PN Codes Vs Chaotic sequences:BER Comparison Perspective M.Sangeetha 1 Department of Electronics and Communication Engineering SRM University, Kattankulathur-603203, Tamil Nadu, India. 1 sangeetha.m@ktr.srmuniv.ac.in Vidhyacharan Bhaskar 2 Department of Electronics and Communication Engineering SRM University, Kattankulathur-603203 Tamil Nadu, India. 2 meetvidhyacharan@yahoo.com Abstract— In this paper, we consider the BER performance of chaotic modulation schemes in Single-Input-Multiple-Output (SIMO) Nakagami fading channels. In particular, we focus on a system that employs Differential chaos Shift keying (DCSK). We consider transceiver scheme which require no channel state information at either the transmitter or the receiver. A distinct chaotic sequence is used at the transmit antenna to spread the data symbols and transmits omni directionally. At each receive antenna, the corresponding differential detection statistics is performed and these statistics are combined with maximum ratio combining for symbol detection. Simulation results show that the proposed schemes can effectively exploit spatial diversity of the underlying SIMO system. The performance of the system is evaluated for both chaotic sequence and PN sequence in terms of Bit Error Rate (BER) for various space diversity levels and average SNRs. Also, the BER performance of these systems is evaluated for various spreading code lengths. Keywords- Differential Chaos Shift Keying, Maximum Ratio combining ,- PN sequence and Single-Input-Multi- Output(SIMO) I. INTRODUCTION Reliability and availability of real-time communication are imperative in the context of wireless communication services. A popular technique used in this scenario is Spread Spectrum (SS). In SS, the spreading process is accomplished using a spreading code. Conventionally, uses a Pseudo-Noise (PN) sequence. These sequences are periodic with a long period and have properties similar to noise which are interesting when the safety of communication is required [1]. Besides the conventional method of PN periodic sequence generation, other methods can be used in SS systems. A promising one is the use of chaotic sequences as spreading codes [2]. A Chaotic signal is deterministic, aperiodic and presents sensitive dependence on initial condition and these properties have increased the interest in using chaos in many fields [3].One of the reason for using chaotic sequence is based on the simplicity of its generation because it can be generated by simply non linear circuitry [4]. There are two basic types of transmission schemes utilizing these chaotic signals. The first method relies on ideas which choose a particular state of a chaotic system to transmit and the same is used in the receiver to synchronize similar chaotic circuits and allows regeneration of the complete set of chaotic states needed for decoding the incoming message sequences. These methods although attractive have not proved to be sufficiently robust with noisy transmission channels. The second type of chaos communication system is characterized by the transmission of a reference signal. The most successful of these types of transmission has been differential chaos shift keying (DCSK) which introduced chaotic processes into existing correlation based schemes. This method transmits a chaotic function for half of the symbol interval and then a duplicate or inverted copy of the same signal in the second half representing a ‘1’ or ‘0’. This is exactly analogous to a BPSK scheme and decoding is achieved by correlation of both halves of the signal [5]. Recent research works address MIMO chaotic communications. Chaotic shift keying, combined with Space- Time Coding (STC), is presented in [6], and a DCSK-STC scheme based on the Alamouti code is proposed in [7]. Channel estimation in a spatial diversity multipath environment is difficult, especially for chaotic communications, due to the difficulty in obtaining synchronization. In this brief, we propose SIMO chaotic communication schemes that do not require CSI and yet can effectively exploit the inherent spatial diversity of the system. In particular, we focus on a single user system that employs Differential Chaos Shift Keying (DCSK). We consider a transceiver scheme which requires no channel state information at either the transmitter or the receiver. SIMO system employs a distinct chaotic sequence/PN sequence at the transmit antenna to spread the data symbols and transmit omnidirectionally. PN sequences used are the Walsh Hadamard codes. At the receiver, differential detection statistics is performed for each receive antenna, and these statistics are then combined with maximum ratio combining which is the optimum linear combining technique for coherent reception with independent fading at each receive antenna in the presence of spatially white Gaussian noise, for symbol detection. The remainder of this brief is organized as follows: Section II describes the system model. The proposed transceiver scheme for SIMO chaotic communication is presented in Section III. Simulation results are shown in Section IV. Finally, Section V presents the conclusions. 475 978-1-4673-4805-8/12/$31.00 c 2012 IEEE