IP400 Project
Phase 3 of the IP400 project is almost complete, which introduces both new hardware and firmware. The hardware, called the Advanced Mesh Network Controller (AMNC), connects to any off the shelf radio, and utilizes a new communication mode called ‘OFDM-AB’, which raises the bar with data speeds previously never realized, while preserving all the mesh networking capabilities of its predecessors.
OFDM (Orthogonal Frequency Division Multiplexing), is a technique that uses several carriers to send data at the same time, instead of a single carrier. OFDM-AB is a creation of society members that uses the audio range of a transceiver, which is independent of the band or on-air transmission mode. It can operate on any amateur band from 6m to 1296MHz, utilizing FM on air. Connection to the radio, for lower data rates, is through the microphone and speaker connections, or for higher speeds, a dedicated data port.
Four different audio bandwidths have been designed into the firmware, from a narrow band mode that works with the old clunker that you purchased at the flea market for $5, up to higher end radios that have wider and flatter passbands. Data rates are dependent on two factors: the audio bandwidth and subcarrier modulation. In the narrowest bandwidth they vary from 2.6K to 19Kb/s, in the widest from 7.7 to 57Kb/s. The subcarrier modulation scheme utilized is dependent on the signal to noise ratio at each end.
The OFDM-AB modem has been integrated into a new release of the firmware that was previously deployed on the mini node, now re-released as the Unified Firmware Platform, which has interchangeable modems, and supports both the previous platform and this one, and will be the basis for future platforms. The firmware is open source and can be downloaded from the GitHub repository.
The Advanced Mesh Network Controller is a single circuit board that can work in a standalone mode or be mounted on a raspberry Pi as a HAT (Hardware attached on Top). In the standalone mode it uses a USB connection to a PC, which can be PC or Linux based, to implement a serial port that can connect to popular data packages that utilize the AX.25 KISS protocol. Software packages such as BBS systems and Winlink can be employed in this mode.
In the HAT mode it has not only the KISS interface using the Pi UAR/T, but also a Serial Peripheral Interface for higher speeds. Also, in this mode it provides an audio path from a second SPI that interfaces with the popular Allstar software, using a custom driver. Any existing repeater system can now be upgraded to now have a data mode as well as audio, and the two modes can co-exist as the repeater will not key on received data messages, and transmitted messages will not open the squelch on a remote radio if a PL tone is utilized. There are two radio ports on the TNC, which could be used independently for repeater and data radios.
All the features that were designed into the previous firmware have been preserved, including sending beacon messages, maintaining a mesh table with routing information, a chat mode as well as ‘ping’, or echo mode to test the quality of a link. An optional GPS receiver can be added in the mobile environment for position reporting, and with the AX.25 interface it is now possible to do SMS messaging or Winlink e-mail using existing radios, concurrently breathing new life into ageing repeater systems and making mobile data practical
For further information, please visit the project website.