3G data modem support is a core feature for the Real Time Passenger Information (RTPI) system designed by Bluewater Systems. The RTPI system is designed to collect and display information about the arrival times of buses at a particular point on the route. This information is provided by a unit on the buses which uses a GPS receiver and GPRS or other wireless communications to pass on positional information to a central server.The choice of the 3G modem was dictated by another requirement: to use a cheaper GSM data modem as an assembly option. Bluewater decided to use the 3G embedded module MC8775 from Sierra Wireless, a low talk and low standby current modem which comes in PCI Express Mini Card form factor.
A Sierra Wireless MC8775 PCI Express Mini Card supports third generation (3G) digital cellular standards and it is globally certified. An MC8775 supports tri-band UMTS (HSDPA): 850/1900/2100 MHz, with forward link up to 3.6Mbps, and quad-band EDGE/GPRS/GSM: 850/900/1800/1900 MHz, with forward link up to 216 Kbps.
Although the data modem has a PCI Express Mini Card form factor, it does not support a PCI Express electrical interface. The host and USIM interfaces, as well as power supply for the 3G/GSM modules, are provided via a PCI Express Mini Card connector. The communication between the 3G data modem and the host (Snapper CL15 module) is provided via a USB 2.0 interface.
The PCI Express Mini Card form factor allows a simple downgrade path if it is cheaper, however, the same form factor GSM data modem designed by Bluewater Systems is desired. Another benefit of having the same form factor for 3G and GSM data modems is a smaller main board and a simple upgrade/downgrade path.