Coordinated Cyclic Shift Hopping for Zadoff-Chu Sequence Interference
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Solution Overview
Problem
Zadoff-Chu sequences used in LTE uplink systems face issues with large cross-correlation properties leading to interference during demodulation, and there are not enough proper mother sequences for sufficient randomization, especially in scenarios where adjacent cells operate with the same ZC mother sequence, affecting orthogonality and separation of control signals from different UEs.
Innovation Solution
A coordinated cyclic shift hopping scheme is implemented, which includes randomization inside and outside a Transmission Time Interval (TTI), using pre-defined shift hopping patterns to maximize cyclic shift separation and rotation, and cell-specific rotations to avoid interference between cells, ensuring improved cross-correlation and interference averaging properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ZC sequences are used for uplink transmission with cyclic shifts for multiplexing, then orthogonality between different UEs is achieved, but cross-correlation interference occurs when sequences of different lengths are used
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the cyclic shift values and sequence lengths based on channel conditions and interference patterns. Different ZC sequence lengths are used for different UEs, and cyclic shifts are optimized to minimize cross-correlation while maintaining orthogonality, directly resolving the contradiction between reliability and harmful factors.
Solution Approach 2:
The patent introduces dynamic cyclic shift hopping patterns that change over time within and across TTIs. This dynamic approach allows the system to adapt to varying channel conditions and interference patterns, maintaining orthogonality while reducing cross-correlation interference through time-varying sequence configurations.
2Productivity
If the same ZC mother sequence is used in adjacent cells, then resource efficiency is improved, but interference between cells increases due to insufficient randomization
Solution Approach 1:
The patent implements periodic cyclic shift hopping patterns that repeat across TTIs and radio frames. This periodic variation in cyclic shifts provides sufficient randomization between adjacent cells using the same ZC mother sequence, reducing inter-cell interference while maintaining resource efficiency through sequence reuse.
Solution Approach 2:
The patent pre-configures cell-specific cyclic shift hopping patterns and sequence assignments before transmission begins. This preliminary randomization through pre-defined hopping patterns ensures that adjacent cells with the same ZC mother sequence experience reduced interference from the outset, while still allowing efficient resource utilization.
3Adaptability or versatility
If high UE speeds are present, then mobility coverage is improved, but orthogonality between ZC sequences deteriorates
Solution Approach 1:
The patent employs dynamic cyclic shift hopping patterns that adapt to high UE speeds by changing cyclic shifts more frequently within TTIs. This dynamic adjustment compensates for the orthogonality deterioration caused by high mobility, maintaining reliable separation between sequences even when UEs are moving rapidly through the network.
Data Source
Figure 1A~1C
Figure 2~3
Figure 4A~5
AI summary
A cyclic shift of a reference signal is quantized as a combination of a cell specific cyclic shift with an outcome of a pseudo-random hopping, and an indication of the cell specific cyclic shift is broadcast in the cell. In one embodiment the cyclic shift is quantized as a modulo operation on a sum of the cell specific cyclic shift, the outcome of the pseudo-random hopping, and a user specific cyclic shift, in which case an indication of the user specific cyclic shift is sent in an uplink resource allocation and a user sends its cyclically shifted reference signal in the uplink resource allocated by the uplink resource allocation. The cyclic shift may also be quantized according to length of the reference signal as cyclic_shift_symbol= (cyclic shift value * length of the reference signal)/12; where cyclic_shift_value is between zero and eleven and cyclic_shift_symbol is the amount of cyclic shift given in reference signal symbols.