Hybrid Precoding Switching for Fronthaul-Limited Cell-Free Massive MIMO

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Solution Overview

Problem

Current precoding procedures in distributed massive MIMO systems face challenges such as increased complexity of access points and reduced cell coverage, while existing solutions that improve spectral efficiency often compromise processing capacity and energy efficiency.

Innovation Solution

A dynamic adaptive hybrid precoding strategy that switches between distributed and centralized signal processing based on fronthaul load, allowing efficient use of available bandwidth and reducing energy consumption by selectively shifting precoding to a central processing unit.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If robust precoding solutions (PMMSE, LP-MMSE) are used to improve spectral efficiency, then spectral efficiency increases, but access point complexity increases

Engineering Contradiction:

Improvespectral efficiencyVSAvoidaccess point complexity

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent implements dynamic precoding where the system switches between distributed precoding at access points and centralized precoding at the network node based on real-time fronthaul bandwidth availability. This dynamic adaptation allows the system to use complex precoding algorithms when resources permit while maintaining simplicity when resources are constrained, resolving the contradiction between spectral efficiency and access point complexity.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent introduces fronthaul bandwidth as an intermediary parameter that mediates between distributed and centralized processing. By monitoring fronthaul conditions and using them to determine precoding location, the system can achieve high spectral efficiency when bandwidth is available while avoiding complexity constraints when bandwidth is limited, thus resolving the contradiction.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If precoding is performed centrally to improve spectral efficiency, then spectral efficiency increases, but fronthaul bandwidth consumption increases

Engineering Contradiction:

Improvespectral efficiencyVSAvoidfronthaul bandwidth consumption

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The system dynamically adjusts precoding location based on fronthaul bandwidth conditions. When fronthaul bandwidth is abundant, centralized precoding is employed to maximize spectral efficiency. When fronthaul bandwidth is constrained, the system switches to distributed precoding at access points, thereby adapting to available resources and resolving the contradiction between spectral efficiency and fronthaul bandwidth consumption.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The patent changes the operational parameter of precoding location (from fixed to variable) based on fronthaul bandwidth conditions. This parameter change allows the system to optimize spectral efficiency when bandwidth permits while reducing fronthaul consumption when bandwidth is limited, effectively resolving the contradiction.

Inventive Principle:

Principle #35Parameter changes

3Device complexity

If distributed precoding is used to reduce access point complexity, then access point simplicity is maintained, but spectral efficiency decreases

Engineering Contradiction:

Improveaccess point simplicityVSAvoidspectral efficiency

Core Design Contradiction:

Device complexityVSProductivity

Solution Approach 1:

The patent implements dynamic precoding selection where access points can operate in simple distributed mode when fronthaul bandwidth is limited, maintaining access point simplicity. When fronthaul bandwidth becomes abundant, the system dynamically switches to centralized precoding to achieve higher spectral efficiency, thus resolving the contradiction between access point simplicity and spectral efficiency.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system provides multi-functionality by enabling access points to perform both simple distributed precoding and more complex centralized precoding operations depending on fronthaul conditions. This universal capability allows the system to maintain access point simplicity when needed while achieving high spectral efficiency when resources permit, resolving the contradiction.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS12531608B2Adaptive hybrid precoding strategy for cell-free massive multiple input multiple output

Publication Date: 2026.01.20 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A network node in a communications network can perform adaptive hybrid precoding. The network node can be communicatively coupled to an access point via a fronthaul. The network node can determine an amount of available bandwidth on the fronthaul. The network node can further determine whether to have the access point perform precoding of signals communicated between the access point and a communication device based on the amount of available bandwidth on the fronthaul. Responsive to determining whether to have the access point perform the precoding, the network node can transmit an indication to the access point indicating whether to perform the precoding.