\relax
\citation{conti2014mobile}
-\citation{li2013survey}
\citation{Nayak04}
\newlabel{sec:introduction}{{1}{1}}
-\citation{yang2014energy,ChinhVu,vashistha2007energy,deschinkel2012column,shi2009,qu2013distributed,ling2009energy,xin2009area,cheng2014achieving,ling2009energy}
-\citation{yang2014energy}
-\citation{ChinhVu}
-\citation{qu2013distributed}
-\citation{shi2009}
-\citation{cheng2014achieving}
-\citation{ling2009energy}
-\citation{xu2001geography}
+\citation{li2013survey}
+\citation{castano2013column,rossi2012exact,deschinkel2012column}
+\citation{}
\newlabel{sec:Literature Review}{{2}{2}}
\newlabel{sec:The DiLCO Protocol Description}{{3}{2}}
\citation{Zhang05}
\newlabel{main_idea}{{3.2}{3}}
\providecommand*\caption@xref[2]{\@setref\relax\@undefined{#1}}
\newlabel{fig2}{{1}{3}}
+\newlabel{cp}{{4}{3}}
\citation{varga}
+\citation{ChinhVu}
+\citation{raghunathan2002energy}
+\citation{raghunathan2002energy}
\newlabel{alg:DiLCO}{{1}{4}}
-\newlabel{cp}{{4}{4}}
\newlabel{eq13}{{3}{4}}
\newlabel{eq14}{{4}{4}}
\newlabel{eq:ip2r}{{5}{4}}
\newlabel{sec:Simulation Results and Analysis}{{5}{4}}
-\citation{ChinhVu}
-\citation{raghunathan2002energy}
-\citation{raghunathan2002energy}
\citation{raghunathan2002energy}
\newlabel{table3}{{1}{5}}
\newlabel{table4}{{2}{5}}
\citation{xu2001geography}
\newlabel{sub1}{{5.2}{6}}
\newlabel{fig3}{{2}{6}}
-\newlabel{fig95}{{3}{7}}
+\newlabel{fig95}{{3}{6}}
\newlabel{fig8}{{4}{7}}
\newlabel{figLT95}{{5}{7}}
\newlabel{sec:Conclusion and Future Works}{{6}{7}}
\bibcite{idrees2014coverage}{Idrees et\nobreakspace {}al., 2014}
\bibcite{li2013survey}{Li and Vasilakos, 2013}
\bibcite{ling2009energy}{Ling and Znati, 2009}
+\bibcite{Sudip03}{Misra et\nobreakspace {}al., 2009}
\bibcite{Nayak04}{Nayak and Stojmenovic, 2010}
\bibcite{pedraza2006}{Pedraza et\nobreakspace {}al., 2006}
\bibcite{qu2013distributed}{Qu and Georgakopoulos, 2013}
challenges in WSNs, which has been addressed by a large amount of literature
during the last few years, is the design of energy efficient approaches for
coverage and connectivity~\cite{conti2014mobile}. Coverage reflects how well a
-sensor field is monitored. The most discussed coverage problems in literature
-can be classified into three types \cite{li2013survey}: area coverage (where
-every point inside an area is to be monitored), target coverage (where the main
-objective is to cover only a finite number of discrete points called targets),
-and barrier coverage (to prevent intruders from entering into the region of
-interest). On the one hand we want to monitor the area of interest in the most
+sensor field is monitored. On the one hand we want to monitor the area of interest in the most
efficient way~\cite{Nayak04}. On the other hand we want to use as less energy as
possible. Sensor nodes are battery-powered with no means of recharging or
replacing, usually due to environmental (hostile or unpractical environments) or
\section{\uppercase{Literature Review}}
\label{sec:Literature Review}
-\noindent In this section, we summarize some related works regarding coverage lifetime maximization and scheduling, and distinguish our DiLCO protocol from the works presented in the literature. Some algorithms have been developed in ~\cite{yang2014energy,ChinhVu,vashistha2007energy,deschinkel2012column,shi2009,qu2013distributed,ling2009energy,xin2009area,cheng2014achieving,ling2009energy} to solve the area coverage problem so as to preserve coverage and prolong the network lifetime.
+\noindent In this section, we summarize some related works regarding coverage problem , and distinguish our DiLCO protocol from the works presented in the literature.\\
+The most discussed coverage problems in literature
+can be classified into three types \cite{li2013survey}: area coverage (where
+every point inside an area is to be monitored), target coverage (where the main
+objective is to cover only a finite number of discrete points called targets),
+and barrier coverage (to prevent intruders from entering into the region of
+interest).
+{\it In DiLCO protocol, the area coverage, ie the coverage
+of every point in the sensing region, is transformed to the coverage of a fraction of points called primary points. }
+
+The major approach to extend network lifetime while preserving coverage is to divide/organize the sensors into a suitable number of set covers (disjoint or non-disjoint) where each set completely covers an interest region and to activate these set covers successively. The network activity can be planned in advance and scheduled for the entire network lifetime or organized in periods, and the set of
+active sensor nodes is decided at the beginning of each period.
