MCS Selection via Sub-channel Segmentation in OFDMA
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Solution Overview
Problem
Existing link adaptation methods in wireless communication systems, particularly in unlicensed bands, face challenges in timely MCS selection due to rapid channel variations and interference, leading to inefficient spectrum usage and delayed adaptations.
Innovation Solution
A method that enables terminal devices and network nodes to instantly determine and select an optimal MCS by measuring sub-carriers, allowing for immediate adjustments based on channel quality indicators across the entire bandwidth, decoupling MU scheduling and link adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If link adaptation is based on implicit feedback using packet error rate, then the system can operate without complex feedback mechanisms, but the adaptation speed is slow due to PER being measured over a long period
Solution Approach 1:
The patent applies preliminary action by having the terminal device measure and report channel quality indicators for multiple sub-channels in advance before actual data transmission begins. The network node pre-determines the optimal MCS and sub-channel assignment based on these advance measurements, enabling fast adaptation without waiting for error rate statistics to accumulate during transmission.
2Adaptability or versatility
If MCS selection is based on CQI feedback from terminals, then the transmitter can use feedback to determine suitable MCS, but the feedback may be inadequate when channel conditions change rapidly or when transmissions occur at different frequency channels
Solution Approach 1:
The patent segments the frequency channel into multiple sub-channels, each with its own channel quality indicator. The terminal device measures and reports CQI for each sub-channel individually, allowing the network node to select the optimal sub-channel and MCS combination. This segmentation enables precise adaptation even when overall channel conditions change rapidly or when operating at different frequency channels.
Solution Approach 2:
The terminal device performs preliminary measurements of channel quality indicators for multiple sub-channels before actual data transmission. This advance characterization of channel conditions allows the network node to pre-determine optimal MCS and sub-channel assignments, ensuring accurate adaptation even when channel conditions change rapidly during operation.
3Productivity
If joint MU scheduling and link adaptation are performed simultaneously to maximize overall throughput, then spectrum usage efficiency improves, but the complexity of the optimization algorithm increases and may not be applicable to unlicensed band systems
Solution Approach 1:
The patent segments the link adaptation process from multi-user scheduling by having the terminal device independently measure and report channel quality indicators for each sub-channel. This segmentation allows the network node to make simple, rule-based MCS selections for each user independently, avoiding complex joint optimization algorithms while still achieving good overall throughput in unlicensed band systems.
Data Source
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AI summary
This disclosure provides a method, performed in a terminal device, for modulation and coding scheme, MCS, selection for a link between a network node and the terminal device in an orthogonal frequency division multiple access, OFDMA, based system. The OFDMA-based system provides a plurality of sub-carriers. The method comprises measuring a channel quality information for a set of sub-carriers corresponding to a sub-channel on which the terminal device transmits and/or receives, and/or on sub-carriers assigned to other terminal devices, and determining a channel quality indicator for the plurality of sub-carriers based on the measured channel quality information. The method comprises determining, based on the channel quality information information, a MCS recommendation to be used on a currently used sub-channel to the network node and/or on at least one other sub-carrier to the network node; and transmitting the determined MCS recommendation and/or the determined plurality of channel quality indicators to the network node.