Downlink Control Information Scheduling for MTC Coverage
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Solution Overview
Problem
Current LTE systems face challenges in supporting low-end Machine-Type Communications (MTC) devices deployed in challenging locations, such as deep inside buildings, due to significant penetration losses and the need for efficient scheduling of downlink control information (DCI) to ensure reliable data transmission.
Innovation Solution
The proposed solution involves scheduling the downlink control information such that the downlink grant ends last among all control messages in a search space, ensuring that all control messages are received before data transmission begins, and allowing for potential frequency changes only after all DCI has been transmitted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If downlink control subframes are repeated multiple times to improve coverage, then coverage improvement is achieved, but scheduling complexity increases and data transmission efficiency decreases
Solution Approach 1:
The patent applies preliminary action by determining the timing of data subframes in advance based on the repetition factor of downlink control subframes. The eNB configures the UE with a repetition factor and uses this to calculate when data subframes will be transmitted, allowing the UE to prepare for data reception without waiting to receive all control repetitions. This resolves the contradiction by maintaining reliable coverage through repetitions while improving scheduling efficiency through pre-determined timing.
Solution Approach 2:
The patent introduces a new parameter - the repetition factor - that explicitly defines the number of times downlink control subframes are repeated. By making this parameter configurable and using it to determine data subframe timing, the system can adapt to different coverage requirements while maintaining efficient scheduling. The repetition factor becomes a key parameter that links control channel reliability to data channel timing, resolving the contradiction between coverage and scheduling complexity.
2Reliability
If data transmission starts only after all control repetitions are transmitted, then control information reliability is ensured, but data transmission delay increases
Solution Approach 1:
The patent applies preliminary action by having the UE determine data subframe timing in advance based on the configured repetition factor. Instead of waiting to receive all control repetitions before starting data reception, the UE uses the repetition factor to calculate when data subframes will occur and prepares accordingly. This can be expressed as: data_subframe_timing = control_subframe_timing + (repetition_factor - 1) * control_subframe_duration. This resolves the contradiction by ensuring control information reliability through repetitions while minimizing data transmission delay through pre-determined timing.
3Productivity
If multiple downlink control messages are transmitted simultaneously to support efficient system operation, then system efficiency improves, but the ability to determine scheduling order becomes more complex
Solution Approach 1:
The patent introduces the repetition factor as a controlling parameter that simplifies scheduling order determination. By configuring the repetition factor in advance, the eNB establishes a clear timing relationship between control and data subframes. The UE uses this parameter to automatically determine when to expect data subframes relative to control subframe repetitions, eliminating the need for complex real-time scheduling order analysis. This resolves the contradiction by enabling efficient simultaneous transmission of multiple control messages while maintaining simple scheduling order determination through parameter-based timing relationships.
Data Source
AI summary
Apparatuses and methods provide for scheduling downlink control information in a wireless network. The apparatuses and methods may determine at least one control message for a user equipment and a downlink grant to be scheduled, and schedule transmission of one of the at least one control message with the downlink grant to precede transmission of related data on a downlink data channel. The apparatuses and methods may alternatively schedule a control message other than downlink grant for a user equipment, determine a downlink grant to be scheduled, and schedule a control message with the downlink grant to end last among all control messages in a search space. The apparatuses and methods may further alternatively schedule control messages for a user equipment, including one control message with a downlink grant and scheduled to end at the same time as or a later time than other control messages in a search space.