+Active node selection is determined based on the problem
+requirements (e.g. area monitoring, connectivity, power
+efficiency). Different methods has been proposed in literature.
+
+{\it DiLCO protocol works in periods, each period contains a preliminary phase for information exchange and decisions, followed by a sensing phase where
+one cover set is in charge of the sensing task.}
+
+Various approaches, including centralised, distributed and localized algorithms, have been proposed to extend the network lifetime.
+%For instance, in order to hide the occurrence of faults, or the sudden unavailability of
+%sensor nodes, some distributed algorithms have been developed in~\cite{Gallais06,Tian02,Ye03,Zhang05,HeinzelmanCB02}.
+In distributed algorithms, information is disseminated throughout the network and sensors decide cooperatively by communicating with their neighbours which of them will remain in sleep mode for a certain period of time.
+The centralized algorithms always provide nearly
+or close to optimal solution since the algorithm has global view of the whole
+network, but such a method has the disadvantage of requiring
+high communication costs, since the node (located at the base station) making the decision needs information from all the sensor nodes in the area.
+
+{\it In DiLCO protocol, the area coverage is divided into several smaller subregions, and in each of which, a node called the leader is on charge for selecting the active sensors for the current period.}
+
+A large variety of coverage scheduling algorithms have been proposed in the literature. Many of the existing algorithms, dealing with the maximisation of the number of cover sets, are heuristics. These heuristics involve the construction of a cover set by including in priority the sensor nodes which cover critical targets, that is to say targets that are covered by the smallest number of sensors. Other approaches are based on mathematical programming formulations and dedicated techniques (solving with a branch-and-bound algorithms available in optimization solver). The problem is formulated as an optimization problem (maximization of the lifetime, of the number of cover sets) under target coverage and energy constraints. Column generation techniques, well-known and widely practiced techniques for solving linear programs with too many variables, have been also used~\cite{castano2013column,rossi2012exact,deschinkel2012column}.
+
+
+{\it In DiLCO protocol, each leader, in each subregion, solves an integer program with a double objective consisting in minimizing the overcoverage and limiting the undercoverage. This program is inspired from the work of \cite{} where the objective is to maximize the number of cover sets.}
+
+
+\iffalse
+
+Some algorithms have been developed in ~\cite{yang2014energy,ChinhVu,vashistha2007energy,deschinkel2012column,shi2009,qu2013distributed,ling2009energy,xin2009area,cheng2014achieving,ling2009energy} to solve the area coverage problem so as to preserve coverage and prolong the network lifetime.
Yang et al.~\cite{yang2014energy} investigated full area coverage problem
a sensor node is divided into epochs. At each epoch, the
base station deduces the current sensing coverage requirement
from application or user request. It then applies the heuristic algorithm in order to produce the set of active nodes which take the mission of sensing during the current epoch. After that, the produced schedule is sent to the sensor nodes in the network.
-
+\fi
\iffalse
achieve increased sensing lifetime of the network.
-\fi
+
The main contributions of our DiLCO Protocol can be summarized as follows:
(1) The distributed optimization over the subregions in the area of interest,
-(2) The distributed dynamic leader election at each round by each sensor node in the subregion,
+(2) The distributed dynamic leader election at each period by each sensor node in the subregion,
(3) The primary point coverage model to represent each sensor node in the network,
(4) The activity scheduling based optimization on the subregion, which are based on the primary point coverage model to activate as less number as possible of sensor nodes to take the mission of the coverage in each subregion, and (5) The improved energy consumption model.
-
+\fi
\iffalse
The work presented in~\cite{luo2014parameterized,tian2014distributed} tries to solve the target coverage problem so as to extend the network lifetime since it is easy to verify the coverage status of discreet target.
%Je ne comprends pas la phrase ci-dessus
The work presented in ~\cite{Zhang} focuses on a distributed clustering method, which aims to extend the network lifetime, while the coverage is ensured.
The work proposed by \cite{qu2013distributed} considers the coverage problem in WSNs where each sensor has variable sensing radius. The final objective is to maximize the network coverage lifetime in WSNs.
-\fi
-\iffalse
+
+
Casta{\~n}o et al.~\cite{castano2013column} proposed a multilevel approach based on column generation (CG) to extend the network lifetime with connectivity and coverage constraints. They are included two heuristic methods within the CG framework so as to accelerate the solution process.
In \cite{diongue2013alarm}, diongue is proposed an energy Aware sLeep scheduling AlgoRithm for lifetime maximization in WSNs (ALARM) algorithm for coverage lifetime maximization in wireless sensor networks. ALARM is sensor node scheduling approach for lifetime maximization in WSNs in which it schedule redundant nodes according to the weibull distribution taking into consideration frequent nodes failure.
Yu et al.~\cite{yu2013cwsc} presented a connected k-coverage working sets construction
