Alternatives to current GPS-RTK services and some implications for CORS infrastructure and operations

This paper reviews the establishment of GPS continuously operating reference stations (CORS) by government agencies and research institutes over the last two decades. The justification for the establishment of CORS networks was initially in support of geodesy and other geoscientific applications, at the global and regional level. However, increasingly GPS CORS network operators have sought ways of making their network infrastructure the basis of a profitable business. This has arisen with the introduction of real-time centimetre-level accuracy services, carrier phase-based modes of operation generally referred to as GPS-RTK (Real-Time Kinematic). One approach is to try to recruit a core group of users who are prepared to pay for the GPS-RTK services. But this is only feasible if the number of users, and the fees that are charged, are sufficient to generate a reasonable return-on-investment (ROI). This ROI (or at the very least “cost-recovery”) is important for many network operators in order that they may provide for the maintenance and upgrade of the CORS infrastructure. On the other hand, there are those who advocate that there is no need to recoup CORS investment, that the installed GPS receivers should be seen as public infrastructure, in a similar manner to roads, bridges, etc. This paper discusses some new business and operational models for GPS-RTK services. These include models for the establishment and operation of CORS infrastructure, service provision, business cases, and options for value-added services beyond the standard GPS-RTK service. One concept is based on a “client-server” model. Currently GPS-RTK service providers have no control over the quality of the results computed by users. This makes it difficult for them to justify charging for their services. What if instead of broadcasting RTK corrections and placing the onus of obtaining a final solution on the user and his equipment, the user’s coordinates are determined by the service provider? Putting the computational effort on the server side will justify more easily the charging of users for a value-added product: an accurate and quality assured position in the local reference frame. This paper describes the client-server concept as well as possible business models that may underpin such a service model. These models include some derived from mobile telephony and service/hospitality businesses. Furthermore, with the projected proliferation of independent, competitive GPS-RTK services, the concept of a GPS data/service “broker” is worth exploring. 1. BACKGROUND TO CORS NETWORKS It is well recognised today that a reference network comprised of permanent stations operating Global Navigation Satellite System (GNSS) receivers on a continuous basis provides the fundamental infrastructure required to meet the needs not only of geodesy and the geosciences, but also of professional GPS users in areas of surveying, mapping and navigation. These high accuracy applications can only be satisfied through the use of the carrier phase-based, differential GPS technique, whereby the “reference” or “base” receiver is located at a station whose coordinates are known in a geocentric datum or reference frame (Rizos 2002). Furthermore, the widespread use of the GPS Real-Time Kinematic (RTK) 1 The umbrella term for all satellite-based navigation systems including their regional augmentations, and generally refers to the current and modernized GPS, the revitalised Glonass, and the planned Galileo systems. The interchange of the terms ‘GPS’ and ‘GNSS’ in the text should not confuse readers, as currently GPS is the only fully operational GNSS.