Signaling Alternative Modulation Coding Schemes in Random Access
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Solution Overview
Problem
Wireless communication systems face challenges in determining and signaling alternative modulation coding schemes (MCSs) not included in default tables, particularly during initial cell acquisition and random access procedures, where low signal-to-noise ratios and interference affect data throughput and robustness.
Innovation Solution
The described techniques enable wireless devices to indicate and determine alternative MCSs by using scaling factors and reserved fields in control channel messages, allowing for the selection of lower code rates and modulation schemes not listed in default tables, thereby enhancing communication robustness and flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If default MCS tables are used for all transmissions, then device complexity is reduced and ease of operation is improved, but adaptability to low signal-to-noise ratio conditions deteriorates and reliability decreases
Solution Approach 1:
The system dynamically selects between default MCS tables and alternative MCS tables based on signal-to-noise ratio conditions. During random access procedures or when SNR is below a threshold, the network device indicates to the terminal device to use alternative MCS tables with lower code rates, enabling adaptive adjustment without increasing device complexity
Solution Approach 2:
The invention changes the MCS parameters (code rate, modulation scheme) by switching between different MCS tables. Alternative MCS tables contain lower code rates and more robust modulation schemes compared to default tables, allowing the system to adapt to poor channel conditions by selecting appropriate table configurations
2Reliability
If alternative MCSs with lower code rates are used, then communication robustness and reliability are improved, but data throughput decreases
Solution Approach 1:
The system dynamically adjusts code rate based on channel conditions by selecting between default and alternative MCS tables. When channel conditions improve (SNR above threshold), the system switches to default MCS tables with higher code rates for maximum throughput. When conditions deteriorate, it switches to alternative tables with lower code rates for robustness, optimizing the trade-off between reliability and productivity
Solution Approach 2:
The network device periodically evaluates signal-to-noise ratio conditions and adjusts MCS table selection accordingly. This periodic adaptation allows the system to transition between robust low-throughput modes and efficient high-throughput modes based on evolving channel conditions
3Device complexity
If standard MCS tables are used during random access procedures, then device complexity is minimized, but adaptability to varying signal conditions and flexibility in MCS selection are reduced
Solution Approach 1:
The network device pre-configures alternative MCS tables with appropriate low code rates and robust modulation schemes before random access procedures begin. During random access, the network device indicates to the terminal device which alternative MCS table to use based on observed signal conditions, enabling flexible adaptation without requiring terminal devices to store or manage multiple MCS tables
Solution Approach 2:
The network device acts as an intermediary that manages alternative MCS tables and provides selection indications to terminal devices. This intermediary approach allows the network to maintain multiple MCS table configurations while terminal devices use only default tables, achieving high adaptability without increasing terminal device complexity
Data Source
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AI summary
Wireless devices may employ techniques for indicating alternative modulation coding schemes (MCSs) (e.g., MCS values or MCS indices not associated with a default list or default MCS table). That is, communications (e.g., such as physical downlink control channel (PDCCH) transmissions carrying downlink control information (DCI), physical downlink shared channel (PDSCH) transmissions carrying uplink grants, etc.) may include information (e.g., in MCS fields and reserved fields) that indicate alternative MCSs for subsequent communications. For example, random access radio network temporary identifier (RA-RNTI) scrambled DCI, random access response (RAR) messages, etc., may indicate an alternative MCS for subsequent messages in a random access procedure (e.g., for a RAR, an RRC connection request, etc.). The alternative MCS may be conveyed by indicating information such as MCS scaling factors, alternative MCS table IDs, MCS indices associated with the alternative MCS table, or some combination thereof.