ACK/NACK Code Allocation for Cross-Interference Reduction
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Solution Overview
Problem
In cellular wireless communication systems, especially in the EUTRA system, there is a challenge in minimizing cross interference between ACK/NACK channels, particularly in fast-moving environments, where the use of cyclic shifts and Walsh codes for multiplexing control information leads to orthogonality loss and increased interference due to time selective fading.
Innovation Solution
The solution involves allocating orthogonal cover Walsh codes to ACK/NACK channels based on cross-interference levels, performing orthogonal cover hopping between slots, and selecting specific subsets of Walsh codes to minimize interference, thereby randomizing interference from neighboring cells and fast-moving user effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If cyclic shifts and Walsh codes are used for multiplexing ACK/NACK channels, then the number of multiplexed channels is increased, but cross interference between channels increases in fast-moving environments
Solution Approach 1:
The patent applies dynamics by making the orthogonal cover code selection variable based on channel conditions and UE velocity. Instead of using fixed Walsh codes, the system dynamically selects orthogonal cover codes from different subsets depending on the detected UE movement state, adapting the multiplexing scheme to minimize interference in fast-moving environments while maintaining capacity in stationary scenarios.
Solution Approach 2:
The patent changes the parameter of orthogonal cover code subset selection based on UE velocity detection. When high mobility is detected, the system switches to using orthogonal cover codes from subsets that are less susceptible to time-selective fading, thereby changing the interference characteristics without reducing the number of multiplexed channels.
2Reliability
If orthogonal cover codes are used for ACK/NACK transmission, then reception reliability is improved, but orthogonality is lost in fast-moving environments due to time selective fading
Solution Approach 1:
The system dynamically adapts the orthogonal cover code selection based on detected UE velocity and channel conditions. For high-speed UEs, the system selects codes from subsets that maintain better orthogonality under time-selective fading, while for low-speed UEs, the full set of orthogonal codes can be used to maximize reception reliability.
Solution Approach 2:
The patent changes the orthogonality parameter by selecting from multiple orthogonal cover code subsets with different correlation properties. When time-selective fading is detected, the system switches to subsets that preserve orthogonality better under such conditions, thereby maintaining reception reliability despite the loss of perfect orthogonality.
3Object-affected harmful factors
If Walsh code subsets are selected to minimize cross interference, then interference from neighboring cells is reduced, but the complexity of code allocation increases
Solution Approach 1:
The patent applies preliminary action by pre-defining multiple orthogonal cover code subsets with known interference characteristics before transmission. The base station detects UE velocity and channel conditions, then selects the appropriate pre-configured subset, avoiding the need for complex real-time optimization while still minimizing cross-interference from neighboring cells.
Data Source
AI summary
A method and apparatus are provided for allocating code resources to ACK/NACK channel indexes, when UEs need ACK/NACK transmission in a wireless communication system in which a predetermined number of orthogonal cover Walsh codes is selected from among available orthogonal cover Walsh codes, at least one subset is formed, having the selected orthogonal cover Walsh codes arranged in an ascending order of cross interference, subsets are selected for use in first and second slots of a subframe, and the orthogonal cover Walsh codes of the subset selected for each slot and ZC sequence cyclic shift values are allocated to the ACK/NACK channel indexes.