Basic Methods Basic Methods
Virpi Mehtälä
TA: Timing advance TA: Timing advance
• In the GSM cellular mobile phone standard, timing
d l d t th l th f ti i l
advance value corresponds to the length of time a signal from the mobile phone takes to reach the base station.
• to compensate for the propagation delay
• Timing advance value – when send MS the signal to BTS
– value 0 to 63 (equates 0 m-35 km) – one unit 3,69 μs equates 550m
• Continuous Timing Advance is an alternative method for assigning timing advance values
Ti i Ad i i ifi f i d
• Timing Advance is significant for privacy and
communications security, as its combination with other variables can allow GSM localization to find the device's position and tracking the mobile phone user
position and tracking the mobile phone user.
RTT: Round trip time RTT: Round trip time
• Round-trip time (RTT), also called round-trip delay, is the time required for a signal pulse or packet to travel from a specific source to a specific
signal pulse or packet to travel from a specific source to a specific destination and back again.
• The result depends on various factors including:
– The data transfer rate, (DTR is the amount of digital data that is moved from one place to another in a given time ) of the source's Internet connection
place to another in a given time ) of the source s Internet connection – The nature of the transmission medium (copper, optical fiber, wireless or
satellite)
– The physical distance between the source and the destination – The number of nodes between the source and the destination
– The amount of traffic on the LAN (local area network) to which the end user is connected
– The number of other requests being handled by intermediate nodes and the remote server
Th d ith hi h i t di t d d th t f ti
– The speed with which intermediate nodes and the remote server function – The presence of interference in the circuit.
TDOA: Time difference of arrival TDOA: Time difference of arrival
• Multilateration is commonly used in civil and military surveillance in civil and military surveillance applications to accurately locate an aircraft, vehicle or stationary emitter by measuring the time difference of arrival (TDOA) of a ( ) signal from the emitter at three or more receiver sites.
• Given two receiver locations and a known TDOA, the locus of
ibl itt l ti i
possible emitter locations is a one half of a two-sheeted hyperboloid.
•
•
• Fig1. A two-sheeted hyperboloid
• In simple terms, with two receivers
at known locations, an emitter can
be located onto a hyperboloid[1].
TDOA Geometry TDOA Geometry
• Consider an emitter (E in Figure) at an unknown location vector
unknown location vector
– E = (x, y, z)
• which we wish to locate. The source is within range of N receivers at known locations
P0 P1 P PN
– P0, P1, ..., Pm, ..., PN.
• The subscript m refers to any one of the receivers:
– Pm = (xm, ym, zm) – 00 m N.≤ m ≤ N.
• The distance (R) from the emitter to one of the receivers in terms of the coordinates is
• The math is made easier by placing the origin at one of the receivers (P0), which makes it's distance to the
emitter
