PRACH Preamble Segmentation for Reduced FFT Load
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Solution Overview
Problem
The existing wireless communication systems require significant FFT processing at the receiving eNodeB, which is resource-intensive and costly, especially with the increasing number of antenna elements needed for 5G technologies, necessitating a reduction in FFT processing to enhance efficiency and reduce hardware and energy consumption.
Innovation Solution
A method where user terminals create PRACH preambles comprising a sequence of identical random access sequences, each of the same length as OFDM symbols, allowing for reduced FFT processing by reusing the same FFT windows for PRACH and other channels, and optionally shortening the preamble with an initial guard time to align with sub-frame intervals, thereby eliminating the need for special PRACH FFT processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PRACH preambles with long sequence lengths are used, then sufficient output power and PRACH coverage are achieved, but significant FFT processing load and hardware complexity are required at the receiving eNodeB
Solution Approach 1:
The PRACH preamble is segmented into multiple identical random access sequences (e.g., 14 sequences of 1800 samples each) instead of using a single long sequence. This segmentation allows the receiving eNodeB to process shorter segments using standard FFT windows, reducing the computational complexity while maintaining the total energy and coverage through the accumulation of multiple sequences
Solution Approach 2:
The invention uses identical copies of the random access sequence repeated multiple times within the PRACH preamble. This copying approach allows the receiver to use the same FFT processing window and algorithms for each copy, eliminating the need for special long-sequence processing hardware while maintaining sufficient output power through the combined energy of all copies
2Power
If the PRACH preamble length is extended to produce sufficient output power, then PRACH coverage is enhanced, but the processing time and computational resources at the receiver increase
Solution Approach 1:
The PRACH preamble employs periodic repetition of the random access sequence at regular intervals within the preamble structure. This periodic action distributes the total energy across multiple time instances, allowing the receiver to accumulate power over time using standard processing windows, thereby achieving sufficient output power without extending the overall processing time beyond normal sub-frame intervals
3Measurement precision
If special PRACH FFT processing is implemented, then accurate timing offset estimation is achieved, but hardware cost and energy consumption increase
Solution Approach 1:
The invention makes the standard OFDM/SC-FDMA FFT processing windows universal for both data channel processing and PRACH processing. By structuring the PRACH preamble to fit within standard FFT window boundaries, the same hardware and algorithms used for regular data processing can also process PRACH, achieving accurate timing offset estimation without dedicated special-purpose hardware or increased energy consumption
Data Source
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AI summary
The present invention relates to a 1. A method in a wireless communications system. The wireless communication system comprising a base station and one or more user equipments, UEs, (4a, 4b). The UE communicates with the base station using OFDM based symbols. The method comprises creating, in a UE, a PRACH preamble, transmitting the PRACH preamble (from the UE to the base station and receiving, in the base station the PRCH preamble. The present invention also related to a corresponding wireless communication system.