TECHNOLOGY AREA(S): Space Platforms
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OBJECTIVE: Develop high-performance acquisition engine for direct acquisition of global positioning system (GPS) M-Code that can achieve time to first fix (TTFF) of 120 seconds with initial time uncertainty (ITU) of 10 ms and jamming/signal ratio of 51 dB.
DESCRIPTION: The traditional means of acquiring GPS signals for military users is the use of the coarse/acquisition (C/A)-code, which is used in nearly all legacy military GPS receivers. The C/A-code, which repeats every 1 ms, is exceptionally easy to acquire, yet vulnerable to jamming and spoofing. The P(Y)-code and M-Code signals are essentially infinite in length, making them difficult to acquire unless the ITU is very small.
Over the past twenty years, technologies have been developed to support implement direct acquisition of the P(Y)-code using large correlator arrays, Fast Fourier Transmitter (FFT) techniques and other approaches. Most of these techniques are applicable to direct acquisition of M-Code as well, although Betz showed (reference 1) that M-Code enables several efficiency enhancements compared to direct P(Y) acquisition.
The last major work on direct M-Code acquisition was completed in 2004, yielding a full acquisition engine implemented in an Application Specific Integrated Circuit (ASIC). This effort, documented in Ref. 1, used a bank of Code Matched Filters (CMFs) and an FFT to implement a high-performance acquisition engine. By optimizing sampling rates and quantization levels and using single sideband processing with noncoherent combining, the DIRAC chip was a suitable proof of concept for demonstrating what was achievable with modest technology.
This topic addresses specific performance goals based on the needs of future military users and advances in signal processing technology. The goal is to achieve 120 seconds TTFF when the J/S is less than or equal to 51 dB and the ITU is 10 ms or less. The type of jamming to be considered is a composite of multiple jammers yielding a Gaussian amplitude distribution and a power spectral density shape equivalent to M-Code. The 51 dB J/S should be referenced to signal power levels ranging from -158 dBW to -133 dBW.
During Phase I and Phase II, the developer may use the version of M-Code known as M-Prime, and documented in IS-GPS-700. Information assurance and anti-tamper considerations should be incorporated in Phase II to enable full capability development in Phase III.
PHASE I: Develop a preliminary design for the GPS M-Code acquisition engine utilizing the M-Prime M-Code.
PHASE II: Demonstrate the GPS M-Prime acquisition engine using a brassboard prototype with field programmable gate arrays (FPGAs) and/or software defined radio.
PHASE III DUAL USE APPLICATIONS: Develop M-Code acquisition engine ASIC using the Modernized Navstar Security Algorithm (MNSA) to implement full M-Code capability. Commercial: Potential application to space receivers or other high-sensitivity applications.
- Betz, John W., Fite, John D., and Capozza, Paul T., "DirAc: An Integrated Circuit for Direct Acquisition of the M-Code Signal," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 447-456.
- Ta, Tung Hai, Shivaramaiah, N., Dempster, A., and Presti, L. L., ”Significance of Cell Correlations in GNSS Matched Filter Acquisition Engines,” IEEE Transactions on Aerospace and Electronic Systems, vol. 48, Issue 2, April 2012, pp. 1264 - 1286.
- Li, Hong, Lu, Mingquan, and Feng, Zhenming, "Direct P(Y)/M-code Acquisition Based on Time-Frequency Folding Technique," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 167-173.
- Barker, Brian C., Betz, John W., Clark, John E., Correia, Jeffrey T., Gillis, James T., Lazar, Steven, Rehborn, Kaysi A., and Straton, John R., "Overview of the GPS M Code Signal," Proceedings of the 2000 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2000, pp. 542-549.
KEYWORDS: GPS, M-Code, direct acquisition, GPS jamming
- TPOC-1: Joung Ha
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