Cascaded Distributed MIMO Beamforming via Intermediate Weights
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Solution Overview
Problem
Massive distributed MIMO systems face challenges with exploding fronthaul loads due to the large number of RUs connecting to the BBU in cascaded topologies, leading to increased deployment costs and system complexity, especially when compared to star topologies.
Innovation Solution
Implementing a method where channel estimation is conducted locally at RUs, with intermediate beamforming weights calculated and combined along the cascaded chain, reducing the need for instantaneous channel information exchange between RUs and BBU, and using MMSE-based beamforming algorithms to enable centralized processing without scaling with the total number of antennas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If centralized beamforming is implemented in massive D-MIMO systems, then beamforming performance is improved, but fronthaul load explodes due to the large number of RUs connecting to the BBU
Solution Approach 1:
The beamforming process is segmented into two parts: centralized beamforming weight calculation at the BBU and local beamforming execution at RUs. The BBU calculates beamforming weights based on channel state information from multiple RUs, while each RU applies the calculated weights locally to serve multiple UEs. This segmentation reduces fronthaul load by avoiding the need to transmit all raw channel data to the BBU.
Solution Approach 2:
Channel state information acts as an intermediary that enables centralized beamforming without requiring direct transmission of all antenna data. Each RU provides condensed channel state information to the BBU, which then computes beamforming weights and returns only the necessary control information, reducing the overall data volume on fronthaul links.
2Device complexity
If a star topology is used to connect RUs to the BBU, then system simplicity is maintained, but deployment costs increase due to the large number of fiber connections required
Solution Approach 1:
Multiple RUs are merged into a cascaded topology where RUs share common fiber connections to the BBU through intermediate nodes. Instead of each RU having a dedicated fiber connection to the BBU, multiple RUs can share the same fiber infrastructure, significantly reducing the total number of fiber connections required and lowering deployment costs.
Solution Approach 2:
The network topology transitions from a two-dimensional star configuration (direct BBU-RU connections) to a multi-dimensional cascaded structure with intermediate nodes. This dimensional change allows for more efficient use of fiber resources and reduces the overall infrastructure required for network deployment.
3Productivity
If the number of RUs connecting to the BBU is increased to serve more UEs, then system capacity is improved, but fronthaul load and system complexity explode
Solution Approach 1:
The system complexity is segmented by distributing beamforming operations between the BBU and RUs. The BBU handles high-level beamforming weight calculation using condensed channel state information, while RUs handle local beamforming execution. This segmentation allows the system to scale capacity by adding more RUs without proportionally increasing fronthaul load or overall system complexity.
Data Source
AI summary
A network entity can be in a communications network that includes a plurality of network nodes communicatively coupled to the network entity via a cascaded topology. The network entity can transmit scheduling information to a first network node of the plurality of network nodes. The scheduling information can indicate user layers to be used for communication with a communication device. The network entity can further receive an indication of an intermediate beamforming weight from the first network node. The network entity can further determine a part of a frequency-domain beamforming weight based on the indication of the intermediate beamforming weight. The network entity can further communicate with the communication device via the first network node using the part of the frequency-domain beamforming weight.