This work was supported by 973-Project of China (No. 2002CB312102); by the National Natural Science Foundation of China (No. 60272044) ;by the Youth Research Fund of Suzhou University (No. Q3119610).
Multitaper spectrum has lower variance than the traditional periodogram. The noise spectrum and the noise to noisy signal spectrum ratio (NNSR) were estimated from the multitaper spectrum of the noisy signal; the pr...