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Inside GNSS • July/August 2006

GPS III Contract Award Set Back

Okay, now it’s official: The GPS Block III contract award has been delayed from Fiscal Year 2006 (FY06) to Fiscal Year 2007 (FY07).

GNSS Solutions • July/August 2006

Orbital Precession, Optimal Dual-Frequency Techniques, and Galileo Receivers

Q: Is it true that the GPS satellite geometry repeats every day shifted by 4 minutes?

A: It is true that the GPS satellite orbits were selected to have a period of approximately one half a sidereal day to give them repeatable visibility. (One sidereal day is 23 hours, 56 minutes, and 4 seconds long or 236 seconds shorter than a solar day.) However, because of forces that perturb the orbits, the repeat period actually turns out to be 244 to 245 seconds (not 236 seconds) shorter than 24 hours, on average, and changes for each satellite.

Inside GNSS • July/August 2006

BOC or MBOC?

Europe and the United States are on the verge of a very important decision about their plans to implement a common civil signal waveform at the L1 frequency: Should that waveform be pure binary offset carrier — BOC(1,1) — or a mixture of 90.9 percent BOC(1,1) and 9.09 percent BOC(6,1), a combination called multiplexed BOC (MBOC). The desire for a common civil L1 signal is enshrined in a 2004 agreement on GNSS cooperation between the United States and the European Union (EU).

GNSS Solutions • May/June 2006

New GNSS Frequencies, Advantages of M-Code, and the Benefits of a Solitary Galileo Satellite

Q: What are the major differences between Galileo and GPS current and forthcoming frequencies?

A: Galileo has been designed to be both independent and interoperable with other GNSSes, and particularly GPS. The search for interoperability makes Galileo look like GPS, while the desire of independence of both systems has the opposite effect.

Inside GNSS • May/June 2006

GPS III, Block IIF Programs Hit New Delays

The GPS program appears to be struggling on several fronts recently.

GPS III, the next-generation modernization project for the space and ground segments, is facing renewed uncertainty and possible schedule delays. At the same time, anticipated first launch of the follow-on block of satellites (Block IIF) with the new civil L5 signal has been postponed.

Inside GNSS • May/June 2006

Civil L1 Signals: Galileo ICD, GPS L1C, New MBOC

Within weeks of a bilateral working group’s recommendation for a common civil GNSS signal design, the European Galileo and U.S. GPS programs have filed draft interface specifications (IS) or interface control documents (ICDs) for the new signals planned for the L1 frequency (around 1575 MHZ).

Inside GNSS • April 2006

ICG Working Group Takes On Issues

An ad hoc working group has begun sorting through issues surrounding the recent formation of the International Committee on GNSS (ICG).

GNSS Solutions • April 2006

Adaptive Antenna Arrays, Multi-GNSS Tropospheric Monitoring, and High-Dynamic Receivers

Q: What is adaptive nulling vs. adaptive beamforming? What are the advantages and disadvantages?

A: Adaptive arrays are perhaps the single most powerful antijamming tool in the GNSS systems engineer’s toolkit. They can provide anywhere from 15 to 90 dB of jamming rejection depending on the specific architecture used. Their main disadvantage is that they require an array of antenna elements, each spaced about four inches apart (center to center), and thus are physically large.

Inside GNSS • March 2006

White House Defense Budget Proposes GPS Funds

The Bush Administration’s Fiscal Year 2007 (FY07) budget proposal for the Department of Defense (DoD), announced in February, allocates $315,314,000 in advanced technology development for GPS, including work on the GPS III program. If approved by Congress, that would represent a sizable increase from the FY06 expenditures of more than $85 million and $33 million in FY05.

Inside GNSS • March 2006

Japan’s GPS Augmentation Systems Gets MTSAT-2

Japan launched its second Multi-Functional Transport Satellite (MTSAT-2) on February 18, opening a new phase of precision air navigation and air traffic control (ATC) over the western Pacific Ocean.

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