I.J. Intelligent Systems and Applications, 2016, 10, 60-67 Published Online October 2016 in MECS (http://www.mecs-press.org/) DOI: 10.5815/ijisa.2016.10.07 Copyright © 2016 MECS I.J. Intelligent Systems and Applications, 2016, 10, 60-67 PSO-Based NBI Resistant Asynchronous MC- CDMA Multiuser Detector Anmol Kumar 1 1 Research Scholar, IKG Punjab Technical University, Kapurthala-144601, India E-mail: goyalruby@gmail.com Rajde e p Kaur 2 2 Assistant Professor, CEC, Landran, Mohali-140301, India E-mail: rajdeepkr9@gmail.co m Abstract —Nowadays with the increase of demand in multimedia communication, a reliable and error-free wireless communication system is the need of the hour. MC-CDMA is being investigated as a potential radio technology to provide fourth generation (4G) and fifth generation (5G) cellular mobile services. Narrowband interference (NBI) signals corrupts the subcarriers of MC-CDMA system and as a result its performance de- grades. All the available NBI elimination methods uses some kind of filters and other circuitry prior to the de- modulator (receiver) to filter out NBI. So addition of extra hardware to the system makes the system complex and slow. Moreover CDMA based systems are affected by digital NBI which gets superimposed with wideband spread spectrum signal. Multiuser detection could be an efficient technique to suppress NBI and multiple access interference (MAI). Computational complexity of opti- mum multiuser detector is an impediment in the way of an efficient multiuser detector. In this paper we propose a particle swarm optimization (PSO) based optimum mul- tiuser detector to eliminate NBI. Simulation results show that performance of proposed PSO based multiuser detec- tor is capable of eliminating NBI with much lesser amount of computational complexity. Index Terms—Multi-Carrier Code Division Multiple Access (MC-CDMA), OFDM, Narrowband Interference (NBI), Multiuser Detection (MUD), Multiple Access Interference (MAI), Particle Swarm Optimization (PSO). I. INT RODUCT ION MC-CDMA was proposed by Linnartz et al .[1] in 1993. MC-CDMA is basically a spread spectrum version of a OFDM based system. So a MC-CDMA system in- corporates features of both OFDM and CDMA and be- cause of its ability to combat frequency selective fading and multipath fading, MC-CDMA is preferred over OFDM [2-6].MC-CDMA is basic radio technology for LTE networks [7]. Nowadays it is being considered as a potential candidate for 4G mobile systems implementa- tion. As shown in Fig. 1 above it can be seen a data symbol (serially transmitted) are multiplied by different spread- ing codes (orthogonal code), so a single data symbol is spread in frequency domain to achieve frequency diversi- ty. This feature of MC-CDMA makes it immune to mul- tipath fading. These data symbols are spread and then modulated by different subcarriers using IFFT. So at the output we get different data symbols separated in time domain and at the same time a single data symbol which is sent on different subcarriers gets separated in frequen- cy domain. This feature of MC-CDMA gives multipath fading immunity. Like CDMA, MC-CDMA systems are also affected by the different types of interference such as AWGN (additive white Gaussian noise) and MAI (multi- ple access interference).MAI is inherent in a CDMA based system because it become very difficult to maintain the orthogonality of spreading waveforms due to several factors such as multipath fading, near-far effect, different timing offsets of different users etc. AWGN on the other hand is inevitable in wireless communication which aris- es because of random agitation of electrons in electronic devices such as modulators, amplifiers etc. It has been observed that apart from MAI and AWGN, MC-CDMA systems also gets affected by short pulses in frequency domain which is termed as narrowband interference (NBI)[8]. Nowadays due to increased demand for high data rate different techniques such as OFDM, MC- CDMA, UWB (ultra wide band), WLAN (wireless local area network),WIMAX(worldwide interoperability for microwave access), OFDM-LTE (4-G) are being em- ployed. Many times these systems operate simultaneous- ly in co-existence with other systems. In some situations it also happens that these systems have to share the same frequency band with other systems and in such a situation one system may act as narrowband interferer for the other user. It may also happen that some intentional jammer deliberately transmit NBI signals to jam a MC-CDMA system. In CDMA based systems spreading and de- spreading process of data bits inherently reject the NBI, but high power NBI signal cannot be filtered out because system processing gain cannot be increased beyond a limit due to bandwidth restriction. Existence of NBI de- grades the performance of MC-CDMA systems because random NBI signals of variable intensity may overlap with different subcarriers leading to corrupt subcarriers as shown in Fig. 2.