Inside GNSS Media & Research

NOV-DEC 2018

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28 InsideGNSS N O V E M B E R / D E C E M B E R 2 0 1 8 www.insidegnss.com S napshot positioning is a technique for determining the position of a Global Navigation Satellite System (GNSS) receiver using only a very brief interval of the received satellite signal, where the sampling time can be more than 100 milliseconds (ms) or even down to as little as 2 ms. In comparison, a conventional GNSS receiver may require anywhere between a few and tens of sec- onds of signal tracking before it is able to compute its first position. Since a snapshot receiver can operate with such a short intervals of signal sam- pling, it is ideally suited for a wide variety of positioning applications where energy use is a significant limitation in adopt- ing conventional GNSS chipset solutions. At the same time, the limited amount of data used requires several changes rela- tive to a conventional GNSS receiver. is article describes the key differences and advantages of a snapshot approach to signal processing and position estima- tion compared to conventional GNSS techniques. Snapshot vs. Traditional Receivers Conceptually, a GNSS receiver can be divided into three logical blocks, as shown in Figure 1: 1. Signal Capture: Collects digital samples of the incoming GNSS Radio Frequency (RF) signals. 2. Signal Processing: Acquires satel- lites that are detectable and outputs measurements – code phase (pseudor- ange), Doppler frequency and, option- ally, carrier phase. 3. Position Estimation: Computes a posi- tion using the code phase and Doppler frequency measurements. One very unique feature of snapshot receivers is its flexibility to reconfig- ure and initiate these logical blocks on and off the device being located. For example, since Signal Processing and Position Estimation can be performed long aer the signal has been captured, the snapshot receiver can be configured to further reduce power consumption on a battery-operated device by offloading these tasks onto another device such as a cloud-based server, if needed. at being said, with the short sampling time in the snapshot approach, Signal Processing and Position Estimation cannot be performed by conventional means. GNSS Solutions is a regular column featuring questions and answers about technical aspects of GNSS. Readers are invited to send their questions to the columnist, Dr. Mark Petovello, Department of Geomatics Engineering, University of Calgary, who will find experts to answer them. His e-mail address can be found with his biography below. GNSS SOLUTIONS MARK PETOVELLO is a professor (on leave) at the University of Calgary. He has been actively involved in many aspects of positioning and navigation since 1997 and has led several research and development efforts involving Global Navigation Satellite Systems (GNSS), software receivers, inertial navigation systems (INS) and other multi-sensor systems. E-mail: mark.petovello@gmail.com What is snapshot positioning and what advantages does it offer over traditional positioning methods? FIGURE 1 High-level block diagram of a GNSS receiver

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