Zadoff-Chu Sequence Generation for LTE Inter-Cell Interference
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Solution Overview
Problem
In the 3GPP LTE system, the use of Zadoff-Chu CAZAC sequences for reference signals leads to significant inter-cell interference due to differences in sequence lengths from neighboring cells, which affects cross-correlation values and signal multiplexing.
Innovation Solution
The method involves generating CAZAC sequences using prime number lengths and employing truncated or padded sequence generation techniques to maximize sequence numbers while maintaining auto- and cross-correlation properties, and grouping sequences to minimize interference by allocating those with high cross-correlation relations to the same cell or Node B.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Zadoff-Chu CAZAC sequences of different lengths are used in neighboring cells, then sequence multiplexing flexibility is improved, but inter-cell interference increases due to significant cross-correlation values
Solution Approach 1:
The patent changes the parameter of sequence length from variable to fixed (all sequences have the same length L in the same cell). This parameter change ensures that cross-correlation values remain controlled and predictable, preventing inter-cell interference while still allowing sequence multiplexing through cyclic shifts and root index variations within the fixed length framework
Solution Approach 2:
The patent applies different sequence generation rules to different locations (cells). Each cell uses sequences of fixed length L, but neighboring cells can use different root indices and cyclic shift values. This local quality approach allows flexibility within each cell while maintaining controlled interference between cells through proper sequence design
2Adaptability or versatility
If reference signal sequences are truncated to match resource block sizes, then sequence length adaptability is improved, but auto-correlation and cross-correlation properties deteriorate
Solution Approach 1:
Instead of truncating sequences, the patent changes the approach by generating sequences of fixed length L that exactly matches the resource block size requirements. This parameter change eliminates the need for truncation while maintaining perfect auto-correlation and cross-correlation properties, as the sequences are designed from scratch with the correct length rather than being cut from longer sequences
Solution Approach 2:
The patent inverts the conventional approach: instead of generating long sequences and truncating them to fit resource blocks, it generates sequences of the exact required length L from the beginning. This inversion eliminates the harmful effects of truncation on correlation properties while achieving the same adaptability goal
3Device complexity
If the same root index ZC sequence is used across all cells, then sequence generation complexity is reduced, but inter-cell interference increases due to overlapping frequency bands
Solution Approach 1:
The patent applies local quality by allowing different root indices in different cells. Each cell can be assigned a specific root index from the available set, creating local differentiation that reduces inter-cell interference. Within each cell, the same root index sequence is used with different cyclic shifts, maintaining simplicity while achieving interference reduction through inter-cell variation
4Quantity of substance
If cyclic shifts are applied to ZC sequences for multiplexing, then user multiplexing capacity is improved, but sequence length variation causes significant cross-correlation with sequences from neighboring cells
Solution Approach 1:
The patent changes the parameter of sequence length to be fixed across all users and cells. By ensuring all sequences have the same length L and are properly designed with appropriate root indices and cyclic shifts, the patent maintains high user multiplexing capacity while controlling cross-correlation values, preventing the significant interference that occurs with variable length sequences
Data Source
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AI summary
Method and transmitting party device for transmitting a reference signal sequence using a Zadoff-Chu (ZC) sequence, the method comprising: acquiring a base sequence among a plurality of base sequences, wherein the plurality of base sequences are divided into groups, wherein each of the plurality of base sequences is generated by a cyclic extension of a q-th root ZC sequence, wherein each of the plurality of groups comprises base sequences having variable lengths, wherein a sequence group index "u" is determined based on a cell of the transmitting party, and wherein the "q" is determined by using the "u" and a length of the q-th root ZC sequence; applying a cyclic shift to the acquired base sequence to generate the reference signal sequence; and transmitting the reference signal sequence to a receiving party.