NPRACH Subcarrier Reservation for NB-IoT Contention-Free Access
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Solution Overview
Problem
Current NB-IoT random access procedures face inefficiencies due to contention-based methods, leading to signaling overhead, resource misallocation, and incompatibility with new RA-RNTI definitions and response formats, especially when transitioning to contention-free access for Release-13 UEs.
Innovation Solution
Reserving specific NPRACH resources for contention-free random access, where a subset of subcarriers is designated for dedicated use by UEs, allowing network nodes to communicate which subcarriers are reserved for contention-free access, thereby enabling efficient resource allocation and reducing signaling overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If contention-based random access is used in NB-IoT, then random access can be performed without dedicated resources, but signaling overhead increases and resource allocation becomes inefficient
Solution Approach 1:
The NPRACH resource is segmented into multiple subcarriers, where a subset of subcarriers is specifically reserved for contention-free random access. This segmentation allows the system to differentiate between contention-based and contention-free access resources, reducing signaling overhead by eliminating the need for random access responses for contention-free preambles while maintaining efficient resource allocation.
Solution Approach 2:
The system performs preliminary allocation of dedicated subcarriers for contention-free random access before the actual random access procedure. By pre-assigning specific subcarriers to UEs for contention-free access, the network avoids the need for subsequent contention resolution signaling and resource allocation messages, thereby reducing overall signaling overhead.
2Productivity
If dedicated NPRACH resources are reserved for contention-free access, then resource allocation efficiency improves, but device complexity increases due to additional resource management
Solution Approach 1:
Instead of managing entirely separate NPRACH resources for contention-free access, the patent applies local quality by reserving specific subcarriers within the existing NPRACH resource. This approach maintains resource allocation efficiency by dedicating particular subcarriers to contention-free access while avoiding the complexity of managing completely separate resource pools, thus reducing device complexity.
Solution Approach 2:
The NPRACH resource structure is designed to serve multiple functions: it supports both contention-based and contention-free random access procedures using the same overall resource framework. By making the NPRACH resource universal and capable of supporting both access types through subcarrier reservation, the system improves resource allocation efficiency without significantly increasing device complexity for resource management.
3Adaptability or versatility
If all subcarriers are allocated for contention-based access, then compatibility with existing UEs is maintained, but new UEs cannot perform contention-free access
Solution Approach 1:
The NPRACH subcarriers are segmented into different functional groups: some subcarriers are reserved for contention-free access while others remain available for contention-based access. This segmentation enables the system to support both access modes simultaneously, providing adaptability for new UEs to use contention-free access while maintaining backward compatibility with existing UEs that rely on contention-based access.
Solution Approach 2:
By reserving only a subset of subcarriers for contention-free access rather than altering the entire NPRACH structure, the patent maintains local quality that ensures backward compatibility. Existing UEs continue to access the NPRACH resource using their established contention-based procedures, while new UEs can utilize the reserved subcarriers for contention-free access, thus achieving both adaptability and reliability.
Data Source
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AI summary
A method (800) in a network node (115) comprises reserving (804), within a Narrowband Physical Random Access Channel (NPRACH) resource (305, 405, 505, 605, 705) comprising a plurality of start subcarriers, a subset of the plurality of start subcarriers for performing a contention-free random access procedure (310, 410, 520, 530, 610, 720, 730). 0 The method comprises communicating (804), to one or more user equipment (UEs) (110), information indicating which of the plurality of start subcarriers within the NPRACH resource are reserved for performing the contention-free random access procedure.