Small Data Transmission in RRC Inactive With Timing Advance Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing communication systems face issues with frequent Idle-Connected-Idle transitions for small data transmission in RRC_INACTIVE state, leading to increased network signaling load, latency, and power consumption, as well as challenges with uplink timing alignment maintenance.
Innovation Solution
A method for small data transmission (SDT) in RRC_INACTIVE state involving the use of a Timing Advance Command MAC CE to manage uplink timing alignment by starting or restarting the Timing Alignment Timer (TAT) upon receiving a TA command, allowing data transmission while TAT is running, and employing various SDT procedures such as 2-step RACH, 4-step RACH, and configured grant-based SDT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE transits from RRC_IDLE to RRC_CONNECTED state for small data transmission, then the data can be transmitted reliably, but the network signaling load increases and latency increases
Solution Approach 1:
The network pre-configures SDT parameters and resources for RRC_INACTIVE state before the UE needs to transmit data. This includes pre-configuring timing advance values, uplink grants, and other transmission parameters so that when small data needs to be sent, the UE can immediately use these pre-configured resources without transitioning to RRC_CONNECTED, thereby reducing latency while maintaining reliable transmission
2Productivity
If the UE frequently transitions between RRC_IDLE and RRC_CONNECTED states for small data transmission, then data transmission can be performed, but power consumption increases
Solution Approach 1:
The UE maintains RRC_INACTIVE state continuously for small data transmissions by using pre-configured uplink resources and timing advance values. This eliminates the need to repeatedly transition to and from RRC_CONNECTED state, allowing the UE to stay in the lower-power RRC_INACTIVE state while still performing data transmissions, thus significantly reducing power consumption
3Device complexity
If the UE transmits data in RRC_INACTIVE state without timing alignment maintenance, then signaling overhead is reduced, but uplink synchronization is lost
Solution Approach 1:
The UE autonomously maintains uplink timing alignment in RRC_INACTIVE state by using pre-configured timing advance values and monitoring timing alignment timers. When the timing alignment timer expires or timing deviation is detected, the UE can perform self-correction using pre-configured uplink resources or initiate a timing advance request, thereby maintaining synchronization without requiring continuous network signaling intervention
Data Source
AI summary
A method for small data transmission (SDT) in RRC_INACTIVE state and related devices are provided. The method includes receiving a first SDT Timing Advance Command Media Access Control (MAC) Control Element (CE) from the network; starting or restarting Timing Alignment Timer (TAT) upon the reception of a Timing Advance (TA) command carried by the first SDT Timing Advance Command MAC CE, for keeping uplink (UL) time alignment during SDT in RRC_INACTIVE state; and when UL data arriving in UE TX buffer, transmitting SDT to the network while the TAT is running. With this method, UL synchronization/timing maintenance in RRC_INACTIVE state is realized.