Narrowband Reference Signal Transmission on Non-Anchor Carriers
Solution Overview
Problem
Current 3GPP NB-IoT specifications do not allow for reliable link quality measurements on non-anchor carriers due to sporadic transmission of narrowband reference signals (NRS), making it impractical to assess link quality, especially when the anchor carrier is heavily loaded while the non-anchor carrier is lightly loaded or vice versa.
Innovation Solution
Implementing a method where a processor in a network node indicates and transmits NRSs in specific paging frames or occasions for subsets of UE groups, allowing NRS transmission even when there is no paging, and using an N-bit bitmap to configure which UE groups receive NRSs, thereby ensuring consistent NRS availability for link quality estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If NRS transmission is only sent when data or signaling is transmitted on non-anchor carriers, then NRS interference on other cells is minimized, but link quality measurements become unreliable due to sporadic NRS availability
Solution Approach 1:
The network node transmits NRS in paging frames before actual data transmission occurs. By performing the reference signal transmission in advance during designated paging occasions, the system ensures NRS availability for link quality measurements without waiting for data traffic, thereby resolving the sporadic availability issue while maintaining interference minimization through targeted transmission timing
Solution Approach 2:
NRS is transmitted periodically in specific paging frames according to a configured schedule, regardless of whether data transmission occurs. This periodic transmission pattern ensures consistent NRS availability for measurements while limiting overall transmission instances to reduce inter-cell interference, directly addressing the contradiction between measurement reliability and interference minimization
2Reliability
If NRS is transmitted continuously on non-anchor carriers, then link quality measurements become reliable, but NRS overhead and inter-cell interference increase
Solution Approach 1:
Instead of uniform continuous NRS transmission across all time instances, the system provides NRS transmission locally at specific paging frames and occasions where measurements are needed. This localized approach ensures measurement reliability at critical moments while avoiding unnecessary NRS transmissions during other periods, thereby reducing overall overhead and energy consumption
Solution Approach 2:
The system implements partial NRS transmission by sending reference signals only during specific paging-related time resources rather than continuously. This partial action provides sufficient NRS for measurement purposes without the excessive transmission that would occur with continuous sending, achieving an optimal balance between measurement reliability and overhead reduction
Data Source
AI summary
Various examples and schemes pertaining to narrowband reference signal (NRS) transmission on non-anchor carriers in narrowband IoT (NB-IoT) are described. A wireless network indicates a subset of one or more paging groups of user equipment (UEs) among a plurality of UEs in an NB-IoT cell. The wireless network then transmits one or more narrowband reference signals (NRSs) in one or more paging frames or one or more paging occasions associated with the subset of one or more paging groups.