Random Access Preamble Cyclic Shift Under Frequency Offset
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Solution Overview
Problem
The existing methods for establishing cyclic shift in wireless communication systems, particularly in the context of CAZAC sequences, face challenges in effectively addressing frequency offsets, which lead to performance deterioration and increased false alarm rates due to the difficulty in discriminating between sequences.
Innovation Solution
A method is introduced to set cyclic shifts based on Doppler frequency, using specific equations to determine secondary variables such as the number of groups, cyclic shifts per group, and additional cyclic shifts, to minimize the impact of frequency offsets and prevent sequence deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If cyclic shift is applied to CAZAC sequence, then sequence discrimination capability is improved, but frequency offset causes performance deterioration and false alarms
Solution Approach 1:
The patent applies preliminary action by pre-calculating and selecting cyclic shift values that are specifically designed to be robust against frequency offset before transmission occurs. The base station determines appropriate cyclic shift values from a restricted set that has been pre-configured to minimize Doppler shift impact, thereby preparing the system in advance to handle frequency offset conditions without requiring real-time adjustments during transmission.
Solution Approach 2:
The patent implements parameter changes by modifying the cyclic shift parameter values based on detected Doppler shift conditions. When frequency offset is detected, the system changes the cyclic shift values applied to the CAZAC sequence, selecting from restricted sets of values that are optimized for high-mobility scenarios. This dynamic parameter adjustment allows the system to adapt to varying frequency offset conditions while maintaining sequence discrimination capability.
2Quantity of substance
If cyclic shift interval is reduced to increase sequence capacity, then more sequences can be supported, but frequency offset causes overlapping and detection errors
Solution Approach 1:
The patent applies segmentation by dividing the cyclic shift values into multiple restricted sets, where each set contains values suitable for specific Doppler shift ranges. Instead of using a single uniform cyclic shift interval, the system segments the parameter space and selects appropriate segments based on detected mobility conditions. This allows efficient use of cyclic shift values while preventing overlap caused by frequency offset.
Solution Approach 2:
The patent implements dynamics by making the cyclic shift interval adaptive rather than fixed. The system dynamically adjusts which restricted set of cyclic shift values is used based on real-time detection of Doppler shift magnitude. This dynamic adaptation allows the system to use smaller intervals when frequency offset is low (increasing sequence capacity) while automatically switching to larger effective intervals when frequency offset is high (preventing detection errors).
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 allows for the establishment of cyclic shift intervals that reduce detection errors and false alarm rates, even when frequency offsets occur, and minimizes the influence of frequency offsets in high-mobility cells by optimizing sequence allocation.
Implementation Method 1
A method for setting cyclic shift to be applied to a given sequence against an effect of a high Doppler frequency higher than a predetermined value is provided
Data Source
AI summary
A method for transmitting a random access preamble to a base station at a user equipment (UE) includes generating the random access preamble from a Zadoff-Chu sequence having a length ‘N’ and a root index ‘M’, wherein the random access preamble is defined by a cyclic shift of the Zadoff-Chu sequence and transmitting the generated random access preamble to the base station via a random access channel, wherein the cyclic shift is given by using a variable corresponding to a Doppler shift of one subcarrier spacing, the variable given by using the root index ‘M’, and wherein the cyclic shift is differently given based on whether the variable is smaller than ⅓ of the length ‘N’.