An Imroved Ofdm Scrambler For 4g Communication Systems

Abstract

ABSTRACT Speech signal transmission is most significant now a days, and the importance of providing a high level of security is increasing. Many researchers have suggested various types of speech scrambling techniques. Among these, FFT scrambler is the most popular technique in speech communication.Since an FFT-based speech scrambler retains a considerable residual intelligibility in the scrambled speech, a new speech-scrambling technique to remove the residual intelligibility from the scrambled speech is to be developed. To achieve efficient security, Orthogonal Frequency Division Multiplexing (OFDM), which is a special form of multi-carrier modulation, can be used as a scrambler. In the OFDM scrambler, the speech signals are transformed into the unintelligible form by the random permutation operation on the transmitter side. The scrambling and descrambling operations are performed by using the same key in the transmitter and the receiver. In this work, to improve the performance of the OFDM scrambler, new techniques are added along with the scrambler. The proposed new technique is based on the combination of the scrambler and the OFDM scheme. The scrambler consists of a random permutation, pseudorandom binary generator and Bernoulli chaotic mapping. This system can scramble the speech without residual intelligibility by the permutation of sample sequences within each time domain OFDM symbol. Without residual intelligibility in the scrambled speech, the proposed OFDM speech scrambler is secure from any attacks by eavesdroppers. In addition, the OFDM speech scrambler needs only two FFT operations instead of the four required by the FFT-based speech scrambler in system structure. In the proposed new scrambling technique, the input speech signal is first subjected to the random permutation which is used to swap the rows of the original speech. The output of the randomly permuted data is again scrambled with the Bernoullichaotic mapping. Then, the output of this block is XORed with the random data generated by the P