Location-based Services Flashcards
Which is the largest source of revenues in the communication market and why
Added-value services because many mobile applications use positioning information
List 5 application areas for LBS in the private sector
- Navigation systems and services
- Fleet and vehicle tracking
- Tourist guide systems
- Nearby points of interest
- Indoor guidance systems
List 4 application areas for LBS in the public sector
- Emergency Management
- Road tax
- Smart cities
- public transportation
What functionality is provided by Google Latitude (Commercial Application) now embedded in Google Maps
Functionality:
- See friends location in real time
- Control who sees your location for how long
- Initiate communication (call, message)
Give an example for an object location service.
- Object includes Bluetooth / RFID for identification
- People move around with their phones as sensors
- Global query service where users can ask for a lost item
Describe the different dimensions of location
Location is a hierarchical construct.
Location
Information | Reference System
Phyiscal | Symbolic Absolute |Relative
GPS Postal address GPS proximity
Describe what the principles of a LBS
- Uses location information to enhance the functionalities provided to the final user
- Relies on automatic obtention of location data
Name three ways to represent a location
- Maps
- Descriptive (left of the gas station)
- Coordination (latitude/longitude)
How is a location automatically obtained
- With positioning
What is positioning and what are its components?
- A process to obtain the spatial position of a target
- parameters observed by measurements
- positioning method
- reference system
- infrastructure & protocols (to coordinate the process)
Name five positioning methods
- Proximity
- Trilateration
- Triangulation
- Dead Reckoning
- Fingerprinting
Explain the positioning method: proximity
Principle: proximity / distance to one reference is detected
- Relative positioning Proximity can be: - binary (in proximity to X or not) - quantitative (a distance) - in relation to one ore more references
Examples:
- Scan for bluetooth devices
- WLAN
- GSM cell ID
(Simplistic way of fingerprinting)
How to obtain a absolute position from proximity
- Device connects to Access Points with BSSID
- DataBases store Location related to a BSSID
- LBS query for location with BSSID as parameter
What is the tradeoff for proximity with the GSM cell ID example
- Size of location area and number of messages send to update location (smaller location areas more messages - always when a area is left sends a message)
How can distance be measured?
- Direct -> measuring tape
- Attenuation -> reduction of signal amplitude
- Time of Flight
- ToA -> Time of Arrival of a signal
- TDoA -> Time Difference of Arrival between 2
signals
- Indirect -> Based on other primary observation
Signals:
- Ultrasound
- Radio signal
- Infrared
Explain how to measure a distance with Ultrasound + ToA
- Transmittor sends ultrasound signal
- Receives responds with ultrasound signal
- Distance is calculated
d = (((T3-T0)-(T2-T1)) X V)/2
What is the principle of Lateration and Trilateration
Principle: Determine the position based on N distance measurement to known points
- Measure distance relative to known points
- N = 3 -> Trilateration (can identify one point at the intersection of the signals of all three base stations)
Consists of Base stations, Terminals, and Pilot signals
Explain how to measure a distance with Ultrasound & Radio + TDoA
- Combined Transmitter (send simultanously both signals)
- Combined receives calulates distance ( measures time diffrence between incoming signals) the receiver does not respond as in case of ToA
d = (T3 - T1) X Vus
What is the principle of Triangulation
Principle: Angulation
- Measures the angle from the location to a known point (Angle of Arrival of incoming signal)
- using antenna arrays
Triangulation: Having 2 angles to calculate location based on trigonometry
What is the principle of Dead Reckoning
Principle: Estimate position based on a previously known position; information about movement
Movement (obtained by accelerometers, gyroscopes):
- Direction of movement
- Velocity or distance
Measure distance relative to last known point
e.g. Positioning in a tunnel
What is the principle of Pattern Matching / Fingerprinting
Principle: Determine position based on a comparison of the current observation with previously stored patterns of signal strengths of multiple reference points
e.g. Use signal from WiFi Access points to determine location
Explain the phases of Pattern Matching / Fingerprinting
Phase 1: Off-line phase (record phase)
- Store previously known patterns in a database and develop a position model
Phase 2: Real-time phase ( operate phase)
- Use the current observation as an input for the positioning model and obtain the position out of it
How does WiFi Fingerprinting work
Record phase:
- Measure for each reference point the RSS (received signal strength) for each SSID
- Create Radio Map (Position Model)
- May require several measurements (line-of-sight, people blocking the signal)
Operate phase:
- Measure the RSS for each SSId
- Look for the reference point with minimal difference
What are the different approaches of fingerprinting?
Empirical vs Modeling
Deterministic vs Probabilistic
