From 2G to 4G, the positioning technologies of cellular networks mainly include E-CID, AoA, ToA, TDOA, etc.

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5G Positioning Technology
From 2G to 4G, the positioning technologies of cellular networks mainly include E-CID, AoA, ToA,
TDOA, etc.
E-CID
The traditional base station is divided into three sectors, one sector corresponds to one cell, each
sector is usually 120 degrees, and each cell has a different identification code (Cell ID).
Since the latitude and longitude of the base station are known, the location of the mobile phone
can be roughly locked based on the Cell ID. But the coverage of a cell is very large, usually, a few
hundred meters to a few kilometers, and the positioning error based only on Cell ID is very large,
so E-CID positioning technology is available.
E-CID, Enhanced Cell-ID, refers to enhanced positioning technology based on Cell ID, including
Cell ID+RTT, Cell+RTT+AoA, etc.
Cell ID+RTT
The RTT (Round Trip Time) measurement is added on the basis of Cell ID, that is, the time of the
signal from the mobile phone to the base station or from the base station to the mobile phone is
obtained through TA (Time Advance), and then multiplied by the speed of light (wireless signal
propagation) Speed) to estimate the distance between the mobile phone and the base station.
In the Cell ID+RTT positioning mode, distance estimation can be performed on three nearby base
stations to improve positioning accuracy.
Cell ID+RTT+AoA
AoA, Angle-of-Arrival, is the angle of incidence of the mobile phone signal transmitted to the

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base station to further determine the location of the mobile phone in the area.
On the basis of Cell ID, adding RTT and AoA assistance can greatly improve positioning accuracy.
E-CID is a positioning method that adds TA, AoA, RSRP, RSRQ, and other auxiliary information on
the basis of Cell ID to improve positioning accuracy.
TOA
TOA, Time of Arrival (time of arrival).
Refers to the calculation of the distance between different base stations and the mobile phone by
measuring the time when the reference signals sent by multiple base stations reach the mobile
phone, and draw a concentric circle with the distance as the radius, and then pass the positioning
algorithm (three-sided positioning algorithm, least two Multiplication algorithm) to estimate the
location of the phone.
TDOA
TDOA, Time Difference of Arrival (time difference of arrival).
The disadvantage of the TOA positioning method is that if the time between the base station and
the mobile phone is not synchronized, both parties do not know the absolute time of signal
transmission, which will cause calculation and positioning errors.
TDOA uses relative time (time difference) to make up for this shortcoming, that is, by measuring
the signal arrival time difference between the mobile phone and two nearby base stations, to
calculate the distance difference between the mobile phone and the base station.
From a mathematical point of view, the location of the mobile phone must be positioned on a
hyperbola with the two base stations as the focus and the distance difference as the fixed
difference. In this way, three or more surrounding base stations can form two or more hyperbolas
in pairs, and the intersection of the hyperbolas in the two-dimensional position coordinates of
the mobile phone.
A-GNSS
A-GNSS, Assisted GNSS, is a network-assisted satellite positioning system.
A-GNSS requires both the network and mobile phones to receive GNSS information.
In A-GNSS, the network can determine the GNSS satellites over the area where the terminal is
currently located, and provide this information to the terminal, so that the terminal can narrow
the satellite search range and shorten the search time based on this information, and complete
the availability faster. Satellite search process.
The terminal can quickly obtain its own location and then send the location information to the
location service center of the network to calculate a more accurate location.
A-GNSS can meet the needs of fast-moving positioning, but it cannot meet the needs of indoor
positioning.
Positioning needs in the 5G era
5G will enable diversified applications in all walks of life. A large number of application scenarios
such as the Internet of Vehicles, autonomous driving, smart manufacturing, smart logistics,
drones, and asset tracking have higher requirements for positioning capabilities, such as vehicle
formation in the Internet of Vehicles, Active collision avoidance requires a positioning accuracy of

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up to 30 cm, and requires a positioning capability that supports high-speed movement and
ultra-low delay; remote control of drones requires 10-50 cm. At the same time, a large number of
applications such as asset tracking, unmanned AGV, and AR/VR are concentrated indoors, and
satellite positioning systems cannot cover them. Therefore, 5G must enhance network
positioning technology to improve positioning accuracy.
According to the 3GPP R16 definition, 5G positioning capabilities must meet the following
minimum requirements:
For 80% of terminals, the horizontal positioning accuracy is better than 50 meters, and the
vertical positioning accuracy is better than 5 meters. The end-to-end delay is less than 30
seconds.
For demanding commercial use cases, 5G positioning capabilities must at least meet the
following requirements:
For 80% of terminals, the horizontal positioning accuracy is better than 3 meters (indoor) and 10
meters (outdoor). For 80% of terminals, the vertical positioning accuracy is better than 3 meters
(indoor and outdoor). The end-to-end delay is less than 1 second.
5G positioning technology
DL-TDOA: The 5G R16 version introduces a new reference signal—PRS (Positioning Reference
Signal), which is used by the UE to perform downlink reference signal time difference (DL RSTD)
measurements on the PRS of each base station. These measurement results will be reported to
the location server.
UL-TDOA: The 5G R16 version enhances SRS (Channel Sounding Reference Signal) to allow each
base station to measure the uplink relative time of arrival (UL-RTOA) and report the
measurement results to the location server.
DL-AoD (Downlink Departure Angle): The UE measures the received downlink reference signal
power (DL RSRP) of each beam/gNB, and then sends the measurement report to the location
server. The location server determines the AoD according to the DL RSRP of each beam. Then
estimate the UE position based on AoD.
UL-AOA (Uplink Angle of Arrival): The gNB measures the angle of arrival according to the beam
where the UE is located and sends the measurement report to the location server.
Multi-cell RTT: gNB and UE perform Rx-Tx time difference measurement on the signal of each cell.
The measurement reports from the UE and gNB will be reported to the location server to
determine the round-trip time of each cell and get the UE location.
E-CID: UE's RRM measurement for each gNB (such as DL RSRP), the measurement report will be
sent to the location server.
All measurement reports related to the positioning must be reported to the location server.
These measurement reports include:
Positioning measurement report reported by UE:
DL RSRP downlink reference signal time difference (DL RSTD) UE RX-TX time difference per
beam/gNB
Positioning measurement report reported by gNB:

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Uplink angle of arrival (UL-AoA) UL-RSRP UL-RTOA (UL relative arrival time) gNB RX-TX time
difference
In short, based on the previous cellular network positioning technology, 5G R16 introduced a new
positioning reference signal (PRS), using DL-TDOA, UL-TDOA, DL-AoD, UL-AOA, E-CID multiple
positioning Technology to work together to improve positioning accuracy.
At the same time, due to the increase in the number and diversity of reference points in the
ultra-dense network in the 5G era, Massive MIMO multi-beam can make AoA estimation more
accurate, and lower network delay can improve the accuracy of the time-based measurement.
These advantages can be further improved 5G positioning capability.
In the future, 5G positioning capabilities will be further enhanced, and the R17 version will also
increase the 5G positioning accuracy to the sub-meter level.