IJCSNS International Journal of Computer Science and Network Security, VOL.8 No.8, August 2008 81 Manuscript received August 5, 2008. Manuscript revised August 20, 2008. A Performance Analysis of Novel Approach for Limited Multiuser Detection Technique using Multisub of Correlation Factor for DS- CDMA System Lokesh Tharani † , Dr. R.P.Yadav †† † Department of ECE, JaganNath Gupta Institute of Engineering & Technology (JNIT), Jaipur, India †† Department of ECE, Malaviya National Institute of Technology (MNIT), Jaipur, India Summary This paper presents the performance analysis of the novel concept of limited multiuser detection (MUD) for direct sequence code division multiple accesses (DS- CDMA). The novel concept uses the correlation properties and bit streaming for reduced complexity architecture to meet real time requirement for asynchronous multiuser detection in wireless communication. To mitigate the effect of multiple access interference (MAI), this paper proposes a novel technique of multiplication and subtraction (Multisub) of cross correlation factor with receiving signal at output of matched filter, which is the first stage of parallel interference cancellation (PIC) multistage multiuser detector. Typically, asynchronous multiuser detector uses multishot detection, which involves block based computations and matrix inversions. Hence, Multisub correlation based suboptimal scheme have been evaluated to decrease the computational complexity and eliminate the need for matrix inversion. Moreover, such novel scheme can have added advantage to avoiding multishot detection if they start from a matched filter outputs. The paper compares the results of the novel scheme with the traditional single user matched filter and PIC multistage multiuser detector at different number of users. The result of the paper shows that bit error rate (BER) is minimize for 15-user and the performance of the limited parallel interference cancellation (PIC) multistage multiuser detector improves in that of other schemes. Key words: Multiuser detection (MUD), parallel interference cancellation (PIC), multiplication & subtraction (Multisub), correlation factor and matched filter. 1. Introduction The code division multiple access (CDMA) is promising technology for future generation and the advent of third generation (3G) cellular systems based mainly on code division multiple access technology and the technological advancement in mobile computing hardware over the last decade have led to a renewal interest in multiuser detection [1] as a effective method to improve the throughput and quality of mobile cellular communication systems. It is known that the capacity of direct sequence code division multiple access (DS-CDMA) system is limited by multiple access interference (MAI) if traditional matched filter detectors are used. To mitigate this problem, multiuser detection [2] was proposed, which jointly uses the information of interfering users to improve the detection performance of desired signal. Multiuser detections cancel the interference from other users to detect desired signal, compared to conventional single user detection using only a matched filter. The desired user’s bits mainly receive interference from the past and future overlapping signals of different users along with their current signal because they are asynchronous. The detection problem [3] in an asynchronous channel is more complicated than in a synchronous channel. The bits of each user are aligned in time for synchronous channel. Assume there are k direct sequence users in a synchronous single path BPSK real channel; the baseband received signal can be expressed as 1 r (t) = A (t) g (t) d (t) + n (t) K k k k k = ∑ (1) Where A k (t), g k (t) and d k (t) are the amplitude, signature code waveform and modulation of the k th user respectively and n(t) is additive white gaussian noise(AWGN) with a two sided power spectral density of N 0 /2 Watt/Hz. The power of the k th signal is equal to the square of its amplitude, which is assumed to be constant over a bit interval. The modulation consist of rectangular pulses of duration T b (bit interval) which take a d k = ± 1 values corresponding to the transmitted data. 2. Conventional DS-CDMA System Model We assume a synchronous CDMA multiuser communication [4] system with binary signaling, non- orthogonal transmission and an additive white gaussian noise channel. The communication system model is identical to the basic synchronous CDMA model described in introduction. The number of users in this system model is denoted by k and multiuser detector considered in this paper operate on the k-dimensional matched filter bank or