GPS vs. A-GPS: Key Differences Explained

This article dives into the comparison between GPS (Global Positioning System) and A-GPS (Assisted Global Positioning System), highlighting their differences. We’ll also explore the different modes of operation within A-GPS, specifically MSA and MSB.

Introduction:

Both GPS and A-GPS are technologies used to pinpoint your location on Earth. GPS is commonly found in vehicles like cars, planes, and ships, while A-GPS is frequently integrated into mobile phones. Although they share the same core purpose, let’s examine their distinct features and how they differ.

What are GPS and A-GPS?

• GPS (Global Positioning System): GPS devices determine their location by directly communicating with satellites orbiting the Earth.

• A-GPS (Assisted Global Positioning System): A-GPS devices obtain location information from network stations (BTS/NodeB/eNodeB) using cellular technologies like GSM, CDMA, or LTE. These base stations, in turn, communicate with satellites and relay the information to the mobile terminal upon request.

How They Work Differently

GPS relies on direct satellite communication, which means it requires a clear view of the sky. Obstructions and interference can slow down the process of acquiring a location.

A-GPS, on the other hand, communicates with network stations, allowing it to function even in cloudy weather or challenging network conditions. However, its performance suffers when a network connection isn’t available. In such cases, A-GPS devices might revert to using GPS functionality (if available) to determine the location.

A-GPS is generally faster than GPS because it doesn’t have to solely rely on direct satellite communication to get location data.

Assisted GPS Modes: MSA and MSB

A-GPS has two primary modes of operation:

• MSA (Mobile Station Assisted): In MSA mode, the A-GPS device receives reference time, acquisition assistance, and other optional data from the mobile network operator. The operator obtains GPS information from satellites via an A-GPS server and stores it in its database. The A-GPS server then calculates the satellite position and provides it to the A-GPS device. Crucially, in MSA mode, the server calculates the position, not the A-GPS device itself.

• MSB (Mobile Station Based): In MSB mode, the A-GPS device receives reference time, location, ephemeris (satellite orbit data), and other data from the A-GPS server. With this data, the A-GPS device calculates the satellite position independently.

GPS vs. A-GPS: A Detailed Comparison

Here’s a table summarizing the key differences between GPS and A-GPS: