Cell-Specific Cyclic Shifting for Block Spread Signal Randomization
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Solution Overview
Problem
In LTE-A wireless communication systems, there is a lack of sufficient block spreading codes to effectively randomize transmissions between adjacent cells, leading to co-channel interference between UEs using the same block spreading code.
Innovation Solution
The method involves cyclically shifting modulation symbols within a group according to a cell-specific shift pattern and applying a unique spreading code to each UE, ensuring that even when the same spreading code is used across cells, the transmissions are randomized, thereby mitigating co-channel interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If block spreading codes are reused across adjacent cells to increase code availability, then code resource efficiency is improved, but co-channel interference between cells increases
Solution Approach 1:
The patent applies dynamic cyclic shifting to the block spreading codes, where each cell applies a cell-specific cyclic shift value to its spreading codes. This dynamic transformation allows the same base spreading codes to be reused across cells while maintaining orthogonality through time-domain separation, thus increasing code availability while preventing co-channel interference.
Solution Approach 2:
The patent introduces a time-domain dimension by applying cyclic shifts to the block spreading codes. Instead of relying solely on code domain orthogonality, the solution moves part of the separation mechanism to the time domain through cyclic shifting, allowing code reuse in the frequency domain while maintaining interference-free operation through time-domain offset.
2Object-affected harmful factors
If scrambling sequences are applied to randomize transmissions, then interference randomization is improved, but system complexity increases due to additional processing blocks
Solution Approach 1:
The patent makes the cyclic shift operation serve multiple functions: it provides interference randomization between cells, maintains orthogonality of spreading codes, and enables code reuse across cells. This multi-functionality eliminates the need for separate scrambling sequences, achieving interference randomization without additional processing complexity.
Solution Approach 2:
The patent combines the interference randomization function with the existing cyclic shift operation used in the DFT-S-OFDMA framework. Instead of adding a separate scrambling step, the solution merges the randomization requirement into the existing time-domain cyclic shifting mechanism, thereby achieving interference mitigation without increasing system complexity.
3Object-affected harmful factors
If additional DFT operations are introduced to increase randomization, then interference mitigation is improved, but computational complexity and processing overhead increase
Solution Approach 1:
The patent applies cyclic shifting to the block spreading codes before the DFT operation. This preliminary action in the time domain creates time-offset versions of the spreading codes, which when transformed via DFT, produce frequency-domain sequences with built-in interference randomization properties, eliminating the need for additional DFT-based randomization stages.
Data Source
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AI summary
A user equipment locally stores a shift pattern that is specific to a cell to which the user equipment is currently attached, and processes a group of modulation symbols or bits for uplink transmission by a) cyclically shifting the modulation symbols or bits within the group according to the stored cell-specific shift pattern, and b) applying a spreading code to the group of symbols or bits. Different embodiments include spatial shifting and frequency bin shifting.