RACH-less Mobility Beam Adaptation for Handover Reliability
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Solution Overview
Problem
In wireless communication systems, particularly in 5G New Radio (NR), the pre-allocated beams for random access channel (RACH)-less mobility can become outdated due to fast user equipment (UE) movement or narrow beamwidth, leading to frequent handover failures, as the pre-allocated uplink resources may not always ensure successful transmission.
Innovation Solution
The method involves a user equipment (UE) receiving a mobility command message with pre-allocated uplink resources and beams, synchronizing with a target cell, and performing uplink transmission using the pre-allocated beams. If the quality of the pre-allocated beams does not meet a criterion, the UE falls back to a random access procedure to ensure successful handover, thereby reducing handover failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If pre-allocated beams are used for RACH-less mobility, then handover latency is reduced, but handover reliability deteriorates due to fast UE movement or narrow beamwidth causing outdated beam allocation
Solution Approach 1:
The patent makes the beam selection dynamic by allowing the UE to adaptively choose from multiple pre-allocated beam pairs based on real-time channel conditions. Instead of using a static pre-allocated beam, the UE dynamically selects the most suitable beam pair from the pre-configured options, resolving the contradiction between fast handover (static allocation) and reliable handover (adaptive selection).
Solution Approach 2:
The patent changes the parameter of beam selection from fixed to variable by introducing multiple pre-allocated beam pairs with different spatial directions. The UE can change which beam pair to use based on channel quality measurements, allowing the system to maintain low latency while adapting to fast movement conditions through parameter variation.
2Power
If narrow beams are used for precise directional transmission, then transmission gain is improved, but beam outdatedness increases due to UE movement making pre-allocated resources obsolete
Solution Approach 1:
The patent segments the single narrow beam into multiple narrow beams (multiple beam pairs) covering different spatial directions. Each beam maintains its high directional gain, but the UE has multiple segmented options to choose from, reducing the risk that any single beam becomes outdated due to UE movement.
Solution Approach 2:
The UE dynamically selects among the segmented beams based on real-time channel conditions. This dynamic selection allows the system to maintain the transmission gain benefits of narrow beams while adapting to UE movement by switching between different beam segments as needed.
3Productivity
If pre-allocated uplink resources are assigned without RACH procedure, then handover speed is increased, but transmission success rate decreases when pre-allocated beams become outdated
Solution Approach 1:
The patent applies preliminary action by pre-allocating multiple beam pairs before handover, but unlike conventional approaches, these pre-allocated resources include multiple directional options. The UE uses these pre-prepared resources immediately (maintaining speed) but can select among multiple pre-configured beams (improving success rate).
Solution Approach 2:
The patent changes the parameter of beam diversity from single to multiple by configuring multiple pre-allocated beam pairs with different spatial parameters. This allows the UE to maintain fast handover using pre-allocated resources while improving transmission success rate through parameter variation in beam selection.
Data Source
AI summary
A method and apparatus for supporting a random access channel (RACH)-less mobility with pre-allocated beams in a wireless communication system is provided. A user equipment (UE) receives a mobility command message which includes information on a pre-allocated UL resource for UL transmission with pre-allocated beams, synchronizes to a target cell, and performs the UL transmission to the target cell via the pre-allocated beams based on the pre-allocated UL resource for UL transmission to transmit a mobility complete message via a UL grant. If the UL transmission fails, the UE may perform RACH procedure.