GNSS Solutions Archives - Page 2 of 4 - Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design

# GNSS Solutions

March 14, 2015

#### How does a GNSS receiver estimate velocity?

Equations 1 – 11

Q: How does a GNSS receiver estimate velocity?

A: Stand-alone single-frequency GNSS receivers represent the largest slice of the commercial positioning market. Such receivers operate mainly in single point position (SPP) mode and estimate velocity either by differencing two consecutive positions (i.e., approximating the derivative of user position) or by using Doppler measurements related to user-satellite motion.

January 16, 2015

#### Why are carrier phase ambiguities integer?

It is well known that carrier phase ambiguities are integer values. Intuitively, this is hard to understand with a common counter-argument progressing along these lines: even if the receiver measures the instantaneous phase of the incoming signal (thus removing any fractional cycle component at the receiver end), the phase of the signal at the satellite cannot be guaranteed to be zero, so how can the ambiguity be integer?

In this article we explain why the carrier phase ambiguities are indeed integer.

November 17, 2014

#### What are the actual performances of GNSS positioning using smartphone technology?

Tables 1, 2, 3 & 4

Q: What are the actual performances of GNSS positioning using smartphone technology?

A: “Where I am?” is the typical question asked by a person when visiting a new city or unknown place. Knowing one’s own location is generally a basic necessity for people, both in indoors and outdoors.

September 24, 2014

#### How do you trust centimeter level accuracy positioning?

Q: How do you trust centimeter level accuracy positioning?

July 21, 2014

#### GNSS Position Estimates

Q: How do measurement errors propagate into GNSS position estimates?

A: Not surprisingly, GNSS positioning accuracy is largely dependent on the level of measurement errors induced by orbital inaccuracies, atmospheric effects, multipath, and noise. This article discusses how, specifically, these errors manifest as position errors.

May 6, 2014

#### How do you compute a relative position using GNSS?

Q: How do you compute a relative position using GNSS?

A: In many applications the absolute position of an object is less important than the relative position to other objects in the vicinity. An obvious example is a collision avoidance system, wherein the proximity of nearly vehicles is much more important than whether the vehicles are located on street “X” or “Y.”

January 19, 2014

#### Ionospheric Scintillation

Ionospheric scintillations are rapid temporal fluctuations in both amplitude and phase of trans-ionospheric GNSS signals caused by the scattering of irregularities in the distribution of electrons encountered along the radio propagation path. The occurrence of scintillation has large day-to-day variability. The most severe scintillations are observed near the poles (at auroral latitudes) and near the equator (within ± 20 degrees of geomagnetic equator).

November 18, 2013

#### Multipath vs. NLOS signals

Q: How Does Non-Line-of-Sight Reception Differ From Multipath Interference?

A: It is well known that GNSS signals may be reflected by buildings, walls, vehicles, and the ground. Glass, metal, and wet surfaces are particularly strong reflectors.

September 4, 2013

#### Network Real Time Kinematic GPS

Q: What is the effect of user and CORS height on NRTK performance?

July 17, 2013

Q: What is a maximum likelihood vector tracking receiver?

A: Vector tracking in GNSS receivers is based on the idea that instead of tracking each satellite’s signal separately, all signals are ultimately related to the position and velocity of the user antenna and thus can be tracked collectively. (See the discussion in this column in Sept/Oct 2012 issue of Inside GNSS by Drs. Lashley and Bevly for more information.)