Water-Filling for Friendly Wide-Band Jamming

We are deriving “Water-Filling” in the realm of jamming with a power constraint. In contrast to the conventional Water-Filling, not the signal power is distributed given a power constraint, but a jamming power is distributed with a corresponding constraint. Instead of the channel capacity, the secrecy capacity is maximized. Additionally, we also apply a minimum mean squared criterion for jamming power distribution as a counterpart to applying it to equalization and precoding. The jamming power is allocated such that it outperforms a simple flat jamming spectrum. As an example, we discuss eavesdropping with a near-field probe. Friendly jamming of this form can reduce leakage to an eavesdropper. To illustrate the procedure, we use USB 2.0 signal spectra, despite of the fact that the independence assumption is violated that one makes use of in Water-Filling. Furthermore, we use the loop of shield and ground to radiate our jamming signal. Later applications that we envisage are, however, on-chip or on-board eavesdropping with dedicated RF designs, also ensuring that interference to other systems will be negligible.