AMPLITUDE SHIFT KEYING (ASK)
Table of Contents
INTRO
The modulated amplitude of the carrier represents the digital information. ASK is used often in optical transmission system. NFC and RFID make use of ASK but typically other methods are preferred due to a higher bandwidth- or power efficiency.
On-Off Keying (OOK)
The simplest form of ASK is On-Off keying (OOK), where the modulation index m=1. This means that the digital state is represented by the presence (binary one) or absence (binary zero) of a carrier.
disp('On-Off Keying');
init;
Time Domain
x=['1';'0';'1';'0';'0']; % bit sequence;
plot_SK(x,'type','ASK','m',1);
Constellation Diagram
x=['1';'0']; % bit sequence;
plot_SK(x,'type','ASK','mode','constellation','m',1) ;
BASK
If the carrier´s amplitude for a binary zero is existent but supressed, a transmitter failure can be detected, but with decreasing m the Binary ASK is more susceptible to noise.
disp('Binary ASK with m<1');
Time Domain
x=['1';'0';'1';'0';'0']; % bit sequence;
m = 0.8
m = 0.8000
plot_SK(x,'type','ASK','m',m);
Constellation Diagram
x=['1';'0']; % bit sequence;
plot_SK(x,'type','ASK','mode','constellation','m',m) ;
Modulator and Demodulator
All methods that are used for amlitude modulation and demodulation can also be used for ASK.
file2sim='ASK_MODEM';
if (do_sim)
init_ASK;
convert_model(file2sim); % create HTML-version of simulinkfile
disp(get_link('-> create ASK 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('ASK in Simulink - block diagram');
figure
image(imread(pic_file))
end
MASK
disp('MASK');
If a symbol is coded by a set of binary digits of the length n, there are possible 
different symbols. In MASK modulation each of these symbols is represented by a particular amplitude of the carrier.
different symbols. In MASK modulation each of these symbols is represented by a particular amplitude of the carrier. Time Domain
x=['000';'100';'111']; % bit sequence;
plot_SK(x,'type','ASK');
Constellation Diagramm
plot_SK(x,'type','ASK','mode','constellation') ;
