FFT Power Detection for LBT in LTE LAA
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Solution Overview
Problem
Current Listen Before Talk (LBT) functionality in LTE License Assisted Access (LAA) fails to meet the tightest timing requirements for power detection in unlicensed frequency bands, leading to network performance degradation, especially when using a secondary carrier with unlicensed spectrum.
Innovation Solution
Implementing an N-point Fast Fourier Transform (FFT) for channel measurement signals to produce a frequency domain signal, allowing for rapid power measurement and analysis, which enables efficient clear channel assessment within the 9 us timing budget.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional channelization and measurement for each channel individually is used, then measurement precision is improved, but processing time increases beyond the 9 us timing requirement
Solution Approach 1:
The patent segments the frequency spectrum into multiple channels and processes them simultaneously using parallel FFT operations. Instead of sequentially measuring each channel individually (which would take 10+ us), the system divides the spectrum into frequency bins through FFT and processes multiple channels in parallel, reducing the total processing time to meet the 9 us requirement while maintaining measurement precision through proper bin filtering and power summation.
Solution Approach 2:
The patent changes the measurement approach from time-domain individual channel measurement to frequency-domain simultaneous measurement using FFT. By transforming the signal to frequency domain and using bin filtering to identify and sum power from specific channels, the system achieves the same measurement precision as individual channel measurement but with significantly reduced processing time.
2Productivity
If LBT functionality is implemented on secondary carrier with unlicensed spectrum, then network performance is improved, but timing requirement compliance deteriorates due to processing time
Solution Approach 1:
The patent applies segmentation by dividing the unlicensed spectrum into multiple frequency channels and processing them simultaneously through parallel FFT operations. This allows the LBT functionality on secondary carrier to complete power detection for all channels within the 9 us timing window, enabling network performance improvement through unlicensed spectrum utilization without violating timing requirements.
Solution Approach 2:
The patent performs preliminary FFT transformation and bin filtering operations in advance to prepare the frequency domain representation of the signal. By pre-processing the signal to identify which frequency bins correspond to the channels of interest before performing final power summation, the system ensures that the complete LBT measurement can be finished within the 9 us timing constraint, thereby enabling secondary carrier operation with improved network performance.
3Speed
If FFT-based power measurement is used, then processing speed is improved, but measurement precision may deteriorate due to frequency bin filtering
Solution Approach 1:
The patent applies local quality by selectively filtering and summing power from specific frequency bins that correspond to the channels of interest, rather than measuring all frequency components. This localized approach to power measurement in the frequency domain maintains precision for the relevant channels while enabling fast parallel processing of multiple channels simultaneously, thus achieving both speed improvement and measurement precision.
Data Source
AI summary
A method performed in a radio access node includes the radio access node receiving a data for transmission to a second radio access node over a communication channel having an unlicensed spectrum. The method further includes, in response to receiving the data, the radio access node receiving a channel measurement signal over the communication channel. The method further includes the radio access node performing an N-point Fast Fourier Transform (FFT) on the channel measurement signal to produce a frequency domain signal with N bins. The method further includes the radio access node performing a power measurement on the frequency domain signal. The method further includes the radio access node analyzing the power measurement of the frequency domain signal. The method further includes the radio access node transmitting the data based on the analysis of the power measurement.