GFSK Mod

Hierarchical block for Gaussian Frequency Shift Key (GFSK) modulation.

The input is a byte stream (unsigned char) and the output is the complex modulated signal at baseband.

Parameters

Samples/Symbol

Samples per baud >= 2 (integer)

Default value = 2

Sensitivity

Given to the Frequency Mod

Default value = 1.0

BT

Gaussian filter bandwidth * symbol time (float)

Default value = 0.35

Verbose

Prints the value of bits per symbol and BT

Default value = Off

Log

Prints the following modulation data to .dat files:

* Chunks to Symbol data is written to "nrz.dat"

* Output of Gaussian filter is written to "gaussian_filter.dat"

* Output of frequency modulator is written to "fmmod.dat"

Default value = Off

Unpack (depreciated in GNU Radio 3.8)

Unpack input byte stream?

Internal Structure

For GNU Radio 3.8:

Packed to unpacked (input:byte, output:byte) --> Chunks to Symbols (input: byte, output: float) --> Interpolating FIR Filter (Float to float(real taps)) --> Frequency Mod --> Multiply const (I/O type:complex)

Example Flowgraph

The flowgraph below shows an example of the GFSK Mod and GFSK Demod blocks in action. We GFSK modulate a 9-bit long bit stream '000111011', and then GFSK demodulate it. The input to the GFSK Mod block is in packet format, whereas the output of GFSK Demod block is in unpacked format. We can use the Repack Bits/ Pack K Bits block to convert the output from GFSK Demod to packed format. Both of these options are shown in the following flowchart. All three bit streams are compared in the QT GUI Time Sink block to make sure that they are the same.

When the flowgraph runs, we see that the red, blue and green signals are the same, meaning that the bit streams before and after the GFSK modulation and demodulation are the same.

In order to replicate the results shown below, make sure you do the following:

1. Make sure you have a vector of 9 bits in your vector source. The vector in above example is (0,0,0,1,1,1,0,1,1).
2. Create a QT GUI Range block with Id = delay.
3. For the Repack Bits block, set the "endianness" value to MSB.
4. Match the input and output types of the blocks as shown in the above flowchart (purple = byte, blue = complex, orange = float)

Source Files

Python files

[1]

Block definition

[2]