Uplink Power Control in RACH-less Handover

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Solution Overview

Problem

In LTE systems, the RACH-less handover procedure lacks a method for controlling initial uplink power in PUSCH due to the skipped RACH procedure, making it impossible to refer to PRACH preamble power and total power ramp.

Innovation Solution

A method where a UE receives an RRC connection reconfiguration message with an uplink grant from a source base station, transmits an RRC connection reconfiguration complete message with initial power, receives NACK and ramping information from a target base station, and ramps the transmission power for retransmission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of time

If RACH procedure is skipped in handover to reduce handover delay, then handover interrupt time is minimized, but initial uplink power control in PUSCH becomes impossible

Engineering Contradiction:

Improvehandover interrupt timeVSAvoidpower control mechanism complexity

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The source base station pre-calculates and determines the initial uplink power for the PUSCH transmission before the handover occurs. This preliminary power determination is included in the handover command, allowing the UE to transmit the RRC connection reconfiguration complete message to the target base station without needing to perform a RACH procedure or perform power control adjustments at the target side.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The power control function is extracted from the target base station and relocated to the source base station. The source base station calculates the appropriate initial power level based on pre-handover measurements and conditions, removing the need for the target base station to perform power control operations after handover.

Inventive Principle:

Principle #2Taking out (Extraction)

2Reliability

If RACH procedure is performed in handover, then uplink power can be controlled through PRACH preamble power and total power ramp, but handover delay time increases

Engineering Contradiction:

Improveuplink power control reliabilityVSAvoidhandover delay time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

All necessary power control parameters and initial power levels are determined in advance by the source base station before the handover is executed. The UE receives these parameters in the handover command and can immediately transmit to the target base station without performing RACH procedures for power control.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent skips the traditional RACH procedure entirely for power control purposes. By using pre-determined power levels from the source base station, the UE can directly transmit the RRC connection reconfiguration complete message on PUSCH to the target base station, rushing through the handover process without the time-consuming RACH steps.

Inventive Principle:

Principle #21Skipping (Rushing through)

Data Source

PatentUS10772045B2Method and apparatus for controlling uplink power in RACH-less handover

Publication Date: 2020.09.08 LG ELECTRONICS INC

AI summary

Provided are a method for a terminal controlling uplink power in a rando access channel-less (RACH-less) handover, and an apparatus for supporting same. The method may comprise the steps of: receiving, from a source base station, an RRC connection reconfiguration message including an uplink grant; transmitting, to a target base station using a first transmission power, an RRC connection reconfiguration complete message, on the basis of the uplink grant; receiving, from the target base station, a NACK corresponding to the RRC connection reconfiguration complete message; ramping the first transmission power to a second transmission power; and transmitting the RRC connection reconfiguration complete message using the ramped second transmission power.