Wireless Response Signal Spreading Using Dynamic Cyclic Shifts
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Solution Overview
Problem
In mobile communication systems, the separation performance of response signals code-multiplexed using ZC and Walsh sequences degrades due to changes in channel conditions, particularly when mobile stations move fast, leading to inter-code interference between Walsh sequences.
Innovation Solution
A radio communication apparatus employing a configuration with a first spreading section using sequences with different cyclic shift values and a second spreading section using orthogonal sequences, where the difference in cyclic shift values between adjacent second sequences is minimized to maintain orthogonality and reduce inter-code interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Walsh sequences are used for second spreading to maintain orthogonality, then separation performance is improved in ideal conditions, but inter-code interference increases when mobile stations move fast due to channel condition changes
Solution Approach 1:
The patent changes the cyclic shift parameter of ZC sequences dynamically. Specifically, it sets the cyclic shift amount to be proportional to the mobile station's speed or channel condition, thereby adapting the sequence parameters to match the channel characteristics and maintain separation performance under varying conditions.
Solution Approach 2:
The patent combines two types of sequences (ZC sequences and Walsh sequences) with different properties into a composite spreading scheme. The ZC sequences provide robustness to channel changes through their cyclic shift property, while the Walsh sequences maintain orthogonality in ideal conditions, creating a composite system that leverages both advantages.
2Measurement precision
If cyclic shift values are increased to separate response signals, then inter-code interference between ZC sequences is reduced, but the number of available sequences is limited
Solution Approach 1:
The patent introduces a new dimension for signal separation by using the cyclic shift parameter of ZC sequences in addition to the traditional Walsh sequence dimension. This creates a two-dimensional spreading space (ZC sequence dimension × Walsh sequence dimension), significantly increasing the number of available multiplexing resources.
Solution Approach 2:
The patent utilizes the cyclic shift parameter as an additional degree of freedom for signal separation. By varying the cyclic shift amount based on mobile station characteristics or resource allocation, the system can differentiate between multiple signals without requiring proportionally larger cyclic shift differences, thus maintaining separation performance while maximizing multiplexing capacity.
3Measurement precision
If sufficient cyclic shift value differences are provided between ZC sequences, then separation performance is maintained, but the flexibility in sequence allocation is reduced
Solution Approach 1:
The patent makes the cyclic shift allocation dynamic rather than static. The cyclic shift amount is adjusted based on real-time channel conditions, mobile station speed, or resource allocation requirements. This dynamic approach maintains sufficient separation performance while providing flexible adaptation to different operational scenarios.
Solution Approach 2:
The patent changes the cyclic shift parameter dynamically to balance separation performance and allocation flexibility. By setting the cyclic shift amount as a function of mobile station characteristics or channel state, the system adapts the separation margin to the actual needs of each transmission, avoiding excessive cyclic shift differences when not required and ensuring adequate separation when necessary.
Data Source
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AI summary
A wireless communication apparatus capable of minimizing the degradation in separation characteristic of a code multiplexed response signal. In this apparatus, a control part (209) controls both a ZC sequence to be used in a primary spreading in a spreading part (214) and a Walsh sequence to be used in a secondary spreading in a spreading part (217) so as to allow a very small circular shift interval of the ZC sequence to absorb the interference components remaining in the response signal; the spreading part (214) uses the ZC sequence set by the control part (209) to primary spread the response signal; and the spreading part (217) uses the Walsh sequence set by the control part (209) to secondary spread the response signal to which CP has been added.