I've had several years of work experience with GPS and would like to share a few things that will hopefully clear up some confusion about the Fascinate's GPS.
GPS satellites orbit the earth in a 12 hour orbit which places them at roughly half the distance from earth of Geosynchronous satellites (which are in a 24-hour orbit so as to stay in a fixed location relative to Earth).
This orbit is much higher than satellites in what is called Low Earth Orbit (LEO)
GPS operates in two frequency bands L1 (1.57542 GHz) and L2 (1.2276 GHz). Dual frequency are used in order to compensate for RF propagation effects of the Troposhere however the L2 band is not available to civilian GPS devices (only the L1 band)
GPS Frequencies have very poor propagation characteristics though solids (in other words they are easily blocked by buildings, trees, etc...)
A lock on a minimum of four satellites is required to obtain PVT (Position, Velocity, Time) data (aka "a fix")
A GPS device only uses GPS satellites where as an aGPS device (assisted GPS) uses additional means, such as cellular, radio, wifi signals for determining location.
***Cold starting of a GPS (not aGPS) device can take up to 12 minutes to obtain a "fix" and begin providing PVT data. Once the device begins receiving this data it sores the data as an almanac. Restarting the GPS chip is then considered a "warm start" as it can use the almanac data as a starting point toward obtaining a "fix". This GREATLY reduces lock time and in most cases will be less than 30 seconds unless the device is more than ~50 miles from the last almanac data point. This is why the very first lock takes forever!
Obtaining a "lock" indoors is virtually impossible without assisted GPS.
Please forgive me for not siting my sources for this information. This is basically my experience with Commercial GPS, it's not gospel. I hope it's helpful to someone. Please take it for what it is worth.
Martian
GPS satellites orbit the earth in a 12 hour orbit which places them at roughly half the distance from earth of Geosynchronous satellites (which are in a 24-hour orbit so as to stay in a fixed location relative to Earth).
This orbit is much higher than satellites in what is called Low Earth Orbit (LEO)
GPS operates in two frequency bands L1 (1.57542 GHz) and L2 (1.2276 GHz). Dual frequency are used in order to compensate for RF propagation effects of the Troposhere however the L2 band is not available to civilian GPS devices (only the L1 band)
GPS Frequencies have very poor propagation characteristics though solids (in other words they are easily blocked by buildings, trees, etc...)
A lock on a minimum of four satellites is required to obtain PVT (Position, Velocity, Time) data (aka "a fix")
A GPS device only uses GPS satellites where as an aGPS device (assisted GPS) uses additional means, such as cellular, radio, wifi signals for determining location.
***Cold starting of a GPS (not aGPS) device can take up to 12 minutes to obtain a "fix" and begin providing PVT data. Once the device begins receiving this data it sores the data as an almanac. Restarting the GPS chip is then considered a "warm start" as it can use the almanac data as a starting point toward obtaining a "fix". This GREATLY reduces lock time and in most cases will be less than 30 seconds unless the device is more than ~50 miles from the last almanac data point. This is why the very first lock takes forever!
Obtaining a "lock" indoors is virtually impossible without assisted GPS.
Please forgive me for not siting my sources for this information. This is basically my experience with Commercial GPS, it's not gospel. I hope it's helpful to someone. Please take it for what it is worth.
Martian
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