May/June 2008

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Use of Multiple GNSS systems creates its own unintened consequences—including the risk of erroneous signals. In civil aviation and other safety-critical applications, receiver autonomous integrity monitoring (RAIM) helps optimize approach and landing operations. But it's not easy to create a methodology that yeilds enough protection while making sure that rare unhealthy signals in one of the GNSS systems is detected in time. NIORAIM, a new approach to integrity, may provide a solution

Russia has an ambitious program in store for its GNSS system: more signals–including CDMA, a larger constellation, expanded augmentation system,and modernized ground control and integrity monitoring.

Following up on their earlier work analyzing and decoding new GNSS signals, researchers from Stanford University and the University of Colorado confirm that GIOVE-B transmits on L1, E5a, and E5b bands with MBOC modulation in L1, and finds the PRN generators in all bands to be 13- or 14-stage Gold codes, not the memory codes specified in the Galileo ICD.

GPS costs next to nothing in the latest consumer products and some may think of positioning, navigation, and time (PNT) as an inexpensive feature they'll pick up with their next cell phone. But in the military realm, things aren't so simple. Here installation costs and standards-based form, fit, and function requirements dominate operational and financial considerations of GPS equipage. Many ships, aircraft, and land vehicles need PNT upgrades while preserving legacy systems. Not a trivial matter, as we see from this engineering case study.

The use of GPS (or GNSS) is only limited by our imaginations. . . How many times have you heard that since someone–probably Charlie Trimble– first coined the phrase back at the dawn of space-based PNT civilization?

Do GNSS augmentation systems certified for aviation use, such as the GPS Wide Area Augmentation System (WAAS), have a function other than improving the accuracy of user navigation? What are WAAS GEO's L1 and L5 differential biases and how are they estimated?

Everyone wants reliable positioning inside buildings, and it presents a major challenge for researchers and product designers. In this second of a two-part series, the authors identify and measure some of the key variables affecting signals indoors and outline a transmission model for their behavior.

Christopher J. Hegarty reviews James L. Farrell's new book