RA-RNTI Calculation for NB-IoT Random Access Response Multiplexing
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Solution Overview
Problem
In NB-IoT systems, when multiple UEs select different frequency resources for random access, the limited size of physical channel transport blocks restricts the number of RARs that can be multiplexed into one MAC PDU, leading to inefficient energy use as only one MAC PDU may contain the correct RAR for a UE, causing other UEs to waste energy decoding multiple PDUs with identical RA-RNTIs.
Innovation Solution
Introducing a coverage enhancement level identity into the RA-RNTI calculation allows RARs from UEs in identical coverage enhancement levels to be multiplexed into one MAC PDU, using identical RA-RNTIs, thereby reducing the probability of incomplete multiplexing and optimizing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple UEs select different frequency resources for random access, then the system supports more concurrent access attempts, but the limited MAC PDU size prevents all RARs from being multiplexed into one PDU, causing UEs to decode multiple PDUs and waste energy
Solution Approach 1:
The patent segments the random access response resources by introducing coverage enhancement level identities, dividing UEs into different groups (CE levels) that use different RA-RNTI calculation methods. This segmentation allows RARs to be properly multiplexed within each group's MAC PDU, preventing UEs from needing to decode multiple PDUs and reducing energy waste while maintaining support for multiple concurrent access attempts.
2Productivity
If RARs are multiplexed into one MAC PDU using identical RA-RNTIs, then transmission efficiency improves, but the limited transport block size restricts the number of RARs that can be accommodated
Solution Approach 1:
The patent divides the UE population into multiple coverage enhancement levels, with each level having its own RA-RNTI space. This segmentation effectively multiplies the total RAR capacity across multiple CE levels, allowing the system to accommodate more RARs overall while maintaining efficient multiplexing within each level's MAC PDU.
Solution Approach 2:
The patent introduces a new dimension (coverage enhancement level identity) to the RA-RNTI calculation, transforming the single-dimension RA-RNTI space into a multi-dimensional space. This allows the system to index RARs not just by frequency resource but also by CE level, effectively increasing the multiplexing capacity without changing the physical PDU size.
3Productivity
If coverage enhancement level identity is introduced into RA-RNTI calculation, then RAR multiplexing efficiency improves, but the system complexity increases due to additional parameters
Solution Approach 1:
The patent performs preliminary classification of UEs into coverage enhancement levels before the random access procedure begins. The network configures and broadcasts CE level information in advance, so that when UEs calculate their RA-RNTI, they simply use pre-determined CE level identities rather than performing complex real-time classifications, thereby reducing calculation complexity while maintaining multiplexing efficiency.
Data Source
AI summary
An apparatus for transmitting a random access response and a communication system, configured in a base station, includes: a determining unit configured to determine a coverage enhancement level to which a user equipment (UE) transmitting a preamble belongs according to a position of a time-frequency resource of the detected preamble; a calculating unit configured to, according to a coverage enhancement level identity corresponding to the UE, calculate a random access wireless network temporary identity (RA-RNTI) used by the UE; and a transmitting unit configured to transmit a random access response (RAR) of the UE, the RAR being scrambled by the RA-RNTI of the UE.