O-RAN Uplink MIMO Split Using O-RU Channel Estimation
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Solution Overview
Problem
Existing O-RAN-based RAN systems face performance degradation in high-speed UE scenarios due to channel aging and inter-cell interference, leading to throughput degradation and interference rejection issues, particularly in massive MIMO systems.
Innovation Solution
Implementing asymmetrical functional splits in the uplink and downlink processing by shifting certain signal processing tasks to the O-RU, such as DM-RS channel estimation, equalization, and demodulation, and enhancing signaling mechanisms through M-plane and C-plane modifications to support these splits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If O-RAN 7-2x split is implemented for UL MIMO processing, then system complexity is reduced and interoperability is improved, but channel estimation accuracy degrades in high mobility scenarios due to channel aging
Solution Approach 1:
The patent performs channel estimation using DM-RS signals before the actual data reception and processing. By preliminarily estimating the channel state at the O-RU using the asymmetrical split, the system prepares accurate channel information in advance, compensating for the time delay issues in high mobility scenarios where channel aging would otherwise degrade accuracy.
Solution Approach 2:
The patent segments the UL MIMO processing functions by performing DM-RS based channel estimation, equalization, and demodulation at the O-RU, while transferring only the processed results to the O-DU. This segmentation allows the O-RU to handle time-critical channel estimation locally, improving accuracy without requiring full processing complexity at the O-RU.
2Measurement precision
If SRS signals are transmitted over a relatively long period for channel estimation, then channel estimation can be performed, but channel aging occurs in high mobility scenarios causing throughput degradation
Solution Approach 1:
The patent changes the timing parameter of channel estimation by using DM-RS signals that are transmitted closer to the actual data reception time, rather than using SRS signals over a long period. This parameter change reduces the time gap between estimation and data transmission, minimizing channel aging effects in high mobility scenarios while maintaining estimation capability.
Solution Approach 2:
The patent introduces DM-RS signals as an intermediary mechanism between the UE and the network for channel estimation. These reference signals serve as a mediator that provides up-to-date channel information at the time of data transmission, replacing the older SRS-based approach that suffered from timing delays and channel aging.
3Reliability
If all received streams for PUSCH are transferred from O-RU to O-DU, then complete signal processing can be performed, but significant fronthaul bandwidth consumption occurs
Solution Approach 1:
The patent extracts and performs the channel estimation, equalization, and demodulation functions at the O-RU using the asymmetrical functional split. By taking out these processing steps from the O-DU and executing them locally at the O-RU, the system transfers only the essential processed results rather than all raw received streams, significantly reducing fronthaul bandwidth consumption while maintaining processing reliability.
Solution Approach 2:
The patent segments the signal processing pipeline into two parts: time-critical channel estimation and equalization performed at the O-RU, and higher-level processing performed at the O-DU. This segmentation allows the system to transfer only necessary processed data between units, reducing the quantity of data transmitted over the fronthaul interface while preserving complete signal processing capability.
4Ease of operation
If combining/digital beamforming matrix elements are calculated using SRS channel estimates, then user pairing and beamforming can be performed, but interference rejection is insufficient in interference-limited scenarios
Solution Approach 1:
The patent performs preliminary channel estimation using DM-RS signals that are transmitted closer to the actual data reception time. By preliminarily establishing accurate channel state information at the O-RU before combining and beamforming operations, the system improves interference rejection capability compared to using older SRS-based estimates, while maintaining ease of beamforming operation.
Data Source
AI summary
A system and method of operating an Open Radio Access Network (O-RAN, in which O-RAN the system includes: a baseband unit (BBU) having an O-RAN centralized unit (O-CU) and an O-RAN distributed unit (O-DU); an O-RAN radio unit (O-RU) remote from the BBU; and a fronthaul interface between the O-RU and the BBU. A functional split of O-RAN functions respectively assigned to O-RU and O-DU for the fronthaul interface between the BBU and the O-RU is different for downlink (DL) and uplink (UL) so that at least one of i) demodulation reference signal (DM-RS)-based channel estimation is performed by the O-DU in the DL and by the O-RU in the UL, ii) equalization is performed by the O-DU in the DL and by the O-RU in the UL, and iii) demodulation is performed by the O-DU in the DL and by the O-RU in the UL.