Uplink Delay Estimation via Frequency Domain Processing
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Solution Overview
Problem
Current methods for uplink transmission delay estimation in wireless communication networks, especially in satellite contexts, face challenges with high complexity and latency, particularly due to the large Doppler frequency shift caused by the high-speed relative motion between satellites and user equipment, which complicates timing uncertainty handling and interferes with signal synchronization.
Innovation Solution
A method that involves receiving random access preambles, applying Fast Fourier Transform, multiplying sequences with complex conjugates, computing weighted sums to determine candidate values, selecting the candidate with the smallest error, and calculating the delay to achieve precise time delay estimation with reduced complexity and latency, even in noisy conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a N-IFFT is applied for each preamble sequence to estimate transmission delay, then measurement precision is improved, but device complexity and processing time increase significantly
Solution Approach 1:
The patent extracts only the necessary information from the received signal by removing cyclic prefixes to obtain preamble sequences, then applies FFT only to these extracted sequences rather than processing the entire received signal. This selective extraction reduces processing complexity while maintaining delay estimation precision.
Solution Approach 2:
Instead of applying IFFT in the time domain as in prior art, the patent inverts the approach by working in the frequency domain: applying FFT to preamble sequences, multiplying by complex conjugates of transmitted sequences, and computing sums of products. This frequency-domain approach achieves the same delay estimation with reduced computational complexity.
2Measurement precision
If a N-IFFT is applied for each preamble sequence to estimate transmission delay, then measurement precision is improved, but processing latency increases
Solution Approach 1:
The patent replaces the time-domain IFFT operation with frequency-domain operations (FFT, complex multiplication, and summation). This substitution leverages the mathematical equivalence between time-domain correlation and frequency-domain multiplication, achieving the same delay estimation result with lower computational complexity and reduced processing latency.
3Reliability
If Doppler frequency shift correction is performed at the UE side, then signal synchronization is improved, but timing uncertainty handling becomes more complex
Solution Approach 1:
The patent moves the delay estimation problem from the time domain to the frequency domain. By analyzing the phase differences of frequency domain samples across multiple subcarriers, the method estimates delay without being directly affected by Doppler frequency shifts. This dimensional transformation allows the base station to handle timing uncertainty more easily while maintaining synchronization accuracy.
Data Source
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AI summary
A method for an uplink transmission delay estimation between a user equipment and a base station in a wireless communication network is disclosed. At least one random access preamble is received by the base station. The cyclic prefix is first removed (S402), an N-FFT is applied (S404) and the obtained sequence in the frequency domain is multiplied (S406) with a complex conjugate of a corresponding transmitted preamble sequence to obtain for each subcarrier k, a sequence of values Zk. A set of sums S[s] is computed (S408) from Zk. C candidate values Γ[c] are calculated (S414), each being a weighted linear combination of Γcs=Ssse−j2πlcss where 1[c,s] is a phase correcting factor. The candidate Copt among the C candidates with a smallest associated error calculated with respect to the sums S[s] is selected. A phase is determined responsive to the selected candidate. A delay is determined (S420) responsive to the determined phase.