Channel Access Procedure for LTE Unlicensed Spectrum Coordination
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Solution Overview
Problem
Conventional Listen Before Talk (LBT) mechanisms in LTE systems for unlicensed spectrum access are inefficient, particularly in supporting multiple User Equipment (UE) multiplexing, as they often lead to situations where the transmission of one scheduled UE blocks other UEs, due to divergent Clear Channel Assessment (CCA) counter values across cells and UEs.
Innovation Solution
A user device and network node configuration that allows multiple UEs to access and transmit on disjoint time-frequency resources, using a channel access procedure where the transmission grant indicates a subset of frequency resources, enabling narrowband or wideband channel access, and reservation signals to reserve channels without interfering with other UEs, thereby improving spectral efficiency and coordination across cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Category 4 LBT with random back-off is used for collision avoidance, then channel access reliability is improved, but system productivity deteriorates due to inefficient channel utilization when multiple UEs need to transmit simultaneously
Solution Approach 1:
The patent segments the channel access procedure by introducing a two-stage LBT mechanism: first a simplified CCA check, then a full Category 4 LBT only if needed. This segmentation allows multiple UEs to efficiently access the channel in parallel when conditions permit, while maintaining reliability through the fallback to coordinated random back-off when collisions are detected
Solution Approach 2:
The patent dynamically adjusts the LBT category based on channel conditions and UE scheduling. The eNodeB can indicate to different UEs whether to perform Category 2 or Category 4 LBT, allowing the system to adapt between efficient parallel access and reliable collision avoidance depending on the situation
2Stability of the object's composition
If random backoff counter values are periodically re-initialized to prevent divergence across cells, then coordination between cells is improved, but transmission efficiency deteriorates due to increased blocking of scheduled UEs
Solution Approach 1:
The patent applies different LBT behaviors to different UEs and cells based on local conditions. Instead of uniform periodic re-initialization, each UE performs LBT independently based on its own scheduling and channel conditions, allowing local optimization without global coordination overhead
Solution Approach 2:
The eNodeB performs preliminary coordination by indicating to each scheduled UE whether to perform Category 2 or Category 4 LBT before the actual channel access. This preliminary indication allows UEs to prepare appropriate LBT procedures in advance, reducing blocking while maintaining coordination
3Productivity
If multiple UEs are scheduled to transmit in the same UL subframe, then spectral efficiency is improved, but channel access reliability deteriorates due to increased collision probability without proper LBT coordination
Solution Approach 1:
The eNodeB acts as an intermediary that coordinates LBT behavior among multiple scheduled UEs. By indicating to each UE whether to perform Category 2 or Category 4 LBT, the eNodeB mediates between the need for high spectral efficiency (multiple simultaneous transmissions) and channel access reliability (collision avoidance)
Data Source
AI summary
A user device and a network node for a wireless communication system are provided. The user device configured to receive a transmission grant indicating a set of frequency resources assigned for transmission to a network node; configured to determine a channel access outcome based on a channel access procedure performed in the set of frequency resources; wherein is configured to transmit a first signal to the network node in the set of frequency resources according to the channel access outcome. The network node configured to transmit a transmission grant to a user device, the transmission grant indicating a set of frequency resources assigned for transmission from the user device to the network node and for performing a channel access procedure; receive a first signal from the user device in the set of frequency resources. The disclosure also relates to a non-transitory computer-readable storage medium.