Communications Toolbox

pskdemod

Phase shift keying demodulation

Syntax

z = pskdemod(y,M) z = pskdemod(y,M,ini_phase) z = pskdemod(y,M,ini_phase,symbol_order)

Description

z = pskdemod(y,M) demodulates the complex envelope y of a PSK modulated signal. M is the alphabet size and must be an integer power of 2. The initial phase of the modulation is zero. If y is a matrix with multiple rows and columns, then the function processes the columns independently.

z = pskdemod(y,M,ini_phase) specifies the initial phase of the modulation in radians.

z = pskdemod(y,M,ini_phase,symbol_order) specifies how the function assigns binary words to corresponding integers. If symbol_order is set to 'bin' (default), the function will use a natural binary-coded ordering. If symbol_order is set to 'gray', it will use a Gray-coded ordering.

Examples

The example below compares PSK and PAM (phase amplitude modulation) to show that PSK is more sensitive to phase noise. This is the expected result because the PSK constellation is circular, while the PAM constellation is linear.

len = 10000; % Number of symbols
M = 16; % Size of alphabet
msg = randint(len,1,M); % Original signal

% Modulate using both PSK and PAM,
% to compare the two methods.
txpsk = pskmod(msg,M);
txpam = pammod(msg,M);

% Perturb the phase of the modulated signals.
phasenoise = randn(len,1)*.015;
rxpsk = txpsk.*exp(j*2*pi*phasenoise);
rxpam = txpam.*exp(j*2*pi*phasenoise);

% Create a scatter plot of the received signals.
scatterplot(rxpsk); title('Noisy PSK Scatter Plot')
scatterplot(rxpam); title('Noisy PAM Scatter Plot')

% Demodulate the received signals.
recovpsk = pskdemod(rxpsk,M);
recovpam = pamdemod(rxpam,M);

% Compute number of symbol errors in each case.
numerrs_psk = symerr(msg,recovpsk)
numerrs_pam = symerr(msg,recovpam)

The output and scatter plots are below. Your results might vary because the example uses random numbers.

numerrs_psk =

   374


numerrs_pam =

     1

pskdemod

Syntax

Description

Examples

See Also