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.