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Power allocation strategies for OFDM Gaussian wiretap channels with a friendly jammer

This paper investigates power allocation strategies over a bank of independent parallel Gaussian wiretap channels where a legitimate transmitter and a legitimate receiver communicate in the presence of an eavesdropper and a friendly jammer. We give algorithms to compute the optimal power allocation strategy of the jammer in the degraded scenario. We also give an algorithm to compute power allocations strategies of the jammer in a general scenario, leading to significant performance gains in relation to isotropic jamming. Additionally, we provide a set of results that cast further insight into the problem. In our scenario, which is applicable to current OFDM communications systems, we demonstrate that the proposed jammer power allocation strategy can lead to considerable secrecy gains.