[Discuss-gnuradio] Running GMSK mod/demod test

[Florian Schlembach]

I trying to run a GMSK mod/demod test under GRC. My objective is to 
create a single GSM-like burst and to store it in a file. The waveform 
should have defined bits (by now I assume them to be random).

Thus I created a flowgraph that looks like this

Random Source (fixed # of samples, no repeat) -> Packet Encoder -> GMSK 
Mod (->File Sink gmsk_tx) -> GMSK Demod -> Packet Decoder -> File Sink 
(integer of bits_out)

1. If I keep increasing the number of bits in Random Source, I have 
noticed that the number generated complex samples (I read them into 
MATLAB using read_complex_binary) stays constant at 8496 complex samples 
until 255 modulated bits. From 255 to 383 it is 2*8496, from 384 to ... 
it is 3*8496. Are these the bursts? Why are the bound to integers of 8496?

2. When forming a loopback, reading the modulated signal and 
demodulating it, the bits_out are not demodulated when reading the file 
bits_out via read_int_binary. Whats wrong with the flowgraph?

I attached the respective .grc file. I appreciate any help!

-Flo

gmsk_test.grc
Description: application/gnuradio-grc