N112-092 TITLE: Non-beam-steering Global Positioning System (GPS) Anti-jam Solution with Minimized Pseudo-range Errors

TECHNOLOGY AREAS: Air Platform, Sensors, Electronics

ACQUISITION PROGRAM: PMA-264, Air Anti-Submarine Warfare Systems

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OBJECTIVE: Develop advanced algorithms with Global Positioning System (GPS) anti-jam capability to meet stringent accuracy requirements and operate with small antennas.

DESCRIPTION: Small Navy platforms will require technology to meet the operational availability and accuracy requirements for upcoming systems. Most common GPS Anti-jam (AJ) antenna systems employ a multi-element phased array antenna known as a Controlled Reception Pattern Antenna (CRPA) working in conjunction with an Antenna Electronics (AE) to minimize interference in the GPS band. Most of the current systems use "nulling" techniques that steer antenna nulls toward the interfering signals by adapting antenna weights. Studies suggest that these techniques introduce error into the GPS solution that may be unacceptable for precision approach and landing. These studies also indicate that a digital beam-steering design rather than a beam-nulling design can better maintain the required accuracies. Although digital beam-steering offers one way of minimizing the carrier phase and pseudo-range biases, it requires a large array (14 inch diameter antenna). These digital beam-steering architectures are very dependent on accurate antenna calibrations and require a tightly coupled digital interface with the GPS receiver. Currently Navy platforms do not have GPS receivers that could directly interface with a digital beam-steering system. Additionally, small Navy platforms may not have the physical room for a 14 inch CRPA. The requirements for a tightly coupled GPS receiver and a 14 inch CRPA drive the cost of the anti-jam solution up to the extent that digital beam-steering anti-jam solutions may not be affordable on many of the Navy�s smaller platforms. Size, weight and power (SWAP) constraints further restrict the ability to add anti-jam capability on smaller platforms. Innovative non-beam-steering antenna signal processing solutions are required to address this technology gap.

Non-beam-steering AJ solutions offer the advantage of requiring no calibration, having smaller antenna array size, lower unit and integration costs, and could be fielded with our current and planned future GPS systems. Determine if there is a non-beam-steering AJ solution, utilizing a small antenna array, (for example, < 5 in. diameter), that maintains the unique carrier phase accuracy and reliability requirements for precision approach and landing while in a jamming environment.

PHASE I: Develop and demonstrate feasibility of innovative non-beam-steering antenna signal processing algorithms. Emphasis should be on mitigating carrier phase distortions in jamming and non-jamming environments. This phase will result in the identification of algorithms, and the assessment of implementation feasibility including complexity. This phase should include detailed simulations and a recommendation on the selected algorithm.

PHASE II: Further develop and mature the algorithm by implementing it in an antenna electronics system and demonstrate its performance with a small antenna array in conjunction with a military avionics GPS receiver. The anti-jam performance and carrier phase integrity should be demonstrated.

PHASE III: Transition the technology developed to an existing Navy platform.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Technology developed under this effort will have potential applications to commercial air vehicles where unintentional interference can occur.

REFERENCES:
1. McGraw, G.A., McDowell, C. & Kelly, J.M. (2006). GPS anti-jam antenna system measurement error characterization and compensation. Proceedings of ION 2006 GNSS Meeting, Fort Worth, TX. http://www.ion.org/search/view_abstract.cfm?jp=p&idno=6871

2. O�Brien, Andrew J. & Gupta, Inder J. (2008). Optimum Adaptive Filtering for GNSS Antenna Arrays. Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008). Savannah, GA. pp. 2796-2805. http://www.ion.org/search/view_abstract.cfm?jp=p&idno=8183

3. Kalyanaraman, S.K. & Braasch, M.S. (2010). GPS Adaptive Array Phase Compensation using a Software Radio Architecture, Navigation, Journal of the ION, 57, 1. http://www.ion.org/search/view_abstract.cfm?jp=j&idno=2518

KEYWORDS: Global Positioning System (GPS); anti-jam; optimum adaptive algorithm; antenna electronics; carrier phase; phase compensation

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