What does the cellular network model mean?

What does the cellular network model mean?

As we all know, Apple's iPad is divided into two versions: WLAN model and WLAN+ cellular network model, also known as WIFI version and cellular network version. The difference between the two is that the cellular network version of iPad can insert a mobile phone card, and you can surf the Internet with the traffic of the mobile phone card without WIFI. From the appearance, it can be seen that there are obvious antenna bands on the back of the cellular network model.

The cellular version of iPad can't make phone calls and send text messages, and the inserted mobile phone card can only be used for surfing the Internet. If you dial this mobile phone number at this time, you will always be prompted "The subscriber you dialed is busy, please dial later". Sending SMS will also prompt that sending failed, but you can send and receive iMessage information.

In terms of price, the cellular network version of iPad is more expensive than the WIFI version of iPad with the same storage capacity 1000 yuan. In addition to plugging in the internet, another important difference of the cellular network version of iPad is navigation and positioning. WIFI iPad only supports iBeacon micro-positioning (a Bluetooth-based positioning technology), while cellular iPad supports auxiliary GPS, GLONASS, Galileo and QZSS positioning systems.

In other words, the WIFI version of the iPad can only rely on Bluetooth and WIFI networks for rough positioning, and the positioning error may be several kilometers or even ten kilometers. The cellular network version of iPad can rely on the built-in GPS chip for accurate positioning, and the error range is between several meters and tens of meters.

Why doesn't "WIFI iPad" support GPS positioning? Is the GPS chip castrated to save costs?

Actually, it's not. Apple uses AGPS-assisted global positioning system. When positioning, on the one hand, the GPS chip receives the positioning signal of the satellite, and on the other hand, the differential calculation is carried out through multiple network transmissions between the cellular network module and the signal base station, and the two work together to calibrate the position and complete the positioning quickly. Because the WIFI version of iPad has no cellular network module, there is no way to transmit data with the base station for location correction, so there is no way to use AGPS. This is not castration, but a sacrifice that has to be made after removing the mobile signal.

If the GPS chip is installed on the WIFI iPad, the hardware without the cellular network module is not impossible to locate. Due to the lack of position calibration of ground base stations, positioning will become slow and may be inaccurate, especially when you move fast. This positioning is of little significance.