Carrier frequency offset (CFO) is a major contributor to the inter-carrier interference in orthogonal frequency division multiplexing (OFDM) systems. In order to overcome CFO at the receiver, a new OFDM symbol structure based on extending the transmitted symbol by inserting extra bits at the front of it before transmission is applied in this paper. The proposed method is capable of correcting frequency offset in the range of multiples of subcarrier spacing depending on the number of added extra bits. This is performed at the expense of transmitted power and data rate due to the insertion of extra bits. Simulation results indicate the performance improvement over both additive white Gaussian noise (AWGN) and multipath fading channels.

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Recently, many chaos-based stream cipher algorithms have been developed. Traditional chaos stream cipher is based on XORing a generated secure random number sequence based on chaotic maps (e.g. logistic map, Bernoulli Map, Tent Map etc.) with the original image to get the encrypted image, This type of stream cipher seems to be vulnerable to chosen plaintext attacks. This paper introduces a new stream cipher algorithm based on dynamic substitution box. The new algorithm uses one substitution box (S-box) and a chaotic shuffling process. Each byte in the plain image vector is substituted using a different S-box to get the cipher image vector. This algorithm is designed to be invulnerable to chosen plaintext attacks. In addition, this algorithm is more secured compared to conventional stream cipher.

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