Analysis of Chaos MIMO Communication System with Fading channels

The security of chaos communication system is superior to other digital communication system, because it has characteristics such as non-periodic, wide-band, nonpredictability, easy implementation and sensitive initial condition. Chaos sequences are non – periodic sequences which are sensitive to their initial conditions i.e. spread factor and time delay respectively. If many antennas are applied to chaos communication system, the capacity of data is proportional to the number of antenna.so it is good way applying multiple-input and multiple-output (MIMO) to the chaos communication system. This paper makes a primary contribution to evaluate the BER performance of Chaos MIMO Communication system in fading channels. The chaotic maps that have been considered are Tent map, Boss map, Henon map and logistic map. The modulation scheme that has been considered is CDSK in presence of AWGN channel and Rayleigh fading channel. Keywords— Chaos maps, Tent map, Boss map, Henon map, Logistic map, MIMO, AWGN channel, Rayleigh channel, CDSK (correlation delay shift keying). INTRODUCTION Earlier use of Linear system was prominent. But with technological advancement, Non-Linear system started to be used by combining it with chaos communication system for improved performance. [1] Chaos communication aims at providing security for transmission of information performed through technologies. [2] The characteristics of Chaos communication include non-periodicity, wide-band, non-predictability and easy implementation. Chaos communication system is decided by initial conditions of equation. It has sensitive characteristic according to initial condition, because chaos signal is changed to different signal when initial condition is changed. [3-4] If the initial condition is known to the intruder, then it becomes sensitive to the outside world. As long as the initial condition concealed from the outside world, it is impossible to predict the chaos signal. The chaotic sequences make the transmitted signal look like noise; therefore, it does not attract the attention of an unfriendly receiver. These characteristics makes the security of chaos communication superior to digital communication systems. Because of this added advantage of security, chaos communication has been extensively studied. During the last two decades or so, lots of digital communication schemes using chaos have been suggested and studied, which utilize either coherent or non-coherent detections for information extraction [5] . Because chaotic synchronization in coherent detection performs poorly, demodulation in chaos based communication schemes with coherent receivers using this synchronization technique becomes a real challenge in noisy environments. Therefore, non-coherent schemes seem more feasible and appealing in practical environments. In 1996, Kolumb ́an et al. proposed the non-coherent differential chaos shift keying (DCSK) which is the most suitable scheme in wireless communications due to its good noise performance [6,7] . However, the prices that it has to pay are low attainable data rate and weakened information security. In 2000, Sushchik et al. proposed the non-coherent correlation delay shift keying (CDSK) whose bandwidth utilization ratio and information security are much better than DCSK. Chaos communication system has many transmitted symbols, because information signal is spread according to the characteristic of chaos map. So, study of chaos system for data rate improvement is necessary. MIMO (Multi Input Multi Output) system transmit data by several paths using several antennas. And, in receiver part, it is a technique which can reduce interference by detecting received signal at each path, and provides a better data rate, link reliability and bandwidth efficiency. MIMO system increase the capacity of data communication in proportion to number of antenna, and provide the high data processing Speed [8] . This paper is organized as follows section II explains what is Chaotic system, Section III gives the Chaotic signals, section IV elaborates the system overview, Section V discuss about the performance evaluation of the system i.e., we will evaluate the performance of different chaotic maps in the CDSK chaotic modulation system and will find out which chaotic map shows superior International Journal of Engineering Research and General Science Volume 3, Issue 2, Part 2, March-April, 2015 ISSN 2091-2730 11 www.ijergs.org performance. Using the superior map obtained from the analysis we proceed to the 2x2 MIMO concepts. In the later stage we compare the performance of BPSK and CDSK over MIMO AWGN channel. And a comparative analysis of the 2x2 Chaotic MIMO Concept and 4x4 chaotic MIMO concept using CDSK Modulation in AWGN channel, Then performance of 2x2 chaotic MIMO and 4x4 chaotic MIMO in Rayleigh channel was analysed. Finally in Section VI we will make the conclusion. CHAOTIC SYSTEM A chaotic dynamical system is an unpredictable, deterministic and uncorrelated system that exhibits noise-like behavior through its sensitive dependence on its initial conditions, which generates sequences similar to PN sequence. They have been successfully employed to various engineering applications such as automatic control, signals processing and watermarking Since the signals generated from chaotic dynamic systems are noise-like, super sensitive to initial conditions and have spread and flat spectrum in the frequency domain, it is advantageous to carry messages with this kind of signal that is wide band and has high communication security. Secure communication with chaos has been developed. [6] These systems tend to be more computationally complex than nonspread communication systems, yet they provide advantageous multipath mitigation and multi-user spectral re-use capabilities. CHAOTIC SIGNALS A chaotic sequence is non-converging and non-periodic sequence that exhibits a noise-like behavior through its sensitive dependence on its initial condition i.e., spread factor and time delay respectively. [4] A large number of uncorrelated, random-like, yet deterministic and reproducible signals can be generated by changing initial value. These sequences so generated by chaotic systems are called chaotic sequences. [7] Chaotic sequences have been proven easy to generate and store. Merely a chaotic map and an initial condition are needed for their generation, which means that there is no need for storage of long sequences. Moreover, a large number of different sequences can be generated by simply changing the initial condition. The secrecy of the transmission is important in many applications. The chaotic sequences help achieve this security from unwanted reception in several ways. SYSTEM OVERVIEW I. Correlation delay shift keying system Existing modulation system consists of a switch in the transmitter, creating the problem of power wastage and eavesdropping occurs by twice transmission. Technique that has been proposed to solve these problems is CDSK system where transmitted signal does not repeat as the switch at the transmitter is being replaced with an adder circuit. Fig .1 Transmitter of CDSK system Fig.1 shows the transmitter of a CDSK system. The chaos signal from the generator is being delayed and is multiplied with the information signal. The resulting signal is being added with the original chaos signal generated from the generator finally producing the transmitter output. (1) Equation (1) indicates transmitted signal from transmitter. Here L denotes the delay time. International Journal of Engineering Research and General Science Volume 3, Issue 2, Part 2, March-April, 2015 ISSN 2091-2730 12 www.ijergs.org Fig.2 Receiver of CDSK system Fig.2 shows the CDSK receiver system. CDSK receiver is correlator based receiver, and it is performed in order to recover the symbol. Received signal and delay received signal are multiplied, and this signal is added as much as the spreading factor. Afterward the signal is quantized according to an appropriate threshold and information signal is recovered through decoding. Equation (2) indicates output value of correlator of CDSK system. Information bits are possible to recover when delay time and spreading factor have to use exact value that is used in transmitted signal. II. Chaos maps In this paper, the types of chaos map that has been considered are Tent map, Boss map, Logistic map and Hénon’s map. a. Tent map Fig.3 Trajectory of tent map Fig.3 shows trajectory of Tent map. The x-axis and the y-axis of fig.3 mean xn and xn+1, and Tent map has trajectory of triangular shape.