Cross-Subframe Scheduling for Unlicensed Carrier Reliability
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Solution Overview
Problem
Current LTE technologies face challenges in maintaining reliable downlink scheduling and HARQ feedback in unlicensed spectrum due to interference from incumbent technologies, especially in heterogeneous network deployments, where the use of unlicensed secondary carriers like LTE-U is essential for capacity augmentation but complicates interference management.
Innovation Solution
The implementation of cross-subframe and multi-subframe scheduling mechanisms for secondary carriers operating in unlicensed bands, using aligned or non-aligned subframe boundaries with primary carriers, to ensure reliable control channel reception and efficient HARQ feedback, leveraging carrier aggregation and advanced duplexing schemes like TDD and FDD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If unlicensed secondary carriers are used to augment network capacity, then network productivity is improved, but reliability of downlink scheduling and HARQ feedback deteriorates due to interference from incumbent technologies
Solution Approach 1:
The patent introduces cross-carrier scheduling as an intermediary mechanism where the primary carrier's control channel schedules downlink transmissions on the secondary carrier. This mediator approach allows the reliable licensed spectrum to protect the unlicensed spectrum, enabling the eNodeB to transmit control information on the primary carrier that references data transmissions on the secondary carrier, thereby maintaining scheduling reliability despite interference in unlicensed bands
Solution Approach 2:
The patent implements preliminary scheduling actions by transmitting downlink control information in advance on the primary carrier before the actual data transmission occurs on the secondary carrier. This allows the scheduler to prepare and allocate resources beforehand, ensuring that scheduling decisions are made while the primary carrier is still reliable, and the secondary carrier can execute these pre-planned transmissions even in interfered conditions
2Reliability
If cross-subframe scheduling is implemented for secondary carriers, then control channel reception reliability is improved, but device complexity increases
Solution Approach 1:
The patent segments the scheduling function by separating control channel transmission from data channel transmission across different carriers. The primary carrier handles control channel functions independently, while the secondary carrier handles data transmission. This segmentation allows each carrier to be optimized for its specific function, with the primary carrier ensuring reliable control information delivery regardless of secondary carrier conditions
Solution Approach 2:
The patent adds a dimensional separation by introducing cross-carrier scheduling that operates in the carrier dimension rather than just time dimension. Instead of only scheduling within the same subframe on the same carrier, the system schedules across different carriers with potentially different subframe timings, adding a carrier dimension to the scheduling approach that improves reliability by separating control and data domains
3Ease of operation
If subframe boundaries are aligned between primary and secondary carriers, then scheduling simplicity is improved, but interference mitigation capability worsens
Solution Approach 1:
The patent introduces dynamic flexibility in subframe alignment by allowing the secondary carrier to operate with different subframe boundaries than the primary carrier. The eNodeB can dynamically adjust the timing relationship between carriers based on interference conditions, enabling the system to adapt to varying interference scenarios while maintaining scheduling functionality through cross-carrier control information
Data Source
AI summary
Technology for performing downlink scheduling is disclosed. One or more subframes can be identified within a defined frame of a primary cell to perform cross-subframe scheduling for a secondary cell. The primary cell can be configured to communicate with a user equipment (UE) using a licensed band and the secondary cell can be configured to communicate with the UE using an unlicensed band. The cross-subframe scheduling can be performed for one or more downlink subframes of the secondary cell using the one or more subframes of the primary cell.