#
# Copyright 2017 Clayton Smith (argilo@gmail.com)
#
# This file is part of gr-nrsc5.
#
# gr-nrsc5 is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# gr-nrsc5 is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with gr-nrsc5. If not, see <http://www.gnu.org/licenses/>.
#
The goal of this project is to implement an HD Radio receiver and transmitter in GNU Radio. HD Radio is standardized in NRSC-5. The latest version of the standard is NRSC-5-D, which can be found at http://www.nrscstandards.org/NRSC-5-D.asp.
So far only a transmitter has been implemented. A stand-alone receiver for RTL-SDR is available here: https://github.com/theori-io/nrsc5/
This block encodes audio into High-Definition Coding (HDC) frames. The input sample rate must be 44,100 samples per second. ADTS headers are added to the output frames to facilitate synchronization. The encoding is performed by a patched version of fdk-aac: https://github.com/argilo/fdk-aac/tree/hdc-encoder
This block encodes Program Service Data PDUs, as described in http://www.nrscstandards.org/sg/nrsc-5-d-reference-docs/1028s.pdf. PSD conveys information (e.g. track title & artist) about the audio that is currently playing.
This block encodes Station Information Service PDUs, as described in http://www.nrscstandards.org/sg/nrsc-5-d-reference-docs/1020s.pdf, and assembles them into the PIDS and SIDS logical channels. SIS provides information about the station. Currently only the short station name (i.e. call sign) is encoded.
This block assembles HDC audio frames and PSD PDUs into the audio transport, producing layer 2 PDUs (as defined in http://www.nrscstandards.org/sg/nrsc-5-d-reference-docs/1014s.pdf and http://www.nrscstandards.org/sg/nrsc-5-d-reference-docs/1017s.pdf).
This block implements Layer 1 FM (as defined in http://www.nrscstandards.org/sg/nrsc-5-d-reference-docs/1011s.pdf). It takes PIDS and Layer 2 PDUs as input, and produces OFDM symbols as output. Only the Hybrid and Extended Hybrid modes have been implemented and tested so far. The All Digital modes are currently under development.
The output bytes map to symbols as follows:
| byte | constellation value |
|---|---|
| 0 | -1-j |
| 1 | -1+j |
| 2 | 1-j |
| 3 | 1+j |
| 4 | 0 (unused channel) |
Several sample flowgraphs are available in the apps folder:
- hd_tx_usrp.grc, hd_tx_usrp.py: tested on a USRP B200
- hd_tx_hackrf.grc, hd_tx_hackrf.py: tested on a HackRF One
- hd_tx_rtl_file.grc, hd_tx_rtl_file.py: produces an output file in the format used by https://github.com/theori-io/nrsc5/
These flowgraphs read a WAV file named sample.wav, which must be encoded at 44,100 samples per second. The license for the supplied sample.wav file is as follows:
Copyright 2013, Canonical Ltd. This work is licensed under the Creative Commons Attribution-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/3.0/ or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA.