PatSea wrote:Jim, are you saying the GPS in a smartphone is not a fully functional GPS as used in many other GPS assisted devices?
PAT--I don't have a metric to use to judge your criterion of "fully functional" for a GPS receiver. Generally a GPS receiver has only one principal function: to deduce its location on earth from reception of the signals from GPS satellites.
I will restate what I said earlier about A-GPS:
The GPS receivers in many smartphones take advantage of very rapid time to first fix by using A-GPS. Some smartphones shut off the power to GPS chips when they are not needed. This can be done because a GPS receiver using A-GPS can have a very fast time to first fix from power-on, perhaps on the order of a second or two of time. This allows the smartphone to not waste battery life keeping the GPS running when it is not being used. My prior remarks described the A-GPS feature. Because A-GPS needs a very fast data connection to the cellular service provider, A-GPS functions are not available when no longer connected to a cellular network.
I don't know any details of how a particular smartphone works, but in general I would expect the people who design them are really smart. In the situation where there is no cellular data network available, the smartphone might be designed to just leave the GPS chip running all the time. While that will reduce battery life, it will help the GPS be able to maintain a position fix and not have to rely on Assisted-GPS to obtain the navigation message.
PatSea wrote:I have used my smartphone for cruising in the middle of Lake Erie, well beyond cell signal coverage, and it performed well.
Your account of a smartphone GPS getting a position fix when not connected to a cellular network does not conflict with my description of A-GPS. If you use a smartphone's GPS function, the GPS receiver remains powered on while it is in use. If you were to shut off a smartphone's cellular data connection, shut off the smartphone and let it sit for a week, then move it to the middle of Lake Erie, turn it on, and measure the time to get a fix, you would find that the GPS receiver in the smartphone would take at least a minute and perhaps much longer to get its initial position solution. That is inherent in all GPS receivers which are not assisted in receiving the navigation message via the cellular telephone network and the A-GPS protocol.
Comparing a smartphone to a dedicated GPS receiver for marine use also should be cognizant of the usually better positioning of the antennas in a dedicated receiver for seeing a clear view of the sky compared with a smartphone. GPS antennas in smartphones are generally inferior to the antennas used with dedicated GPS receivers because of their inclusion in the smartphone enclosure and close proximity to many other electrical devices. Because most of the time a smartphone is able to use A-GPS, the deficiency in their antennas is masked somewhat.