Probabilistic Amplitude Shaping

Technical Explanation

Instead of changing the physical coordinates of constellation points (like geometric shaping), Probabilistic Amplitude Shaping (PAS) keeps points on a standard square grid but alters the probability of transmitting each point. Using a distribution matcher, inner low-power symbols are transmitted frequently, while outer high-power corner symbols are transmitted rarely, following a Maxwell-Boltzmann distribution and closing the gap to Shannon capacity.

Key Functions

• Transmitting low-energy constellation points more frequently than high-energy points
• Distribution matcher circuits converting uniform data bits into shaped symbol distributions
• Seamless integration with standard, mature square-QAM receiver demodulators
• Continuous fine-grained tuning of transmission data rates without changing symbol rates
• Adopted across high-capacity coherent optical backhaul and 6G Sub-THz radio links