Receiver Operations: Difference between revisions

Revision as of 17:58, 30 March 2011

Receivers
Title	Receiver Operations
Author(s)	GMV
Level	Medium
Year of Publication	2011

In the first years of GNSS, when only GPS was available for public use, a receiver was not expected to perform as the navigation devices we see today. In fact, a first-generation GPS receiver could be designed to only process 4 or 5 signals at any given time, as it was deemed suitable for positioning applications. Today, with the increased availability and potencial of different GNSS signals and constellations, any receiver is expected to track at least 10 or 12 signals in parallel channels, and up to hundreds, resulting in a more accurate solution.

This way, and despite the many differences in target applications or implementation philosophy, most receivers share some common control capabilities at their core:

Channel management, where each channel is managed depending on the opeartion mode, and resources are allocated as needed. For every step of the computations, the each channel is managed

Signal processing,

Navigation solution computation, V Position Velocity Acceleration, que calcula la posición y velocidad de los satélites empleados en la navegación

Although common, these (and other) tasks are not necessary parallel, nor always in place. The following sections detail several receiver operation modes controlled and managed within a receiver, that fall under the above categories.

Operation modes

One thing most GNSS receivers have in common is how they operate in terms of processing chain, from reception of signals to solution outputs. Alhough their types, architectures, and applications may vary, the operations of receivers apply transversly:

RF stage: the first stage of a receiver comprises the antenna and front end, responsible for the RF processing chain.

Start-up: a receiver starts processing the samples from the RF stage in different ways, depending on the available a priori information.

Acquisition: the first step, in many cases, is the search for visible satellites that can be tracked and used in the computed solution.

Tracking: after the initial determination of the satellites to track, several signal processing algorithms are use to continuously track the satellite's motion relative to the user.

Lock detection: a receiver constantly performes decisions to assess the quality of the observables in terms of noise or uncertainty, and these decisions determine the probability of a given tracked signal being "lost". This decision can yield a loss of lock, and the receiver channel is free to process other signals (e.g. start acquisition for other satellites).

Solution output: when tracking is successfull for a large enough period of time, and for enough satellites, the navigation message can be decoded from each signal, and the extracted information is used to compute the best solution needed - in most cases, the user's PVT solution.