Quadratic polynomial fitting of total energy of null subcarriers in underwater acoustic OFDM communication
Yang Chen1, Bin Zhou2, Jingwei Yin2
1School of Information Science and Engineering, Changzhou University, Gehu Road 1, Changzhou, China
2Science and Technology on Underwater Acoustic Laboratory, Nantong Str. 145, Harbin, China
Doppler scale estimation is one key module in underwater acoustic (UWA) orthogonal frequencydivision multiplexing (OFDM) communication. In this paper, null subcarrier based blind Doppler scale estimation is considered, which is an extremal problem. The cost function is constructed of the total energy of null subcarriers through DFT. The frequencies of null subcarriers are calculated according to non-uniform Doppler shifts at each tentative scaling factor. Then it is proofed that the cost function can be fitted as a quadratic polynomial near the global minimum. So the accurate location of the global minimum can be achieved through polynomial interpolation. This theory is a basement of developing new methods of Doppler scaling estimation and is verified through an experiment conducted in shallow water.