LBT Priority Class Assignment for Uplink Grant Transmission
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In Licensed-Assisted Access (LAA) LTE systems, the double Listen-Before-Talk (LBT) protocol at both eNB and UE leads to UL transmission starvation due to prolonged LBT processes, especially when coexisting with Wi-Fi, and the 4-subframe processing delay restricts initial UL grants, degrading UL performance.
Innovation Solution
Assigning a high LBT priority class to UL grants and enabling cross-TxOP scheduling with indications for the type of LBT to perform, allowing UL transmissions to occur outside the initial TxOP and reducing the need for double LBT processes, thereby alleviating UL starvation and enhancing UL performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If double LBT protocol is performed at both eNB and UE, then coexistence with Wi-Fi is improved, but UL transmission opportunities are reduced due to prolonged LBT processes
Solution Approach 1:
The eNB performs LBT before transmitting the UL grant to the UE. By doing the LBT operation in advance (preliminarily) before the UL transmission is scheduled, the system reduces the total number of LBT operations needed. The UL grant includes an indication of the LBT priority class that the UE should use, allowing the UE to skip performing its own separate LBT operation or perform a simplified version, thus resolving the contradiction between ensuring coexistence (through LBT) and maintaining UL transmission opportunities (by reducing LBT overhead).
Solution Approach 2:
Different LBT priority classes are assigned to different UL grants based on local conditions and requirements. The eNB can configure different LBT priority classes (e.g., class 1 with shortest defer period, class 4 with longest defer period) for different UEs or different UL transmissions. This localized differentiation allows critical UL transmissions to use shorter LBT processes while non-critical transmissions use longer LBT processes, thereby maintaining both coexistence and UL transmission opportunities.
2Reliability
If 4-subframe processing delay is applied to restrict initial UL grants, then downlink transmission control is improved, but UL performance is degraded
Solution Approach 1:
The invention changes the parameter of LBT defer period based on the LBT priority class assigned to the UL grant. Instead of using a fixed 4-subframe processing delay for all UL grants, the system dynamically adjusts the LBT defer period parameter according to the priority class. High-priority UL grants (class 1) use shorter defer periods while low-priority grants (class 4) use longer defer periods. This parameter change resolves the contradiction by allowing flexible control of DL transmissions while improving UL performance through reduced delays when appropriate.
3Productivity
If LBT priority class is assigned to UL grant, then UL transmission efficiency is improved, but LBT protocol complexity increases
Solution Approach 1:
The eNB performs the LBT operation and determines the appropriate LBT priority class in advance before scheduling the UL transmission. The UL grant includes an embedded indication of the LBT priority class that the UE should use. This preliminary action transfers the complexity of LBT priority determination to the eNB (which has better channel knowledge and control capabilities) while simplifying the UE's task to merely following the indicated priority class, thus improving UL transmission efficiency without excessively increasing overall system complexity.
Solution Approach 2:
The UL grant acts as an intermediary that carries the LBT priority class indication from the eNB to the UE. Instead of requiring the UE to independently determine LBT parameters or implement complex LBT decision logic, the system uses the UL grant as a mediator to convey the appropriate LBT priority class. This intermediary approach simplifies the LBT protocol implementation at the UE while maintaining efficient UL transmissions, resolving the contradiction between efficiency and complexity.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A network device (e.g., an evolved Node B (eNB), user equipment (UE) or the like) can operate to enable the assigning of different listen-before-talk (LBT) priority classes or levels within a same DL transmission for scheduling UL transmissions, either in the same transmission opportunity as the UL grant or another transmission opportunity outside of the UL grant. Other data elements or traffic of the DL transmission can be multiplex with the UL grant, such as LBT parameters or a PUSCH, while each can be separately and selectively assigned different or equivalent LBT priority classes. The device can operate to process or generate communications on an unlicensed band or a licensed band in response to UL grants and indications provided via a DL transmission on a first transmission opportunity.