MCS Table Adaptation for 256-QAM in LTE Systems
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Solution Overview
Problem
Current LTE systems face challenges in efficiently managing modulation and coding schemes, particularly in high Signal-to-Interference-plus-Noise Ratio (SINR) conditions, where existing schemes do not adequately cover higher spectral efficiencies, leading to suboptimal data transmission performance.
Innovation Solution
The implementation of additional modulation and coding schemes, specifically including 256-QAM, within the LTE system's MCS table, allowing for higher-order modulations to be used in stable and good channel conditions, extending the SINR range covered by the MCS table without increasing the MCS field size, and reinterpreting existing code points to support these higher-order modulations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If existing MCS tables with modulation schemes up to 64-QAM are used, then the system maintains backward compatibility and covers lower to medium SINR ranges, but spectral efficiency is limited in high SINR conditions
Solution Approach 1:
The MCS table is segmented into two separate tables: a first MCS table for coverage-enhanced modes (lower spectral efficiency, more robust) and a second MCS table for peak spectral efficiency modes (higher spectral efficiency, 256-QAM). This segmentation allows the system to select the appropriate table based on channel conditions, thereby resolving the contradiction between achieving high spectral efficiency and maintaining broad SINR range coverage.
Solution Approach 2:
The system dynamically switches between the first and second MCS tables based on channel conditions and coverage enhancement requirements. The network can selectively activate which MCS table to use, allowing adaptive optimization between spectral efficiency and coverage, thus resolving the contradiction between these two opposing requirements.
2Adaptability or versatility
If the MCS field size is increased to support additional modulation schemes, then more modulation and coding schemes can be represented, but signaling overhead increases
Solution Approach 1:
The existing 5-bit MCS field is made multi-functional by introducing a coverage enhancement indicator that repurposes certain code points to indicate selection of the first MCS table versus the second MCS table. This allows the same field to serve both its original function of indicating MCS indices and the additional function of selecting between two different MCS tables, thereby supporting more modulation schemes without increasing field size.
Solution Approach 2:
The interpretation of MCS field values is changed based on the coverage enhancement indicator. Certain code points in the MCS field are reinterpreted to mean different things depending on whether coverage enhancement is activated. This parameter change allows the system to support additional modulation schemes (256-QAM) without requiring additional bits in the signaling field.
3Reliability
If coverage enhanced modes are activated, then reliability is improved in poor channel conditions, but spectral efficiency is reduced
Solution Approach 1:
The system dynamically selects between the first MCS table (coverage enhanced) and the second MCS table (peak spectral efficiency) based on real-time channel conditions and network configuration. When coverage enhancement is needed, the first table with more robust modulation schemes is selected, improving reliability. When channel conditions are good, the second table with 256-QAM is selected, maximizing spectral efficiency. This dynamic selection resolves the contradiction between reliability and spectral efficiency.
Solution Approach 2:
Different parts of the MCS table are optimized for different qualities: the first MCS table is optimized for reliability with more robust modulation schemes suitable for poor channel conditions, while the second MCS table is optimized for spectral efficiency with 256-QAM suitable for good channel conditions. By selecting the appropriate table for the local channel conditions, the system achieves both high reliability when needed and high spectral efficiency when possible.
Data Source
AI summary
The present disclosure relates to adaptive modulation and coding scheme selection and signaling in a communication system. In particular, a modulation and coding scheme to be used for transmission of a data is selected from a set of predetermined modulation and coding schemes. The predetermination of the set is performed by selecting the set from a plurality of predefined sets. The sets have the same size, so that a modulation and coding selection indicator signaled to select the modulation and coding scheme may be advantageously applied to any of the selected sets. Moreover, a second set includes schemes with a modulation not covered by the schemes of a first set, and which is of a higher order than any modulation in the first set.