Evaluating the average probability of symbol error for different bandpass modulation schemes Comparing different modulation schemes based on their error performances. Channel coding: Transforming signals to improve communications performance by increasing the robustness against channel impairments (noise, interference, fading, ) Waveform coding: Transforming waveforms to better waveforms Structured sequences: Transforming data sequences into better sequences, having structured redundancy. “Better” in the sense of making the decision process less subject to errors