Design and application of multifrequency signals

The use of the fast fourier transform (FFT) algorithm in commercially available and custom-built digital spectrum analysers has resulted in an increasing interest in system identification in the frequency domain. Historically, pseudo-random binary signals have been widely used as perturbation signals for system identification because they are easy to generate using simple shift-register circuitry, which has resulted in their incorporation in a number of signal generators. However, their properties are not particularly well suited to frequency-domain system identification. This has led to the design of more suitable signals for this type of identification, but these have tended to remain primarily a research tool because they have not been easy to generate. This problem has largely disappeared with the widespread availability of programmable read only memories and some of these designs are just beginning to appear on commercial hardware and software packages. The author reviews some of these other designs