Binomial Pulse-Position Modulation for Free-Space Optical Channels
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Solution Overview
Problem
Current Pulse-Position Modulation (PPM) techniques, including ultra-wideband schemes like differential PPM and combinatorial PPM, face challenges in increasing spectral efficiency and capacity while maintaining decoding complexity within channel bandwidth constraints, and lack inherent coding gain against fading and turbulence in Free-Space Optical (FSO) communications.
Innovation Solution
The implementation of encoded binomial pulse position modulation (BPPM) signals with random, sparse sets of multiple pulses per channel usage interval, combined with encoding techniques like Reed-Solomon codes, to enhance capacity and provide coding gain against fading and turbulence, utilizing non-radix 2 Galois fields and finite rate of innovations for sparse signal reconstruction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional PPM schemes (M-ary PPM, DPPM, CPPM) are used, then spectral efficiency and capacity can be improved, but decoding complexity increases and channel bandwidth requirements increase
Solution Approach 1:
The invention segments the PPM signal into sparse pulses within a channel usage interval, where only a small number of pulses are transmitted out of many possible positions. This segmentation allows the receiver to focus decoding efforts on identifying the positions of these sparse pulses rather than processing a dense sequence, thereby reducing decoding complexity while maintaining spectral efficiency
Solution Approach 2:
The invention changes the parameter of pulse density from dense (conventional PPM) to sparse (encoded BPPM with compressive sensing). By transmitting signals with a small number of pulses per channel usage interval and using compressive sensing reconstruction, the system achieves high spectral efficiency without proportionally increasing decoding complexity, as the sparsity enables efficient signal recovery algorithms
2Reliability
If conventional PPM schemes are used, then modulation capability is achieved, but coding gain against fading and turbulence is not provided
Solution Approach 1:
The invention applies error correction encoding (such as Reed-Solomon codes) to the BPPM signal before transmission. This preliminary encoding action adds redundancy to the sparse pulse positions, enabling the receiver to correct errors caused by fading and turbulence. The encoding is performed once during signal generation, providing ongoing protection against channel impairments without requiring complex real-time processing at the receiver
Solution Approach 2:
The invention combines multiple techniques into a composite modulation scheme: binomial pulse position modulation (BPPM) with error correction coding and compressive sensing. This composite approach integrates the pulse positioning capability of BPPM with the error protection of coding theory and the efficient reconstruction of compressive sensing, achieving both reliability against fading/turbulence and reduced decoding complexity
3Productivity
If narrow pulses are used per channel usage to increase quantization, then capacity increases, but pulse width becomes constrained by channel bandwidth
Solution Approach 1:
The invention moves from the time domain constraint (narrow pulse width) to the spatial/sparse domain by utilizing pulse positions across a channel usage interval. Instead of increasing capacity by making pulses narrower in time, the system increases capacity by selecting from many possible pulse positions within the interval, with only a sparse subset being transmitted. This dimensional shift allows high capacity without requiring extremely narrow pulses that would be constrained by channel bandwidth
Data Source
AI summary
Concepts, systems and methods are provided herein for generating encoded binomial pulse position modulation (BPPM) signals having random, sparse sets of multiple pulses per channel usage interval for use in Free-Space Optical (FSO) communications. A data symbol can be modulated into a set of BPPM pulses for transmission over a FSO channel and a signal can be generated having the set of BPPM pulses over a predetermined time interval. The BPPM pulses can be encoded into one or more codewords based on a number of error correction bits to form a coded signal using the one or more codewords to represent the signal having the set of pulses for transmission over the free-space optical channel. The coded signal can be filtered and sampled to generate a set of samples. Position and amplitude data for the samples can be determined to reconstruct and decode the coded signal.