-\begin{figure}
+\begin{figure*}
\begin{center}
-\includegraphics[scale=0.3]{reseau.png}
+\includegraphics[scale=0.2]{SensorNetwork.png}
\begin{scriptsize}
-An example of a sensor network ofsize 10. All nodes are video sensor
-except the 5 and the 9 one which is the sink.
-\JFC{reprendre la figure, trouver un autre titre}
-\end{scriptsize}
-\caption{SN with 10 sensor}\label{fig:sn}.
+An example of a sensor network of size 10.
+All nodes are video sensors (depicted as small discs)
+except the 9 one which is the sink (depicted as a rectangle).
+Large lircles represent the maximum
+transmission range which is set to 20 in a square region which is
+$50 m \times 50 m$.
+\end{scriptsize}
+\caption{Illustration of a Sensor Network of size 10}\label{fig:sn}.
\end{center}
-\end{figure}
+\end{figure*}
Let us first recall the basics of the~\cite{HLG09} article.
The video sensor network is memorized as a connected non oriented
-oriented labelled graph.
+graph.
In this one,
the nodes, in a set $N$, are sensors, links, or the sink.
Furthermore, there is an edge from $i$ to $j$ if $i$ can
-send a message to $j$. The set of all edges is further denoted as
+send a message to $j$, \textit{i. e.}, the distance betwween
+$i$ and $j$ is less than a given maximum
+transmission range.
+All the possible edges are stored into a sequence
$L$.
Figure~\ref{fig:sn} gives an example of such a network.
where
$a_{il}$ is 1 if $l$ starts with $i$, is -1 if $l$ ends width $i$
and 0 otherwise.
-
+Moreover, the outgoing links(resp. the incoming links) are represented
+with the $A^+$ matrix (res. with the $A^-$ matrix), whose elements are defined:
+$a_{il}^+$ (resp. $a_{il}^-$) is 1 if the link $l$ is an outgoing link from $i$
+(resp an incoming link into $i$) and 0 otherwise.
Let $V \subset N $ be the set of the video sensors of $N$.
Let thus $R_h$, $R_h \geq 0$,
be the encoding rate of video sensor $h$, $h \in V$.
-Let $\eta_{hi}$ be the production rate of the node $i$,
-for the session initiated by $h$. More precisely, we have
+Let $\eta_{hi}$ be the rate inside the node $i$
+of the production that has beeninitiated by $h$. More precisely, we have
$ \eta_{hi}$ is equal to $ R_h$ if $i$ is $h$,
is equal to $-R_h$ if $i$ is the sink, and $0$ otherwise.
-We are then left to focus on the flows in this network.
+Let us focus on the flows in this network.
Let $x_{hl}$, $x_{hl}\geq 0$, be the flow inside the edge $l$ that
-issued from the $h$ session and
+issued from the node $h$ and
let $y_l = \sum_{h \in V}x_{hl} $ the sum of all the flows inside $l$.
Thus, what is produced inside the $i^{th}$ sensor for session $h$
is $ \eta_{hi} = \sum_{l \in L }a_{il}x_{hl} $.
The encoding power of the $i$ node is $P_{si}$, $P_{si} > 0$.
-
-The distortion is bounded $\sigma^2 e^{-\gamma . R_h.P_{sh}^{}2/3} \leq D_h$.
-
+The emmission distortion of the $i$ node is
+$\sigma^2 e^{-\gamma . R_i.P_{si}^{}2/3}$
+where $\sigma^2$ is the average input variance and
+$\gamma$ is the encoding efficiency coefficient.
+This distortion
+is bounded by a constant value $D_h$.
The initial energy of the $i$ node is $B_i$.
-
+The transmission consumed power of node $i$ is
+$P_{ti} = c_l^s.y_l$ where $c_l^s$ is the transmission energy
+consumption cost of link $l$, $l\in L$. This cost is defined
+as foolows: $c_l^s = \alpha +\beta.d_l^{n_p} $ where
+$d_l$ represents the distance of the link $l$,
+$\alpha$, $\beta$, and $n_p$ are constant.
+The reception consumed power of node $i$ is
+$P_{ri} = c^r \sum_{l \in L } a_{il}^-.y_l$
+where $c^r$ is a reception energy consumption cost.
