NB-IoT TDD Resource Mapping for Early Cell Search Exit
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Solution Overview
Problem
NB-IoT systems prior to Rel-15 struggle to distinguish between FDD and TDD modes during cell search, leading to increased power consumption and system access latency for user equipment that do not support TDD, as they cannot accurately identify TDD cells and thus encounter errors during the cell search and system information reading process.
Innovation Solution
A resource mapping scheme is introduced for NB-IoT TDD cells, where the mapping of NPSS, NSSS, NPBCH, and SIB1-NB signals in subframes is altered compared to FDD mode, allowing user equipment to differentiate between FDD and TDD modes by encountering detection errors when attempting to access a TDD cell, thereby exiting the search process early and reducing power consumption and latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If NB-IoT UE in deep coverage performs cell search and system information reading, then the UE can access the network, but the process lasts several seconds causing high power consumption and access latency
Solution Approach 1:
The patent applies preliminary action by performing cell type identification (FDD vs TDD) at the beginning of the cell search process, before complete system information reading. The UE uses the detected cell configuration to determine compatibility and decide whether to continue the access process, thereby avoiding unnecessary prolonged searching and reducing access latency.
Solution Approach 2:
The patent inverts the traditional approach by having the UE actively determine cell compatibility through detection rather than passively attempting full access and then failing. The UE detects cell-specific reference signals and system information to identify TDD cells, then proactively terminates the search process when incompatibility is detected, reversing the conventional error-after-access pattern to error-prevention.
2Measurement precision
If NB-IoT UE attempts to access TDD cells without TDD support, then the UE cannot camp on the cell, but the cell search process continues for several seconds causing high power consumption
Solution Approach 1:
The patent extracts the cell compatibility determination step from the complete cell access process. By separating the cell type identification (FDD/TDD detection) as an independent preliminary step, the UE can quickly determine incompatibility and exit without performing the full power-consuming system information reading and access procedures on incompatible TDD cells.
Solution Approach 2:
The patent applies skipping by allowing the UE to rush through the cell search process when incompatibility is detected. Once the UE determines that a cell is a TDD cell and it does not support TDD, it immediately skips the remaining access steps and switches to other cells, thereby minimizing power consumption on incompatible cells.
3Adaptability or versatility
If NB-IoT systems support both FDD and TDD modes, then the system becomes more versatile, but UEs prior to Rel-15 cannot distinguish TDD cells from FDD cells during cell search
Solution Approach 1:
The patent uses color changes metaphorically by introducing distinct detectable characteristics for TDD cells (such as specific cell-specific reference signal configurations or system information indicators) that allow UEs to visually 'identify' the cell type. These distinctive features act like color markers that enable quick differentiation between FDD and TDD cells during cell search.
Solution Approach 2:
The patent introduces an intermediary detection mechanism (such as specific reference signal patterns or system information elements) that mediates between the cell's TDD/FDD configuration and the UE's ability to detect it. This intermediary provides a detectable signal or information element that bridges the gap between the cell's internal configuration and the UE's external observation capability.
Data Source
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AI summary
The present disclosure provides a resource mapping and transmission method and a corresponding base station and user equipment. The method comprises: generating radio frames for NB-IoT TDD, and in the radio frames for NB-IoT TDD, mapping a Narrowband Primary Synchronization Signal "NPSS," a Narrowband Secondary Synchronization Signal "NSSS," a Narrowband Physical Broadcast Channel "NPBCH," and a Narrowband System Information Block Type 1 "SIB1-NB" to subframes selected from subframes 0, 4, 5, and 9 of the radio frames, wherein the NPSS, the NSSS, the NPBCH, and the SIB1-NB are respectively mapped into different subframes and are not respectively mapped into the subframes 5, 9, 0, and 4; and transmitting the generated radio frames. According to embodiments of the present invention, user equipment not supporting NB-IoT TDD can exit a search for an NB-IoT TDD cell as early as possible.