1349 | International Journal of Current Engineering and Technology, Vol.4, No.3 (June 2014) Research Article International Journal of Current Engineering and Technology E-ISSN 2277 – 4106, P-ISSN 2347 - 5161 ©2014 INPRESSCO ® , All Rights Reserved Available at http://inpressco.com/category/ijcet Study and Simulation of DS-CDMA over Communication Channels Purneshwari Varshney Ȧ* , Dixit Dutt Bohra Ḃ Ȧ Department of Electronics & Communication Engineering, JIET Group of Institutions, Jodhpur, Rajasthan, India Ḃ Department of Electronics & Communication Engineering, Jodhpur National University, Jodhpur, Rajasthan, India Accepted 02 May 2014, Available online 01 June 2014, Vol.4, No.3 (June 2014) Abstract Performance of synchronous DS-CDMA systems over multipath fading channel and AWGN Channel is evaluated. The synchronous DS-CDMA system is well known for eliminating the effects of multiple access interference which limits the capacity and degrades the BER performance of the system. This paper investigated the bit error rate (BER) performance of a synchronous DS-CDMA system over AWGN and Rayleigh channel, which is affected by the different number of users, as well as different types spreading codes. The promising simulation results explore the comparative study of different DS-CDMA system parameter and showed the possibility of applying this system to the wideband channel. In this paper, Rayleigh channel and AWGN Channel are introduced and investigated the bit error rate (BER) performance of a synchronous DS-CDMA system over these channels. In the DS-CDMA system, the narrowband message signal is multiplied by a large bandwidth signal, which is called the spreading of a signal. The spreading signal is generated by convolving a GOLD sequence code with a chip waveform whose duration is much smaller than the symbol duration. Keywords: BER, AWGN, GOLD Sequence. 1. Introduction 1 Direct-sequence code-division multiple access (DS- CDMA) is currently the subject of much research as it is a promising multiple access capability for third and fourth generations mobile communication systems. Code- division multiple access (CDMA) is a technique whereby many users simultaneously access a communication channel. The users of the system are identified at the base station by their unique spreading code. The signal that is transmitted by any user consists of the user’s data that modulates its spreading code, which in turn modulates a carrier. An example of such a modulation scheme is quadrature phase shift keying (QPSK). In this Paper, we introduce the Rayleigh channel and AWGN Channel, and investigated the bit error rate (BER) performance of a synchronous DS-CDMA system over these channels. In the DS-CDMA system, the narrowband message signal is multiplied by a large bandwidth signal, which is called the spreading of a signal. The spreading signal is generated by convolving a GOLD sequence code with a chip waveform whose duration is much smaller than the symbol duration. All users in the system use the same carrier frequency and may transmit simultaneously. The receiver performs a correlation operation to detect the message addressed to a given user and the signals from other users appear as noise due to de-correlation. The synchronous DS-CDMA system is presented for eliminating the effects of multiple access *Corresponding author: Purneshwari Varshney interference (MAI) which limits the capacity and degrades the BER performance of the system. MAI refers to the interference between different direct sequences users. With increasing the number of users, the MAI grows to be significant and the DS-CDMA system will be interference limited. The spreading GOLD sequences in a DS-CDMA system need to have good cross-correlation characteristics as well as good autocorrelation characteristics. The goal is to reduce the fading effect by supplying the receiver with several replicas of the same information signal transmitted over independently fading paths. 2. DS-CDMA System Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. This allows several users to share a band of frequencies. This concept is called multiple access. CDMA employs spread spectrum technology and a special coding scheme to allow multiple users to be multiplexed over the same physical channel. A digital method for simultaneously transmitting signals over a shared portion of the spectrum by coding each distinct signal with a unique code. There are different ways to spread the bandwidth of the signal:  Direct sequence  Frequency hopping  Time hopping  Chirp spread spectrum  Hybrid systems