The overall consumed power of the $i$ node is
$P_{si}+ P_{ti} + P_{ri}=
P_{si}+ \sum_{l \in L}a_{il}^{+}.c^s_l.y_l +
-\sum_{l \in L} a_{il}^{-}.c^r.y_l \leq q.B_i.
-$
-
-The objective is thus to find $R$, $x$, $P_s$ which minimize
- $q$ under the following set of constraints
+\sum_{l \in L} a_{il}^{-}.c^r.y_l $.
+%\leq q.B_i.
+%$
+
+The objective is thus to find $R$, $x$, $P_s$ which maximizes
+the network lifetime $T_{\textit{net}}$, or equivalently which minimizes
+$q=1/{T_{\textit{net}}}$.
+Let $B_i$ is the initial energy in node $i$.
+One have the equivalent objective to find $R$, $x$, $P_s$ which minimizes
+$q^2$
+under the following set of constraints:
\begin{enumerate}
\item $\sum_{l \in L }a_{il}x_{hl} = \eta_{hi},\forall h \in V, \forall i \in N $
\item $ \sum_{h \in V}x_{hl} = y_l,\forall l \in L$
\item $\dfrac{\ln(\sigma^2/D_h)}{\gamma.P_{sh}^{2/3}} \leq R_h \forall h \in V$
\item \label{itm:q} $P_{si}+ \sum_{l \in L}a_{il}^{+}.c^s_l.y_l +
-\sum_{l \in L} a_{il}^{-}.c^r.y_l \leq q.B_i, \forall i \in N$
+c^r.\sum_{l \in L} a_{il}^{-}.y_l \leq q.B_i, \forall i \in N$
+\item $\sum_{i \in N} a_{il}q_i = 0, \forall l \in L$
\item $x_{hl}\geq0, \forall h \in V, \forall l \in L$
\item $R_h \geq 0, \forall h \in V$
\item $P_{sh} > 0,\forall h \in V$
\begin{array}{l}
P_{si}+ \sum_{l \in L}a_{il}^{+}.c^s_l.\left( \sum_{h \in V}x_{hl} \right) \\
\qquad +
- \sum_{l \in L} a_{il}^{-}.c^r.\left( \sum_{h \in V}x_{hl} \right) \leq q.B_i, \forall i \in N
+ \sum_{l \in L} a_{il}^{-}.c^r.\left( \sum_{h \in V}x_{hl} \right) \leq q_i.B_i, \forall i \in N
\end{array}
$$
+and where the following constraint is added
+$$ $q_i > 0, \forall i \in N $$
+
They thus replace the objective of reducing
\label{eq:obj2}
\end{equation}
where $\delta$ is a regularisation factor.
-This indeed introduces quadratic fonctions on variables $x_{hl}$ and
+This indeed introduces quadratic functions on variables $x_{hl}$ and
$R_{h}$ and makes some of the functions strictly convex.
The authors then apply a classical dual based approach with Lagrange multiplier
\end{equation}
The proposed algorithm iteratively computes the following variables
-untill the variation of the dual function is less than a given threshold.
+until the variation of the dual function is less than a given threshold.
\begin{enumerate}
\item $ u_{hi}^{(k+1)} = u_{hi}^{(k)} - \theta^{(k)}. \left(
\eta_{hi}^{(k)} - \sum_{l \in L }a_{il}x_{hl}^{(k)} \right) $
\item
$\begin{array}{l}
\lambda_{i}^{(k+1)} = \max\left\{0, \lambda_{i}^{(k)} - \theta^{(k)}.\left(
- q^{(k)}.B_i \right. \left.\\
+ q^{(k)}.B_i \right. \right.\\
\qquad\qquad\qquad -\sum_{l \in L}a_{il}^{+}.c^s_l.\left( \sum_{h \in V}x_{hl}^{(k)} \right) \\
\qquad\qquad\qquad - \left.\left. \sum_{l \in L} a_{il}^{-}.c^r.\left( \sum_{h \in V}x_{hl}^{(k)} \right) - P_{si}^{(k)} \right) \right\}
\end{array}
=
\arg \min_{p > 0}
\left(
-v_h^{(k)}.\dfrac{\ln(\sigma^2/D_h)}{\gamma p ^{2/3}} + \lambda_h^{(k)}p
+v_h^{(k)}.\dfrac{\ln(\sigma^2/D_h)}{\gamma p^{2/3}} + \lambda_h^{(k)}p
\right)
$
