NR Unlicensed Random Access via LBT and 2-Step Procedure
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Solution Overview
Problem
There is a need for enabling the co-existence of different radio access technologies (RATs) on unlicensed frequency spectra without undesirable interference, particularly for New Radio (NR) systems using Licensed Assisted Access (LAA) carriers.
Innovation Solution
The implementation of a 2-step and 4-step random access procedure for NR in unlicensed spectrum, involving a user equipment (UE) that generates a random access message with a preamble and data portion, performs listen-before-talk (LBT) operations, and transmits these messages to a base station, ensuring successful transmission and response within specific windows, while also handling contention and bandwidth segmentation for successful access.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple radio access technologies operate on the same unlicensed frequency spectrum, then spectrum utilization is improved, but interference between different RATs increases
Solution Approach 1:
The patent implements listen-before-talk (LBT) operations before random access message transmission. The UE performs clear channel assessment (CCA) and LBT procedures in advance to detect whether the unlicensed spectrum is occupied by other RATs or systems. This preliminary action prevents interference by ensuring the channel is clear before NR transmission begins, resolving the contradiction between spectrum utilization and interference avoidance
Solution Approach 2:
The patent introduces dynamic transmission opportunities based on LBT outcomes. The random access procedure adapts to real-time spectrum conditions by dynamically determining whether to transmit Msg1, Msg3, or both simultaneously. This dynamic approach allows the system to flexibly utilize unlicensed spectrum when available while avoiding interference with other RATs, balancing spectrum utilization and interference prevention
2Adaptability or versatility
If traditional 4-step random access procedure is used in unlicensed spectrum, then compatibility with existing systems is maintained, but access latency increases
Solution Approach 1:
The patent merges the traditional 4-step random access procedure into a 2-step procedure for unlicensed spectrum. By combining Msg1 (preamble) and Msg3 (data) into a single transmission opportunity, and merging Msg2 (random access response) and Msg4 (contention resolution) into one response message, the patent reduces the number of separate transmissions and LBT operations required. This merging maintains compatibility through standardized procedures while significantly reducing access latency in unlicensed spectrum
3Reliability
If repeated preamble sequences and data segments are transmitted, then reception reliability is improved, but transmission time increases
Solution Approach 1:
The patent implements selective repetition based on channel conditions and LBT outcomes. Instead of always transmitting repeated preambles and data segments, the system performs partial repetitions only when necessary for reliability. The UE can transmit one or both of Msg1 and Msg3 in different occasions based on LBT success, providing enhanced reliability when needed while avoiding unnecessary transmission time overhead when channel conditions are good
Solution Approach 2:
The patent employs periodic transmission opportunities for random access messages in unlicensed spectrum. The UE attempts transmissions at periodic intervals following LBT procedures, with repeated attempts allowed if initial transmissions fail. This periodic approach provides reliable delivery through multiple opportunities while managing transmission time efficiently by spacing attempts appropriately
Data Source
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AI summary
The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. A user equipment includes a processor configured to generate a random access (RA) message comprising a preamble portion including one or more repeated preambles constructed using a same sequence, and a CP that precedes repeated preamble sequences, and a data portion including one or more data segments with each data segment including a number of repeated data symbols and a CP that precedes the repeated data symbols, wherein a UE-ID is included in the data portion, and perform an LBT operation for the RA message in an unlicensed spectrum. A transceiver is configured to transmit, when a result of the LBT operation for the RA message allows, the RA message to a base station (BS). BS includes a transceiver configured to receive an RA message in an unlicensed spectrum from a UE, and to transmit a responded RA message in response to the RA message within a RAR window.