OTDOA vs U-TDOA: Differences Explained

This page compares OTDOA (Observed Time Difference of Arrival) with U-TDOA (Uplink Time Difference of Arrival), highlighting the key differences between them. OTDOA relies on measuring the UE’s (User Equipment) position using downlink signals, while U-TDOA uses uplink signals.

OTDOA (Downlink Observed Time Difference of Arrival)

How OTDOA works

• Defined in 3GPP Release 9.
• It’s a downlink-based technology.
• UE-assisted: The UE receives downlink signals from the serving cell and several neighboring cells. It then calculates the time difference between signals from the serving cell and the neighbors to determine its position.
• In LTE networks, a special reference signal called PRS (Positioning Reference Signal) is transmitted regularly to facilitate this estimation.
• The UE sends the RSTD (Reference Signal Time Difference) information back to the network. The eNBs (evolved Node B or base stations) use this feedback to determine the UE’s position.
• OTDOA is a UE-based method. The mobile device itself is responsible for measuring the time differences.

U-TDOA (Uplink Time Difference of Arrival)

U-TDOA

• Defined in 3GPP Release 11.
• It’s an uplink-based technology.
• eNB-assisted: Highly sensitive receivers at the eNBs receive uplink transmissions from the UE. These receivers determine the time differences of arrival, and therefore the UE’s position.
• Network-based location estimation: U-TDOA doesn’t require any UE interaction for position determination. The network handles the calculations.