The SCREAM Approach for Efficient Distributed Scheduling with Physical Interference in Wireless Mesh Networks

It is known that CSMA/CA channel access schemes are not suitable to meet the high traffic demand of wireless mesh networks. One possible way to increase traffic carrying capacity is to use a spatial TDMA (STDMA) approach in conjunction with the physical interference model, which allows more aggressive scheduling than the protocol interference model on which CSMA/CA is based. However, a major difficulty in using STDMA with physical interference is the inherent complexity of this interference model. While an efficient, centralized solution for STDMA with physical interference has been recently proposed, no satisfactory distributed approaches have been introduced so far. In this paper, we first prove that no localized distributed algorithm can solve the problem of building a feasible schedule under the physical interference model. Motivated by this, we design a global primitive, called SCREAM, which is used to verify the feasibility of a schedule during an iterative distributed scheduling procedure. Based on this primitive, we present two distributed protocols for efficient, distributed scheduling under the physical interference model, and we prove an approximation bound for one of the protocols. We also present extensive packet-level simulation results, which show that our protocols achieve schedule lengths very close to those of the centralized algorithm and have running times that are practical for mesh networks

OaSis: An Application Specific Operating System for an Embedded Environment

Portable and affordable assistive devices are calling necessities for the physically challenged population putting forth the requirement of designing embedded systems tuned to specific assistive applications. In this paper, we present a low footprint embedded operating system, OaSis, which forms the core of embedded devices being developed for the speech impaired, the visually impaired and those with neuro-motor disorders. The target hardware, housing OaSis and on which the applications are ported is Geode GX1-233 processor based POS-563 of Advantech. The system is presently being ported to more energy efficient ARM based platform. This system currently supports three applications: Shruti – a Vernacular speech interface