In this paper, we present a new water-filling algorithm for power allocation in Orthogonal Frequency Division Multiplexing (OFDM) -based cognitive radio systems. The conventional water-filling algorithm cannot be directly employed for power allocation in a cognitive radio system, because there are more power constraints in the cognitive radio power allocation problem than in the classic OFDM system. In this paper, a novel algorithm based on iterative water-filling is presented to overcome such limitations. However, the computational complexity in iterative water-filling is very high. Thus, we explore features of the water-filling algorithm and propose a low-complexity algorithm using power-increment or power-decrement water-filling processes. Simulation results show that our proposed algorithms can achieve the optimal power allocation performance in less time than the iterative water-filling algorithms.Keywords-cognitive radio, orthogonal frequency division multiplexing, water-filling algorithm, power allocation.
In this paper, we will further expand upon our proposed Discrete Spring Transform (DST) steganographic attack. We will explore further applications of the transform and how it may be used to defeat multiple steganographic schemes, specifically cur rent video steganography schemes. The effectiveness of the pro posed algorithm will be shown by attacking a multi-dimensional steganographic algorithm embedded in video sequences, where the scheme operates in two different dimensions of the video. The attack is successful in defeating multiple steganographic schemes verified by determining the BER after DST attack which always remains approximately 0.5. Furthermore, the attack preserves the integrity of the video sequence which is verified by determining the PSNR which always remains approximately above 30dB.
Lost audio packet steganography (LACK) is a steganography technique established on the VoIP network. LACK provides a high-capacity covert channel over VoIP network by artificially delaying and dropping a number of packets in use to convey stegnogram. However, the increasing loss of packets will hurt the quality of the VoIP service. The quality deterioration will not only affect the legitimate VoIP service but also constrain the capacity of the covert channel. Discrete spring transform (DST) is proven to be a way to eliminate the perceptual redundancy in the multimedia signal. In this paper, the DST is applied on the LACK so that the perceptual redundancy of the voice frames is suppressed. In this way, the less redundant VoIP frames with perceptual equivalent quality can be transmitted in a channel whose capacity is squeezed by the established covert channel. As a result, the VoIP perceptual quality can be maintained with the existence of the covert channel. Meanwhile, the proposed DSTbased method demonstrates the possibilities in exploiting the perceptual space of the multimedia signal. The simulation results show that the DST on LACK achieves up to 24 % more capacity over the LACK scheme.
Digital audio signal provides a large capacity for embedding hidden messages using digital steganography techniques. How to prevent hazardous steganography embedding on the Internet becomes an important task in the field of network security. For the Internet environment, the steganography attack method is required to be generic and real time. An active wardenbased attack method is potential to be a generic method for the steganography attack. A discrete spring transform (DST)-based generic active warden steganography attack framework has been proposed by us. In this paper, based on the DST, a real-time steganography attack method is proposed. The potential unauthorized hidden message is removed in a real-time manner when uploading or downloading the audio signal. The real-time signal perceptual quality control is achieved by the automatic feedback from the objective audio quality evaluation model. The attack parameters are adaptively changed to reach a balance between the attack performance and the audio signal quality. The simulation results validate the proposed method in terms of the steganography attack performance and the audio signal quality after the attack.
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