Gear Shifting in Skywave Radio Systems
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Solution Overview
Problem
High-frequency radio communication channels used in long-distance financial trading applications face significant latency and noise issues, leading to bandwidth limitations that can cause delays in financial instructions, which are financially detrimental.
Innovation Solution
A gear shifting technique is developed that dynamically adjusts modulation mode and equalization to optimize performance, using multiple demodulator-equalizer units to determine if modulation complexity should be increased or decreased based on error-free packets, packet-error ratio, and signal-to-noise ratio, favoring message erasures over errors by limiting bit corrections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If higher complexity modulation modes are used, then channel throughput increases, but receiver error performance deteriorates
Solution Approach 1:
The system dynamically switches between different modulation modes (QPSK, 16-QAM, 64-QAM, 256-QAM) based on real-time channel conditions. The modulation mode is not fixed but adapts to changing signal-to-noise ratio and error rate conditions, allowing the system to optimize between throughput and error performance dynamically
Solution Approach 2:
The system changes the modulation parameter (complexity order) based on channel quality metrics such as packet error rate and signal-to-noise ratio. When channel conditions improve, the system transitions to higher-order modulation to increase throughput; when conditions deteriorate, it switches to lower-order modulation to maintain error performance
2Reliability
If longer equalizer processing time is used, then error performance improves, but system latency increases
Solution Approach 1:
The equalizer processing length is dynamically adjusted based on channel conditions and current modulation mode. The system uses shorter equalizers for higher-order modulations where error performance is more sensitive to latency, and longer equalizers when channel conditions warrant more aggressive equalization
Solution Approach 2:
The system performs preliminary equalization with available processing length before decoding, and uses the detected error rate and packet quality to determine if additional processing is needed. This allows the system to prepare messages for potential retransmission without waiting for complete initial processing
3Reliability
If more bit corrections are permitted, then error performance improves, but message accuracy deteriorates due to erasure favoring
Solution Approach 1:
The system deliberately limits the number of bit corrections permitted during decoding, even when the decoder has the capability to correct more errors. This partial action (limiting corrections) prevents the decoder from making excessive corrections that could lead to wrong message interpretation, thereby maintaining message accuracy while still achieving sufficient error performance through other means such as retransmission
Data Source
AI summary
A gear shifting technique has been developed in which modulation and equalization are shifted to achieve optional performance. In one form, two or more equalizers, each associated with a demodulator and message decoder, determine if the modulation being used can be increased in complexity in order to increase the channel throughput or determine if the modulation method should be reduced in complexity in order to improve the receiver error performance. The quality metrics can based on which equalizer-demodulator-decoder is set to first detect a valid message. Other factors can be considered with this technique such as a packet-error ratio and a signal-to-noise ratio. In a financial trading system, message erasures can be favored over errored messages by limiting the number of bit or symbol corrections permitted per message to less than the maximum possible for the selected decoding schemes.