Re: [Discuss-gnuradio] Using GMSK Mod to send digital data (e.g. an ASCII string)

[embyte]

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 3.5.6.1 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:
>  >>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 don’t
> 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 Sun, Jul 21, 2013 at 1:44 AM, embyte <address@hidden
> <mailto:address@hidden>> wrote:
>
>     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[0];
>
>     [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!
>
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