Random Access Preamble Sequence Design for 5G Timing Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current random access techniques in wireless communication systems, particularly in LTE, require large FFTs for PRACH preamble detection, leading to increased complexity and power consumption, and are limited by assumptions of low propagation delays and Doppler shifts, which are not suitable for emerging 5G technologies with many antenna elements and varying propagation conditions.
Innovation Solution
A method for generating preamble sequences using identical short sequences and offset indicator sequences, allowing for the same FFT size to be used for both data and preamble processing, which resolves ambiguity in arrival time estimation and supports operation in both small and large cells by concatenating short sequences with offset indicators at specific locations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large FFT is used for PRACH preamble detection, then detection accuracy is improved, but device complexity and power consumption increase
Solution Approach 1:
The PRACH preamble detection process is segmented into two stages: first, a small FFT is applied to the entire preamble sequence to identify candidate positions; second, larger FFTs are applied only to selected candidate regions. This segmentation allows accurate detection while reducing overall computational complexity by avoiding a single large FFT across the entire preamble duration.
2Measurement precision
If large FFT is used for PRACH preamble detection, then detection accuracy is improved, but power consumption increases
Solution Approach 1:
The detection process is divided into coarse and fine stages. The small FFT operates on the entire preamble sequence with low power consumption to identify candidate regions. Subsequent larger FFTs are performed only on these limited candidate regions, significantly reducing total power consumption compared to performing a large FFT across the entire preamble sequence while maintaining detection accuracy.
3Measurement precision
If PRACH preamble covers long time interval, then timing offset estimation range is improved, but assumptions on propagation conditions become more restrictive
Solution Approach 1:
The long PRACH preamble sequence is processed in segmented fashion using small FFT across the entire duration to capture wide timing offsets, followed by targeted larger FFTs on candidate regions. This allows the system to maintain adaptability to varying propagation conditions (high mobility, frequency errors, Doppler shifts) while achieving accurate timing offset estimation over large ranges.
Solution Approach 2:
The detection approach dynamically adapts to propagation conditions by first identifying candidate regions using small FFT, then applying larger FFTs only where needed. This dynamic two-stage process removes restrictive assumptions about low mobility and stable propagation conditions, allowing the system to handle diverse 5G scenarios including high-speed mobility and varying Doppler conditions.
4Reliability
If dedicated large FFT is implemented for each antenna, then random access detection reliability is improved, but hardware requirements increase
Solution Approach 1:
For multi-antenna systems, the small FFT is applied to all antenna elements simultaneously to identify common candidate regions. Then, larger FFTs are applied only to these candidate regions for each antenna, reducing the total number of large FFT operations needed while maintaining detection reliability across multiple antennas.
Solution Approach 2:
The small FFT processor is designed to handle multiple antenna inputs simultaneously, performing a universal initial detection stage that identifies candidate regions for all antennas. This universal processing reduces the need for separate dedicated large FFT hardware for each antenna, lowering overall hardware requirements while maintaining multi-antenna detection reliability.
Data Source
AI summary
The present disclosure relates to random access in wireless communication systems, and in particular to a wireless device, a preamble receiver, and methods for processing random access preamble signals. A disclosed method in a wireless device comprises generating (S11) one or more identical short sequences having a same time duration as an OFDM symbol used for carrying data traffic in a radio access network of the wireless device. The method also comprises generating (S12) at least one offset indicator sequence different from each of the short sequences, and constructing (S13) the preamble sequence by concatenating the at least one offset indicator sequence and the one or more identical short sequences in time, such that each of the at least one offset indicator sequence has a respective pre-determined location in the preamble sequence.