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# Copyright 2016 Clayton Smith (argilo@gmail.com)
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The goal of this project is to implement an HD Radio receiver and transmitter in software, for use with GNU Radio. HD Radio is standardized in NRSC-5. The latest version of the standard is NRSC-5-C, which can be found at http://www.nrscstandards.org/NRSC-5-C.asp.

To transmit an HD Radio signal on 95.7 FM:

1. Run python pids_gen.py && python psd_gen.py && python p1_gen.py && python l1_gen.py to generate OFDM symbols.
2. Plug in a USRP B200/B210 and run ./hd_tx_usrp.py. Or plug in a HackRF and run ./hd_tx_hackrf.py.

The following tools have been implemented so far:

This script produces SIS (Station Information Service) PDUs (as defined in http://www.nrscstandards.org/SG/NRSC-5-C/1020sI.pdf) and assembles them into the PIDS logical channel. Each byte of the output file (pids.raw) contains one bit of the PIDS channel.

Currently it produces only the "station name - short format" message which contains the station's four-letter callsign followed by an optional "-FM" suffix.

This script generates PSD (Program Services Data) transport PDUs (as defined in http://www.nrscstandards.org/SG/NRSC-5-C/1028sD.pdf and http://www.nrscstandards.org/SG/NRSC-5-C/1085sC.pdf) for use in the audio transport. The PDUs contain metadata such as the song & artist name. Output is written to psd1.raw through psd8.raw for channels HD1 through HD8 respectively.

This script assembles audio packets and PSD PDUs into the audio transport, producing the P1 logical channel (as defined in http://www.nrscstandards.org/SG/NRSC-5-C/1014sI.pdf and http://www.nrscstandards.org/SG/NRSC-5-C/1017sG.pdf). It reads PSD PDUs from psd*.raw and writes the P1 logical channel bytes to p1.raw.

For Reed Solomon encoding, p1_gen.py uses reedsolo 0.3, written by Tomer Filiba, which can be found in reedsolo.py. The generator polynomial (defined in the rs_generator_poly function) was changed to match the one defined in http://www.nrscstandards.org/SG/NRSC-5-C/1019sG.pdf section 6.3.

This script implements Layer 1 FM (as defined in http://www.nrscstandards.org/SG/NRSC-5-C/1011sG.pdf). It reads in PIDS and P1 PDUs from pids.raw and p1.raw respectively, and writes OFDM symbols to symbols.raw. So far only Primary Service Mode MP1 is implemented.

These GNU Radio flowgraphs transmit a hybrid (analog & digital) FM signal. The analog portion is simply a 1 kHz tone. The OFDM symbols for the digital portion are read from symbols.raw. The FFT size is 2048, and each byte of the symbol file contains one channel's OFDM symbol, which can be one of the following values: