“…For a detailed discussion we refer to [39]. For example, progress in the design of test signals for channel identification [40,41], extension to the multiple-input multiple-output (MIMO) case [42,43], stochastic channels [44,45], channels with unknown carrier [42,46], constraints on the channel estimation [47], and others. These results address many of the problems discussed in [2] and provide solutions based on the classical analysis.…”