Random Access Preamble Retransmission in 5G Unlicensed Bands
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Solution Overview
Problem
The current 5G wireless communication system design for operation on unlicensed carriers faces challenges with random access (RA) procedure delays and RA-RNTI ambiguity due to large RAR window sizes, which can lead to retransmission delays and identification issues in unlicensed bands.
Innovation Solution
The proposed methods involve a terminal and base station configuration to monitor and retransmit RA preambles within adjusted RAR windows, allowing for reduced retransmission delays and resolving RA-RNTI ambiguity by signaling extended RAR windows and retransmission times, enabling efficient RA procedures in unlicensed bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a large RAR window size is used to ensure reliable reception of random access response, then the reliability of RA procedure is improved, but the retransmission delay increases and RA-RNTI ambiguity occurs
Solution Approach 1:
The RAR window is segmented into multiple sub-windows or time slots, allowing the terminal to monitor for RAR in divided time periods. This segmentation enables the terminal to perform channel sensing at multiple opportunities within the extended window without causing ambiguity, as each sub-window can be independently managed for sensing and reception purposes.
Solution Approach 2:
The terminal performs channel sensing in advance before the expected RAR transmission time. By conducting sensing operations prior to the RAR window and at designated intervals within it, the terminal ensures the channel is ready for RAR reception while avoiding the need for extended sensing periods that would cause ambiguity. This preliminary sensing action resolves the contradiction by preparing the channel beforehand rather than extending the monitoring window.
2Adaptability or versatility
If the RAR window size is extended to accommodate unlicensed carrier constraints, then the adaptability to unlicensed spectrum is improved, but the device complexity increases due to extended monitoring and sensing requirements
Solution Approach 1:
The RAR window configuration is made dynamic and adjustable based on the specific unlicensed carrier conditions and terminal capabilities. Instead of using a fixed extended window, the system adapts the window size and sensing timing dynamically, reducing complexity by using only the necessary monitoring duration required for the current operational context rather than a permanently extended configuration.
Solution Approach 2:
The terminal performs channel sensing periodically at designated intervals within the RAR window rather than continuously. This periodic sensing approach reduces device complexity by interrupting the sensing operation at specific intervals, allowing the terminal to maintain adaptability to unlicensed carriers while avoiding the continuous monitoring complexity that would arise from extended real-time sensing throughout the entire RAR window.
Data Source
AI summary
A communication method and system for converging a fifth generation (5G) communication system for supporting higher data rates beyond a fourth generation (4G) system with a technology for Internet of things (IoT) are provided. The communication method and system 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 method by a terminal for performing a random access (RA) procedure is provided. The method comprises transmitting a first RA preamble to a base station, initiating to monitor a first RA response (RAR) as a response to the first RA preamble in an RAR window, and based on the terminal failing to receive the first RAR in until end of a retransmission time, transmitting a second RA preamble to the base station.