UE Triggered Handover for Extended C-DRX Power Savings

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Solution Overview

Problem

In wireless communication devices, longer Connected Discontinuous-Reception (C-DRX) cycles in LTE connected mode lead to higher handover failure rates due to weakened signal strength during the extended power-down periods, causing issues with decoding neighbor base station measurements and resulting in radio link failures.

Innovation Solution

User Equipment (UE) devices proactively initiate a handover procedure by reestablishing a connection with a neighboring base station determined to have better radio quality, rather than relying on a measurement report to the current serving cell, thereby avoiding additional Radio Resource Control (RRC) signaling and enabling a longer C-DRX cycle for power savings.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If the C-DRX cycle is extended to save power, then battery life is improved, but handover failure rate increases

Engineering Contradiction:

Improvebattery lifeVSAvoidhandover failure rate

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The UE performs measurements and identifies a target base station before the serving base station becomes too weak. By having the target base station ready to receive the RRC connection reestablishment message in advance, the handover process is accelerated and made more reliable even with extended C-DRX cycles.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The UE autonomously selects a target base station based on measurement results and directly initiates connection reestablishment with that target without waiting for network-triggered handover. This self-service approach allows the UE to proactively manage handover timing and reduce dependency on network responses during extended sleep periods.

Inventive Principle:

Principle #25Self-service

2Use of energy by moving object

If the C-DRX cycle is extended to save power, then power consumption is reduced, but signal strength weakens

Engineering Contradiction:

Improvepower consumptionVSAvoidsignal strength

Core Design Contradiction:

Use of energy by moving objectVSStrength

Solution Approach 1:

The UE measures and identifies a target base station with sufficient signal strength before the current serving base station's signal degrades below usable levels. This preliminary identification ensures that when handover is triggered, the target base station can immediately provide strong signal coverage.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The UE skips the traditional measurement report and network-decision phase by directly initiating RRC connection reestablishment with the pre-identified target base station. This rushed-through approach minimizes the time spent in a weak signal state and quickly transitions to a base station with adequate signal strength.

Inventive Principle:

Principle #21Skipping (Rushing through)

3Device complexity

If traditional handover procedure is used with measurement reports, then network control is maintained, but additional RRC signaling increases

Engineering Contradiction:

ImproveRRC signalingVSAvoidnetwork control

Core Design Contradiction:

Device complexityVSExtent of automation

Solution Approach 1:

Instead of the UE reporting measurements to the network and waiting for handover commands, the UE inverts the process by directly initiating connection reestablishment with the target base station. This inversion eliminates multiple RRC signaling messages while the network maintains awareness through the reestablishment procedure.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The invention extracts and removes the intermediate measurement report and network handover decision steps from the traditional handover procedure. By taking out these signaling-heavy steps and replacing them with a direct RRC connection reestablishment to the target base station, the overall signaling complexity is reduced.

Inventive Principle:

Principle #2Taking out (Extraction)

Data Source

PatentUS10412651B2User equipment triggered handover with long connected-discontinuous-reception cycle in connected mode

Publication Date: 2019.09.10 APPLE INC

AI summary

While operating in connected discontinuous reception (C-DRX) mode, a wireless communication device may initiate handover operations when a neighboring base station is determined by the wireless communication device to be a better serving cell than a base station operating as the current serving cell for the wireless communication device. Instead of transmitting a measurement report to the current serving cell, the wireless communication device may select one of the neighboring base stations as the new serving cell, responsive to measurements of the current serving cell and the neighboring cells performed by the wireless communication device during the on-duration of the C-DRX cycle. This enables a longer C-DRX cycle, which leads to the wireless communication device saving more power during non-real-time sensitive background data transmissions, while also avoiding higher handover failure rates and extra Radio Resource Control signaling that may need to be performed as a result of radio link failure.