RACH-less Handover via Target Base Station MAC Message
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Solution Overview
Problem
Conventional handover procedures in wireless communications require unnecessary time due to the need for Timing Advance (TA) determination after handover initiation, and RACH-less handovers lack a method to synchronize uplink transmissions without the Random-Access Channel (RACH) procedure.
Innovation Solution
A UE device requests a Media Access Control (MAC) message from a target base station, which includes TA information, using an RRC Connection Reconfiguration message, allowing the UE device to determine when the handover is complete without performing the RACH procedure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RACH procedure is performed during handover to determine Timing Advance, then uplink synchronization is achieved, but handover delay increases
Solution Approach 1:
The target base station pre-calculates and stores Timing Advance values based on historical data and path loss estimates before the handover is executed. When handover occurs, the pre-calculated TA value is immediately provided to the UE without requiring RACH procedure, thus achieving uplink synchronization while reducing handover delay
Solution Approach 2:
The patent enables skipping the RACH procedure by providing TA information through alternative means (pre-calculation, path loss estimation, or direct signaling from source base station). This allows the system to rush through the handover process by eliminating the time-consuming RACH steps while still achieving the necessary uplink synchronization
2Productivity
If the RACH procedure is skipped in RACH-less handover to reduce delay, then handover speed increases, but a method to synchronize uplink transmissions is lacking
Solution Approach 1:
The patent introduces an intermediary mechanism where the target base station uses path loss estimation and historical data to calculate TA values, or where the source base station directly provides TA information to the target base station. This intermediary approach enables RACH-less handover while maintaining uplink synchronization through alternative TA determination methods
3Measurement precision
If TA determination is performed after handover initiation in conventional systems, then accurate Timing Advance is achieved, but unnecessary time is consumed
Solution Approach 1:
The target base station performs TA calculation in advance using available information such as path loss estimates and historical data before the handover is executed. This preliminary TA determination eliminates the need for post-handover TA calculation, reducing handover time while maintaining accuracy through sophisticated estimation algorithms
Data Source
AI summary
In order to perform a RACH-less handover from a source base station to a target base station, a UE device generates a request that the target base station is to send a Media Access Control (MAC) message to the UE device. The request can be sent with a Radio Resource Control (RRC) Connection Reconfiguration Complete message. Alternatively, an RRC message sent from a UE device functions as an implicit request that the target base station is to send a MAC message to the UE device. The request can also be configured to specify a particular MAC Control Element that the target base station should send. The target base station transmits the requested MAC message, along with TA information, if required. The UE device determines when the handover has been completed, based at least partially on when the requested MAC message is received from the target base station.