NR-Light UE LBT Configuration via MAC-CE
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Solution Overview
Problem
NR-light user equipment (UEs) experience increased overhead and power consumption due to monitoring downlink control channels for dynamic scheduling, especially when communicating in unlicensed spectra, where listen-before-talk (LBT) uncertainty adds to the burden.
Innovation Solution
NR-light UEs are configured to monitor for physical downlink shared channel (PDSCH) transmissions over periodically scheduled resources without a corresponding downlink grant, receiving a medium access control (MAC) control element that indicates a channel access configuration for unlicensed spectrum access, allowing them to transmit acknowledgments without continuous grant monitoring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If NR-light UEs continuously monitor downlink control channels for dynamic scheduling, then scheduling responsiveness is improved, but overhead and power consumption increase
Solution Approach 1:
The patent implements periodic monitoring of downlink control channels instead of continuous monitoring. UEs are configured to monitor PDCCH at specific periodic intervals determined by RRC configuration, which reduces power consumption while maintaining adequate scheduling responsiveness. This periodic action allows UEs to enter low-power states between monitoring occasions.
Solution Approach 2:
The patent uses RRC-configured grants (Type 1 and Type 2) to pre-allocate uplink resources in advance without requiring dynamic scheduling. Type 1 grants provide resources without PDCCH indication, while Type 2 grants provide resources with PDCCH indication. This preliminary allocation eliminates the need for continuous control channel monitoring for uplink scheduling, significantly reducing power consumption while maintaining scheduling capability.
2Speed
If NR-light UEs continuously monitor downlink control channels for dynamic scheduling, then scheduling responsiveness is improved, but overhead increases
Solution Approach 1:
RRC-configured grants pre-allocate uplink resources through higher-layer signaling rather than dynamic PDCCH scheduling. Type 1 grants allocate resources directly via RRC configuration without requiring PDCCH downlink grants, while Type 2 grants use PDCCH for activation but with pre-configured parameters. This reduces control channel overhead and signaling burden on the network.
3Reliability
If LBT procedures are performed for each uplink transmission in unlicensed spectrum, then channel access reliability is improved, but communication overhead and access delay increase
Solution Approach 1:
The base station performs LBT procedures in advance to acquire channel occupancy time (COT) before scheduling uplink transmissions. When the base station has acquired COT, it can schedule multiple uplink transmissions within this granted period without requiring UEs to perform separate LBT for each transmission. This preliminary channel acquisition reduces access delay while maintaining reliability through the base station's superior LBT capability.
Solution Approach 2:
A single LBT procedure performed by the base station serves multiple uplink transmission opportunities within the acquired COT. The base station's channel access grants universal permission for multiple UEs to transmit uplink data without each UE performing individual LBT, reducing overall access delay and improving spectral efficiency while maintaining channel access reliability.
Data Source
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AI summary
Methods, systems, and devices for wireless communications are described. A user equipment may monitor for a transmission over a set of periodically scheduled resources (e.g., semi-persistently scheduled resources)) of a downlink shared channel in an unlicensed spectrum. The user equipment may receive the transmission, where the transmission indicates a channel access configuration (e.g., a listen-before-talk configuration) for accessing the unlicensed spectrum. In some cases, the transmission may include a medium access control (MAC) control element (MAC-CE) that indicates the channel access configuration. The transmission may additionally indicate at least one uplink channel over which the user equipment may transmit a message and/or a channel occupancy time associated with a successful acquisition of the unlicensed spectrum by the base station. The user equipment may transmit a message (e.g., an acknowledgement) based on the channel access configuration.