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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, 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

collapse all

Modulate and demodulate a noisy MSK signal. Display the number of received errors.

Define the number of samples per symbol for the MSK signal.

nsamp = 16;

Initialize the simulation parameters.

numerrs = 0;
modPhase = zeros(1,2);
demodPhase = zeros(1,2);
demodState = complex(zeros(nsamp,2));

The main processing loop includes these steps:

  • Generate binary data.

  • MSK modulate the data.

  • Pass the signal through an AWGN channel.

  • Demodulate the MSK signal.

  • Determine the number of bit errors.

for iRuns = 1:20
    txData = randi([0 1],100,2);
    [modSig,modPhase] = mskmod(txData,nsamp,[],modPhase);
    rxSig = awgn(modSig,20,'measured');
    [rxData,demodPhase,demodState] = mskdemod(rxSig,nsamp,[],demodPhase,demodState);
    numerrs = numerrs + biterr(txData,rxData);
end

Display the number of bit erros.

numerrs
numerrs =

     0

References

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

Introduced before R2006a

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