In the beginning, there was just one GNSS — the Global Positioning System — and just one fully available signal on the L1 frequency.
Eventually, some clever scientists discovered how to exploit certain characteristics of the encrypted L2 signal to come up with so-called codeless and semi-codeless techniques that enabled dual-frequency positioning. This hastened the development of user equipment that used the carrier phase of signals as well as the code to deliver high-precision results.
Today, the airwaves are full of many kinds of GNSS signals on many different frequencies. The simplest kinds of receivers such as are found in mobile phones, however, still use just one frequency, L1. But as applications move up the value chain of accuracy, ever-more-sophisticated signal-processing techniques are appearing in more types of GNSS receivers — both single- and dual-frequency.
A great divide remains, however, between commercial GNSS equipment that operates only on a single frequency and those that process signals on two or more frequencies. To help us sort out the differences between the two and the current state of the art in high-precision GNSS receivers, we called on Kyle O’Keefe, professor of geomatics engineering at the University of Calgary and a member of the school’s the Position Location And Navigation (PLAN) group.