SiRFstar III

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A modern SiRFstarIII chip based 20-channel GPS receiver with WAAS/EGNOS support.

SiRFstarIII is the latest GPS microcontroller chip manufactured by SiRF Technology. GPS microcontroller chips are usually found within GPS receivers and are responsible for interpreting signals from GPS satellites and deriving a position, based on the time it takes radio waves to travel from the satellites to the location of the chip.

The SiRFstarIII chip is distinguished from earlier SiRF chips and from GPS chipsets made by other manufacturers (Garmin or Trimble for example), largely due to its faster Time to First Fix (TTFF) and its ability to acquire and maintain a signal lock in urban or densely covered forest environments. The enhanced abilities of the SiRFstarIII chips is made possible by several features:

The chip supports 20 parallel channels, meaning that the chip can process the signals from 20 different GPS satellites at one time, although until the European Union's Galileo positioning system system is operational this feature cannot be fully utilised.
The chip can also make use of Assisted GPS to reduce the time needed to calculate its location. This feature makes the chip useful for cell phone manufacturers who want or need to support location services (such as the E911 legislation in the United States).
Reviewers have praised the SiRFstarIII chipset for its superior sensitivity and tracking capabilities [1]. GPS Receivers based on this chipset have routinely performed better than receivers based on other chipsets [2]. Currently it is the accepted opinion that the SiRFstarIII chipset performance is the defacto standard for a GPS receiver.

[edit] Sources of Inaccuracy and Imprecision

As with any other GPS device, the accuracy and precision of the SiRFstarIII chip can be affected by many factors, such as signal multipathing, ionospheric interference, poor satellite triangulation geometery, etc. More information about these factors can be found in the general GPS article.