Random Access Preamble Transmission in Unlicensed Band
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current LTE systems only support downlink transmission in the unlicensed band, limiting the provision of various services and requiring the development of uplink transmission methods to enhance communication capabilities.
Innovation Solution
Implementing a random access process for uplink transmission in the unlicensed band, utilizing a method that includes a BS transmitting a random access preamble order with specific time/frequency information, allowing the UE to perform clear channel assessment and transmit the random access preamble within designated windows, and enabling re-attempts if initial transmission fails.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If LTE systems use unlicensed band for downlink transmission only, then interference with WLAN is reduced, but uplink transmission capability is limited and communication quality deteriorates
Solution Approach 1:
The system performs Clear Channel Assessment (CCA) before uplink transmission to detect whether the channel is occupied by WLAN or other systems. This preliminary detection prevents interference by identifying busy channels in advance, allowing the LTE system to adaptively access the unlicensed band only when the channel is clear.
Solution Approach 2:
The random access procedure is designed to be dynamic and adaptive, where the UE can perform multiple CCA attempts and adjust transmission timing based on channel conditions. The system transitions from static downlink-only operation to dynamic uplink transmission capability, adapting to the shared nature of the unlicensed spectrum.
2Productivity
If multiple communication nodes share the unlicensed band in contention-based manner, then frequency utilization is improved, but channel access conflict increases and transmission reliability deteriorates
Solution Approach 1:
The random access procedure implements feedback mechanisms where the base station responds to UE preamble transmissions with acknowledgment messages. This feedback loop allows the system to confirm successful channel access and adjust subsequent transmissions, improving reliability in the contention-based environment.
Solution Approach 2:
The system performs preliminary CCA checks before transmission and uses random backoff timing to stagger access attempts from multiple nodes. This preliminary preparation reduces the probability of simultaneous collisions, thereby improving channel access reliability while maintaining high frequency utilization.
3Object-affected harmful factors
If CCA is performed before every uplink transmission, then interference with other systems is minimized, but transmission delay increases and productivity deteriorates
Solution Approach 1:
The CCA procedure is segmented into different types: immediate CCA before random access preamble transmission, and deferred CCA for subsequent data transmissions. This segmentation allows critical control signals to access the channel quickly while less time-sensitive data can tolerate longer waiting periods, reducing overall transmission delay while maintaining interference avoidance.
Solution Approach 2:
The system performs CCA periodically at defined intervals and uses timer-based mechanisms to limit the maximum waiting time. This periodic approach ensures that transmissions are not indefinitely delayed while still providing sufficient opportunity to detect and avoid interference from other unlicensed band users.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Provided are a method for performing a random access process in an unlicensed band, and a device using the same. The device receives a random access preamble (RAP) order instructing the transmission of a RAP. The device performs a clear channel assessment (CCA) in an unlicensed cell during an RAP window so as to transmit the RAP when the device succeeds in CCA.