SBIR-STTR Award

JDAM and similar DGPS based military applications impose tight error budgets on PPS receivers. Validation of these capabilities proves challenging with traditional ground-based and GPS-based reference systems. Available carrier-phase DGPS systems have great potential as reference systems, but their response to signal blockage and high dynamics is poor. Simple cascaded IMU formulations are inadequate under these very rigorous reception regimes, and therefore fundamental improvements in phase tracking robustness are needed. A new algorithm is proposed consisting of two stages: a) an integrated demodulation/navigation phase tracker, and b) a dual-frequency ambiguity resolution scheme optimized for P/Y service. The first stage employs optimal filtering of raw IQ correlator outputs at 1OOHz, using navigation domain covariances, IMU aiding, and carrier phase DGPS corrections. The Tracking and Imaging Systems signal simulator will be used to explore candidate algorithms in the high dynamics environment. Phase I activities include feasibility studies of aided and dual antenna versions of the carrier phase algorithms, and definition of modular interfaces between the carrier phase processor's CPU and the host GPS receiver's CPU. Efforts lead to early Phase II demonstration of the algorithms on NRaD's GPS simulator.

JDAM and similar applications impose meter-level error budgets on navigation. Validation in the military flight envelope is challenging and expensive. Existing carrier phase truth systems are capable of decimeter performance, but fail in realistic maneuvers and blockages. In Phase I, TISI overcame these problems by processing raw baseband data from all satellites in a powerful adaptive filter structure. Patented, this is known as Integrated Demodulation/Navigation (IDN). Simulations were performed with single and multiple antennas, with and without IMU, in figure 8, dive, and aileron roll maneuvers up to 18gs. Optimal combining of dual antennas mitigated satellite blockage. Instabilities encountered in tightly coupled GPS/IMU configurations were eliminated. The algorithm combines its robust 100 Hz carrier phase data with host 10 Hz P-code pseudoranges , to produce decimeter navigation quality. In phase II, a demonstration processor will be developed in tree stages: a desktop standalone version with IMU, a desktop version interfaced with HDIS, and a PC-104 format version interfaced with HDIS. Off- the-shelf board level components are utilized. Extensive RF simulations and vehicle tests are scheduled. The final task feasibility study of a directly embedded IDN algorithm within the host.

Benefit:
Improvements in the blockage, multipath, jamming and spoofing are urgently needed by many user segments. The algorithms and processor developed here are the basis of a new generation of robust decimeter systems, meeting the needs of a large and rapidly growing civilian military DGPS market.

Keywords:
Algorithms, DGPS, Processor, Modular, Carrier, aiding, phase, IMU