PhD Dissertation Defense of CS Scholar, Shama Siddiqui
Title: A Study on Channel Polling Mechanisms for
Wireless Sensor Networks
Date: Monday, November 27, 2017
Time: 10:30 a.m.
Venue: Room MAS-1 (Seminar Room), Adamjee
Building, IBA Main Campus, Karachi, Pakistan
Advisor: Dr. Sayeed Ghani
National Examiners:
Dr. Nadeem Ahmed
Dr. Majid
Iqbal
Abstract
Due to the highly application specific nature of WSN,
hundreds of Media Access Control (MAC) protocols have
been proposed in the past. The focus of these protocols
has been on optimizing the performance parameters such
as energy, delay, throughput and reliability, and among
these improving energy efficiency of WSN has always been
the primary goal. MAC protocols have taken various
approaches to manage the energy consumption of WSN nodes
efficiently, channel polling using Low Power Listening
(LPL) is one of them.
Channel polling refers to the channel listening by the
receiving nodes mostly in asynchronous MAC protocols,
which significantly governs energy, delay and lifetime
of the network. Therefore, it is required to adjust the
polling intervals in accordance with the incoming
traffic patterns. All of the previous protocols either
polled the channel periodically regardless of the
traffic arrival patterns, or they attempted to adjust
the polling intervals based on the past arrival
patterns. However, none of the previous protocols
focused on studying the influence of polling interval
distribution on the WSN performance. Hence, the research
gap identified for this dissertation is to study the
influence of varying polling interval distributions for
the MAC protocol and to develop an asynchronous
duty-cycle based MAC protocol: Adaptive and Dynamic
Polling-MAC (ADP-MAC), which is based on this concept.
The protocol has been developed to be a dynamic energy
efficient MAC protocol, which adapts to a wide range of
WSN applications, particularly those with dynamic
traffic patterns. A Receiver Initiated
Pseudo-Synchronization (RIPS) scheme has been integrated
with the protocol to ensure that nodes get back into
communication after a certain period of being out of
synchronization. The study took the novel approach of
switching the polling interval distribution of the
receiver nodes by monitoring the Co-efficient of
Variation (CV) of the incoming traffic. The CV is hence
intended to be used as an indicator of the variance
present in not just the generated traffic but ultimately
the traffic arriving at the receiving nodes. To
represent different applications of WSN Constant-Bit
Rate (CBR), Poisson and Bursty Arrivals have been used;
whereas three types of polling distributions have been
studied: Deterministic, Exponential and Dynamic. The
performance of ADP-MAC has been evaluated with the
features of Dynamic Polling set ON and OFF, and when the
Dynamic Polling is set OFF, the protocol conducts either
deterministic or Exponential Polling. Closely linked to
the energy performance of ADP-MAC is the use of packet
concatenation and block acknowledgment mechanisms, which
have also been analyzed.
The single-hop and multi-hop performance of ADP-MAC has
been evaluated through implementing the design in TinyOS
for mica2 platform. Avrora emulator has been used for
simulations and Awk script was written for data parsing
from the output file. The experiments are conducted for
varying number of nodes, message generation intervals
and polling intervals, among other parameters. The
mechanisms of Adaptive & Dynamic Polling and packet
concatenation are separately studied to unveil the
contribution of each aspect of ADP-MAC.
It has been found that in terms of energy consumption
and delay, ADP-MAC with Deterministic Polling serves
best for CBR Arrivals, ADP-MAC with Exponential Polling
serves best for Poisson Arrivals and finally, ADP-MAC
with Dynamic Polling serves best for the Bursty
Arrivals. These observations have led to the major
finding of this dissertation that when the traffic
arrival and polling interval distribution of ADP-MAC are
in conformance, the performance in terms of both delay
and energy turns out to be the best. On the other hand,
ADP-MAC with Dynamic Polling results in best performance
in terms of packet loss regardless of the type of
arrivals.
The performance comparison of ADP-MAC has been shown
against an established MAC protocol: Synchronized
Channel Polling MAC (SCP-MAC). The results show that
ADP-MAC outperforms SCP-MAC in terms of energy
consumption, delay and packet loss. The major reason for
the superior performance of ADP-MAC is that it does not
need synchronization and reduces contention, idle
listening and overhearing; moreover, the Adaptive
Polling mechanism dynamically selects the corresponding
and best polling interval distribution based on the
traffic arrival patterns, hence reducing the energy
consumption associated with preamble transmissions and
excessive polling.