Uplink Synchronization in Unlicensed LTE via Early CCA
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Solution Overview
Problem
In LTE systems deployed on unlicensed frequency bands, there is a challenge in avoiding mutual interference with other wireless systems like WiFi or radar, and in efficiently establishing uplink synchronization, which can lead to increased delay and reduced network spectrum utilization.
Innovation Solution
The method involves a UE receiving uplink synchronization command information, which includes resource allocation for uplink signals, and transmitting the random access signal, such as PRACH, in the first idle PRACH resource subframe within a predetermined window, based on CCA detection, to minimize interference and optimize spectrum usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If CCA detection is performed before PRACH transmission on unlicensed carriers, then interference with other wireless systems is reduced, but uplink synchronization delay increases
Solution Approach 1:
The UE performs CCA detection in advance before the scheduled PRACH transmission time. If the channel is found idle, the UE transmits the random access preamble immediately in the first available PRACH opportunity, rather than waiting for the scheduled time. This preliminary channel assessment and early transmission approach reduces the synchronization delay while maintaining interference avoidance.
Solution Approach 2:
The patent introduces dynamic adjustment of PRACH transmission timing based on CCA results. The UE adaptively determines the actual transmission moment within the PRACH opportunity window, selecting the earliest available slot after successful CCA. This dynamic timing adjustment allows the system to balance between interference avoidance and delay reduction.
2Reliability
If PRACH transmission is scheduled at a fixed time after PDCCH order, then transmission timing is predictable, but channel may be occupied leading to transmission failure
Solution Approach 1:
The UE performs CCA detection before the scheduled PRACH transmission time to preliminarily assess channel availability. This advance detection allows the UE to identify suitable transmission opportunities and avoid congested channels, thereby improving transmission success rate while managing detection complexity through efficient timing.
Solution Approach 2:
The UE autonomously performs CCA detection and self-determines the optimal PRACH transmission timing based on channel conditions. This self-service mechanism enables the UE to adapt to dynamic channel environments without requiring complex network coordination, improving reliability while keeping the system relatively simple.
Data Source
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AI summary
The present disclosure provides several methods, user equipment (UEs) and base stations for transmitting uplink signals. After receiving uplink synchronization command information, the UE may transmit an uplink signal on at least one idle unlicensed cell. Besides, the UE may try to transmit the uplink signal on multiple uplink signal resources within an uplink signal transmission window. By using the present disclosure, transmission probability of uplink signals may be improved, and time delay of uplink synchronization may be shortened.