License-Assisted CTS Transmission to Mitigate Hidden-Node Collisions
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Solution Overview
Problem
In wireless communication systems operating in shared or unlicensed radio frequency spectrum, hidden nodes can cause interference due to undetected RTS/CTS exchanges, leading to collisions and inefficient resource usage.
Innovation Solution
Implementing license assisted RTS and CTS transmissions, where UEs transmit CTS signals in licensed spectrum while communicating in unlicensed spectrum, using designated resources and frequency hopping to mitigate interference from hidden nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If RTS/CTS signals are transmitted only in unlicensed spectrum, then the system maintains simplicity in signal transmission, but hidden nodes cause interference and collisions due to undetected signal exchanges
Solution Approach 1:
The patent transmits CTS signals in two different dimensions: unlicensed spectrum (original dimension) and licensed spectrum (new dimension). This dual-spectrum approach ensures that hidden nodes cannot cause collisions because the licensed spectrum transmission provides an additional reliable communication path that is independent of unlicensed spectrum interference.
Solution Approach 2:
The licensed spectrum acts as an intermediary medium to carry CTS signals. Since licensed spectrum is protected and does not suffer from the same hidden node problems as unlicensed spectrum, it serves as a reliable mediator to ensure successful CTS delivery and prevent collisions in the unlicensed spectrum.
2Reliability
If CTS signals are transmitted in licensed spectrum, then interference from hidden nodes is mitigated, but the system complexity increases due to dual-spectrum operations
Solution Approach 1:
The patent segments the CTS signal transmission into two parts: one in unlicensed spectrum and one in licensed spectrum. This segmentation allows the system to leverage the advantages of both spectra - the unlicensed spectrum for primary communication and the licensed spectrum for reliable CTS delivery - while managing complexity through structured resource allocation.
Solution Approach 2:
The CTS signal serves multiple functions simultaneously: it acknowledges the RTS in unlicensed spectrum and also provides collision protection by being transmitted in licensed spectrum. This multi-functionality reduces the need for separate mechanisms, thereby managing system complexity while improving reliability.
3Object-affected harmful factors
If frequency hopping is used for CTS transmission, then interference mitigation is enhanced, but the resource allocation complexity increases
Solution Approach 1:
The patent employs periodic frequency hopping for CTS transmission in licensed spectrum. The hopping follows a predetermined pattern with specific periodicity, which simplifies resource allocation by making the frequency transitions predictable and manageable. This periodic action effectively mitigates interference while keeping resource allocation complexity under control through structured timing and frequency selection.
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AI summary
Methods, systems, and devices for wireless communication are described. A user equipment (UE) or base station communicating in an unlicensed radio frequency spectrum band may transmit a signal (e.g., a request-to-send (RTS) or clear-to-send (CTS) signal) in a licensed radio frequency spectrum band to decrease the likelihood that neighboring devices will transmit interfering communications. Specific resources may be designated in the licensed radio frequency spectrum band for transmitting these signals, and these resources may be associated with specific unlicensed channels. Signaling in the licensed radio frequency spectrum band may also carry an indication of the unlicensed channel being used or other information relevant to the unlicensed communication. The RTS/CTS signaling in licensed radio frequency spectrum band may be transmitted during a downlink transmit opportunity or an uplink transmit opportunity, or both. Different energy detection thresholds may apply to RTS/CTS signals in licensed and unlicensed spectrum.