Outer Loop Adjustment for Link Adaptation in MIMO Systems
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Solution Overview
Problem
Current wireless communication systems face challenges in link adaptation, particularly in MIMO systems, where using a single outer loop for both code words can lead to throughput degradation due to incorrect assumptions about channel conditions, especially at higher data rates where cell-specific reference signal interference from neighbor cells is dominant.
Innovation Solution
Implementing a method that switches between two outer loop adjustment processes based on channel quality, using a first outer loop adjustment process at high channel quality and a second, faster-converging process at low channel quality, to determine optimal modulation and coding levels for each code word transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single outer loop adjustment process is used for both code words in MIMO transmissions, then the system complexity is reduced, but throughput degradation occurs due to incorrect assumptions about channel conditions
Solution Approach 1:
The patent segments the single outer loop adjustment process into two separate processes: a first outer loop adjustment process for determining link adaptation of a first code word, and a second outer loop adjustment process for determining link adaptation of a second code word. This segmentation allows each code word to be adjusted independently based on its specific channel conditions, resolving the contradiction by sacrificing some system complexity to gain significant throughput improvement.
2Measurement precision
If outer loop adjustment is used to track channel conditions, then link adaptation accuracy is improved, but convergence speed is reduced at low channel quality
Solution Approach 1:
The patent implements dynamic adjustment of outer loop parameters based on channel quality conditions. At high channel quality (high SINR), the system uses a first outer loop adjustment process with specific increment values optimized for accurate tracking. At low channel quality (low SINR), the system switches to a second outer loop adjustment process with different increment values that enable faster convergence. This dynamic adaptation resolves the contradiction by optimizing the adjustment process for current channel conditions.
Solution Approach 2:
The patent changes the parameters of the outer loop adjustment process based on SINR conditions. Specifically, it modifies the increment values applied to the GINR (Gain to Interference plus Noise Ratio) depending on whether the channel quality is high or low. This parameter change allows the system to achieve both accurate tracking and fast convergence by selecting appropriate increment values for different operating conditions.
3Ease of operation
If a single GINR adjustment is applied to both code words, then the control mechanism is simplified, but performance degradation occurs when code words experience different interference levels
Solution Approach 1:
The patent segments the single GINR adjustment mechanism into two independent GINR adjustments: a first GINR for the first code word and a second GINR for the second code word. Each GINR is adjusted independently based on its specific channel conditions and interference levels. This segmentation maintains reliability by allowing differential adjustment while preserving ease of operation through systematic control of each code word's parameters.
Solution Approach 2:
The patent applies local quality by allowing different GINR adjustment parameters for different code words based on their local channel conditions. When code words experience different interference levels from cell-specific reference signals or other sources, each code word receives tailored adjustment parameters optimized for its specific situation. This local optimization resolves the contradiction by maintaining simplicity through systematic control while achieving reliability through condition-specific adjustment.
Data Source
AI summary
A method and system for performing link adaptation are disclosed. According to one aspect, a method in a wireless communication system for performing link adaptation is provided. The method includes, when a first measure of channel quality is higher than a first predetermined amount, using a first outer loop adjustment process directed to determining link adaptation for a first data transmission transmitted to a wireless device. The method also includes, when the first measure of channel quality is lower than a second predetermined amount, using a second outer loop adjustment process different from the first outer loop adjustment process directed to determining link adaptation for a second data transmission transmitted to the wireless device.