| Communications Blockset™ | |
CPM, in Digital Baseband sublibrary of Modulation
The CPM Demodulator Baseband block demodulates a signal that was modulated using continuous phase modulation. The input is a baseband representation of the modulated signal. The M-ary number parameter, M, is the size of the input alphabet. M must have the form 2K for some positive integer K.
The input can be either a scalar or a frame-based column vector and must be of type single or double.
The Modulation index, Frequency pulse shape, Rolloff, BT product, Pulse length, Symbol prehistory, and Phase offset parameters are as described on the reference page for theCPM Modulator Baseband block.
Internally, this block creates a trellis description of the modulation scheme and uses the Viterbi algorithm. The Traceback length parameter, D, in this block is the number of trellis branches used to construct each traceback path. D influences the output delay, which is the number of zero symbols that precede the first meaningful demodulated value in the output.
If the input signal is sample-based, then the delay consists of D+1 zero symbols.
If the input signal is frame-based, then the delay consists of D zero symbols.
If the Output type parameter is set to Integer, then the block produces odd integers between -(M-1) and M-1.
If the Output type parameter is set to Bit, then the block produces groupings of K bits. Each grouping is called a binary word.
In binary output mode, the block first maps each input symbol to an intermediate value as in the integer output mode. The block then maps the odd integer k to the nonnegative integer (k+M-1)/2. Finally, the block maps each nonnegative integer to a binary word, using a mapping that depends on whether the Symbol set ordering parameter is set to Binary or Gray. For more information about Gray and binary coding, see Binary-Valued and Integer-Valued Signals in Communications Blockset User's Guide.
The input signal can be an upsampled version of the modulated signal. The Samples per symbol parameter is the upsampling factor. It must be a positive integer. For more information, see Upsampled Signals and Rate Changes in Communications Blockset User's Guide.
The size of the alphabet.
Determines whether the output consists of integers or groups of bits.
Determines how the block maps each integer to a group of output bits. This field is active only when Output type is set to Bit.
The number of half-revolutions of phase shift in the modulated signal after modulating the latest symbol of 1.
The type of pulse shaping that the corresponding modulator uses to smooth the phase transitions of the modulated signal.
Number of symbol intervals of the largest lobe of the spectral raised cosine pulse. This field is active only when Frequency pulse shape is set to Spectral Raised Cosine.
The rolloff factor of the raised cosine filter. This field appears only when Frequency pulse shape is set to Spectral Raised Cosine.
The product of bandwidth and time. This field appears only when Frequency pulse shape is set to Gaussian.
The length of the frequency pulse shape.
The data symbols used by the modulator before the start of the simulation.
The initial phase of the modulated waveform.
The number of input samples that represent each modulated symbol.
The number of trellis branches that the Viterbi Decoder block uses to construct each traceback path.
The output data type can be boolean, int8, int16, int32, or double.
CPFSK Demodulator Baseband, GMSK Demodulator Baseband, MSK Demodulator Baseband, Viterbi Decoder
[1] Anderson, John B., Tor Aulin, and Carl-Erik Sundberg. Digital Phase Modulation. New York: Plenum Press, 1986.
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