Performance of the Smart Antenna Aided Multicarrier DS-CDMA Uplink Bin Hu, Lie-Liang Yang and Lajos Hanzo School of ECS, University of Southampton, SO17 1BJ, UK. Tel: +44-23-8059 3125, Fax: +44-23-8059 4508 Email: bh202r,lly,lh@ecs.soton.ac.uk; http://www-mobile.ecs.soton.ac.uk Abstract— In this contribution a generalized MC DS-CDMA system invoking smart antennas for improving the achievable per- formance of the system is studied, which is capable of suppress- ing the multiuser interference, while achieving frequency, time and spatial diversity. In the considered MC DS-CDMA sys- tem the receiver employs multiple receive antennas and each of the receive antennas consists of several antenna array elements. Four types of optimum linear combining schemes are investi- gated. In these optimum linear combining schemes the weight vec- tors are derived based on the optimization criteria of Minimum Variance Distortionless Response (MVDR), of Maximum Signal- to-Interference-plus-Noise Ratio (MSINR), of Minimum Mean- Square Error (MMSE) and of Minimum Power Distortionless Re- sponse (MPDR). The paper is concluded with a comparative per- formance study of various antenna array models employing the above optimization criteria. I. I NTRODUCTION In recent years numerous research contributions have ap- peared on the topic of Multi-Carrier Direct Sequence Code Division Multiple Access (MC DS-CDMA), which constitutes an attractive scheme [1],[2],[3],[4], based on a combination of DS-CDMA and OFDM. The multitone DS-CDMA system pro- posed in [3] and the orthogonal MC DS-CDMA system [1],[4] are capable of efficiently exploiting the transmission bandwidth and mitigating the effects of frequency selective multipath in- terference, while achieving both frequency and time diversity. On the other hand, smart antennas have been used for improv- ing the performance of wireless systems, since they are capa- ble of radiating and receiving energy in and from the intended directions, which potentially reduces the interference amongst wireless users [5],[6],[7]. In this contribution we discuss the generalized MC DS- CDMA system investigated in [8], [9], which includes the sub- classes of multitone DS-CDMA [3] and orthogonal MC DS- CDMA [4] as special cases. The transmitter of the generalized MC DS-CDMA system is portrayed in Fig.1. The novelty of this paper is that we combine the above-mentioned general- ized MC DS-CDMA system [8], [9] with smart antennas for the sake of improving the performance of the system by sup- pressing the multiuser interference, while achieving frequency, time and spatial diversity. Specifically, in our considered sys- tem the base-station receiver employs multiple receive anten- nas and each of the receive antennas consists of several antenna The financial support of the Mobile VCE, UK; EPSRC, UK and that of the European Union is gratefully ackowledged. Serial-to-parallel converter Data Tb bk1 bk2 Symbol duration Ts = UTb × ck(t) bkU sk(t) ∑ 2 1 × × × UV V cos(2πf11t + φk,11) cos(2πf12t + φk,12) cos(2πf1V t + φk,1V ) Fig. 1. The kth user’s transmitter schematic for the generalized multicarrier DS-CDMA system. array elements. At the receiver the antenna array outputs are combined using one of the four types of optimum linear com- bining schemes. These optimum linear combining schemes are based on the Minimum Variance Distortionless Response (MVDR), the Maximum Signal-to-Interference-plus-Noise Ra- tio (MSINR), the Minimum Mean-Square Error (MMSE) and the Minimum Power Distortionless Response (MPDR) opti- mization criteria, respectively. The achievable performance of the generalized MC DS-CDMA systems using the above- mentioned optimum linear combining schemes is investigated and compared, when operating in various propagation environ- ments. Furthermore, several different antenna array models are employed in our simulations. The rest of this paper is organized as follows. In Section II the philosophy of the generalized multicarrier DS-CDMA sys- tem invoking smart antennas is described and characterized. The statistical analysis of the receiver’s decision variable is pro- vided in Section III. In Section IV a range of linear combining based antenna array weight optimization schemes are invoked for deriving the decision variables, while the attainable perfor- mance is studied in Section V. Finally, we offer our conclusions in Section VI. II. SYSTEM DESCRIPTION A. Transmitted Signal In this subsection, the generalized MC DS-CDMA system of Fig. 1 [8], [9], [10] is reviewed. At the transmitter side, the bi- nary data stream having a bit duration of T b is serial-to-parallel (S/P) converted to U parallel sub-streams. The new bit duration 191 0-7803-8521-7/04/$20.00 (C) 2004 IEEE