%%?Phase?Shift?Keying?Simulation
%?This?demo?shows?how?to?simulate?a?basic?Quarternary?Phase?Shift?Keying
%?（QPSK）?communication?link?and?to?generate?empirical?performance?curves
%?that?can?be?compared?to?theoretical?predictions.

%?Copyright?1996-2004?The?MathWorks?Inc.
%?$Revision:?1.12.2.5?$?$Date:?2004/04/12?23:01:29?$

%%?Initializing?variables
%?The?first?step?is?to?initialize?variables?for?number?of?samples?per
%?symbol?number?of?symbols?to?simulate?alphabet?size?（M）?and?the?signal
%?to?noise?ratio.?The?last?line?seeds?the?random?number?generators.

nSamp?=?8;?numSymb?=?100;???
M?=?4;?SNR?=?14;?
seed?=?[12345?54321];????????
rand（‘state‘?seed（1））;?randn（‘state‘?seed（2））;

%%?Generating?random?information?symbols
%?Next?use?RANDSRC?to?generate?random?information?symbols?from?0?to?M-1.
%?Since?the?simulation?is?of?QPSK?the?symbols?are?0?through?3.?The?first
%?10?data?points?are?plotted.

numPlot?=?10;
rand（‘state‘?seed（1））;
msg_orig?=?randsrc（numSymb?1?0:M-1）;
stem（0:numPlot-1?msg_orig（1:numPlot）?‘bx‘）;
xlabel（‘Time‘）;?ylabel（‘Amplitude‘）;

%%?Phase?modulating?the?data?
%?Use?PSKMOD?to?phase?modulate?the?data?and?RECTPULSE?to?upsample?to?a
%?sampling?rate?8?times?the?carrier?frequency.?Use?SCATTERPLOT?to?see?the
%?signal?constellation.

grayencod?=?bitxor（0:M-1?floor（（0:M-1）/2））;?
msg_gr_orig?=?grayencod（msg_orig+1）;
msg_tx?=?pskmod（msg_gr_origM）;
msg_tx?=?rectpulse（msg_txnSamp）;
h1?=?scatterplot（msg_tx）;
set（h1‘position‘[93?680?420?420]）;

%%?Creating?the?noisy?signal
%?Then?use?AWGN?to?add?noise?to?the?transmitted?signal?to?create?the?noisy
%?signal?at?the?receiver.?Use?the?‘measured‘?option?to?add?noise?that?is
%?14?dB?below?the?average?signal?power?（SNR?=?14?dB）.?Plot?the
%?constellation?of?the?received?signal.

randn（‘state‘?seed（2））;
msg_rx?=?awgn（msg_tx?SNR?‘measured‘?[]?‘dB‘）;
h2?=?scatterplot（msg_rx）;

%%?Recovering?information?from?the?transmitted?signal
%