International Journal of Computer Applications (0975 – 8887) Volume 113 – No. 13, March 2015 9 Application of Modified Chaotic Sine Map in Secure Communication Bibhakar Saha Dept. of ECE, GITAM Institute of Technology Visakhapatnam, India Sai Tej Malasani Dept. of ECE, GITAM Institute of Technology Visakhapatnam, India J. B. Seventline Dept. of ECE, GITAM Institute of Technology Visakhapatnam, India ABSTRACT In the recent years, a lot of research has been done in the field of covert chaotic communication involving many known chaotic maps and the results have been very promising. In this paper the generation of binary sequence using modified chaotic sine map is discussed. The auto correlation and the cross correlation properties of the generated sequence is observed. Also, the BER of chaotic shift keying system is analyzed to check the feasibility of the generated sequence in communication purpose. The possibilities of using the generated binary sequences in radar pulse compression techniques is also explored and Peak Side lobe Ratio (PSLR) obtained is compared with other existing binary sequences. General Terms Modified sinusoidal iterator, secure communication technique, Pulse compression Keywords CSK, Chaotic sin map, PSLR, BER 1. INTRODUCTION In a conventional radio communication mechanism the transmitted signal is transmitted in a narrow frequency band. The high power spectral density has its own disadvantages which includes selective fading, interference from other radio channels etc. Chaos communication is used to overcome such problems. Chaos communication systems have the characteristics such as non-periodicity, wide-band, and non- predictability [1]. In chaos communication systems, binary sequences generated using chaotic maps called chaotic sequences are used. These maps are simple polynomial maps or simple nonlinear dynamic equations which exhibits simple chaotic behavior. Also, chaos communication system is decided by initial conditions of equation, and it has sensitive characteristic depending on the initial condition, because chaos signal is changed to different signal when initial condition is changed [2][3]. Because of these characteristics, the security of chaos communication system is superior to digital communication system. Chaotic sequences increases the bandwidth of the transmitted signal greater than the required bandwidth for the signals transmission. The characteristics of an ideal code or a sequence that is required to spread the signal involves properties that includes zero or near zero cross correlation, impulse like auto correlation, codes need to be wideband to be able to spread the signal and should be easy to generate. The added advantages of using chaotic spreading sequences are that an infinite number of spreading sequences exist and that the spread signal is less vulnerable to interception [4]. In this paper, a modified sine map for Chaotic shift keying (CSK) spread spectrum communication is proposed and is compared with the existing sine map and logistic chaotic maps. Chaos users evaluate the BER performance according to chaos modulation system [5] [6].The proposed new chaos map has a better BER performance according to analysis of probability density function. In pulse compression technique of pulse radars, the transmitted signal or carrier is frequency or phase modulated and the received signal is processed in the receiver by the matched filter which is used to increase the range resolution as well as the signal to noise ratio [7]. A sequence or code defines the manner in which the carrier is modulated in the phase coded pulse compression technique. The autocorrelation property which is the compressed output of the matched filter and the Peak Side lobe Ratio (PSLR) is an essential criteria in determining the performance of a range resolution pulse radar. The PSLR is obtained from the auto- correlation function. Binary barker sequences are generally used for radar pulse compression, but, they exist only up to a length of 13 with a PSLR of -22.3 dB [8].Since longer length sequences with low PSLR values are required in some applications, binary chaotic pulse compression codes generated using chaotic logistic map was reported recently [9].The advantage of this code over the other existing binary codes are they can be generated easily for any length. In this paper, the application of another chaotic map called modified sinusoidal iterator used to generate binary pulse compression codes is discussed. The performance analysis of the generated code is compared with other existing codes. 2. CHAOS SEQUENCE 2.1 Sinusoidal Iterator A simple sinusoidal iterator is studied in this section [10]. The simplified sinusoidal iterator is represented by equation (1)   +1 =A ∗ sin ( ∗  ) (1) It generates chaotic sequence in (0, 1). 2.2 Modified Sinusoidal Map The modified sinusoidal map is a scaled and shifted version of equation (1)   +1 =2 ∗(  +1 − 0.5 ) (2) where,  +1 is the output chaotic sequence and A=1. Figure (1), gives a two-dimensional phase diagram of the modified sinusoidal map for initial value of 0.1, and it clearly shows the quadratic curve of the difference equation which also exists for other famous maps such as logistic map, henon map etc.. Scaling and shifting the chaos map will not change the chaotic properties of the generator but will provide an increase in the signal power (Ps) and a decrease in the variance (σ 2 ) which is used to determine the BER [11].