PHASE SHIFT KEYING (PSK)
Table of Contents
Intro
The modulated phase of the carrier represents the digital information. PSK is bandwidth efficient and power inefficient compared to FSK. While PSK is less susceptible to noise it requires the same bandwidth as ASK, but the process of demodulation is more complex than in ASK or FSK. PSK is used in WLAN, satellite broadcasting, Bluetooth and RFID applications.
BPSK
The simplest form of PSK is Binary PSK (BPSK) using two phases separated by 180°. It is quite robust to noise, but not suitable for higher data rates.
Typically but not necessarily the phase of a logical one is 0° and 180° for a logical zero. This can be achieved by an inversion of the carrier´s amplitude to indicate a logical zero.
disp('BPSK');
init;
Time Domain
x=['1';'0';'1';'0';'0']; % bit sequence;
figure();
plot_SK(x,'type','PSK');
Constellation Diagram
figure();
plot_SK(x,'type','PSK','mode','constellation') ;
Modulator and Demodulator
A Binary PSK modulator only needs to multiply the carrier by 
depending on the information signal. The demodulator needs an oscillator which is synchronized to the unmodulated carrier, since the phase of the carrier contains the information,
depending on the information signal. The demodulator needs an oscillator which is synchronized to the unmodulated carrier, since the phase of the carrier contains the information,file2sim='PSK_MODEM';
if (do_sim)
init_PSK;
convert_model(file2sim); % create HTML-version of simulinkfile
disp(get_link('-> PSK in Simulink',file2sim));
[TX_signal,carrier,MOD_signal,RX_signal,t]=sim_model(file2sim);
figure
plot_MOD(t,TX_signal,carrier,MOD_signal,RX_signal)
end
pic_file=strcat(file2sim,pic_ext,'.jpg');
if exist(pic_file,'file')
disp('PSK in Simulink - block diagram');
figure
image(imread(pic_file))
end
MPSK
If a symbol is coded by a set of binary digits of the length n, there are possible 
different symbols. In MPSK modulation each of these symbols is represented by a particular phase of the carrier.
different symbols. In MPSK modulation each of these symbols is represented by a particular phase of the carrier. disp('MPSK');
Time Domain
x=['000';'100';'111']; % bit sequence;
figure();
plot_SK(x,'type','PSK');
Constellation Diagram
figure();
plot_SK(x,'type','PSK','mode','constellation') ;
DPSK
One drawback of the PSK is the complexity of demodulation, because a synchronized reference oscillator is necessery. If not the absolute phase of the carrier reflects the symbol, but the difference to the preceding phase we talk about delta PSK. At the center of a data symbol the phase shift to the preceding data symbol has to be identified. Therefore a non-coherent demodulation is possible because slight variations of the reference oscillator´s frequency are tolerable, but the power efficiency of an ordinary PSK is better.
disp('DPSK');
Time Domain
x=['100';'000';'110']; % bit sequence;
figure();
plot_SK(x,'type','DPSK');
Constellation Diagram
figure();
plot_SK(x,'type','DPSK','mode','constellation') ;
