The GPS satellites orbiting the earth are transmitting radio waves, similar to that of an FM radio station. GPS satellites only transmit; they do not receive. The GPS radio waves are picked up by the receiver on your navigation system, phone, or any GPS antenna. We all share the same GPS satellites, so there very few points of differentiation here. There are various GPS chipsets that might perform better than others but in the vehicle tracking industry, most are about equal. GPS signals can be blocked by heavy or dense materials. A parking garage, tall buildings (canyon effect), or a pine tree forest may block some GPS signals. Under 99% of normal conditions, GPS signals are readily available. GPS signals are processed by the GPS tracker and then transmitted to a server using a cellular or satellite communication network. Wi-Fi or Passive options are impractical and far less popular because they come with many issues.
GPS data is just data being moved on a carrier network, similar to a picture or email, but much smaller in size. Cellular networks are the most cost-effective method of communication, but there are areas with little or no coverage due to a lack of cell towers. GPS signals that are sent with telematics and engine diagnostics data significantly increase the amount of data being transmitted. The more data, the higher the cost. In high availability scenarios, customers may opt to add satellite modems for failover or go with satellite communication only.
To communicate globally and in the most remote areas, the GPS data is sent back to communication satellites, instead of cellular towers. These are different than the GPS satellites. The cost of satellite communication is significantly higher, therefore the amount of data transmitted is reduced to make it cost-effective to use satellite communication. Most GPS trackers that use satellite communication only transmit every 1-30 minutes, or by exception. To put it in perspective, a call on a cellular network might cost $0.02 per minute on average, while a call on a satellite phone might cost $2.00 per minute.