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8 - QAM for multicode CDMA with interference cancellation

from Part III - Evolved 3G mobile communications

Published online by Cambridge University Press:  27 May 2010

Jiangzhou Wang
Jiangzhou Wang
Affiliation:
University of Kent, Canterbury
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Summary

This chapter studies MQAM for downlink multicode CDMA systems with interference cancellation to support high data rate services. In the current 3G WCDMA systems, in addition to multicode transmission, MQAM is employed for HSDPA due to its high spectral efficiency. In frequency selective fading channels, multipath interference seriously degrades the system performance. In this chapter, theoretical analysis is presented to show that with the help of interference cancellation technique, MQAM may be employed in high SNR cases to increase system throughput. Moreover, it is found that when using the interference cancellation technique, extra pilot power should be invested for more accurate channel estimation, and consequently better BER performance can be achieved.

Introduction

MQAM modulated multicode CDMA is proposed for HSDPA in the 3G standards, by which the throughput can be increased without extra bandwidth investment. As mentioned in Chapter 1, the introduction of multicode transmission causes multipath interference in frequency selective fading channels due to multipath propagation delays. In this chapter, a coherent Rake receiver with interference cancellation is studied.

Moreover, in WCDMA systems, a common pilot channel is used for channel estimation at the receiver. However, channel estimation error occurs since the received pilot channel signal suffers from the multipath interference and AWGN noise, which affects the coherent data decision and the regeneration of multipath interference, and thus degrades the system performance. The effects of imperfect channel estimation and additive multipath interference on system performance are investigated.

Type
Chapter
Information
High-Speed Wireless Communications
Ultra-wideband, 3G Long Term Evolution, and 4G Mobile Systems
 , pp. 214 - 228
Publisher: Cambridge University Press
Print publication year: 2008

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References

Third generation partnership project, www.3gpp.org.
Wang, J. and Chen, J., “Performance of wideband code division multiple access systems with complex spreading and imperfect channel estimation,” IEEE J. Select. Areas Commun., vol. 19, pp. 152–163, Jan. 2001.CrossRefGoogle Scholar
Chen, J., Wang, J. and Sawahashi, M., “multicode interference cancellation for multicode wideband code division multiple access systems,” IEEE J. Select. Areas Commun., vol. 20, pp. 450–462, Feb. 2002.CrossRefGoogle Scholar
Tang, X., Alouini, M.-S., and Goldsmith, A. J., “Effect of channel estimation error on M-QAM BER performance in Rayleigh fading,” IEEE Trans. Commun., vol. 47, pp. 1856–1864, Dec. 1999.CrossRefGoogle Scholar
Higuchi, K., Fujiwara, A. and Sawahashi, M., “Multipath interference canceller for high-speed packet transmission with adaptive modulation and coding scheme in W-code division multiple access forward link,” IEEE J. Select. Areas Commun., vol. 20, pp. 419–432, Feb. 2002.CrossRefGoogle Scholar
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Benedetto, S. and Biglieri, E., Principles of Digital Transmission with Wireless Applications. New York: Kluwer, 1999.Google Scholar
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