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[Discuss-gnuradio] Running GMSK mod/demod test

From: Florian Schlembach
Subject: [Discuss-gnuradio] Running GMSK mod/demod test
Date: Mon, 12 Aug 2013 13:05:51 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6

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!


Attachment: gmsk_test.grc
Description: application/gnuradio-grc

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