CoMP Phase Combining via ACK/NACK Feedback
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Solution Overview
Problem
In coordinated multipoint (CoMP) transmission systems, the lack of inter-point phase feedback information leads to uncertainty in achieving constructive signal combination, resulting in potential system performance degradation due to convergence in the destructive combining area, especially for outer loop link adaptation algorithms.
Innovation Solution
Adapting the inter-point combiner phase based on ACK/NACK messages received from user equipment, where a NACK indicates potential destructive combining, allowing for phase adjustment to maintain transmission in the constructive combining area without additional feedback, thereby minimizing offset for outer loop link adaptation and improving system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If per point CQI feedback is used without inter-point phase feedback, then device complexity and feedback overhead are reduced, but system performance degrades due to uncertainty in achieving constructive signal combination
Solution Approach 1:
The system uses already-transmitted ACK/NACK messages to convey phase combination information without requiring additional dedicated feedback resources. The ACK/NACK messages serve dual purposes: error indication and phase information carrier, allowing the system to self-adjust the combiner phase using existing communication overhead.
Solution Approach 2:
The invention changes the interpretation and usage of existing feedback parameters (ACK/NACK messages) to encode inter-point phase information. By mapping ACK/NACK patterns to specific phase combinations, the system transforms ordinary error feedback into a mechanism for phase adaptation without adding new feedback channels or increasing overall feedback overhead.
2Reliability
If additional inter-point phase feedback is implemented, then signal combination reliability improves, but feedback overhead and device complexity increase
Solution Approach 1:
The ACK/NACK messages perform multiple functions simultaneously: they indicate packet reception status (traditional function) and convey inter-point phase information (new function). This multi-functionality allows the system to obtain phase feedback without dedicating separate feedback resources, thereby avoiding additional feedback overhead while improving signal combination reliability.
Solution Approach 2:
The system repurposes existing error feedback messages to carry phase adaptation information. Instead of requiring separate phase feedback channels, the system makes the existing ACK/NACK mechanism serve the additional purpose of phase information transmission, eliminating the need for additional feedback resources.
3Device complexity
If outer loop link adaptation operates without accurate phase information, then system simplicity is maintained, but throughput decreases due to convergence in destructive combining area
Solution Approach 1:
The system implements a feedback mechanism where ACK/NACK messages are used to convey phase information back to the transmission points. This feedback loop allows the outer loop link adaptation to adjust the combiner phase based on actual reception outcomes, enabling convergence toward constructive combining and improving throughput without requiring complex additional algorithms.
Solution Approach 2:
The invention modifies the operation of the outer loop link adaptation by incorporating phase adjustment based on ACK/NACK patterns. The adaptation algorithm changes the combiner phase parameter dynamically, allowing the system to escape from destructive combining states and converge to constructive combining, thereby improving throughput while maintaining algorithmic simplicity.
Data Source
AI summary
An arrangement is described for adapting outer loop precoder phase combiner in a radio communication system having coordinated multipoint transmission. In the arrangement ACK/NACK-message received as a response to a transmitted data packet is used for adapting the phase. When a NACK-message is received the phase may be adapted or it may be further determined if the error was due to error in channel code or due to destructive inter-point signal combining. If the error was due to destructive combining the phase is adjusted.