% vim: set ts=2 sw=2 noet spell:

\begin{tikzpicture}[
		% show background rectangle,
		box/.style = {
			font = \small\sffamily,
			draw, thick, fill = white,
			minimum height = 14mm,
			minimum width = 28,
			text width = 28mm, align = center,
		},
		circ/.style = {
			draw, thick, circle, fill = white,
			minimum size = 10mm, inner sep = 0pt,
			font = \Huge,
		},
	]

	% --------------------------------------------------------	

	\coordinate (TX) at (0, 0);
	\matrix[
		nodes = {box}, column sep = 14mm, row sep = 10mm,
		inner sep = 3mm, fill = lightgray!20,
		anchor = north west,
	] at (TX) {
		\node (SRC) {\textbf{Source}\\ Digital data}; &
		\node (FRA) {\textbf{Framer}\\ Data Packets}; &
		\node (MOD) {\textbf{Modulator}\\ QPSK or 16-QAM}; \\
	};

	\draw[very thick, -latex]
		(SRC) edge node[midway, above] {\(m\)} (FRA)
		(FRA) edge (MOD)
	;

	\node[
		gray,
		anchor = south west,
		font = \ttfamily,
	] at (TX) {Transmitter};

	% --------------------------------------------------------

	\coordinate (CHN) at ($(MOD.south east)+(3mm, -11mm)$);
	\matrix[
		row sep = 5mm, inner sep = 3mm, fill = lightgray!20,
		anchor = north east,
	] at (CHN) {
		\node[circ] (PLUS) {\(+\)}; %
		\node[left = 14mm of PLUS] (AWGN) {AWGN}; &
		\node[minimum width = 12mm] {}; \\
		\node[circ] (TIMES) {\(\times\)}; %
		\node[left = 14mm of TIMES] (FADING) {Fading}; \\
	};

	\draw[very thick, -latex]
		(AWGN) edge node[midway, above] {\(n(t)\)} (PLUS)
		(FADING) edge node[midway, above] {\(f(t)\)} (TIMES)
		(MOD) edge node[midway, right] {\(s(t)\)} (PLUS)
		(PLUS) edge (TIMES)
	;

	\node[
		gray,
		anchor = south west,
		font = \ttfamily,
	] at ($(CHN) - (62mm, 0)$) {Channel Model};

	% --------------------------------------------------------

	\coordinate (RX) at (0, -68mm);
	\matrix[
		nodes = {box},
		column sep = 14mm, row sep = 5mm,
		inner sep = 3mm, fill = lightgray!20,
		anchor = north west,
	] at (RX) {
		\node (PFC) {\textbf{Fine phase and freq. correction}}; &
		\node (EQL) {\textbf{Equalizer} \\ Amplitude}; &
		\node (CLK) {\textbf{Clock Recovery} \\ Symbol peak}; \\
		\node (DMO) {\textbf{Demodulator}}; &
		\node (DFR) {\textbf{Deframer} \\ Error detection}; &
		\node (SIN) {\textbf{Sink} \\ User interface}; \\
	};

	\draw[very thick, -latex]
		(TIMES) edge node[midway, right] {\(r(t)\)} (CLK)
		(CLK) edge (EQL)
		(EQL) edge (PFC)
		(PFC) edge (DMO)
		(DMO) edge (DFR)
		(DFR) edge (SIN)
	;

	\node[
		gray,
		anchor = south west,
		font = \ttfamily,
	] at (RX) {Receiver};
\end{tikzpicture}