To provide a Position, Velocity, and Time (PVT) navigation solution, an autonomous GPS receiver must work within the limitations of the GPS system (the observable being the L1 signal as received by its antenna) as well as those of the receiver itself. There is a set of tasks that must be accomplished by any GPS receiver to achieve a fix from a cold start. In early receivers, the cold start Time to First Fix (TTFF) was relatively long due to hardware and software limitations. However, today’s receiver designs have evolved to the point where the TTFF is essentially due to the (slow) speed of data transmission by the GPS satellites (assuming good signal conditions). Motivated in part by the E-911 mandate, developers have come up with several schemes for assisting a receiver with data that would otherwise have to come from the GPS signal.
This paper discusses some of the Assisted GPS (AGPS) schemes.
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