LTE Unlicensed Spectrum Downlink Procedures
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Solution Overview
Problem
Wireless communication networks, particularly LTE/LTE-A systems, face interference and congestion issues due to increasing demand for mobile broadband access, which degrades performance and necessitates efficient use of unlicensed spectrum to alleviate congestion.
Innovation Solution
Implementing OFDMA communication signals over unlicensed spectrum for synchronization and system broadcast signals, with non-clear channel assessment (non-CCA) subframes for transmission, allowing base stations to determine and transmit these signals effectively, and enabling user equipment to receive and communicate based on these signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If LTE/LTE-A systems use unlicensed spectrum to alleviate congestion, then network capacity and mobile broadband access are improved, but interference from other wireless RF transmitters and neighbor base stations increases
Solution Approach 1:
The patent segments the unlicensed spectrum usage by introducing specific subframe types (CCA subframes and non-CCA subframes) within the LTE frame structure. This segmentation allows the system to perform clear channel assessments at specific intervals while transmitting critical signals like synchronization and broadcast signals in protected non-CCA subframes, thereby managing interference systematically while maintaining network capacity.
Solution Approach 2:
The patent implements preliminary action by performing Clear Channel Assessment (CCA) before transmitting data in CCA subframes. The base station assesses the channel condition in advance and only transmits data if the channel is clear, preventing collisions with other wireless transmitters. This preliminary checking mechanism reduces interference while allowing efficient use of unlicensed spectrum for high-capacity communications.
2Reliability
If base stations transmit synchronization and broadcast signals continuously, then user equipment can maintain reliable communication, but network congestion and interference increase
Solution Approach 1:
The patent implements periodic action by transmitting synchronization signals and broadcast signals only in specific non-CCA subframes at regular intervals (e.g., every 10ms or 20ms). Instead of continuous transmission, these critical signals are sent periodically in predetermined subframes, reducing overall network congestion and interference while maintaining sufficient reliability for user equipment to synchronize and access the network.
Solution Approach 2:
The patent applies local quality by creating special non-CCA subframes with protected status specifically for synchronization and broadcast signal transmission. These subframes have different characteristics from regular data subframes - they are exempt from CCA requirements and provide guaranteed transmission opportunities. This localized protection ensures communication reliability for critical signals without imposing restrictions on data transmission in other subframes, thus maintaining network efficiency.
3Object-affected harmful factors
If clear channel assessment is performed before every transmission, then interference is reduced, but transmission latency and complexity increase
Solution Approach 1:
The patent segments the transmission opportunities into CCA subframes (where CCA is performed) and non-CCA subframes (where CCA is not required). By segmenting the frame structure this way, the system performs CCA only periodically in CCA subframes rather than before every single transmission. This reduces the overall time loss from CCA operations while still providing interference reduction through periodic channel assessment.
Solution Approach 2:
The patent performs CCA as a preliminary action only in CCA subframes before transmitting data, rather than before every transmission. This preliminary assessment is done at scheduled intervals, allowing the system to reduce interference through periodic channel checking while minimizing the time penalty associated with repeated CCA operations. The non-CCA subframes then allow transmissions without additional CCA delays.
Data Source
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AI summary
Long term evolution (LTE)/LTE-Advanced (LTE-A) deployments with unlicensed spectrum leverage more efficient LTE communication aspects over unlicensed spectrum, such as over WIFI radio access technology. In order to accommodate such communications, various downlink procedures may be modified in order to handle communications between licensed and unlicensed spectrum with LTE/LTE-A deployments with unlicensed spectrum.