\begin{eq}
\alpha\left(t\right)s(t)+n(t)
\end{eq}
where $\alpha\left(t\right)$ is the channel amplitude gain a random variable with Rayleigh distribution,; $s\left(t\right)$ is the modulated symbol, and $n\left(t\right)$ is the additive white Gaussian noise (AWGN).
\begin{eq}
E_s/N_0
\end{eq}
where the expectation operator is denoted by $\mathbb{E}\left(.\right)$, $E_s$ is the energy per modulated symbol, and $N_0$ is the noise power spectrum density.
Though the data rate can be displayed by $R=K/N$, where it represents the number of information bits sent in transmission of a binary symbol over the channel. Since generally $N>K$, we have $R<1$.