Hello list, I would like to transmit some data using gnu-radio. My data is a binary representation of an ASCII string. I wrote my own block that builds the frame (header, payload, CRC, trailer) as an array of 256 bytes (0s or 1s): gr_make_io_signature(0, 0, 0) gr_make_io_signature(1, 1, sizeof(char)) char *out = (char *) output_items; [build the frame] memcpy (out, frame, 256); noutput_items = 256; My question are: 1. Still I have to insert a "Packer Encoder" between my code and the GMSK mod? If yes, with which parameters? The GMSK mod is configured with Samples/Sym=50 , BT=0.4. 2. Can someone explain me how to use the bitrate parameter? I mean, should I "sync" the output of my block with the modulator? If yes, how? I tried to redirect the transmitted signal to a file, and use a receiver (that I know working), but without success. The parameters used in the receiver's GMSK demod are the same configured in the modulator. Thanks!
on 2013-07-20 22:41
on 2013-07-21 07:53
>>1. Still I have to insert a "Packer Encoder" between my code and the GMSK mod? If yes, with which parameters? The GMSK mod is configured with Samples/Sym=50 , BT=0.4. No. U can make custom packet structure and in that case u need not to use Packet-Encoder. >>2. Can someone explain me how to use the bitrate parameter? I mean, should I "sync" the output of my block with the modulator? If yes, how? Sync is not required because Signal-Processing blocks in GR dont understand bitrate/sampling-rate. If u have connected Transmitter-FG with USRP, then u can determine the "effective bitrate" of transmitter by calculating it backwards from USRP-sink sampling-rate. symbol-rate = usrp-sampling-rate / samples-per-symbol bit-rate = symbol-rate * modulated_bits_per_symbol -Adeel
on 2013-07-24 12:34
Hello Adeel/ML, this is fine, thanks. Next doubt is the data format as input of the GMSK block. Should it be as sequence of unsigned char bits ("01010101 00000000") or unsigned char bytes ("\x55\x00")? Looking at the Mod code (gmsk.py), the modulator first does a bytes_to_syms(). Second, in GRC 126.96.36.199 there are 2 GMSK modulator blocks, called: - GMSK Mod (Samples/Symbols, BT) - GMSK Modulator (Samples/Symbols, 3dB Time-Bandwith Product, Pulse Duration) What's their difference, and what are the meaning for the parameters on the 2nd (GMKS Modulator)? Thanks! Il 21/07/2013 07:52, Adeel Anwar ha scritto: