NBIoT NPDCCH Monitoring Windows for Long-RTD NTN Power Saving
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Solution Overview
Problem
In Non-Terrestrial Networks (NTN), the long receiver and transmitter distance (RTD) in Narrowband Internet-of-Things (NBIoT) leads to unnecessary power consumption due to extended monitoring of control signals, as the timing relationships are affected by the extended HARQ process number, causing inefficient power usage in UE specific search spaces.
Innovation Solution
Introduce a gap period during which the UE does not monitor control signals, positioning the NPDCCH monitoring window at the end of the last time slot for receiving the first control signal and before the data transmission, thereby optimizing power consumption by skipping unnecessary monitoring during this period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE monitors NPDCCH continuously in NTN with long RTD, then control signal reception reliability is maintained, but power consumption increases due to extended monitoring period
Solution Approach 1:
The monitoring period is segmented into two parts: a first monitoring period starting from a first monitoring occasion after receiving first downlink data, and a second monitoring period starting from a second monitoring occasion after receiving second downlink data. The second monitoring period is shorter than the first, allowing the UE to reduce monitoring duration and power consumption while maintaining reliability for HARQ-ACK feedback.
Solution Approach 2:
The monitoring duration is made dynamic rather than fixed. The UE adapts the monitoring period length based on the specific downlink data reception timing and HARQ-ACK feedback requirements, enabling shorter monitoring periods when possible to reduce power consumption while maintaining necessary reliability.
2Loss of time
If the UE extends NPDCCH monitoring to cover long RTD periods in NTN, then timing relationship coverage is improved, but unnecessary power wastage occurs during extended delay periods
Solution Approach 1:
Instead of monitoring NPDCCH for the entire extended RTD period, the UE performs partial monitoring only during necessary time windows when control signals are actually expected. The monitoring occasions are strategically positioned to cover only the essential timing relationships required for HARQ-ACK feedback, avoiding excessive monitoring during periods when no control signals are transmitted.
3Reliability
If the UE monitors NPDCCH in every subframe to ensure no control signal is missed, then control signal detection completeness is improved, but device complexity and processing load increase
Solution Approach 1:
The continuous monitoring requirement is segmented into discrete monitoring occasions rather than requiring monitoring in every subframe. The UE only needs to check for NPDCCH at specific predefined occasions, significantly reducing processing load while maintaining detection completeness for all relevant control signals.
Solution Approach 2:
Instead of continuous monitoring, the UE performs periodic monitoring at specific monitoring occasions determined by the monitoring pattern. This periodic approach reduces the frequency of monitoring operations while ensuring that all necessary control signals are detected at their expected transmission times.
Data Source
AI summary
Methods and apparatuses for monitoring NPDCCH in NBIoT are disclosed. A method comprises receiving a first control signal scheduling a data transmission; and monitoring a second control signal from a start time slot to an end time slot, wherein the start time slot is a gap period behind the last time slot for receiving the first control signal, and the end time slot is a time period ahead of the first time slot for the data transmission.