Air-to-Ground Uplink Cell Selection in Unlicensed Spectrum
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Solution Overview
Problem
Existing 3GPP NR specifications do not account for asymmetric interference conditions in air-to-ground networks operating in unlicensed spectrum, leading to suboptimal cell selection and potential overloading of high-capacity cells by distantly-located UEs, which compromises network capacity and connectivity.
Innovation Solution
Utilization of reserve bits in broadcast signals to indicate uplink access constraints, such as interference levels and UE distance from the cell, allowing UEs to select appropriate serving cells based on directional and spatial conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If UEs select serving cells based solely on downlink signal quality (SINR), then the selected cell provides the best downlink signal, but the uplink signal quality may be insufficient due to non-symmetric RF paths and directional interference
Solution Approach 1:
The base station performs preliminary assessment of uplink interference conditions in different spatial directions and encodes this information in broadcast signals before UEs attempt cell selection. This allows UEs to make informed decisions about which cells to select, avoiding cells with poor uplink conditions, thereby ensuring both downlink and uplink connection quality from the outset
Solution Approach 2:
The system implements a feedback mechanism where the base station monitors uplink interference conditions and feeds this information back to UEs through broadcast signals. This feedback loop enables UEs to adapt their cell selection decisions based on real-time uplink conditions, resolving the asymmetry between downlink measurement and uplink performance
2Area of stationary object
If high-capacity cells serve all UEs including distantly-located ones, then these cells provide wide coverage, but the network capacity is compromised due to overloading from far UEs
Solution Approach 1:
The system applies local quality by encoding spatially-dependent access constraints in broadcast signals, allowing different regions around a cell to have different access policies. Distant UEs receive indications to avoid high-capacity cells, while proximate UEs are permitted to access them, thereby preserving network capacity for cells while maintaining wide coverage
Solution Approach 2:
The base station performs preliminary classification of UEs based on their distance and encodes appropriate access constraints in broadcast signals before UEs attempt connection. This preliminary action prevents distant UEs from overloading high-capacity cells, ensuring that network capacity is preserved while coverage area remains extensive
3Ease of operation
If existing 3GPP NR specifications are used without modification, then implementation is straightforward, but asymmetric interference conditions in unlicensed spectrum cannot be properly managed
Solution Approach 1:
The system uses existing broadcast signal structures for multiple purposes: conveying standard cell information and simultaneously encoding spatially-dependent uplink access constraints. This multi-functionality allows the system to maintain ease of operation by using existing protocols while gaining the adaptability to manage asymmetric interference conditions in unlicensed spectrum
Data Source
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AI summary
Techniques for controlling or managing uplink access of a UE to a base station using unlicensed spectrum includes signaling an indication of different uplink access constraints so the UE connects to the base station when the UE and/or the uplink direction between the UE and the base station meet the uplink access constraints. The indication may be broadcast in a reference or synchronization signal, e.g., by utilizing unused or undesignated bits. Uplink access constraints may include a threshold distance of UEs from the base station, interference in the uplink direction (which may differ from interference in the downlink direction), etc. Based on the indicated constraints, the UE may determine whether or not to consider the base station as a candidate serving cell for wireless network access. The UE may be an in-flight aircraft and the base station may be a logical cell of a network that provides in-flight connectivity services.