Multi-Carrier Random Access for Unlicensed Band Latency Reduction
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Solution Overview
Problem
Wireless communication systems face challenges in reducing latency caused by channel access in unlicensed bands, particularly due to the listen before talk (LBT) mechanism, which increases access latency and affects user equipment (UE) operations.
Innovation Solution
A method and apparatus that involve transmitting a physical random access channel (PRACH) on at least one carrier in a first carrier group based on channel sensing results, receiving a random access response (RAR) on at least one carrier in a second carrier group, and subsequently transmitting a physical uplink shared channel (PUSCH) based on the RAR, to optimize random access procedures and reduce latency in unlicensed bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the listen before talk (LBT) mechanism is used for channel access in unlicensed bands, then channel access is controlled to avoid interference, but access latency increases
Solution Approach 1:
The patent segments the carrier into multiple carrier groups (first carrier group for PRACH transmission, second carrier group for RAR reception) and allows parallel channel sensing across different carriers. This segmentation enables simultaneous LBT operations on multiple carriers, reducing the overall access latency while maintaining reliable channel access control in unlicensed bands.
Solution Approach 2:
The patent performs channel sensing (LBT) in advance before the actual data transmission. By sensing the channel status beforehand on multiple carriers and using the sensing results to determine transmission timing, the system reduces the latency caused by waiting for channel availability during the actual transmission process.
2Device complexity
If random access procedure is performed on single carrier, then procedure is simple, but latency is increased due to sequential channel access
Solution Approach 1:
The patent transitions from single-carrier random access to multi-carrier random access by introducing a frequency dimension. Multiple carriers are organized into carrier groups, and the random access procedure is extended across multiple frequency resources, allowing parallel PRACH transmissions and RAR receptions on different carriers simultaneously, thereby reducing access latency.
Solution Approach 2:
The patent merges multiple carriers into carrier groups and combines their channel sensing results to determine the transmission timing. By merging the LBT results from multiple carriers, the system can identify the earliest available carrier for transmission, reducing the overall access latency compared to sequential single-carrier access.
3Measurement precision
If channel sensing is performed on all carriers, then accurate channel status is obtained, but sensing time is increased
Solution Approach 1:
The patent applies partial action by performing channel sensing on a subset of carriers rather than all carriers simultaneously. The base station determines a timing for performing LBT based on sensing results from available carriers, and can select carriers for sensing based on their availability and status, reducing sensing time while maintaining sufficient accuracy for transmission decisions.
Data Source
AI summary
The present disclosure relates to a wireless communication system. More specifically, the present disclosure relates to: a method for transmitting a physical random access channel (PRACH) in at least one carrier from among a first carrier group on the basis of a channel sensing result, receiving a random access response (RAR) in at least one carrier from among a second carrier group in response to the transmission of the PRACH, and transmitting a physical uplink shared channel (PUSCH) on the basis of the RAR; and an apparatus therefor.