Random Access Msg3 COT Sharing to Avoid UE Category 4 LBT
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In Next Generation Wireless Communication Systems (NR-U), the random access channel (RACH) and scheduling procedures on unlicensed spectrum face challenges due to listen-before-talk (LBT) failures, leading to increased latency and resource inefficiencies, particularly in scenarios where timing alignment is not necessary, such as with stationary UEs or small cells.
Innovation Solution
Implementing a Channel Occupancy Time (COT) sharing indicator in the Random Access Response (RAR) message to allow UEs to skip Category 4 LBT for Msg3 transmissions within a shared COT period initiated by the gNB, using mechanisms like updating the RAR format to include COT sharing indicators, such as a bit, channel access type, and priority class, to facilitate efficient resource utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Category 4 LBT is performed before Msg3 transmission, then channel access reliability is improved, but transmission latency increases and resource efficiency deteriorates
Solution Approach 1:
The gNB performs Category 4 LBT and acquires channel occupancy time (COT) before the UE transmits Msg3. By preliminarily securing the channel through downlink transmission, the gNB creates a shared COT window that the UE can utilize without performing its own Category 4 LBT, thus resolving the contradiction between reliable channel access and reduced latency
Solution Approach 2:
The COT sharing indicator acts as an intermediary mechanism that transfers channel access rights from the gNB to the UE. This indicator, included in downlink messages (RAR or DCI), mediates the channel access process by informing the UE that it can transmit within the gNB's acquired COT without performing Category 4 LBT, thereby reducing latency while maintaining reliability
2Reliability
If Category 4 LBT is performed before Msg3 transmission, then channel access reliability is improved, but energy consumption increases
Solution Approach 1:
The gNB performs the energy-intensive Category 4 LBT operation before the UE transmits Msg3. By preliminarily acquiring channel occupancy through downlink transmission, the gNB eliminates the need for the UE to perform its own Category 4 LBT, thus conserving UE battery energy while maintaining channel access reliability
Solution Approach 2:
The COT sharing indicator serves as an intermediary that transfers channel access permissions from gNB to UE. This mechanism allows the UE to skip energy-consuming LBT operations by relying on the gNB's previously acquired COT, effectively reducing UE energy consumption while preserving reliable channel access
3Productivity
If COT sharing indicator is included in RAR message, then Msg3 transmission efficiency is improved, but message format complexity increases
Solution Approach 1:
The COT sharing indicator is designed to be a versatile mechanism that can be integrated into existing downlink message structures (RAR or DCI). By making the indicator adaptable to different message formats and transmission scenarios, the solution improves Msg3 transmission efficiency without significantly increasing overall system complexity
Solution Approach 2:
The COT sharing indicator is applied selectively based on specific transmission conditions. The indicator is only included when COT sharing is applicable (e.g., when the gNB has acquired COT and wants to share it with the UE for Msg3 transmission), allowing efficient Msg3 transmission in suitable scenarios while maintaining simple message formats in other cases
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
A method of operating a user equipment, UE, in a wireless communication system includes receiving (802) a first random access procedure message from a base station, the first random access procedure message containing a channel occupancy time, COT, sharing indicator that indicates a shared COT period associated with the first random access procedure message, and transmitting (804) a second random access procedure message to the base station within the shared COT period. A method of operating a base station includes transmitting (902) a first random access procedure message to a user equipment, UE, the first random access procedure message containing a channel occupancy time, COT, sharing indicator that indicates a shared COT period associated with the first random access procedure message, and receiving (904) a second random access procedure message from the UE within the shared COT period.