
 A Function of Time, Frequency, Lag, and Doppler  O'Neill, Williams (ResearchIndex) (Site not responding. Last check: 20071022) 
  They are the signal in time, the spectrum, the autocorrelation function of the signal, and the autocorrelation function of the spectrum. 
  The variables of these functions are denoted, respectively, as time, frequency, lag, and doppler. 
  In timefrequency analysis, these functions of one variable are extended to quadratic functions of two variables. 
 citeseer.ist.psu.edu /97696.html (467 words) 
