Tutorial: How to Synchronize Carrier and Timing Loops in Digital Modems
Wednesday, October 31, 2018: 9:00 AM - 12:00 PM
Digital Signal Processing has become the standard method of signal conditioning and signal processing in modulators and demodulators of modern communication systems. These systems require acquisition and tracking of frequency and phase of carrier and timing clock from the received signal when neither carrier nor clock is present. The synchronization information must be extracted from implicit side information embedded in the modulated signal or from explicit side information accompanying the modulated signal in pilot signals. Synchronization techniques abound with ad-hoc methods developed by clever analog designers. Many sub-optimal synchronization techniques evolved prior to the development of optimal synchronization techniques. Many techniques were developed prior to the heavy reliance on DSP in receivers. As the transition to DSP occurred, analog based synchronization schemes often survived the transformation and are employed directly as digitized versions of analog techniques. An important lesson to be learned in DSP based solutions is that a return to first principles may offer performance benefits. We do that in this presentation. We start with a review of receiver structures, parameters to be estimated, eye diagrams, and constellation diagrams. We then review phase lock loops and their digital counterparts as well as simple performance measures. We then examine timing recovery schemes operating with and without the benefit of data decisions. Finally, we discuss carrier frequency and phase recovery schemes. The synchronization processes for several modern communication systems will be discussed and used to illustrate the material discussed in the presentation. MATLAB demonstrations are used throughout the presentation to illustrate many of the concepts developed in the tutorial.