An in car GPS navigation device determines its position by receiving signals via which type of communication link?

Introduction / Context:
Global Positioning System devices, commonly called GPS, are now built into many cars and smartphones. They can determine position anywhere on the globe with good accuracy, provided they can receive signals from satellites. Understanding the basic communication channel used by GPS helps clarify how these devices work and why they require a clear view of the sky. This question asks you to identify the type of link that an in car GPS uses to obtain its location information.

Given Data / Assumptions:
- The device is a standard GPS receiver installed in an automobile.
- GPS satellites orbit the Earth and transmit signals continuously.
- The receiver is passive; it listens to signals but does not need to transmit back for basic positioning.
- The communication medium is wireless and operates through the atmosphere.

Concept / Approach:
GPS satellites broadcast precise timing and orbital information using radio signals in the microwave region of the electromagnetic spectrum. A GPS receiver in the car picks up these signals from multiple satellites. By measuring the travel time of the signals and knowing the positions of the satellites, the receiver computes its own position on the Earth's surface. The channel used is therefore a satellite based radio communication link, not infrared reflection from signs, wired cables or short range local signals.

Step-by-Step Solution:
Step 1: Recall that GPS stands for Global Positioning System and relies on a constellation of satellites. Step 2: Understand that each GPS satellite broadcasts radio signals containing timing and positional data. Step 3: The GPS receiver in the car receives these signals from several satellites at once. Step 4: By comparing the arrival times of the signals and using known satellite positions, the receiver calculates its distance from each satellite. Step 5: Using these distances, it performs a trilateration calculation to determine its own exact location. Step 6: Thus, the communication channel is radio communication from satellites, specifically in microwave frequency bands.

Verification / Alternative check:
Practical observations confirm this explanation. GPS reception is poor inside tunnels, inside thick walled buildings or under heavy tree cover because the receiver cannot see enough satellites and cannot receive their radio signals clearly. No connection to underground cables or road signs is needed, and the system works on the ocean or in remote deserts where there are no such infrastructure elements. Technical documentation on GPS systems always mentions radio frequency bands such as the L1 and L2 bands, confirming that radio signals from satellites are used.

Why Other Options Are Wrong:
Infrared beams reflected from road signs: GPS does not rely on roadside reflectors; it needs signals from orbiting satellites and works even where there are no signs.
Electrical signals sent through underground cables: GPS receivers are not physically connected to cables, and the system is designed to work wirelessly anywhere on the globe.
Short range Bluetooth links from smartphones only: While some apps can share location via Bluetooth, the original position information still comes from satellite radio signals, not purely from nearby phones.

Common Pitfalls:
Some learners confuse GPS with mobile data or internet services and think the device needs a cellular network to know its position. In reality, GPS positioning uses direct satellite radio signals, and mobile data is used only to download maps or traffic information. Remember that the core of GPS is satellite based radio communication, and that is the link the question is asking about.

Final Answer:
An in car GPS navigation device determines its position using radio signals transmitted from navigation satellites orbiting the Earth.