Chapter 5 - Resolving Errors

Resolving errors is fundamental to the performance of a GNSS receiver. How a manufacturer develops a receiver, including both hardware and software design elements, directly impacts the effectiveness of error resolution. The more errors a receiver can eliminate, the higher the degree of positioning accuracy and reliability it can achieve.

What is the ideal technique to correct for errors? There really is no “best way”, as it all depends on the positioning performance required by the end user application. Using the GNSS receiver in your cell phone to find that new restaurant does not require the same level of performance as landing an unmanned helicopter on a moving platform, for example.

There are trade-offs between the different methods of removing errors in GNSS signals. The methods employed depend on the unique requirements of each application such as level of accuracy, system complexity, solution availability, reliability and cost.

In Chapter 2, we introduced the basic concepts of GNSS positioning, specifically as they apply to single-point positioning, where a single GNSS receiver operates individually, or “standalone,” to determine its location and time. In this chapter, we introduce methods by which GNSS receivers improve performance by using more advanced techniques that mitigate or eliminate errors within the position calculation. Fundamentally GNSS positioning all starts with the simple mathematical formula of: Velocity = Distance ÷ Time. Therefore, factors that affect the distance to the satellite or the time it takes for a satellite signal to arrive at the antenna need to be addressed.

Luckily, some very smart people have developed techniques to resolve errors. In general, these techniques can be described as follows:

A. Averaging of repeated observations at the same location (the least efficient method).

B. Modeling of the phenomenon that is causing the error and predicting the correction values.

C. Differential Corrections (DGNSS). 

In this chapter we will examine a number of correction techniques, how they work and some of the benefits and challenges of each method. But let’s first look at the concepts of multi-constellation/ multi-frequency and code versus carrier phase GNSS measurements and their impact on error resolution and positioning performance.

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Multi-Constellation and Multi-Frequency

GNSS Measurements

Satellite Based Augmentation Systems

Real-Time Kinematic (RTK)

Precise Point Positioning (PPP)

GNSS Data Post-Processing