Lecture Slides

Positioning in IoT

Positioning determines a device's geographical location by using signals from various sources such as gateways or satellites. This process often includes estimating the device's movement (trajectory and speed) and mapping the surrounding area (Simultaneous Localization and Mapping or SLAM).

Applications

Time-Based Techniques

Here are the key time-based positioning techniques used in IoT:

Time of Arrival (ToA) Measures signal travel time from transmitter to receiver. Requires time synchronization between nodes.
- Each base station measures the time it takes for a signal to travel from the device to reach it
- Distance is calculated using the formula: distance = speed of signal × time of travel
- Since radio signals travel at the speed of light (c ≈ 3×10⁸ m/s), even small timing errors can lead to significant position errors
- At least three base stations are needed for 2D positioning (trilateration)
- All nodes must have precisely synchronized clocks for accurate measurements
- Imagine drawing a circle around each base station and find the intersections of all three circles
Time Difference of Arrival (TDoA) Calculates position based on differences in signal arrival times at multiple anchor nodes. Only requires synchronization between anchor nodes.

TDoA positioning works by measuring the difference in arrival times of signals between multiple anchor nodes (base stations). Here's why we use hyperbolas:
- For any two base stations, the difference in distances to a point creates a hyperbola - all points with the same time difference lie on this curve
- With three or more base stations, we get multiple hyperbolas - the intersection point of these hyperbolas gives us the device's location
The key advantages of TDoA over ToA are:
- Only anchor nodes need to be synchronized, not the mobile device
- The mobile device doesn't need to transmit timing information, making it more energy efficient
- Works well in large-scale deployments where precise device timing might be impractical
Round Trip Time (RTT) Measures the complete signal journey time - from transmitter to receiver and back. No node synchronization needed.
Phase of Arrival (PoA) Uses signal phase shift to determine distance. Frequently combined with ToA, TDoA, and RSSI methods to achieve higher accuracy.

Direction-Based Techniques

Angle of Arrival (AoA) Uses directional antennas to measure the angle of received signals. Requires at least two anchor nodes for 2D positioning. Provides high accuracy at short distances without requiring node synchronization.
Angle of Departure (AoD) Measures the angle at which signals leave the transmitter. Commonly implemented in modern systems like Bluetooth 5.1, often working alongside AoA.
Combined Techniques AoA and AoD can be integrated to enhance both positioning accuracy and system reliability across various IoT applications.

Signal-Based Techniques

RSSI

RSSI-Based Range Estimation measures the power level of received signals to calculate distances between transmitters and receivers. This widely-used technique is valued for its simplicity and cost-effectiveness in wireless communication systems.