Adaptive Data Rate Forward-Scatter Radio System
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Solution Overview
Problem
Tropospheric-scatter radio systems face challenges in adaptive data rate communication due to fading channels with dispersive effects, particularly in forward-scatter environments, where existing technologies struggle with efficient signal demodulation and error correction at low signal-to-noise ratios and high-order signal constellations, especially in systems with orthogonal polarization transmissions.
Innovation Solution
A transmitter/receiver apparatus and method that employs dual-polarization transmissions and adaptive receiver techniques, using channel estimation and equalization to compensate for fading, with a Least-Means Squared Error optimization approach for channel and equalizer calculations, enabling efficient operation at noisy uncoded signal-to-noise ratios and across a range of multipath widths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If adaptive equalization and fading compensation techniques are used, then signal demodulation performance is improved, but system complexity increases
Solution Approach 1:
The system dynamically adjusts equalization span, data rate, and modulation order based on measured channel parameters (delay spread, signal-to-noise ratio, polarization correlation coefficient). This allows the receiver to adapt its complexity to match actual channel conditions, using more sophisticated equalization only when necessary.
Solution Approach 2:
The equalization span is made dynamic rather than fixed, allowing the receiver to expand or contract the equalization window based on measured delay spread values. This dynamic adjustment optimizes performance while avoiding unnecessary computational complexity in conditions requiring less equalization.
2Productivity
If higher-order signal constellations are used, then data rate is improved, but performance at low signal-to-noise ratios deteriorates
Solution Approach 1:
The system dynamically selects modulation order and data rate based on measured signal-to-noise ratio and channel conditions. When signal-to-noise ratio is low, the system automatically reduces to more robust lower-order constellations. When conditions improve, higher-order modulations are enabled to increase data rate.
Solution Approach 2:
The modulation order is changed as a variable parameter rather than being fixed, allowing the system to optimize the trade-off between data rate and reliability based on current channel quality measurements.
3Productivity
If orthogonal polarization transmissions are used, then frequency spectrum efficiency is improved, but mutual interference between polarizations occurs
Solution Approach 1:
The receiver measures the polarization correlation coefficient and feeds this information back to the transmitter. Based on this feedback, the transmitter adjusts its processing to account for the measured polarization coupling, reducing mutual interference through adaptive signal processing.
Solution Approach 2:
The patent introduces polarization correlation compensation as an intermediary processing step that mediates between the two orthogonal polarization channels. This compensation mechanism reduces the harmful coupling effects while preserving the frequency efficiency benefits of dual-polarization operation.
4Adaptability or versatility
If large equalization span is used to cover large delay spread, then coverage range is improved, but computational complexity increases
Solution Approach 1:
The equalization span is made dynamic, automatically adjusting its size based on measured delay spread values. When delay spread is small, the equalization span is reduced to minimize complexity. When delay spread increases, the span expands to maintain coverage, balancing performance and computational requirements.
Data Source
AI summary
A transmitter/receiver apparatus and method provide adaptive data rate fading compensation that utilize dual-polarization transmissions at a constant modulation-symbol rate over a forward-scatter radio link and that employ adaptive receiver techniques that operate efficiently at the noisy uncoded signal-to-noise ratio threshold of present-day forward-error correction codes over the range of multipath widths in such forward-scatter environments. The dual-polarization transmissions support both dual transmission and dual diversity configurations. The adaptive receiver techniques include adaptive channel matched filtering and adaptive equalizing at the modulation-symbol rate.