Open RAN RTT Location via RU-DU Timing Offset Compensation
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Solution Overview
Problem
The introduction of Open RAN base station architectures introduces uncertainty into Round Trip Time (RTT) measurements due to unpredictable delays in the open interface fronthaul network, which can affect the accuracy of mobile device location services in 5G wireless communication systems.
Innovation Solution
The solution involves scheduling a Positioning Reference Signal (PRS) and Sounding Reference Signal (SRS) transmission by the Radio Unit (RU) with the DU or CU determining the timeslot, allowing the RU to measure the time difference and the UE to report its internal delay, enabling the DU or CU to calculate the accurate RTT by subtracting the UE's internal delay from the RU's observed time difference, thereby refining the position estimate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Open RAN architecture with disaggregated RU/DU/CU is used, then network flexibility and vendor interoperability are improved, but fronthaul synchronization uncertainty increases
Solution Approach 1:
The base station is segmented into separate functional units (RU, DU, CU) that can be independently deployed and managed. The RU handles radio frequency functions while the DU handles digital signal processing, connected via open fronthaul interfaces. This segmentation enables multi-vendor deployments and architectural flexibility while maintaining defined interfaces for synchronization.
Solution Approach 2:
A synchronization function is introduced as an intermediary mechanism between the RU and DU/CU. This function provides timing reference signals and synchronization information through the open fronthaul interface, mediating the timing relationship between disaggregated units and eliminating uncertainty in RTT measurements despite the open interface architecture.
2Measurement precision
If RTT measurement is performed in disaggregated O-RAN architecture, then location service capability is improved, but measurement accuracy deteriorates due to open interface delays
Solution Approach 1:
The synchronization function performs preliminary actions by establishing timing relationships and providing synchronization references before RTT measurements are conducted. By pre-synchronizing the RU and DU/CU through timing reference signals, the system eliminates uncertainty in the open fronthaul interface delays, enabling accurate RTT-based location measurements.
Solution Approach 2:
The synchronization function implements feedback mechanisms where the DU/CU provides timing advance information and synchronization status back to the RU. This feedback loop allows the RU to adjust its timing and compensate for fronthaul delays, maintaining measurement accuracy despite the disaggregated architecture.
Data Source
AI summary
An approach for estimating Round Trip Time (RTT) such as used for estimating a location of mobile User Equipment (UE) devices, particularly adapted for Open Radio Access Networks (O-RANs) that disaggregate basestation functions into a Radio Unit (RU) and a Distributed Unit (DU) or Central Unit (CU). A Positioning Reference Signal (PRS) is transmitted by the RU according to schedule determined by the DU or CU. A Sounding Reference Signal (SRS) is returned by the UE to the DU or CU, with an estimate by the UE of its internal delay. The RU reports an estimate of the difference seen between a time of transmission of the PRS and time of reception of the SRS. The RTT is then estimated by subtracting the UE's internal delay from this difference. RTTs taken between the UE and two or more RU's may further determine a location of the UE.