Radio Link Monitoring in Small Cell Networks

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Solution Overview

Problem

In LTE small cell networks, radio link monitoring (RLM) and radio link failure (RLF) detection is limited to primary serving cells, leaving secondary serving cells unmonitored, which can lead to unknown link failures in drift eNBs, affecting UE transmission, power consumption, and user experience due to latency and overhead in information exchange between anchor and drift eNBs.

Innovation Solution

Implementing RLM/RLF procedures in both anchor and drift eNBs, where the UE performs monitoring across all serving cells, including secondary cells, and sends RLF indicators for handover, allowing the anchor eNB to reconfigure connections and switch to a drift eNB, ensuring timely and efficient handling of link failures.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If RLM/RLF detection is limited to primary serving cells only, then the system complexity is reduced and information exchange overhead between anchor and drift eNBs is minimized, but link failures in secondary serving cells remain undetected causing transmission errors and degraded user experience

Engineering Contradiction:

Improvelink failure detection accuracyVSAvoidmonitoring system complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent segments the monitoring function by introducing separate RLM/RLF detection mechanisms for primary serving cells and secondary serving cells. The UE performs independent monitoring on PCELL through standard RLM procedures and on SCELLs through additional RLM procedures configured by the network, allowing failures to be detected in both cell types without requiring a complete redesign of the monitoring system

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies preliminary action by configuring the UE to perform RLM on secondary serving cells before actual link failures occur. The network configures RLM parameters and thresholds in advance, enabling the UE to proactively detect deteriorating link quality on SCELLs and trigger RLF detection before transmission errors occur

Inventive Principle:

Principle #10Preliminary action

2Reliability

If RLM is performed on all serving cells including secondary cells, then link failure detection coverage is improved, but power consumption increases due to additional monitoring activities

Engineering Contradiction:

Improvecoverage of link failure detectionVSAvoidUE power consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The patent applies local quality by making RLM configuration cell-specific rather than uniform across all cells. The network configures RLM parameters, thresholds, and monitoring requirements individually for each secondary serving cell based on its importance, channel conditions, and traffic requirements. This allows the UE to perform intensive monitoring only on critical SCELLs while reducing or skipping monitoring on less important cells, optimizing the trade-off between detection coverage and power consumption

Inventive Principle:

Principle #3Local quality

3Reliability

If information exchange between anchor eNB and drift eNBs is implemented for RLF handling, then coordinated failure recovery is improved, but latency and signaling overhead increase

Engineering Contradiction:

Improvecoordinated failure recoveryVSAvoidfailure handling latency

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent merges the RLF detection and handling functions at the UE side for both anchor and drift eNBs. The UE independently monitors RLF conditions on cells from both eNBs and can trigger RLF procedures without requiring continuous coordination with both eNBs. This reduces the need for back-and-forth signaling between anchor and drift eNBs while maintaining coordinated recovery through the existing RRC connection with the anchor eNB

Inventive Principle:

Principle #5Merging (Combining)

Data Source

PatentUS9794839B2Mechanism for radio link monitoring and radio link failure handling in small cell networks

Publication Date: 2017.10.17 INTELLECTROS LLC

AI summary

A method of radio link monitoring (RLM) and radio link failure (RLF) handling over a small cell network is proposed. In a wireless network, a user equipment (UE) establishes a radio resource control (RRC) connection with a base station (eNB), which is UE anchor. The UE applies carrier aggregation for multiple component carriers (CCs) configured as multiple serving cells. The aggregated serving cells are served by the anchor eNB and other drift eNB(s). The UE performs RLM/RLF over PCELL and SCELL belonging to corresponding cell groups. When RLF happens in a serving cell, the UE and the eNB apply certain actions over the serving cell or all serving cells in the group. RLF procedures in anchor eNB and in drift eNB are proposed. Both UE side and network side behaviors are included.