OFDM for Underwater Acoustic Communications

Chapter 6Detection, Synchronization and Doppler Scale Estimation

In practical communication systems, a vital component of receiver design is to detect the arrival of the useful signal from the transmitter. As illustrated in Figure 5.1, once the useful signal is detected, the receiver starts recording the waveform, and employs an appropriate synchronization algorithm to identify the starting point of the useful signal from the recorded waveform. Note that in the presence of platform motions, the transmitted signal is usually dilated or compressed at the receiver side. Synchronization and Doppler scale estimation therefore often operate together.

Three key components in the OFDM receiver design will be discussed in this chapter.

• Preamble detection. As revealed in Figure 5.1, a preamble is usually transmitted prior to OFDM blocks for incoming signal detection. Depending on the preamble structure, two popular methods exist. The first method is to perform cross correlation between the received signal and the transmitted preamble which is known to the receiver. In this method, Doppler-insensitive waveforms are usually adopted to account for channel variations. The second method is to embed certain structure in the transmitted preamble, and signal detection can be accomplished by monitoring the structure of the incoming signal at the receiver side. In this method, the receiver can be ignorant of the transmitted preamble and only needs to know the preamble structure. In this chapter, ...