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\title[Crowncom13]
{Whether and When to Share: Spectrum Sensing as An Evolutionary Game}
\author[]
{Ying Dai, Jie Wu}
\institute[temple]
{Department of Computer and Information Sciences, Temple University}
\date[]
{}

\begin{document}

\begin{frame}
  \titlepage
\end{frame}

\section{Introduction}

\begin{frame}
\frametitle{Motivation}

\begin{itemize}
  \item Spectrum sensing is the key phase to identifying the spectrum availability in cognitive radio networks (CRNs).

  \pause
  \vspace{0.2cm}

  \item The fundamental task of spectrum sensing contains two aspects:

  \pause

  {\small{~~~~$\circ$
  Protect the active primary users.}}

\pause

  {\small{~~~~$\circ$ Detect the available channels.}}

\pause

\vspace{0.2cm}

\item The objectives of secondary users are to maximize the utilization of the
available spectrum and to prevent interference with primary users.

\end{itemize}
\note{Cognitive radio networks (CRNs) enable secondary
users to utilize the licensed spectrum when primary
users are not using it. Spectrum sensing is the key phase
to identifying the spectrum availability. The fundamental task
of spectrum sensing is that: when primary users are using the licensed
spectrum, each secondary user should be able to detect it, and should
quit transmitting on the corresponding spectrum band. When
primary users are not using the licensed spectrum, each secondary user should be
able to identify the corresponding spectrum band as available.
The objectives of secondary users are to maximize the utilization of the
available spectrum and to prevent interference with primary users.}

\end{frame}

\begin{frame}
\frametitle{Motivation}

\begin{itemize}
\item How to measure the performance of spectrum sensing:

\pause

\vspace{0.2cm}


  {\small{~~~~$\circ$ Probability of detection: the probability
of a secondary user detecting a primary user when the spectrum is occupied
by the primary user;}}


 {\small{~~~~$\circ$ Probability of false alarm: the probability of a secondary user falsely declaring a primary user as present, when it is actually not occupied.}}


\pause

\vspace{0.2cm}

\item To ensure the spectrum
sensing quality, adequate sample collection is required over
a period of time for analysis by secondary users.

\end{itemize}

\note{Read the slide.}
\end{frame}


\begin{frame}
\frametitle{Motivation}

\begin{itemize}
  \item However, the time spent by the
secondary user on spectrum sensing will reduce the time spent on data
transmission.

\pause

\vspace{0.2cm}

  \item For each secondary user, there is a tradeoff between the time used for spectrum sensing and the time used for data transmission.

 \pause

\vspace{0.2cm}

  \item One effective approach to solve this is cooperative sensing.

\end{itemize}

\note{The time spent by the
secondary user on spectrum sensing will reduce the time spent on data
transmission. On the other side, the time spent on spectrum sensing cannot decrease too much for ensuring the spectrum sensing performance.  Therefore, for each secondary user, there is a tradeoff between the time used for spectrum sensing and the time used for data transmission.One effective approach to solve this is cooperative sensing, which is about having each secondary user share their sensing results and cooperate with each other. Many works have done on this issue.}
\end{frame}

\begin{frame}
\frametitle{Motivation}

\begin{itemize}
  \item Many works apply game theory on cooperative spectrum sensing.

     {\small{~~~~$\circ$ They determine the relative
probability of a secondary user participating.}}

 {\small{~~~~$\circ$ The strategy set is usually \{contribute, not contribute\}.}}

\pause

\vspace{0.2cm}

  \item We consider an extended strategy set, including ``when to share''.

\end{itemize}

\note{ Many works apply game theory on cooperative spectrum sensing. They determine the relative
probability of a secondary user participating. And the strategy set is usually \{contribute, not contribute\}.

However, We consider not only whether for a secondary user to contribute or share its sensing results, but also when to share its sensing results during the spectrum sensing phase.}
\end{frame}

\section{Problem Formulation}
\begin{frame}
\frametitle{System Model}

Each time slot is divided into three parts.

  \begin{center}
\includegraphics[scale=0.80]{1.eps}
\end{center}


\note{Each time slot $T$ is divided into three parts: sensing phase $T_s$, sharing phase with a maximal length of $T_c$, and data transmission phase $T_d$. The sensing phase is for each node to sense the channel independently. We assume that for each node, the time spent on independent sensing is static. The sharing phase is for each node to send its sensing results over the signaling channel. }

\end{frame}

\begin{frame}
\frametitle{System Model}
\begin{itemize}
  \item Suppose the minimal time required for sending the sensing results when there is no conflict is $t_c$. Then $T_c$ is divided into $\lceil\frac{T_c}{t_c}\rceil$ sub slots.

      \vspace{0.2cm}

      \pause

  \item For a certain SU, it can choose whether to share its sensing results or not. If a node decides not to share its sensing results, its sharing time length would be 0.

