PPM Waveform Generation Using Lookup Table Feedback
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Solution Overview
Problem
Current methods for generating Pulse Position Modulated (PPM) lidar waveforms are computationally intensive and limited in applicability, particularly when creating waveforms that are too long, leading to reduced peak-to-maximum-sidelobe ratios (PMSLR) and increased hardware constraints such as size, weight, and power consumption.
Innovation Solution
A method involving a two-column lookup table to efficiently generate long PPM waveforms by selecting candidate modulation levels, updating the lookup table based on differences between code elements, and discarding elements that exceed a desired maximum sidelobe height, allowing for the creation of high-performance waveforms with extremely high PMSLRs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If conventional methods are used to generate long PPM waveforms, then waveform length can be increased, but computational complexity and processing time increase significantly
Solution Approach 1:
The patent segments the waveform generation process into modular components: initializing a base code, iteratively appending candidate elements, and using a two-column lookup table to track code differences. This segmentation allows long waveforms to be built incrementally without requiring complex full-waveform processing at each step.
Solution Approach 2:
The patent performs preliminary actions by pre-initializing a base PPM code and pre-structuring the two-column lookup table before the main waveform generation loop. This preliminary setup enables efficient iterative expansion without repeated complex calculations, reducing overall computational burden.
2Duration of action of moving object
If waveform length is extended to improve signal detection, then peak-to-maximum-sidelobe ratio decreases, but the invention maintains high PMSLR through efficient code construction
Solution Approach 1:
The patent implements feedback by continuously monitoring code differences through the two-column lookup table during iterative element selection. When a candidate element would create unacceptable sidelobes (exceeding maximum sidelobe height), the algorithm detects this through the lookup table and backtracks or selects alternative elements, ensuring PMSLR constraints are maintained throughout waveform construction.
Solution Approach 2:
The patent changes parameters by dynamically adjusting waveform code elements based on lookup table data. Instead of using fixed or random elements, the algorithm selects modulation levels that optimize the distribution of code differences, thereby maintaining high PMSLR even as waveform length extends to over 10^6 elements.
3Ease of manufacture
If existing techniques are used for waveform generation, then implementation is straightforward, but runtime and memory requirements become prohibitive for very long waveforms
Solution Approach 1:
The patent uses copying by maintaining a compact two-column lookup table that replicates and organizes code difference information efficiently. Instead of storing or processing full waveform data repeatedly, the algorithm copies and updates only the essential difference metrics in the lookup table, dramatically reducing memory requirements and runtime for long waveform generation.
4Measurement precision
If PPM waveforms are used for unambiguous ranging, then range accuracy improves, but current generation methods are limited in applicability
Solution Approach 1:
The patent achieves universality by creating a waveform generation algorithm that can produce PPM codes of any desired length while maintaining high PMSLR. The method is adaptable to different application requirements (varying waveform lengths, different maximum sidelobe heights) and can be implemented across different lidar systems, making it broadly applicable beyond the limitations of existing techniques.
Data Source
AI summary
A lidar for generating long PPM waveforms receives an initial PPM code element including a number of code elements and a desired maximum sidelobe height; b) generates a two-column lookup table; c) selects a candidate modulation level; d) compares the values of the number of times a code element difference has been observed in the initial PPM code element from the lookup table against the desired maximum sidelobe height; e when a value of the number of times exceeds the desired maximum sidelobe height, discards the selected candidate modulation level, decrements corresponding values in the lookup table and repeats steps c to d; f otherwise, appends the selected candidate modulation level to the end of the initial PPM code element to update the initial PPM code element, and repeats steps c to f N times to generate a PPM waveform of length N.