In this paper, we propose an efficient technique to mitigate the effects of both multiple access interference (MAI) and intersymbol interference (ISI) in downlink wireless CDMA systems. A hybrid scheme comprising beamforming at the base station and a regularized zero forcing equalizer at the mobile unit is suggested and studied. The proposed scheme uses the beamforming to reduce the effect of the MAI. Then, the regularized zero forcing equalizer is used to reduce the effect of ISI and provide a better estimate of the data. The performance of the proposed scheme is studied and compared with traditional schemes. Our simulation results show a noticeable performance improvement by using the proposed scheme with low complexity at the mobile unit.
2. Rong, Z., "Simulation of adaptive array algorithms for CDMA systems," M.S. Thesis, Virginia Tech, Sep. 1996.
3. Litva, J. and T. K. Lo, Digital Beamforming in Wireless Communications,, Artech House, Boston, MA, 1996.
4. Alam, F., "Space time processing for third generation CDMA systems," Ph.D. Dissertation, Blacksburg, Virginia, Nov. 2002.
5. Elmusrati, M. and H. Koivo, Multi-path MVDR smart antenna algorithm for frequency selective channels, Proc. INICA 2003, 369-371, VDE Verlag Gmbh, Berlin, 2003.
6. Liberti, J. and T. Rappaport, Smart Antennas for Wireless Communications, Prentice Hall, 1999.
7. Godara, L., "Application of antenna array to mobile communicommunications, Part II: Beamforming and direction of arrival considerations," Proc. IEEE, Vol. 85, No. 8, 1195-1245, Aug. 1997.
8. Klein, A., "Data detection algorithms specially designed for the downlink of CDMA mobile radio systems," Proc. IEEE VTC, Vol. 1, 203-207, May 4--7, 1997.
9. Al-kamali, F. S., M. I. Dessouky, B. M. Sallam, and F. E. El-Samie, "Frequency domain interference cancellation for single carrier cyclic prefix CDMA systems," Progress In Electromagnetics Research B, Vol. 3, 255-269, 2008.
10. Al-kamali, F. S., M. I. Dessouky, B. M. Sallam, and F. E. ElSamie, "Performance evaluation of cyclic prefix CDMA systems with frequency domain interference cancellation," Digital Signal Processing Journal, Vol. 19, No. 1, 2-13, Elsevier Inc., Jan. 2009.
11. Rugini, L., P. Banelli, and S. Cacopardi, "A full-rank regularization technique for MMSE detection in multiuser CDMA systems," IEEE Commun. Lett., Vol. 9, No. 1, 34-36, Jan. 2005.
12.Alpha Concept Group, Wideband direct sequence CDMA (WCDMA) evaluation document (3.0), Tdoc SMG 905/97, Spain, Dec. 15--19, 1997.