NGHam, short for Next Generation Ham Radio, is a set of protocols for packet radio communication. Its usage is similar to the existing AX.25 protocol. The standard covers three sub-protocols:
- NGHam radio protocol
- NGHam serial port protocol (comparable with KISS for AX.25)
- NGHam extensions - a modular extension using the payload for addressing, position, voice, statistics etc.
Main features:
- Very robust: Allows decoding with lower SNR compared to 1200 baud AFSK AX.25 due to the use of a sync word with good autocorrelation properties and Reed Solomon FEC over the whole remaining packet.
- High throughput: As the sync word eliminates the need for a long preamble and FEC increases chance of successful packet reception, the throughput will be higher than for 9600 baud AX.25.
- Better spectral efficiency: Significantly better spectral efficiency than 1200 baud AFSK, and somewhat better than 9600 baud G3RUH modulation due to the reduced deviation.
- More efficient channel access: CSMA is the default access method, but TDMA with automatic time-synchronization is being developed and is tested.
- Clear distinction between communication layers: The NGHam radio protocol has no addressing or other higher level information, and can be used without NGHam Extension.
Youtube video: NGHam demonstration with Owl VHF and TDMA
Content:
| File/folder | Description |
|---|---|
| documentation/ | More documentation. |
| fec-3.0.1/ | FEC library by Phil Karn for Reed Solomon. (http://www.ka9q.net/code/fec/) |
| platform/ | User provided - MUST BE CUSTOMIZED. |
| ccsds_scrambler.h | Pre-generated array from scrambling polynomial. |
| crc_ccitt.h | CRC-code used in NGHam. |
| ngham.h | The main NGHam encoder/decoder functions. |
| ngham_packets.h | Declarations of the TX/RX packet structs etc. |
| ngham_paths.h | User provided - MUST BE CUSTOMIZED. |
| ngham_spp.h | Serial port protocol for communication with the host. |
Not finished:
| File/folder | Description |
|---|---|
| ngham_extension.h | An extension of the payload field in the NGHam radio protocol (enabled by a flag in the NGHam header). |
Usage (for NGHam RF protocol):
- Provide your own sync word correlator and GMSK (de)modulator.
- The demodulator should start outputting data only after sync word is detected.
- Build all files in the root except "ngham_spp.c". From the folder "fec-3.0.1", build "decode_rs_char.c", "encode_rs_char.c" and "init_rs_char.c".
- "ngham_paths.h" and the code in "platform/" must be customized.
// Initialize Reed Solomon arrays - only do this once!
ngham_init_arrays();
// Initialize state machine
ngham_init();
// Send a packet containing the payload "TEST"
tx_pkt_t p;
p.pl[0] = 'T';
p.pl[1] = 'E';
p.pl[2] = 'S';
p.pl[3] = 'T';
p.pl_len = 4;
p.ngham_flags = 0;
ngham_encode(&p);
// Receive packet. If a complete packet is received, function ngham_action_handle_packet will be called.
while (demodulator_data_available()) ngham_decode(get_byte_from_demodulator());
-- Jon Petter Skagmo, LA3JPA, 2014