Random Access Procedure for Unlicensed Band Wireless Systems
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Solution Overview
Problem
In wireless communication systems, particularly in unlicensed bands, the random access procedure faces challenges due to limited radio resources and high latency, which affects the efficient transmission and reception of data and control information between user equipment (UE) and base stations (BS).
Innovation Solution
A method for performing a random access procedure in a wireless communication system involves transmitting multiple random access preambles, detecting corresponding responses, and selecting an uplink grant for payload transmission only after a successful 'listen before talk' (LBT) procedure, while incrementing a preamble transmission counter and considering the procedure failed if all attempts fail, and discarding other uplink grants without performing LBT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple random access preambles are transmitted in unlicensed band, then the probability of successful access is improved, but the time consumption and latency increase due to multiple LBT procedures
Solution Approach 1:
The base station performs preliminary action by providing multiple uplink grants in advance before the UE needs to transmit payload. These grants are prepared beforehand with different time resources, allowing the UE to quickly select from pre-prepared options rather than waiting for new grants after each LBT attempt, thus reducing access latency while maintaining multiple access opportunities
Solution Approach 2:
The system implements dynamic selection of uplink grants based on real-time LBT outcomes. The UE dynamically chooses which uplink grant to use depending on which LBT procedure succeeds first among the multiple provided grants. This dynamic adaptation allows the system to balance between trying multiple preambles for reliability and selecting the fastest successful path to minimize latency
2Adaptability or versatility
If multiple uplink grants are provided for payload transmission, then the flexibility and success rate of payload transmission is improved, but the device complexity and resource management difficulty increase
Solution Approach 1:
The uplink grants are segmented into multiple distinct time resources, with each grant associated with a specific time slot. The UE segments its transmission strategy by selecting only one grant based on LBT success, rather than managing all grants simultaneously. This segmentation simplifies the UE's resource management complexity while maintaining the flexibility of having multiple grants available for different time scenarios
Solution Approach 2:
The system extracts and discards unused uplink grants after selection. Once the UE selects one uplink grant based on LBT success, the other grants are taken out from active management and discarded. This extraction principle reduces the complexity of managing multiple grants by converting them from a set of simultaneously managed resources to a selection-from-options scenario, where only the selected grant requires active management
Data Source
AI summary
The present invention relates to a method for performing a random access procedure by a user equipment in a wireless communication system. In particular, the method includes transmitting a first number of random access preambles; detecting a second number of random access responses corresponding to the first number of random access preambles; and transmitting an payload using one uplink grant for which a listen before talk (LBT) procedure is firstly successful among a second number of uplink grants included in the second number of random access responses.