It is difficult to acquire GNSS (Global Satellite Navigation System) signals in challenging environments such as urban canyons and indoors without any assistance information. The time-to-first-fix process is extremely long for positioning in such environments, especially for the case when the user is moving. In order to speed up the time-to-first-fix process, the receiver needs assistance information from a server for quickly acquiring and tracking the GNSS signals. This chapter introduces the assisted GNSS solution. It covers the topics of acquisition assistance, sensitivity assistance, and implementation for smart phones. The objective of the chapter is to provide the readers with a general overview of the Assisted-GNSS (A-GNSS) solution from the aspects of how the A-GNSS solution speeds up the acquisition process and improves the tracking sensitivity, what kinds of assistance data are needed, and how the assistance data is delivered to the mobile users. The chapter includes sections for an introduction to the topic, acquisition assistance, sensitivity assistance, A-GNSS implementation for smart phones, future directions, and brief conclusions.
Wide Area RTK: A satellite navigation system based on precise real-time ionospheric modelling