Communications Toolbox

mskdemod

Minimum shift keying demodulation

Syntax

z = mskdemod(y,nsamp) z = mskdemod(y,nsamp,dataenc) z = mskdemod(y,nsamp,dataenc,ini_phase) z = mskdemod(y,nsamp,dataenc,ini_phase,ini_state) [z,phaseout] = mskdemod(...) [z,phaseout,stateout] = mskdemod(...)

Description

z = mskdemod(y,nsamp) demodulates the complex envelope y of a signal using the differentially encoded minimum shift keying (MSK) method. nsamp denotes the number of samples per symbol and must be a positive integer. The initial phase of the demodulator is 0. If y is a matrix with multiple rows and columns, then the function treats the columns as independent channels and processes them independently.

z = mskdemod(y,nsamp,dataenc) specifies the method of encoding data for MSK. dataenc can be either 'diff' for differentially encoded MSK or 'nondiff' for nondifferentially encoded MSK.

z = mskdemod(y,nsamp,dataenc,ini_phase) specifies the initial phase of the demodulator. ini_phase is a row vector whose length is the number of channels in y and whose values are integer multiples of pi/2. To avoid overriding the default value of dataenc, set dataenc to [].

z = mskdemod(y,nsamp,dataenc,ini_phase,ini_state) specifies the initial state of the demodulator. ini_state contains the last half symbol of the previously received signal. ini_state is an nsamp-by-C matrix, where C is the number of channels in y.

[z,phaseout] = mskdemod(...) returns the final phase of y, which is important for demodulating a future signal. The output phaseout has the same dimensions as the ini_phase input, and assumes the values 0, pi/2, pi, and 3*pi/2.

[z,phaseout,stateout] = mskdemod(...) returns the final nsamp values of y, which is useful for demodulating the first symbol of a future signal. stateout has the same dimensions as the ini_state input.

Examples

The example below illustrates how to modulate and demodulate within a loop. To provide continuity from one iteration to the next, the syntaxes for mskmod and mskdemod use initial phases and/or state as both input and output arguments.

% Define parameters.
numbits = 99; % Number of bits per iteration
numchans = 2; % Number of channels (columns) in signal
nsamp = 16; % Number of samples per symbol

% Initialize.
numerrs = 0; % Number of bit errors seen so far
demod_ini_phase = zeros(1,numchans);  % Modulator phase
mod_ini_phase = zeros(1,numchans);    % Demodulator phase
ini_state = complex(zeros(nsamp,numchans)); % Demod. state

% Main loop
for iRuns = 1 : 10
    x = randint(numbits,numchans); % Binary signal
    [y,phaseout] = mskmod(x,nsamp,[],mod_ini_phase);
    mod_ini_phase = phaseout; % For next mskmod command
    [z, phaseout, stateout] = ...
       mskdemod(y,nsamp,[],demod_ini_phase,ini_state);
    ini_state = stateout;  % For next mskdemod command
    demod_ini_phase = phaseout; % For next mskdemod command
    numerrs = numerrs + biterr(x,z); % Cumulative bit errors
end
disp(['Total number of bit errors = ' num2str(numerrs)])

The output is below.

Total number of bit errors = 0

References

[1] Pasupathy, Subbarayan, "Minimum Shift Keying: A Spectrally Efficient Modulation," IEEE Communications Magazine, July, 1979, pp. 14-22.

mskdemod

Syntax

Description

Examples

References

See Also