OTDOA RSTD Estimation via FFT Window Pair
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Solution Overview
Problem
Current OTDOA implementations in LTE networks are complex and inefficient, particularly when measuring Reference Signal Time Difference (RSTD) for non-serving eNodeBs, as they require time-domain correlation, which is more complex than frequency-domain processing and not suitable for higher timing ranges.
Innovation Solution
A method using frequency-domain processing with two FFT windows to estimate RSTD, employing coherent combining and iFFT to convert back to the time domain, allowing for reduced complexity and resource efficiency while covering timing ranges beyond the cyclic prefix.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If time-domain correlation is used to estimate RSTD, then measurement accuracy is maintained, but computational complexity increases significantly
Solution Approach 1:
The patent replaces the time-domain correlation mechanism with a frequency-domain processing mechanism using FFT and IFFT operations. The complex time-domain correlation is substituted by transforming signals to frequency domain, performing simpler operations there, and transforming back, thereby reducing computational complexity while maintaining RSTD estimation accuracy.
Solution Approach 2:
The patent changes the domain parameter from time-domain to frequency-domain processing. By applying FFT to convert time-domain signals to frequency-domain representations, the patent transforms the correlation operation into a more computationally efficient form that can be executed with reduced complexity while preserving measurement precision.
2Device complexity
If FFT window size is limited to cyclic prefix duration, then frequency-domain implementation is optimal, but timing range coverage is insufficient for non-serving eNodeBs
Solution Approach 1:
The patent segments the timing measurement process by introducing multiple FFT windows (first and second FFT windows) that operate at different time offsets. This segmentation allows the system to cover extended timing ranges beyond the cyclic prefix duration while maintaining the efficiency of frequency-domain processing in each segment.
Solution Approach 2:
The patent extends the measurement capability by adding a temporal dimension through multiple FFT windows positioned at different offsets. Instead of relying on a single FFT window limited to CP duration, the patent uses multiple windows arranged in time to cover the extended RSTD range required for non-serving eNodeB measurements.
3Adaptability or versatility
If search window size exceeds cyclic prefix length, then non-serving eNodeB measurements are enabled, but frequency-domain implementation becomes invalid
Solution Approach 1:
The patent segments the extended search window into multiple FFT windows, each with size equal to or less than the cyclic prefix length. This segmentation preserves the validity of frequency-domain implementation for each segment while collectively covering the extended search range needed for non-serving eNodeB measurements.
Solution Approach 2:
The patent introduces multiple FFT windows as intermediary structures that bridge the gap between the limited CP duration and the extended search window requirement. Each FFT window acts as an intermediary processing unit that operates within valid frequency-domain constraints while collectively enabling extended timing range measurements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides a less complex and more resource-efficient solution for OTDOA, with minimal performance degradation compared to optimal methods, suitable for large network deployments and multiple eNodeB measurements.
Implementation Method 1
executing an FFT per OFDM symbol of the PRS for each FFT window of the FFT window pair; obtaining a first FFT output vector per OFDM symbol of each FFT window
Implementation Method 2
executing an iFFT to convert to the time domain; calculating an estimated value of reference signal time difference RSTD
Data Source
AI summary
A computer implemented method for providing OTDOA timing information comprising defining an FFT window pair for estimating a value of reference signal time difference “RSTD” for at least one base station and a reference cell, receiving a PRS from the at least one base station and the reference cell, executing an FFT per OFDM symbol of the PRS for each FFT window of the FFT window pair, obtaining a first FFT output vector per OFDM symbol of each FFT window, for each first output vector, descrambling tones corresponding to the known position of the PRS, wherein all other tones are set to zero, combining vectors based on respective first FFT output vectors, executing an iFFT to convert to the time domain; and calculating an estimated value of reference signal time difference “RSTD” for the at least one base station and the reference cell.