TABLE OF CONTENTS Synchronization, which is composed of estimation and control, is one of the most important functionalities of the receiver. It must be first performed by the receiver when receiving information data.
In an OFDM system, synchronization can be divided into three different parts carrier frequency offset synchronization, DFT window timing synchronization, and subcarrier recovery. As shown in Section 4.8, an OFDM system is very sensitive to frequency offset, which may be introduced in the radio channel, so accurate frequency offset synchronization is essential. Especially for burst mode data transmission in wireless LAN applications, we must keep the overhead, namely, the number of pilot symbols required for the synchronization, as low as possible. DFT window timing synchronization corresponds to symbol timing synchronization in single carrier transmission. However, it is much more difficult, because there is always an "eye opening" in each single carrier modulated symbol, whereas there are many "zero crossings" in each OFDM symbol. Therefore, normal synchronization algorithms such as zero-forcing cannot be adopted. Furthermore, subcarrier recovery means simultaneous regeneration of reference signals at all subcar riers used.
This chapter discusses pilot-assisted DFT window timing/frequency offset synchronization and subcarrier recovery methods suited for burst mode OFDM data transmission. Accurate synchronization often requires accurate estimation, so some estimation methods are also investigated in this chapter. Section 5.2 introduces Schmidl's DFT window timing/frequency offset estimation method [1] and presents the theoretical analysis and computer simulation results. Section 5.3 discusses two DFT window timing synchronization/ subcarrier recovery methods, which periodically insert time domain...
