Link Adaptation Margin Estimation for Wireless Systems
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Solution Overview
Problem
Existing link adaptation methods in wireless communication systems converge slowly, especially at low to medium traffic loads, leading to inefficient radio link resource utilization due to poor channel quality prediction, particularly in OFDM-like systems with small resource block allocations.
Innovation Solution
A method and arrangement that derive a link adaptation margin estimate by obtaining predicted and actual parameters, calculating error distributions, and using these to support link adaptation, allowing for faster updates and joint interference measurement across user terminals, with separate estimation and measurement of Signal-to-Interference-and-Noise Ratio (SINR) components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional outer-loop algorithms are used for link adaptation, then the system can maintain stability, but the convergence speed is slow and resource utilization is inefficient
Solution Approach 1:
The patent segments the link adaptation process into two independent components: fast inner-loop channel quality estimation (CQI) and slow outer-loop block error rate (BLER) compensation. By separating these functions, the system can update channel quality rapidly while maintaining accurate link adaptation margins, resolving the contradiction between speed and reliability.
Solution Approach 2:
The patent applies preliminary action by pre-calculating and storing the relationship between CQI values and corresponding MCS indices in lookup tables. This allows the base station to quickly determine appropriate transmission parameters without performing complex real-time calculations, thereby achieving fast convergence while maintaining accuracy.
2Productivity
If filtering and back-off strategies are applied for channel quality estimation, then system stability is improved, but spectral efficiency and throughput are reduced
Solution Approach 1:
The patent implements feedback mechanisms where the base station monitors actual transmission performance (ACK/NACK signals) and uses this information to adjust the link adaptation margin. This closed-loop feedback allows the system to maintain stability through controlled adjustments while maximizing spectral efficiency by avoiding excessive conservative margins.
Solution Approach 2:
The patent dynamically changes the link adaptation margin parameter based on observed BLER performance. When performance is better than expected, the margin is reduced to improve throughput; when performance degrades, the margin is increased to restore stability. This adaptive parameter adjustment resolves the contradiction between productivity and stability.
3Measurement precision
If a single outer-loop algorithm is used for all resource block allocations, then implementation is simplified, but performance deteriorates for small allocations
Solution Approach 1:
The patent applies local quality by implementing separate link adaptation mechanisms for different resource allocation sizes. Small resource block allocations use one adaptation strategy optimized for their characteristics, while large allocations use another strategy. This localized approach improves prediction accuracy for each case without requiring a single complex universal algorithm.
Solution Approach 2:
The patent uses partial action by applying different levels of outer-loop compensation based on allocation size. For small allocations where statistics are poor, more aggressive compensation is applied. For large allocations with better statistics, less compensation is needed. This selective application of compensation strategies improves overall accuracy without uniform complexity.
Data Source
AI summary
Method and arrangement in a network entity for supporting link adaptation in a wireless communication system. The method comprises obtaining 204 one or more predicted parameters related to the quality of a radio link. The method further comprises measuring 206 one or more actual parameters, corresponding to the one or more predicted parameters. The method further comprises deriving 208 one or more error distributions based on the difference between the predicted and actual one or more parameters, from which error distributions a link adaptation margin estimate is derived, based on a predetermined radio link quality target. The link adaptation margin estimate is then used for supporting link adaptation for the radio link.