneously used channels. An analysis of this model reveals the potential of a MAC protocol for TR modulation with frequency offsets

Traffic-adaptive duty cycle adaptation in TR-MAC protocol for wireless sensor networks

The Medium Access Control (MAC) layer can influence the energy consumption of a wireless sensor network (WSN) to a significant level. TR-MAC is an energy-efficient preamble sampling based MAC protocol for low power WSNs suitable for low data rate and low duty cycle scenario. However, low data rate is not always maintained in wireless sensor networks which often have to deal with event-driven scenarios where a sudden event rapidly increases traffic load within the network. In this paper we propose a traffic-adaptive duty cycle adaptation mechanism in order to provide responsiveness to traffic rate variations for TR-MAC protocol. This mechanism increases throughput and decreases packet delay while maintaining energy-efficiency without any extra information exchange among the sensor nodes in the network