Carrier Synchronization

Communication systems require local oscillators at both the transmitter and the receiver. The frequency and phase offset between these oscillators is inevitable due to various channel imperfections and transmission delay. Due to these imperfections, phase error is introduced in the received signal causing an incorrect representation of the transmitted data. In order to recover the data, a coherent detection is required and is achieved through a digital phase-locked loop (PLL). The coherent detection requires estimation of the instantaneous phase offset of every data point in the constellation grid with respect to where it should be. That information is then fed to a direct digital synthesizer which generates coherent sine and cosine carriers to correct the phase error.  Upon completing carrier synchronization, data can be decoded. This is a crucial component of the SDR for successful demodulation of data.