Carrier Phase Tracking Considerations For Commodity Sdr Hardware

Software Defined Radio (SDR) is a general technique for processing Radio Frequency (RF) signals in software, and has been an active area of research and development for about the last twenty years. SDR is attractive to the research community due to the fast development and test cycles entailed by a largely software based implementation of communications and signal processing algorithms. However, every SDR requires some hardware to convert the portion of the RF spectrum of interest into a stream of digital samples. Driven largely by the varied requirements of the telecommunications industry, a number of manufacturers have developed low cost commodity SDR hardware platforms.In the GNSS context, SDR, or software receivers, have been widely used in research and development and a large number of both open source and commercial software receivers are available. Most of these receivers provide interfaces for processing samples from commodity SDR hardware. However, given that this hardware has not been designed with the GNSS use-case in mind, it is interesting to investigate what impact using such hardware may have on the achievable navigation performance of a software GNSS receiver - in particular in relation to carrier phase processing.Tracking the carrier phase brings many benefits in GNSS signal processing - data demodulation performs better, code tracking can be improved by carrier aiding, range measurements can be improved via carrier smoothing and, not least, so-called carrier phase (or accumulated delta range) measurements can be made, enabling high precision Carrier Phase Differential GNSS (CPDGNSS).In this work we perform a thorough investigation of the capabilities of a number of commodity SDR platforms in relation to carrier phase tracking. Focus is given to the ability to provide code carrier coherence, a key requirement for carrier aiding, carrier smoothing and carrier phase measurement generation.