Wireless Communications Systems Design

10Synchronization

In wireless communications, a transmitter put data in radio resources such as time and frequency and a receiver should be able to pull data out. The synchronization performs this role in the receiver of wireless communication systems. Synchronization techniques are an indispensable part of the wireless communication receiver like a conductor of orchestras unifies performers and forms an ensemble. The receiver needs to detect a packet and find an accurate starting position. In addition, it should correct several synchronization errors such as timing offsets (caused by channel delay), carrier frequency offsets (caused by Doppler effect and local oscillator mismatch between transmitter and receiver), phase noises (caused by phase rotation of the channel), and sampling frequency offsets (caused by mismatch between DAC and ADC). In particular, OFDM systems are very sensitive and vulnerable to these synchronization errors. It is a tricky part of the wireless communication system design. In this chapter, we will look into synchronization errors and their effects, review synchronization techniques, and design ML synchronization block in the OFDM system.

10.1 Fundamental Synchronization Techniques for OFDM System

Synchronization techniques can be classified into data-aided methods, decision-directed methods, and non-data-aided methods. The data-aided methods use a reference signal (training symbols, preambles, pilots, etc.) which is known in the receiver side. ...