NPR (New Packet Radio) is a custom radio protocol, designed to transport bidirectional IP trafic over 430MHz radio links (ham radio frequencies 420-450MHz). This protocol is optimized for "point to multipoint" topology, with the help of managed-TDMA.
Bitrate is up to 500kbps (net, effective bitrate).
The radio modem is cheap (~80$) and home-made, with a 433MHz ISM module inside. The modem is connected locally with Ethernet, therefore no specific software is needed on PC.
The modem is easy to build and reproduce.
You can add a DMR radio amplifier in order to achieve 20W radio power or more.
The main usage is an extension of HSMM - Hamnet - AREDN networks.
All the project is open-source : hardware, software, protocol specification.
NPR kits FOR SALE: sale temporarilly stopped. A new sale will start before end of october, probably world-wide.
I have tested the PA (power amplifier) P8X from DF2FQ. Not recommended for use with NPR, because it does not integrate an RX-preamplifier, which is needed in order to compensate poor RF4463 sensitivity. Refer to "Advanced user guide" annex 4.
15th Sept 2019:
Sale is temporarily stopped. A new sale will start end of october, shipping world-wide.
New modulations parameters. I switch to GFSK instead of GMSK, with double deviation (compared to GMSK), because radio sensitivity is greatly improved (4dB or more). The radio chip that I use is too bad for GMSK, much better for GFSK, refer to (french) discussion here. WARNING: the new modulation parameters are not compatible with previous ones. Radio bandwidth can be increased, refer to new documentation.
New firmware released with lots of features : new modulation parameters, frequency resolution improved to 1kHz, Frequency shift feature (currently useless), and new command "version". Refer to release notes.
A new dedicated firmware is released for 2m band, with the same source code. (mainly for UK).
For your information, the next part of the development will be the "Frequency Division Duplex" feature, with 2 modems at Master side (one for RX, the other for TX), plus one RF duplexer.
Please feel free to comment these lists of evolution, and express your requests, or your priorities. Either here or in the public chat.
Better FEC algorithm, because currently it is very poor. If you can give me some help, I don't understand a lot standard FEC algo (with all these Maths).
Regular temperature check and re-calibration of SI4463 if necessary -> done! (firmware 2019_06_16 and above)
Increase to 15 clients instead of currently 7 maxi. → Probably not feasible with current hardware at Master side, not enough RAM (new hardware under study)
Possible evolutions, if people are interested (raw order, no priority order):
Static IP management of some modems → Removed because you can use future "L2 pure ethernet transport feature" which will be more flexible
Management via pure serial port (instead of USB)
L2 Ethernet transport configuration (instead of currently L3 IPv4); could enable more flexibles topologies, and IPv6 compatibility. But a little bit less efficient.
Extension of frequency range to 420-450MHz instead of currently 430-440MHz (IARU region 1 limits) -> done! (firmware 2019_06_16 and above)
Other modulation parameters, with lower datarates, in order to decrease RF bandwidth -> Done (firmware 2019_06_16 and above)
QoS necessary in order to transport VoIP data over an NPR network
Very hypothetical evolution:
Totally new design, microcontroller with more RAM, PCB optimized for automatic PCB assembly line. Goal would be to mass produce fully assembled modems. Probability low, only if enough people are interested.
Frequencies split between uplink and downlink (in case you use NPR Master in a tower where a UHF FM repeater is already present). Additionally, the Master could be used in "FDD" (Frequency Division Duplex) mode in order to use these 2 frequencies simultaneously, like 2G or 3G mobile phones. 2 modems required at Master side. Complex!