Credit: Image licensed by Ingram Publishing. a close loop software defined radar (SDR) to establish cognitive approaches with a real measurement system. The waveform can be generated and transmitted directly by an arbitrary waveform generator and acquired by an oscilloscope. The environment is controlled with an industrial robot as depicted in Figure 2. All devices are connected to a central processing unit to realize the closed loop and to ensure the synchronization. y ¼ ys;i þ w ¼ ðhi þ cÞ Ã s þ w (1) is represented by a convolution of the waveform s with the target response hi and the clutter c. The concept of Matched Illumination maximizes the signal to noise ratio, under the constraint of an energy limitation Ex . The so called water-filling solution [10],[17],[15] 2 qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi!3 jHðfÞj2 Gww ðfÞ Gww ðfÞ 5 jSðfÞj ¼ max40; Ex À Gcc ðfÞ jHðfÞj2 2 SNR IMPROVEMENT (2) For the assumption of a linear, time invariant channel with white additive Gaussian noise wðtÞ $ Nð0; Rww ¼ Is 2w Þ, the complex receive signal is defined with respect to the power spectral density of the clutter Gcc ðfÞ and the noise Gww ðfÞ. Because this solution Figure 1. Three-layer model of a cognitive radar architecture modified from [5]. Figure 2. Setup for the close loop SDR. (a) Example of a turn table experiment. (b) Schematic of the close loop system. DECEMBER 2019 IEEE A&E SYSTEMS MAGAZINE 31