Definition: A communications receiver in which the phase of the sinusoidal signal carrying the message modulation is determined by receiver circuitry and used to demodulate the message.

Note: By establishing signal phase, that is the ability to distinguish between plus and minus of a sinusoid, a receiver is able to recover data based on modulation schemes which shift the phase of a transmitted signal. Coherent receivers use the absolute phase of received signals to recover information. Extra receiver complexity, usually in the form of a phase-locked-loop, is required in a Coherent Receiver. The benefit achieved at the expense of this increased receiver complexity is the higher efficiency of coherent modulation techniques in terms of the signal power required to achieve a certain bit error rate or the bandwidth required. Partially Coherent Receivers use differences in phase symbol-to-symbol of the received signal to extract their information. Another alternative to a Coherent Receiver is a non-Coherent Receiver, which can only tell the difference between the signals themselves, not plus or minus phases of these signals. Noncoherent modulation usually requires more power than coherent modulation to achieve a given error rate.