A transmitter, a receiver, and a signal processing method are provided. The transmitter includes a constellation mapper, a signal conversion module, a digital signal processor, and a digital-to-analog converter. The constellation mapper is configured to determine a mapping relationship between a bit stream and a constellation point in a polar coordinate system, and generate a constellation symbol data flow according to the mapping relationship. The signal conversion module is configured to convert the constellation symbol data flow into an amplitude signal and a phase signal, where the amplitude signal is a 2-level analog signal, and the phase signal is an 8-level digital signal. The digital signal processor is configured to perform digital signal processing on the phase signal, to generate a multi-level digital signal. The digital-to-analog converter is configured to convert the multi-level digital signal into a multi-level analog signal.