Cyclic Shift Interval for Frequency Offset in CAZAC Sequences
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Solution Overview
Problem
The existing methods for establishing cyclic shifts in CAZAC sequences are ineffective in preventing performance deterioration due to frequency offsets, leading to increased detection errors and false alarms, especially in high-mobility cells.
Innovation Solution
A method is introduced to set cyclic shifts based on Doppler shifts, using specific variables such as the number of groups, cyclic shifts per group, and additional shifts to minimize the impact of frequency offsets, by calculating these variables through equations that account for the sequence length and root index, thereby establishing an optimal cyclic shift interval that avoids overlapping with channel responses and aliases.
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 excessive performance deterioration and false alarms
Solution Approach 1:
The patent changes the cyclic shift parameter dynamically based on the frequency offset condition. When frequency offset is detected, the system adjusts the cyclic shift value to a predetermined range that avoids aliasing overlap, thereby maintaining sequence discrimination capability while preventing performance deterioration caused by frequency offset.
Solution Approach 2:
The patent applies preliminary anti-action by pre-determining appropriate cyclic shift values that compensate for expected frequency offset effects. Before frequency offset causes severe aliasing, the system proactively selects cyclic shift values from a predetermined range that ensures channel response aliases do not overlap, thus preventing performance deterioration in advance.
2Quantity of substance
If cyclic shift interval is reduced to increase sequence capacity, then more sequences can be allocated, but frequency offset causes aliasing overlap and detection errors increase
Solution Approach 1:
The patent makes the cyclic shift interval dynamic rather than fixed. The system determines the appropriate cyclic shift interval based on the actual frequency offset conditions in the cell, allowing it to adapt between smaller intervals (when frequency offset is low) and larger intervals (when frequency offset is high), thus optimizing both sequence capacity and detection accuracy.
Solution Approach 2:
The patent changes the cyclic shift interval parameter according to frequency offset measurements. By adjusting this parameter dynamically, the system can allocate more sequences in cells with low frequency offset while maintaining detection accuracy in cells with high frequency offset by using larger intervals that prevent aliasing overlap.
3Ease of manufacture
If conventional cyclic shift allocation is used in high-mobility cells, then implementation is simple, but frequency offset leads to excessive false alarms and throughput degradation
Solution Approach 1:
The patent introduces feedback by measuring the frequency offset in the cell and using this information to determine appropriate cyclic shift values. The system continuously monitors frequency offset conditions and adjusts cyclic shift allocation accordingly, creating a closed-loop system that reduces false alarms while maintaining implementation feasibility through standardized procedures.
Data Source
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AI summary
A method for establishing a cyclic shift sequence to provide against the frequency offset is disclosed. The method calculates a distance between a channel response position of the sequence and an alias channel response position caused by a frequency offset, calculates the number of cyclic shifts per group according to the calculated distance, and establishes the cyclic shift (CS)- applying interval. This method easily establishes a cyclic shift (CS) interval at a specific location having no overlapping by considering a channel response of a reception (Rx) sequence and an alias location of this reception (Rx) sequence, although a reception (Rx) signal is shifted by a channel delay spreading or a propagation delay irrespective of categories of a domain generating a sequence, so that it can greatly reduce the number of the detection errors and the false alarm rate. And, if a sequence of the cyclic shift (CS) is allocated to a cell having a frequency offset of more than a predetermined level, the present invention can minimize the influence of a frequency offset on a high-mobility cell.