LBT-Based Reference Signal Indication for Accurate UE Measurements
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Solution Overview
Problem
In LTE systems deployed in unlicensed spectrum bands, the mandatory transmission of reference signals conflicts with the Listen Before Talk (LBT) procedure, leading to interference and erroneous UE measurements, which degrade network performance for functions like mobility and positioning.
Innovation Solution
A transmitter node dynamically provides an indicator to a receiver node when the wireless radio channel is idle, allowing the receiver to use reference signals only in time resources containing the indicator, and refrains from transmitting if the channel is occupied, thus aligning with LBT principles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the network node transmits reference signals in a predetermined manner regardless of channel occupancy status, then the UE can perform accurate measurements, but the reference signals cause unacceptable interference with neighboring network nodes and disturb their own transmissions
Solution Approach 1:
The patent applies dynamics by transitioning from static, predetermined reference signal transmission to dynamic transmission based on real-time channel occupancy status. The network node determines whether to transmit reference signals in each subframe based on whether it has obtained occupancy permission from the eNodeB, allowing the transmission behavior to adapt to changing channel conditions while maintaining measurement accuracy and reducing interference.
2Object-generated harmful factors
If the network node defers transmission of reference signals when the channel is occupied, then interference is reduced, but the UEs will still try to estimate the signals and produce erroneous measurements with bias
Solution Approach 1:
The patent implements feedback by having the network node send a Downlink Indicator Signal (DLS) to inform UEs whether reference signals will be transmitted in the upcoming subframe. This feedback mechanism allows UEs to adjust their measurement behavior accordingly - only attempting measurements when reference signals are actually transmitted - thereby maintaining measurement accuracy while enabling dynamic transmission deferral to reduce interference.
3Reliability
If the network node always transmits reference signals at indicated time-frequency locations, then UE measurements are reliable, but the mandatory transmission conflicts with the Listen Before Talk (LBT) procedure required in unlicensed bands
Solution Approach 1:
The patent resolves this contradiction by making reference signal transmission dynamic rather than mandatory. The network node determines in each subframe whether to transmit reference signals based on whether it has obtained occupancy permission through the LBT procedure. This dynamic approach allows the system to comply with LBT requirements in unlicensed bands while maintaining measurement reliability when transmission does occur.
Solution Approach 2:
The Downlink Indicator Signal provides feedback to UEs about the actual transmission status of reference signals, enabling UEs to reliably determine whether measurements should be performed. This feedback mechanism ensures measurement reliability by synchronizing UE measurement behavior with the actual reference signal transmission status, which varies based on LBT outcomes in unlicensed spectrum.
Data Source
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AI summary
A novel way for transmitting physical signals by a transmitter node (20, 40) based on the LBT principle, and informing a receiver node (30, 50) in cases where the transmission of the physical signals has been deferred or does not occur in a certain time resource, is presented. A transmitter node (20, 40) listens to a wireless radio channel during a first time resource. If there is no activity, or if the activity is below a threshold, the transmitter node (20, 40), in a second time resource, transmits an indicator indicating that one or more physical signals are also transmitted in the second time resource. A receiver node (30, 50) detects if an indicator is present in the time resource. If the receiver node (30, 50) detects the indicator, the receiver node (30, 50) may also receive and use one or more reference signals in the current time resource for doing one or more tasks.