Chapter 6
Synchronization
6.1 Introduction
The issue of synchronization inevitably arises in all signal transmission systems. In digital transmission, although the bit streams are inherently discrete-time signals, all the physical media, such as radio channels or transmission lines, are continuous-time in nature. In wireless communications, most physical transmission media are inefficient in transmitting baseband signals. Consequently, the digital baseband transmitted signal has to be converted to a continuous-time waveform and then modulated by a higher-frequency carrier signal. After the modulated signal passes through the physical media, several inverse processing procedures, including sampling, digitization, and demodulation, are applied. Figure 6.1 illustrates a simplified diagram of a wireless communication system.
In wireless communication receivers, coherent demodulation needs to make use of a local oscillation (LO) signal that has exactly the same carrier frequency and phase as the carrier signal contained in the received signal. Furthermore, accurate sampling clock frequency and phase allow the demodulator to recover the transmitted digital data more effectively. Unfortunately, the receiver is unsynchronized with ...