ABSTRACT
This chapter presents the processing of digital signals using higher-order spectral techniques [1–4] to evaluate the performance of coherent transmission systems, especially the bispectrum method in which the signal distribution in the frequency domain is obtained in a plane. Thus, the cross-correlation as well as the signals themselves can be spatially identified. Thence, we can evaluate the impairments imposed on the transmission systems due to different causes of such degradations. Although equalization has not been described here in this chapter, the techniques for equalization using higher-order spectrum can be found in Refs. [1–3]. The higher order will require additional processors but is compensated by additional dimensions to separate the linear and nonlinear impairments. These issues will be described in the following sections of this chapter.
