Uplink Transmission Gap Management in Unlicensed Spectrum
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Solution Overview
Problem
Current signaling methods for LTE in unlicensed spectrum do not fully address the inefficiencies in uplink transmissions, particularly when network nodes do not use partial transmission time intervals, leading to increased gaps between downlink and uplink transmissions and reduced flexibility in managing Listen-Before-Talk (LBT) parameters, which can result in interference and reduced system performance.
Innovation Solution
A method where user equipment (UE) receives a timing advance command and information about a gap within an uplink subframe from a network node, allowing the UE to perform transmissions after the specified gap, thereby optimizing the location and duration of gaps to minimize interference and enhance simultaneous access to the unlicensed spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If network nodes do not use partial transmission time intervals, then downlink and uplink transmissions are separated in time, but this increases gaps between transmissions and reduces system performance
Solution Approach 1:
The network node performs downlink transmission in a partial TTI that occupies only part of the subframe, preparing the channel for subsequent uplink transmission. This preliminary action allows the uplink to start sooner without interfering with downlink, reducing the gap between transmissions while maintaining reliability through controlled channel access timing.
2Reliability
If UEs perform LBT before uplink transmission, then channel access is controlled, but this reduces flexibility in managing LBT parameters and increases interference
Solution Approach 1:
The system dynamically adjusts LBT parameters based on whether partial TTIs are used. When partial TTIs are employed, the network can control the timing more precisely, allowing flexible adjustment of LBT parameters like defer periods and contention window sizes. This dynamic adaptation maintains channel access control while improving flexibility in managing LBT behavior under different transmission scenarios.
3Object-affected harmful factors
If gaps between downlink and uplink transmissions are increased, then interference is reduced, but this reduces the probability of concurrent UE access to unlicensed spectrum
Solution Approach 1:
The transmission time interval is segmented into partial TTI portions for downlink and uplink, with a minimized gap in between. This segmentation allows the system to maintain short gaps for high concurrent access probability while using frequency separation and precise timing control to manage interference. The partial TTI structure enables multiple UEs to access the channel simultaneously by coordinating their transmissions in the segmented time-frequency resources.
Data Source
AI summary
A method in a communication device for managing uplink transmissions from the communication device to a network node. The method includes obtaining a timing advance value, the timing advance value indicating a time period in which the communication device shall advance a first uplink subframe transmission to the network node, obtaining information about a location of a gap within the first uplink subframe, the gap having a predefined duration, the location of the gap occurring after the time period indicated in the timing advance value, and performing the first uplink subframe transmission after the predefined duration.