GNSS Solutions

January 1, 2018

What is navigation message authentication?

Q: What is navigation message authentication?  

A: As of today, all open civil GNSS signals are transmitted in the clear, conforming to interface specifications that are fully available in the public domain. Receivers will accept any input that conforms to the specifications and treat it as if it came from a GNSS satellite. Combined with the extremely low power levels of GNSS signals this makes it almost trivially simple to spoof a GNSS receiver.

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By Inside GNSS
July 28, 2017

How is Public Safety reliant on GNSS and is this a concern?

Q: How is Public Safety reliant on GNSS and is this a concern?

A: Much like many industries and organizations, as the nature of Public Safety grows and evolves, its members have looked to leverage available technologies that help them achieve their goals. In this case, the goals are first and foremost Public Safety followed closely by Member Safety whether it be police, fire or others.

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By Inside GNSS
April 1, 2017

Would you prefer to have more signals or more satellites?

Q: Would you prefer to have more signals or more satellites?

A: This is somewhat of a classic GNSS question, but before getting to the answer, let’s seek some clarity about what is being asked. First, by definition, “more” signals or “more” systems must be referenced against some baseline configuration. This is commonly assumed to be a GPS L1 C/A solution, and this assumption is also used herein.

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By Inside GNSS
January 24, 2017

Is it possible to build a low-cost system to detect and locate a single GNSS jammer in near-real time?

Q: Is it possible to build a low-cost system to detect and locate a single GNSS jammer in near-real time?

A: GNSS jammers are an ongoing threat to the reliable use of GNSS. The problem of geolocating GNSS jammers can be addressed using a time-difference-of-arrival (TDOA) processing technique; however, this problem is quite different than geolocating jammers in other radio frequency systems. The two main differences are:

(1) No GNSS are available to use as a timing reference.

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By Inside GNSS
November 13, 2016

Challenges of Ray-Tracing for GNSS Applications

Figures 5 – 8

Q: What are the challenges of ray-tracing for GNSS applications?

A: Simulating the propagation and reception of GNSS signals in complex environments is a challenging task. Indeed, the user always has to trade off between the computation time and the reliability of the output. Moreover, the motion of GNSS satellites, atmospheric effects, and building geometry are always difficult to model.

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By Inside GNSS
March 18, 2016

What are the fundamentals of an effective GNSS test plan?

Q. What are the fundamentals of an effective GNSS test plan?  

A. One aspect of GNSS development that engineers often find challenging is the lack of common testing standards and procedures. This can make life difficult for the engineer tasked with constructing a test plan for a new GNSS-enabled system. How much testing is proportionate, at which stages of development? What are the key performance parameters to measure? What apparatus is best suited to the application, and what are the appropriate pass/fail criteria?

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By Inside GNSS
January 18, 2016

What is Doppler collision and is it a problem in GNSS?

Figure 1, 3, 4 & 5

Q: What is Doppler collision and is it a problem in GNSS?

A: Doppler collision is a physical effect in code-division multiple access (CDMA) systems where code measurement errors are observed due to cross-correlation effects. Doppler collision may occur when the Doppler frequency between signals from two different transmitters is smaller than the code lock loop bandwidth. 

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By Inside GNSS
November 19, 2015

How Important Is It to Synchronize the Code and Phase Measurements of a GNSS Receiver?

Q: How Important Is It to Synchronize the Code and Phase Measurements of a GNSS Receiver?

A: Precise timing lies at the heart of GNSS implementation and operation and is generally well understood in terms of synchronizing individual satellites and/or receivers. Recent results, however, have demonstrated that timing of code and phase measurements in a receiver can have significant implications for the timing community in particular.

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By Inside GNSS
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