Distributed Base Station Fronthaul Interference Mitigation

Solution Overview

Problem

Current distributed base station systems face challenges in balancing the complexity of remote radio units (RRUs) with the capacity limitations of fronthaul links, particularly in handling inter-cell interference in uplink MIMO systems, which affects scalability and performance.

Innovation Solution

The method involves decomposing MIMO processing into two parts, with the RRU performing computationally lighter tasks like maximum ratio combining and the BBU handling more complex interference cancellation, using a reformulated zero-forcing method that includes interference covariance estimation to reduce fronthaul traffic and mitigate inter-cell interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the number of antennas in the RRU is increased to support massive MIMO, then the spectrum efficiency and network capacity are improved, but the required fronthaul link capacity increases dramatically

Engineering Contradiction:

Improvespectrum efficiencyVSAvoidfronthaul link capacity

Core Design Contradiction:

ProductivityVSQuantity of substance

Solution Approach 1:

The patent segments the MIMO processing into two parts: maximum ratio combining (MRC) is performed at the RRU, while interference cancellation is performed at the BBU. This segmentation allows the RRU to perform only the computationally lighter MRC operation, reducing the fronthaul capacity requirement from transporting all N antenna signals to transporting only K user-layer signals, where K is much smaller than N.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the interference cancellation function from the RRU and places it at the BBU. By taking out the complex interference cancellation operation from the RRU, the system reduces the processing burden and fronthaul capacity requirements at the RRU, while maintaining the ability to handle inter-cell interference through the BBU's computational resources.

Inventive Principle:

Principle #2Taking out (Extraction)

2Quantity of substance

If MIMO processing is moved to the RRU to reduce fronthaul capacity, then the fronthaul load is reduced, but the RRU complexity increases significantly

Engineering Contradiction:

Improvefronthaul capacityVSAvoidRRU complexity

Core Design Contradiction:

Quantity of substanceVSDevice complexity

Solution Approach 1:

The patent segments the MIMO processing into two parts: maximum ratio combining (MRC) is performed at the RRU, while interference cancellation is performed at the BBU. This segmentation allows the RRU to perform only the computationally lighter MRC operation, reducing the fronthaul capacity requirement from transporting all N antenna signals to transporting only K user-layer signals, where K is much smaller than N.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the interference cancellation function from the RRU and places it at the BBU. By taking out the complex interference cancellation operation from the RRU, the system reduces the processing burden and fronthaul capacity requirements at the RRU, while maintaining the ability to handle inter-cell interference through the BBU's computational resources.

Inventive Principle:

Principle #2Taking out (Extraction)

3Device complexity

If traditional PHY-RF split is used with simple RRU, then the RRU implementation is simple, but the system cannot effectively handle inter-cell interference in uplink MIMO

Engineering Contradiction:

ImproveRRU implementation complexityVSAvoidinter-cell interference mitigation

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent segments the MIMO processing into two parts: maximum ratio combining (MRC) is performed at the RRU, while interference cancellation is performed at the BBU. This segmentation allows the RRU to perform only the computationally lighter MRC operation, reducing the fronthaul capacity requirement from transporting all N antenna signals to transporting only K user-layer signals, where K is much smaller than N.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent extracts the interference cancellation function from the RRU and places it at the BBU. By taking out the complex interference cancellation operation from the RRU, the system reduces the processing burden and fronthaul capacity requirements at the RRU, while maintaining the ability to handle inter-cell interference through the BBU's computational resources.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS11706054B2Methods, distributed base station system, remote radio unit and base band unit system for handling uplink signals

Publication Date: 2023.07.18 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

AI summary

A distributed base station system comprises a remote radio unit, RRU, and a base band unit, BBU, connected to the RRU over a fronthaul link, the RRU being connected to N antennas. The method comprising by the RRU: obtaining uplink signals as received at the N antennas from a number of User Equipment, UEs, wirelessly connected to the RRU; obtaining a channel estimation matrix of the wireless communication channels; determining an interference covariance estimation matrix based on the obtained channel estimation matrix and on other channel information different from the channel estimation matrix; sending information on the channel estimation matrix and on the interference covariance estimation matrix to the BBU; determining intermediate signals based on the uplink signals, the channel estimation matrix and the interference covariance estimation matrix, and sending the intermediate signals to the BBU.