Distributed Base Station Beamforming Weights
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Solution Overview
Problem
In distributed base station systems, the current method of calculating beamforming weights based on outdated channel estimation degrades beamforming performance due to UE mobility and time-varying interferences.
Innovation Solution
The proposed solution involves a two-part beamforming process, where the first part is performed in the RRU based on initial beamforming weights sent from the BBU, and the second part is performed in the BBU using updated beamforming weights calculated from a second reference signal sent with uplink signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If beamforming weights are calculated in the BBU based on outdated channel estimation, then the BBU can perform centralized processing, but the beamforming performance degrades due to UE mobility and time-varying interferences
Solution Approach 1:
The beamforming process is segmented into two parts: first beamforming weights are calculated in the BBU based on initial channel estimation, while second beamforming weights are calculated in the RRU based on updated channel estimation from current reference signals. This segmentation allows centralized processing for initial setup while enabling distributed updates for maintaining performance under changing conditions.
2Reliability
If the RRU performs complete beamforming processing, then beamforming performance is maintained, but the RRU complexity and cost increase
Solution Approach 1:
The beamforming function is segmented between BBU and RRU: the BBU calculates and sends first beamforming weights, while the RRU calculates and applies second beamforming weights locally. This segmentation maintains beamforming performance without requiring the RRU to perform complete beamforming processing, thereby reducing RRU complexity.
Solution Approach 2:
Instead of requiring the RRU to perform complete beamforming processing, the system applies partial beamforming by using pre-calculated first beamforming weights from the BBU and supplementing them with local second beamforming weights. This partial action approach maintains sufficient beamforming performance while significantly reducing RRU processing requirements.
3Device complexity
If channel estimation is performed periodically, then the system can maintain simplified processing, but the beamforming weights become outdated and performance degrades
Solution Approach 1:
The system implements feedback mechanisms where reference signals are transmitted continuously or periodically, and the RRU calculates updated channel estimation and second beamforming weights based on these current reference signals. This feedback loop ensures that beamforming weights remain accurate despite UE mobility or changing interference conditions, without requiring complex centralized processing.
Data Source
AI summary
A method performed by a distributed base station system of a wireless communication network. The distributed base station system comprises a base band unit (BBU) and a remote radio unit (RRU) connected to each other over a fronthaul link. The method comprises receiving uplink signals at N antennas of the RRU from a number of user equipment (UEs) connected to the RRU. The BBU determines first beamforming weights based on a first reference signal that is has received from the UEs and sends the first beamforming weights to the RRU. The RRU then determines intermediate signals from the first beamforming weights and the uplink signals and sends the intermediate signals to the BBU. The BBU then determines second beamforming weights from a second reference signal it has received from the RRU. Then, the BBU determines an output signal based on the intermediate signal and the second beamforming weights.