April 2009 - Airborne Telemetry Relay System (TMRS) flying with 10-channel Digital Beamforming (DBF)
This project began in late 2004 and the first system was delivered in February 2008 for installation on a deHavilland Dash-8 twin turboprop aircraft. It entered a flight testing phase in May 2008, and a second system was installed in 2009. CDSI has continued to support operational use of these aircraft since then, and has provided many in-situ upgrades of firmware and software to improve operations and add functionality.
The DBF System replaces a 5-channel conventional phased array antenna (1990 era) with an all-digital 10-channel dual-polarized S-band antenna and controller, providing up to 20Mbps throughput on any channel in the Telemetry band. It also provides several forms of simultaneous output for each channel, including demodulated digital data (with bit-sync) and analog baseband output used both for onboard digital recording as well as analog IF output (suitable for downlink or IF recording).
The physical antenna (built by Malibu Research Associates) occupies about half the space of the legacy one and also weighs half as much. This was achieved by replacing most of the RF plumbing with 224 LNBs (Low-Noise Block Downconverters). The IF output from each of these 224 elements was then cabled to 4 equipment racks in the cabin. Within these racks, each signal was sampledby a 500-MHz A/D converter, and after that point, all the processing is achieved digitally via 56 commercial VME boards and custom firmware to achieve:
- Optimal Spatial and Polarization Combination
- Multi-symbol demodulation
- Digital-to-IF upconversion
Essentially, this is a large software-radio system with 2240 digital receivers synchronized at 250MHz. The tracking system forms monopulse outputs from each digitally-formed beam, and can handle maneuvering targets at speeds in excess of Mach 5 with SNR down to a few dB. The entire signal-processing system is controlled by a single in-rack VME host computer running open-source Linux code along with CDSI's proprietary algorithms.
Since delivering these Systems in 2009, CDSI has continued to advance its DBF technology and algorithms, and has recently demonstrated a small-scale array that takes advantage of next-generation FPGAs to produce a significantly more powerful and flexible DBF subsystem with much lower SWAP and cost.