Duty-cycle Medium Access Control for Directional Wireless Sensor Networks

Abstract

Directional communication in wireless sensor network minimizes interference and thereby increases reliability and throughput performances of the network. Such advantages of Directional Wireless Sensor Networks (DSNs) have attracted the interests of researchers and industry experts around the globe. Furthermore, the sensor nodes with directional antennas provide extended network lifetime and better coverage performances. However, designing a communication protocol for wireless networks with directional antennas is a challenging problem due to lack of synchronization, asymmetry-in-gain, hidden terminal and deafness problems. Our endeavor in this dissertation is to address the aforementioned challenges in neighbor discovery and medium access control in Directional Sensor Networks. One of the key challenges of a directional node is to discover its neighbors due to difficulty in achieving synchronization among directed transmissions and receptions. Existing solutions suffer from high discovery latency and poor percentage of neighbor discovery either due to lack of proper coordination or centralized management of the discovery operation. In this thesis, we develop a collaborative neighbor discovery (COND) mechanism for DSNs. Using polling mechanism, each COND node directly discovers its neighbors in a distributed way and collaborates with other discovered nodes so as to allow indirect discovery. It helps to increase the neighbor discovery performance signi cantly. A Markov chain-based analysis has been carried out to quantify theoretical performances of the proposed COND system. The performance of the COND system is evaluated in NetworkSimulator Version-3 (NS-3), and the results reveal that it greatly reduces the discovery latency and increases neighbor discovery ratio compared to state-of-the-art approaches. The second contribution of this thesis is to develop a low duty-cycle directional medium access control protocol, termed as DCD-MAC, where, each pair of (parent and child sensor) nodes performs synchronization with each other before data communication. Each parent node in the network schedules data transmissions of its childs in such a way that the number of collisions occurred during transmissions from multiple nodes is minimized. A sensor node remains active only when it needs to communicate with others; otherwise, it goes to sleep state. The DCD-MAC exploits localized information of nodes in a distributed manner and it gives weighted-fair access of transmission slots to the nodes. As a nal point, we have studied the performances of our proposed MAC protocol through extensive simulations in NS-3 and the results show that the DCD-MAC gives better reliability, throughput, end-to-end delay and network lifetime compared to the related directional MAC protocols.