Velocity

2014

NovAtel's Annual Journal of GNSS Technology Solutions and Innovation

Issue link: http://velocitymagazine.epubxp.com/i/380251

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novatel correct 2014 For more Solutions visit http://www.novatel.com velocity 19 each with multiple, independent OCDSs. Op- erating multiple control stations and OCDS allows TerraStar to deliver the best possible availability, continuity, redundancy and qual- ity of the service for its customers. To generate corrections, each OCDS uses data obtained from TerraStar's private receiver net- work. This network consists of more than 80 GPS and GLONASS reference stations located around the globe. These correction products are delivered to NovAtel CORRECT-enabled receivers via Inmarsat L-Band satellite communication links. By delivering corrections over satellite, machine guidance systems do not need local base-station infrastructure, cellular modem or Wi-Fi radio, greatly simplifying the user's hardware configuration. NovAtel CORRECT uses the correction data in advanced algorithms to provide highly stable kinematic positions with less than 5 cm horizon- tal RMS error. PPP Error Mitigation At the heart of all GNSS positioning solutions are range measurements and their associated observation equations. GNSS signals, how- ever, are corrupted by a host of bias and other errors, such that the measured ranges can de- viate substantially from the true ranges. Ad- vancements in GNSS positioning have, to a large degree, been due to progresses made in the modelling and mitigation of these various error sources. Error mitigation approaches can essentially be divided into three categories: 1. Signal combinations 2. Models 3. Externally-provided information PPP is at the apex of GNSS error mitigation and uses all of the approaches listed above. For instance, to remove the effects of the iono- sphere, PPP uses combinations of signals on different frequencies. Troposphere errors are reduced by troposphere delay models, and then further mitigated by zenith delay dy- namic models. PPP correction providers sup- ply corrections that remove the effects of sat- ellite clock and orbit errors. Research in troposphere delay demonstrates the advancements in error mitigation that have made PPP possible. When GNSS positioning was first calculated, the effects of the tropo- sphere were disregarded altogether. Not long after, simple models using empirically-derived constants were introduced to mitigate the tro- posphere effects. These models were then re- fined and improved. " " The TerraStar PPP feed includes corrections for both GPS and GLONASS, maximizing satellite availability and giving the best solution geometry.

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