A direct decoder method for OFDM with carrier frequency pilot in underwater acoustic communication systems

Abstract

In this paper, we propose a new decoder method at the receiver of system to compensale Doppler frequency shift for OFDM-based underwater acoustic communication systems. At the transmitter, in order to save bandwidth, we do not use additional signal header (preamble) in each OFDM frame as proposed in many conventional approaches. Instead, the central sub-carrier is reserved for pilot transmission. This subcarrier is so-called as the carrier frequency pilot (CFP), which is used to detect the Doppler frequency. At the receiver, in [1], two synchromization steps are deploved. The first step, the Doppler frequency is roughly estimated on the basic of the detected carrier frequency. In the second step, we use the CFP to regulate the estimated Doppler frequency, this regulation is called as fine synchronization. The use of Doppler compensation scheme in [1] is relatively complex because in order to calculate Doppler accuracy, it is necessary to pertorm two steps. Therefore. I propose an algebraic computation of Doppler frequency shift with one step. The results of the Doppler frequency shift calculation will be used to re-sample the received signal using the re-sampling matrix. The advance of using this matrix is thai it can be calculated with any decimal, not an integer such as using the matlab function available in [1].