Adaptive Spreading Code Assignment for Up-Link MC-CDMA

Multi-carrier (MC) code division multiple access (CDMA) is able to take the advantages of OFDM and CDMA and is a potential technique for future wireless communications. For an uplink MC-CDMA system, the symbols of different users are spread in the frequency domain. However, the frequency-selective fading of wireless channels destroys the othogonality of the spreading codes for different users and causes multiple access interference (MAI), especially for a network with full load. To reduce the impact of MAI, we adaptively assign spreading codes according to channel state information and MAI environments. Since it requires high computational complexity to find an optimal set of spreading codes for all active users, we develop several simplified approaches to search the suboptimal spreading code sets. It is demonstrated by the computer simulation that the adaptive spreading code assignment, even though suboptimal, can significantly improve the performance of MC-CDMA systems.

[1]  Ramjee Prasad,et al.  Overview of multicarrier CDMA , 1997, IEEE Commun. Mag..

[2]  Timothy O'Farrell.  NEW SIGNATURE CODE SEQUENCE DESIGN TECHNIQUES FOR CDMA SYSTEMS , 1991 .

[3]  T. M. Lok.  Optimal uplink sequence assignment for multicarrier CDMA systems in Rayleigh fading channels , 2003, Fourth International Conference on Information, Communications and Signal Processing, 2003 and the Fourth Pacific Rim Conference on Multimedia. Proceedings of the 2003 Joint.

[4]  David Mottier,et al.  A spreading sequence allocation procedure for MC-CDMA transmission systems , 2000, Vehicular Technology Conference Fall 2000. IEEE VTS Fall VTC2000. 52nd Vehicular Technology Conference (Cat. No.00CH37152).

[5]  C.-C. Jay Kuo,et al.  Design of MAI-free MC-CDMA systems over frequency-selective fading channels via codeword selection , 2005, Proceedings. (ICASSP '05). IEEE International Conference on Acoustics, Speech, and Signal Processing, 2005..

[6]  Hassan El Ghazi,et al.  Efficient Spreading Code Allocation Strategy for a Downlink MC-CDMA System in a Time Varying Frequency Selective Channel , 2006, 2006 IEEE 17th International Symposium on Personal, Indoor and Mobile Radio Communications.

[7]  Jeffrey G. Andrews,et al.  Optimum power control for successive interference cancellation with imperfect channel estimation , 2003, IEEE Trans. Wirel. Commun..

[8]  R. Pyndiah,et al.  Impact of the spreading sequences on the performance of forward link MC-CDMA systems , 2004, Eighth IEEE International Symposium on Spread Spectrum Techniques and Applications - Programme and Book of Abstracts (IEEE Cat. No.04TH8738).

[9]  Matti Latva-aho,et al.  Simple spreading code allocation scheme for downlink MC-CDMA , 2002 .