TECHNOLOGY AREAS: Ground/Sea Vehicles, Weapons

ACQUISITION PROGRAM: Strategic Systems Programs, DRPM, ACAT I

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), which controls the export and import of defense-related material and services. Offerors must disclose any proposed use of foreign nationals, their country of origin, and what tasks each would accomplish in the statement of work in accordance with section 3.5.b.(7) of the solicitation.

OBJECTIVE: Develop a system to couple with a military GPS receiver to enhance submersible navigation performance.

DESCRIPTION: A submarine�s inertial navigation system is the critical input to the weapon�s subsystem. The inertial navigation system errors grow with time and GPS has been the prime method of bounding the inertial navigation system for all Navy submarines. The utilization of GPS by submarines presents unique challenges and opportunities. The unique aspects include:
a) Its infrequent availability while maintaining covertness
b) The availability of a high accuracy ship�s inertial navigation system
c) The availability of a high accuracy atomic time standard
d) The reduced effect of instantaneous accuracy on a time rms accuracy basis
e) The difficulty associated with antenna modifications on masts/periscopes

In conventional GPS receivers, the acquisition process must occur in real time, implying that the signal must always be available in real time. This furthermore means that the antenna must be exposed during the lengthy code acquisition process. The capability of recording and replaying a GPS signal provides an alternate strategy. By storing the broadband signal, the signal can be "recirculated" in non real-time among the correlator resources. Instead of having to slew the correlator resources in real time to the incoming signal until synchronization is achieved, the recorded signal can be played back ("recirculated") in post time without requiring further signal collection. Thus the storage capability could reduce exposure time for those platforms for which stealthiness is a premium. Since, at least theoretically, the recorded signal can be "recirculated" forever, the storage concept guarantees an "eventual" acquisition within the given exposure time. The technique can be made complementary to massively parallel correlator techniques. For this large time uncertainty, only the signal storage capability enables viable exposure times, although at the expense of post exposure data processing time.

This SBIR involves exploring the potential opportunities of a Submersible GPS Enhancement and Playback System, which is an appliqué to a Military Off-the-Shelf (MOTS) GPS receiver, with the goals of reduced exposure time, improved availability and integrity. These goals shall be accomplished while still working in conjunction with a MOTS GPS Receiver Module. Amongst the enhancements to be examined include the capability of recording and playing back the GPS signal in post time. Post time processing enables increased robustness against friendly and enemy interference. The contractor shall analyze operational enhancements which may accrue as a result of this augmentation. The contractor shall analyze time-to-first-fix (TTFF), integrity and accuracy impacts of employing extended range ephemerides applicable permission for durations of up to 180 days (within or without the context of the record/playback capability). The contractor shall provide system block diagrams with proposed mechanizations of the record/playback capability. The block diagrams shall identify major hardware and software blocks as well as the interfacing proposed with the MOTS GPS receiver.

Technical challenges include, but are not limited to:
a) Streaming raw L-Band digitized data at rates of greater than 150 Megabytes/second to storage which pushes this envelope of current off-the-shelf storage media technology. This extremely high data rate is necessary due to the 30 Megahertz bandwidth and the dynamic range of the required measurements.
b) Storing and "recirculating" this data over a sufficiently long duration - The duration of data must be concomitant with maximum submarine exposure time. This corresponds to storage requirements on the order of a 75 Gigabytes over approximately a several minute period.
c) Developing algorithms to detect and excise interfering signals - GPS robustness in the presence of friendly and adversarial interference is a major DoD initiative. The utilization of post-processing is an innovative approach that has yet to be accomplished and enables algorithmic enhancements based on smoothing (in addition to filtering) approaches thereby increasing jamming attenuation and spoofer recognition.

PHASE I: Determine requirements and develop the architecture for the Submersible GPS Enhancement and Playback System including the utilization of extended duration ephemerides. Document how the system would operate, any technical issues, and components needed.

PHASE II: Develop and demonstrate a prototype Submersible GPS Enhancement and Playback System. Evaluate and document algorithm and system performances with respect to GPS availability, TTFF and robustness.

PHASE III: Transition the Submersible GPS Enhancement and Playback System into the TRIDENT navigation subsystem, with applicability to GPS M-Code.

PRIVATE SECTOR: Although not initially designed for commercial use, less complex systems can be used in civilian applications such as testing GPS receivers, and automobile and railroad navigation systems where GPS signal becomes weak and intermittent due to foliage, tunnels, and multipath in urban environments.

REFERENCES
1. P. Groves, "Principles of GNSS, Inertial, and Multisensor Integrated Navigation Systems", Artech House, Boston, MA 2008

2. M. May, A. Brown, B. Tanju, "Applications of Digital Storage Receivers for Enhanced Signal Processing", Proceedings of ION GPS �99, Nashville, TN September 1999

3. H. Wen, P. Huang, J. Dyer, A Archinal, J. Fagan, "Countermeasures of GPS Signal Spoofing", The University of Oklahoma

4. B. Parkinson, J Spilker, "Global Positioning System: Theory and Applications", VOL:II, American Institute of Aeronautics and Astronautics, Inc, Washington, DC 1996

5. P. Misra, P. Enge, "Global Positioning System Signals, Measurements, and Performance" 2nd Edition, Ganga-Jamuna Press, Lincoln, MA 2006

KEYWORDS: GPS, navigation, submersible, time-to-first-fix (TTFF), GPS enhancement, GPS integrity

** TOPIC AUTHOR (TPOC) **

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