Sub-Symbol Slot Reservation for LTE Unlicensed Spectrum
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Solution Overview
Problem
Current LTE systems face challenges in improving time granularity during wireless communication, particularly when deploying LTE in unlicensed spectra, which requires efficient channel assessment and synchronization with existing technologies like WLAN, while adhering to regulatory requirements such as Listen-Before-Talk (LBT) protocols.
Innovation Solution
The implementation of a reservation signal that fills sub-symbol slots between channel availability determination and the start of a subsequent symbol, using Clear Channel Assessment (CCA) slots and sequences like Constant-Amplitude-Zero-Autocorrelation (CAZAC) sequences, to reserve channels and align data transmission with LTE frame timing, enhancing channel utilization and compliance with regulatory standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If LTE systems deploy in unlicensed spectra using traditional symbol-based timing, then synchronization with licensed LTE operations is maintained, but time granularity is insufficient for efficient channel assessment and coexistence with other technologies like WLAN
Solution Approach 1:
The patent divides a symbol period into multiple sub-symbol slots, each capable of independent channel assessment and reservation signal transmission. This segmentation enables finer time granularity for LBT operations while maintaining the overall symbol-based LTE timing structure, resolving the contradiction between measurement precision and system complexity
Solution Approach 2:
The patent introduces a new time dimension by dividing the existing symbol period into sub-symbol slots, creating a hierarchical time structure. This dimensional refinement allows precise channel access control at sub-symbol level while preserving symbol-level synchronization with licensed LTE, achieving both fine granularity and low complexity
2Productivity
If LTE systems perform Clear Channel Assessment at symbol boundaries only, then synchronization with LTE frame timing is maintained, but channel utilization efficiency decreases due to inability to access channels immediately when they become free
Solution Approach 1:
The patent performs Clear Channel Assessment in sub-symbol slots before the actual data transmission begins. By conducting channel assessment preliminarily in these intermediate slots and transmitting reservation signals to secure the channel, the system ensures immediate channel access when free, eliminating waiting time while maintaining LTE timing synchronization
Solution Approach 2:
The patent introduces sub-symbol slots as intermediary time units between symbol boundaries. These intermediary slots serve as buffer periods for channel assessment and reservation signal transmission, enabling efficient channel access without disrupting the LTE frame timing structure, thus improving productivity without increasing time loss
3Reliability
If reservation signals are transmitted in every sub-symbol slot, then channel reservation reliability is maximized, but energy consumption increases
Solution Approach 1:
The patent transmits reservation signals selectively in certain sub-symbol slots rather than every slot. By performing channel assessment and sending reservation signals only when necessary (when channel is free or needs to be secured), the system achieves sufficient channel reservation reliability while minimizing energy consumption through partial action rather than continuous transmission
Data Source
AI summary
A method and apparatus can be configured to determine that a sub-symbol slot is an unoccupied sub-symbol slot. The unoccupied sub-symbol slot corresponds to an unoccupied operating channel. The unoccupied sub-symbol slot is located within the duration of a first symbol. The method may also comprise transmitting a reservation signal in at least one sub-symbol slot between the unoccupied sub-symbol slot and the beginning of a second symbol. The number of sub-symbol slots within the duration of the first symbol is larger than one.