Adaptive Modulation Coding in OFDM Sub-Carriers
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Solution Overview
Problem
In OFDM communication systems, the bit-interleaved coded modulation scheme results in low frequency selectivity, leading to reduced error correction capability for quasi-static frequency selective fading channels, which decreases resource efficiency and requires increased transmit power or reduced data rate to meet error correction requirements.
Innovation Solution
The system divides the entire frequency band into sub-carrier bands, calculating power and transmission bits for each sub-carrier based on available coding methods, selecting the coding method with the highest data rate and determining the modulation method accordingly to optimize data transmission with minimal transmit power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bit-interleaved coded modulation scheme is used, then coding diversity is achieved, but frequency selectivity is reduced leading to lower error correction capability
Solution Approach 1:
The frequency band is divided into multiple sub-carrier bands, and the coding scheme is applied separately to each sub-carrier band. This segmentation allows the system to maintain frequency selectivity within each sub-carrier while achieving coding diversity across the entire bandwidth, resolving the contradiction between error correction capability and frequency selectivity.
Solution Approach 2:
Different coding rates are applied to different sub-carrier bands based on their individual channel conditions. This local quality approach enables optimized error correction for each sub-carrier while maintaining overall system performance, addressing the limitation of uniform coding in bit-interleaved schemes.
2Reliability
If transmit power is increased to meet error correction requirements, then error correction capability is improved, but resource efficiency decreases
Solution Approach 1:
The system dynamically adjusts the coding rate for each sub-carrier band based on real-time channel conditions. This dynamic adaptation allows the system to use lower transmit power when channel conditions are good while maintaining error correction capability when needed, eliminating the need for constant high power transmission.
Solution Approach 2:
The coding rate parameter is changed for each sub-carrier based on channel quality indicators. By varying the coding rate parameter across different sub-carriers, the system achieves optimal error correction with minimal energy consumption, resolving the contradiction between reliability and resource efficiency.
3Reliability
If data rate is reduced to meet error correction requirements, then error correction capability is improved, but productivity decreases
Solution Approach 1:
The data transmission is segmented across multiple sub-carrier bands, each carrying data at its optimal rate. This allows the system to maintain high overall productivity while ensuring error correction capability through selective coding on each sub-carrier, rather than reducing the rate uniformly across all channels.
Solution Approach 2:
The system applies coding only to sub-carriers that require it based on channel conditions, rather than applying uniform coding to all sub-carriers. This partial action approach maintains high data rates on good channels while providing error correction where needed, optimizing the trade-off between productivity and reliability.
Data Source
AI summary
A method and apparatus for controlling AMC in an OFDM communication system in which an entire frequency band is divided into a plurality of sub-carrier bands. In the AMC controlling method, power and a number of transmission bits are calculated for each of the sub-carriers in a predetermined method for each of coding methods available in the OFDM communication system. A data rate for each of the coding methods is calculated based on the number of transmission bits and the power for each sub-carrier. A coding method having a highest of the calculated data rates is selected and a modulation method is determined according to a number of transmission bits in the determined coding method.