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

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Today, let’s talk about how the positioning technology in the 5G era is realized.


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 up to 30 cm, and 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) measurement on the PRS of each base station. These measurement results will be reported 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 based on the DL RSRP of each beam. Then estimate the UE position based on AoD.

UL-AOA (Uplink Angle of Arrival): 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 (such as DL RSRP) for each gNB, and the measurement report will be sent to the location server.

All measurement reports related to positioning must be reported to the location server. These measurement reports include:

Positioning measurement report reported by UE:

  • DL RSRP per beam/gNB
  • Downlink reference signal time difference (DL RSTD)
  • UE RX-TX time difference

Positioning measurement report reported by gNB:

  • Uplink angle of arrival (UL-AoA)
  • UL-RSRP
  • UL-RTOA (UL relative time of arrival)
  • 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 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 sub-meter level.

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