iPhone AGPS 服务并不需要激活的运营商服务?
iPhone的内置GPS是AGPS：
A typical A-GPS-enabled cell phone will use a data connection (internet, or other) to contact the assistance server or a standard network connection for A-GPS information. If it also has functioning autonomous or standalone GPS, it may use standard GPS, which is sometimes slower on Time To First Fix, but does not lead to network dependent downsides, such as failure to work outside of network range, or charges for data traffic.[3] Some A-GPS solutions do not have the option of falling back to standalone or autonomous GPS.
source: http://www.wmexperts.com/articles/gps_vs_agps_a_quick_tutorial.html
实际使用iPhone过程中，我发现两个有趣的现象：
1. 没有运营商网络信号的时候，iPhone完全不能定位。
这个结论很容易得出，在我出去到荒野地区没有电话信号的地方的时候，我试图打开iphone的map, 发现很久都没有办法定位 （不仅仅是不能显示地图，而是无法定位）
2. 有运营商的网络信号，但SIM卡没有激活的服务，iPhone可以准确定位
这出乎我的意料之外。 前些时候在iPhone中插入一张vodafone的SIM测试，毫无疑问是不能用的（iPhone是O2绑定的），但让我吃惊的是定位完全正常，而且是典型的步骤，首先定位到cell所在的小区，然后精确通过卫星定位。
在这篇文章里看到了aGPS芯片可能工作的４种模式：
- Standalone - Your handset has no connection to the network, and uses only the GPS satellite signals it can currently receive to try and establish a location.
- MS Based - Your handset is connected to the network, and uses the GPS signals + a location signal from the network.
- MS Assisted - Your handset is connected to the network, uses GPS signals + a location signal then relays its 'fix' to the server, which then uses the signal strength from your phone to the network towers to further plot your position. You can still maintain voice communication in this scenario, but not 'Internet/Network service' ie Web Browser, IM, streaming TV etc..
- MS Assisted/Hybrid - Same as above, but network functionality remains. Normally only in areas with exceptional coverage.
standalone模式其实和一个传统的GPS没有区别。
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