Several different types of synchronization are often required in a digital communication system. Carrier synchronization is required if processing at the receiver requires a coherent reference, symbol synchronization is required to know when individual symbols start/stop, and frame synchronization is often required to know when frames of data start/stop. This video introduces some of these synchronization concepts, and the following videos investigate specific schemes in more detail.

A phase lock loop (PLL) can be used to track the phase of an incoming signal and create a reference waveform with matched phase for coherent processing. We provide the block diagram of a simple phase lock loop (PLL) and show how the feedback loop provides an input to the voltage controlled oscillator (VCO) that is proportional to the phase error between the input signal and the generated reference.

For amplitude modulated signals like binary phase shift keying (BPSK), an additional squaring operation is needed within the phase lock loop (PLL). This video analyzes a BPSK squaring loop and shows how a coherent reference is generated coherent BPSK processing.

This video examines a Costas Loop for coherent reference generation and data demodulation. Similar to the previous videos, the block diagram of this system can generate a coherent reference that tracks the input signal phase. In addition, the Costas Loop also generates a baseband version of the signal, i.e. it also performs data demodulation.

Symbol synchronization is performed in digital communication systems to determine the starting time of the incoming signal. This is needed to ensure subsequent correlation processing starts/stops at the correct time. The symbol synchronization approach described here uses a late-gate/early-gate technique to generate an error signal that is proportional to the symbol timing error. This error is then used to control a voltage controlled clock (VCC). The VCC adjusts its timing to minimize the input error signal and achieve symbol synchronization.