On the Relationship between Network Congestion and Local Contention in IEEE 802.15.4 Based Networks

3rd International Conference on Sensor Technologies and Applications -- JUN 18-23, 2009 -- Athens, GREECEWOS: 000274635500005Due to the specific operation of wireless sensor networks (WSN) and especially to the multi-hop nature of many WSNs, local contention can lead to network-wide congestion and reduce both the efficiency and the lifetime of the network. In this paper we study the interdependence between end-to-end congestion and local contention including different mobility patterns using three different application scenarios. In each of the scenarios discussed, all nodes send information to a sink which is the PAN coordinator. In the first one, all the nodes are static, in the second one the sink is static while the nodes are moving and in the third one the sink is static while the rest of the nodes are mobile. The work is based on the slotted CSMA/CA MAC adopted in IEEE 802.15.4 protocol specification for LR-WPAN. Results show the effects of changing local contention regulating parameters like activity periods, number of MAC layer retransmissions and transmission buffer size on the overall network congestion.IARIA, IEEE Comp Soc, Greece Chapte

Channel Estimation with Fully Connected Deep Neural Network

In this study, we focus on realizing channel estimation using a fully connected deep neural network. The data aided estimation approach is employed. We assume the transmission channel is Rayleigh and it is constant over the duration of a symbol plus pilot transmission. We develop and tune the deep learning model for various size of pilot data that is known to the receiver and used for channel estimation. The deep learning models are trained on the Rayleigh channel. The performance of the model is discussed for various size of pilot by providing Bit Error Rate of the model. The Bit Error Rate performance of the model is compared to theoretical upper bound which shows that the model successfully estimates the channel

A cross-layer fault tolerance management module for wireless sensor networks

It is a well-established fact that wireless sensor networks (WSNs) are very power constraint networks, but besides this, they are inherently more fault-prone than any other type of wireless network and their protocol design is very application specific. Major reasons for the faults are the unpredictable wireless communication channel, battery depletion, as well as fragility and mobility of the nodes. Furthermore, as traditional protocol design methods have proved inadequate, the cross-layer design (CLD) approach, which allows for interactions between different layers, providing more flexible and energy-efficient functionality, has emerged as a viable solution for WSNs. In this study we define a fault tolerance management module suitable to the requirements, limitations, and specifics of WSNs, encompassing methods for fault detection, fault prevention, fault management, and recovery. The suggested solution is in line with the CLD approach, which is an important factor in increasing the network performance. Through simulations the functionality of the network is evaluated, based on packet loss, delay, and energy consumption, and is compared with a similar solution not including fault management. The results achieved support the idea that the introduction of a unified approach to fault management improves the network performance as a whole