Uplink Ranging System Using Twiddle Factor Segmentation
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Solution Overview
Problem
In OFDMA/TDD mobile communication systems, achieving absolute time synchronization among uplink signals from multiple terminals is challenging due to temporal and positional differences, leading to signal orthogonality loss and increased timing error search times.
Innovation Solution
A fast uplink ranging system that generates and duplicates ranging codes, performs inverse fast Fourier transform, and uses complex exponential twiddle factors to predict even or odd time delays, reducing the number of complex exponential searches required for timing error correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the base station sequentially multiplies all possible complex exponential values to find timing error, then the timing error can be accurately identified, but the number of searches becomes excessively large and response time increases
Solution Approach 1:
The patent segments the timing error search space by dividing it into multiple regions and using correlation value thresholds to identify which region contains the correct timing error. This segmentation reduces the number of complex exponential multiplications needed by focusing searches only on relevant regions rather than exhaustively searching all possible values.
Solution Approach 2:
The patent performs preliminary correlation calculations between received signals and ranging codes before conducting the full timing error search. These preliminary correlation values are used to determine the most likely timing error region, allowing the system to prepare and narrow down the search space before executing the computationally intensive complex exponential multiplications.
2Adaptability or versatility
If ranging codes are transmitted from multiple terminals through ranging channels, then uplink ranging capability is provided, but signal orthogonality is lost due to temporal and positional differences between terminals
Solution Approach 1:
The patent changes the parameter of signal representation by expressing received signals in terms of complex exponential functions with unknown timing errors. This parameter transformation allows the base station to model and compensate for temporal and positional differences between terminals mathematically, maintaining orthogonality despite varying transmission conditions.
Solution Approach 2:
The patent implements a feedback mechanism where the base station measures timing errors based on correlation values and complex exponential multiplications, then uses these measurements to adjust and equalize the timing of signals from different terminals. This feedback loop ensures that orthogonality is restored and maintained despite initial temporal and positional differences.
Data Source
AI summary
The present invention relates to a fast uplink ranging system and method in a mobile communication system. According to the present invention, a fast uplink ranging system transmits two pairs of ranging codes having the same value at locations spaced by half of FFT pointers. The fast uplink ranging system calculates a correlation value using the received two pairs of ranging codes. An order in which complex exponential twiddle factors for removing complex exponential terms corresponding to a time delay are searched is determined using the correlation value. Therefore, it is possible to reduce a time required for searching a timing error of a terminal using non-periodic symmetry of complex exponential twiddle factors corresponding to the timing error, compared with a known method of searching a complex exponential twiddle factor.