synchronous detection

An estimate of the channel phase and attenuation is recovered. It is then possible to reproduce the transmitted signal and demodulate.
Requires a replica carrier wave of the same frequency and phase at the receiver.
The received signal and replica carrier are cross-correlated using information contained in their amplitudes and phases.
Also known as synchronous detection

The most common, and easiest, way to transmit digital signals is to use two different voltage levels for the two binary digits. Codes that follow this strategy share the property that the voltage level is constant during a bit interval; there is no transition (no return to a zero voltage level). Can have absence of voltage used to represent binary 0, with a constant positive voltage used to represent binary 1. More commonly a negative voltage represents one binary value and a positive voltage represents the other. This is known as Nonreturn to Zero-Level (NRZ-L). NRZ-L is typically the code used to generate or interpret digital data by terminals and other devices.