CQI Table Design for 256QAM in LTE Systems
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Solution Overview
Problem
Current LTE systems do not support 256 Quadrature Amplitude Modulation (256QAM), which limits data rate in high Signal to Interference Plus Noise Ratio (SINR) scenarios, and modifying existing Channel Quality Indication (CQI)/Modulation Coding Scheme (MCS)/Transport Block Size (TBS) tables to include 256QAM is challenging without compromising link adaptation performance or increasing table size.
Innovation Solution
Designing CQI/MCS/TBS tables with 256QAM entries that maintain the same size as existing tables by reusing or removing low SINR region entries, using an offset mechanism in the reserved part of the MCS table, and sampling with different dB spacings to support 256QAM without affecting existing modulation schemes' performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If 256QAM is added to support high data rate, then spectral efficiency is improved, but table size increases
Solution Approach 1:
The patent applies parameter changes by modifying the sampling grid spacing (dB spacing) in different SINR regions to accommodate 256QAM. Specifically, it uses approximately 3 dB spacing for low SINR region, 2 dB spacing for medium SINR region, and 2.5 dB spacing for high SINR region. This non-uniform sampling approach allows 256QAM entries to be integrated into existing CQI/MCS tables without increasing their overall size, while still providing adequate resolution for high-order modulation in high SINR conditions.
2Productivity
If 256QAM entries are added to CQI/MCS tables, then spectral efficiency is improved, but link adaptation performance deteriorates
Solution Approach 1:
The patent applies local quality by implementing region-specific sampling strategies within the CQI/MCS tables. Different SINR regions (low, medium, high) are assigned different sampling densities and grid spacings tailored to their specific requirements. The high SINR region uses 2.5 dB spacing optimized for 256QAM, while low SINR regions maintain coarser spacing appropriate for more robust modulations. This localized optimization ensures that link adaptation performance is maintained in each region while enabling 256QAM support where appropriate.
3Adaptability or versatility
If existing CQI/MCS tables are modified to include 256QAM, then compatibility is maintained, but table design complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the CQI/MCS table into distinct SINR regions (low, medium, high), each with its own sampling grid and spacing characteristics. This segmentation allows independent optimization of each region while maintaining the overall table structure. The low SINR region uses 3 dB spacing, medium SINR uses 2 dB spacing, and high SINR uses 2.5 dB spacing. This segmented approach simplifies the design process compared to a uniform table structure, as each region can be designed and validated independently.
Data Source
AI summary
According to some embodiments, a method of determining a modulation coding scheme in a wireless network comprises receiving a CQI index, wherein the CQI index comprises a four-bit value associated with a channel quality of a wireless signal and identifying an entry in a CQI table based on the CQI index. The CQI table comprises: a first contiguous plurality of table entries associated with low SINR, each entry based on a first sampling grid; a second contiguous plurality of table entries associated with medium SINR, each entry based on a second sampling grid; and a third contiguous plurality of table entries associated with high SINR, each entry based on a third sampling grid. The method further comprises determining a modulation coding scheme based on the identified entry in the CQI table and encoding a transmission block according to the determined modulation coding scheme.