SIB1-NB Repetition Subframe Mapping in NB-IoT
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Solution Overview
Problem
Legacy NB-IoT wireless devices in Rel-13 and Rel-14 are unaware of additional subframes used for SIB1-NB transmission, leading to interference with downlink channels and inefficient resource utilization due to high overhead in valid/invalid subframe bitmap configuration and limited scheduling information capacity in the MIB-NB.
Innovation Solution
A predetermined mapping or pattern for additional SIB1-NB subframes is signaled using the valid/invalid subframe bitmap, allowing legacy devices to omit monitoring during invalid subframes, while new devices can reinterpret these subframes for additional SIB1-NB repetitions, and utilize spare subframes for other DL channels, with efficient signaling using a small bitmap or index value in the MIB-NB.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional subframes are used for SIB1-NB transmission to improve acquisition performance, then system information acquisition performance is improved, but legacy wireless devices cannot correctly identify these subframes leading to interference with downlink channels
Solution Approach 1:
The patent introduces an intermediary mechanism (valid subframe bitmap and repetition subframe indication) that mediates between the new system requirement for additional SIB1-NB transmissions and the legacy device's inability to recognize these subframes. This intermediary signaling allows legacy devices to correctly identify and avoid interfering with downlink channels while new devices can utilize the additional subframes for improved acquisition performance
2Loss of information
If valid/invalid subframe bitmap configuration is used to indicate subframes for SIB1-NB repetitions, then subframe identification is improved, but signaling overhead increases due to the length of the bitmap
Solution Approach 1:
The patent segments the subframe indication into two parts: a valid subframe bitmap that identifies which subframes are valid for downlink transmissions, and a separate repetition subframe indication that specifies which of those valid subframes are used for SIB1-NB repetitions. This segmentation allows for more efficient signaling by only indicating the necessary subframes rather than using a complete bitmap for all subframes
Solution Approach 2:
The patent applies local quality by making the subframe indication specific and localized to only the subframes that are actually used for SIB1-NB repetitions, rather than using a general-purpose bitmap for all subframes. This allows the signaling to be optimized for the specific need of indicating repetition subframes, reducing overall overhead
3Loss of information
If scheduling information for additional SIB1-NB subframes is signaled in MIB-NB, then scheduling information is provided, but the limited size of MIB-NB restricts the amount of information that can be signaled
Solution Approach 1:
The patent extracts the repetition subframe indication from the MIB-NB and places it in the SIB1-NB message. This extraction allows the MIB-NB to maintain its limited size while still providing the necessary scheduling information for additional SIB1-NB subframes. The MIB-NB contains only the essential scheduling parameters, while the more detailed repetition subframe information is provided in the SIB1-NB
Data Source
AI summary
Embodiments described herein relate to methods and apparatus for determining which 5 of a plurality of subframes are repetition subframes, wherein repetition subframes are subframes scheduled for use by abase station to transmit a repetition of a system information block. A method comprises receiving a first mapping comprising information designating a subset of the plurality of subframes as invalid subframes; and determining, based on the first mapping and a second mapping, which of the 0 subframes designated as invalid subframes are repetition subframes, wherein the second mapping comprises information designating at least one of the subset of the plurality of subframes as a repetition subframe.