Closed-Loop LBT for Hidden Node Interference in 5G Unlicensed Spectrum

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Solution Overview

Problem

Current Listen Before Talk (LBT) mechanisms in wireless communication networks face challenges in avoiding hidden node interference, especially when interfering nodes are outside the sensing range of the transmitting node, leading to inefficiencies in channel reuse and increased latency in 5G networks.

Innovation Solution

Implementing a closed-loop LBT mechanism that coordinates clear channel assessments between base stations and mobile devices using LBT triggers, allowing synchronized channel assessments and feedback to ensure channel availability before scheduling transmissions, thereby reducing interference and improving channel reuse efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If traditional LBT mechanism is used, then channel access is simplified, but hidden node interference increases and channel reuse efficiency decreases

Engineering Contradiction:

ImproveLBT mechanism complexityVSAvoidchannel reuse efficiency

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent implements a feedback mechanism where the base station receives LBT result information from the terminal device and uses this feedback to determine whether to schedule uplink transmission. The terminal performs LBT, reports the result to the base station, and the base station makes the final scheduling decision based on both the terminal's LBT result and its own channel assessment, creating a closed-loop feedback system that improves channel reuse efficiency while maintaining manageable complexity

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent performs preliminary clear channel assessment at the base station before requesting LBT from the terminal. The base station assesses the channel environment in advance, then requests the terminal to perform LBT and report results. This preliminary action allows the base station to make informed scheduling decisions and reduces the likelihood of hidden node interference by having advance knowledge of channel conditions

Inventive Principle:

Principle #10Preliminary action

2Ease of operation

If traditional LBT mechanism is used, then system operation is simpler, but latency increases due to hidden node interference

Engineering Contradiction:

Improvesystem operation simplicityVSAvoidtransmission latency

Core Design Contradiction:

Ease of operationVSLoss of time

Solution Approach 1:

The feedback mechanism enables faster transmission by allowing the base station to make accurate scheduling decisions based on terminal-reported LBT results. When the channel is clear, the base station can immediately schedule uplink transmission without waiting for additional confirmation, reducing latency while maintaining simple operation through the standardized feedback protocol

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The base station performs preliminary channel assessment and prepares scheduling decisions in advance based on terminal LBT results. This preliminary preparation reduces the time needed for transmission scheduling and execution, thereby reducing latency while keeping the system operation straightforward through pre-planned scheduling actions

Inventive Principle:

Principle #10Preliminary action

3Device complexity

If base station performs only independent LBT, then device complexity is reduced, but hidden node interference outside sensing range cannot be avoided

Engineering Contradiction:

Improvebase station LBT complexityVSAvoidhidden node interference

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The terminal device performs LBT and provides feedback information about the channel state to the base station. This feedback includes the terminal's LBT result and may include information about detected signals or channel conditions. The base station combines this feedback with its own independent LBT results to make a comprehensive scheduling decision, thereby detecting hidden node interference that the base station alone might miss due to sensing range limitations

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The patent merges the base station's independent LBT assessment with the terminal's LBT feedback to create a combined channel state understanding. The base station schedules uplink transmission only when both its own assessment and the terminal's reported assessment indicate the channel is clear, combining multiple sensing perspectives to avoid hidden node interference while maintaining reasonable device complexity

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS20250024496A1Close loop listen before talk for NR operation in unlicensed spectrum

Publication Date: 2025.01.16 AT&T INTELLECTUAL PROPERTY I L P

AI summary

Various embodiments disclosed herein provide for a closed loop Listen Before Talk (LBT) which is a coexistence mechanism used by wireless technologies such as Wi-Fi, to access unlicensed shared spectrum, such as the ISM UNII bands (5 GHz). The embodiments disclosed herein enable a base station to coordinate the LBT process at both the base station and a receiver in order to avoid hidden node interference where the interfering nodes are outside the sensing range of the transmitting node. The base station device can send an LBT trigger to the receiver to synchronize the clear channel assessments that are performed at each device to determine if there is any activity on the channel. The receiving device can send back a report to the base station device, and if no activity on the channel is detected, the base station device can schedule a transmission on the channel.