       \vspace{0.2cm}

      \pause

  \item If it chooses to cooperate with others, it needs to choose one sub slot of $T_c$ to send the sensing results.

       {\small{~~~~$\circ$ The sensing results are confirmed to be received successfully through the ACKs. The sharing phase of a node ends as long as one ACK is received.
       }}

      {\small{~~~~$\circ$ Before that, the current secondary user keeps listening to the signaling channel for others' sensing results.}}

\end{itemize}

\note{read the slide.}
\end{frame}

\begin{frame}
\frametitle{Objective $\&$ Constraints}

\begin{itemize}
  \item The constraints here are the requirements of the performance of spectrum sensing.

  {\small{~~~~$\circ$ Both the probability of detection and probability of false alarm have to meet the required threshold.}}

  \pause

  \vspace{0.2cm}


  \item The objective is defined based on each secondary user's view, which is to maximize its own utility.

      {\small{~~~~$\circ$ The utility is related to the throughput of the secondary user considering both  active and inactive status of primary users.}}

\end{itemize}

\note{First read the slide. Then the detailed definitions are in our paper.}
\end{frame}

\section{Game Model}
\begin{frame}
\frametitle{Evolutionary Game}

\begin{itemize}
  \item We build the evolutionary game for our model.

  {\small{~~~~$\circ$ The key insight is that many behaviors involve the interactions of multiple strategies of different players, and the success of any strategy depends on how it interacts with others.}}

  \vspace{0.2cm}
  \pause

  \item The objective is to find the evolutionarily stable strategy (ESS), which tends to persist once it is adopted by most players.

        {\small{~~~~$\circ$ Due
to dynamics in the spectrum availability in CRNs, there is
not a static stable strategy for each user conducting spectrum
sensing.}}

\end{itemize}
\note{read the slide}
\end{frame}

\begin{frame}
\frametitle{Game Model}

\begin{itemize}
   \item The secondary users in our model consider both whether and when to share their sensing results.

       \vspace{0.2cm}

       \pause

   \item Based on this intuition, we have the definition of the strategy set for our model.

  {\small{~~~~$\circ$ The strategy set of an SU is $\{(C, j)\}$, where $j \in \{0, 1, ... , \lceil\frac{T_c}{t_c}\rceil\}$. $j=0$ means the SU denies to share its sensing results. Otherwise, the SU sends its sensing results at the $j$th sub slot of $T_c$.}}

  \vspace{0.2cm}

       \pause

   \item The payoff of each secondary user is defined based on the throughput after it adopts one strategy.

 \end{itemize}
\end{frame}

\begin{frame}
\frametitle{Game Model}

\begin{itemize}
  \item We prove the existence of ESS in our game model and give the replicator dynamics that can have a secondary user converge to the ESS.

      \pause

  \item The algorithm for each secondary user is basically to adjust its strategy based on its payoff and the replicator dynamics.


  \begin{center}
\includegraphics[scale=0.40]{1.png}
\end{center}

\end{itemize}

\note{read the slide. For the algorithm, just say ``here is the details of our algorithm''.}

\end{frame}

\section{Experiment}
\begin{frame}
\frametitle{Experiment Settings}

\begin{itemize}
  \item We use four USRPs to evaluate our model.


  \item Three USRPs simulate three secondary users. One USRP simulates the primary user.

  \item The three secondary users work on three subbands with different central frequencies: 1.3GHz, 1.30025GHz and 1.3005GHz.

  \item The primary user works on all three subbands at the same time.



\end{itemize}
\note{Here is the settings of our four USRPs.}
\end{frame}

\begin{frame}
\frametitle{Experiment Settings}

Some other settings:

\begin{itemize}
  \item The time slot length to 20s here (for better synchronization).


  \item The static sensing time is set to 5s, which is divided into 5 sub slots.


  \item The window size for each secondary to calculate the average throughput
is 4 slots.

  \item The bandwidth of each secondary is 50k bps and the gain at
each receiver is set to 20.
\end{itemize}
\note{Here is the settings of some other parameters.}
\end{frame}


\begin{frame}
\frametitle{Experiment Results}

The experimental results of three secondary users:

  \begin{center}
\includegraphics[scale=0.40]{T-PROB1.eps}
\end{center}


\end{frame}

\section{Conclusion}

\begin{frame}
\frametitle{Conclusion}
\begin{itemize}
  \item We consider both whether-to-share and when-to-share for the cooperative spectrum sensing in CRNs.

      \vspace{0.2cm}

  \item We apply an evolutionary game model and define a novel strategy set for each player.

  \vspace{0.2cm}

  \item We prove the existence of the evolutionary stable strategy (ESS) and provide a practical algorithm.

  \vspace{0.2cm}

  \item We evaluate our model and the parameter influences through experiments.

\end{itemize}

\end{frame}


\begin{frame}
  \begin{center}
    \LARGE \emph{Thank you!}
  \end{center}
\end{frame}

\end{document} 