© 2000 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

IEEE Transactions on Communications
Volume 48 Number 11, November 2000

Decentralized Multiuser Detection for Time-Varying Multipath Channels

Page 1840.

Abstract:

Multiple-access interference (MAI) and time-varying multipath effects are the two most significant factors limiting the performance of code-division multiple-access (CDMA) systems. While multipath effects are exploited in existing CDMA systems to combat fading, they are often considered a nuisance to MAI suppression. We propose an integrated framework based on canonical multipath-Doppler coordinates that exploits channel dispersion effects for MAI suppression. The canonical coordinates are defined by a fixed basis derived from a fundamental characterization of propagation effects. The basis corresponds to uniformly spaced multipath delays and Doppler shifts of the signaling waveform that capture the essential degrees of freedom in the received signal and eliminate the need for estimating arbitrary delays and Doppler shifts. The framework builds on the notion of active coordinates that carry the desired signal energy, facilitate maximal exploitation of channel diversity, and provide minimum-complexity MAI suppression. Progressively powerful multiuser detectors are obtained by incorporating additional inactive coordinates carrying only MAI. Signal space partitioning in terms of active/inactive coordinates provides a direct handle on controlling receiver complexity to achieve a desired level of performance. System performance is analyzed for two characteristic time scales relative to the coherence time of the channel. Adaptive receiver structures are identified that are naturally amenable to blind implementations requiring knowledge of only the spreading code of the desired user.

References

1. J. G. Proakis, Digitial Communications, 3rd ed.   New York: McGraw-Hill, 1995.
2. D. Slepian, "On bandwidth", Proc. IEEE, vol. 64, pp.  292-300,  Mar.  1976.
3. S. Verdu, Multiuser Detection, Cambridge: U.K.: Cambridge Univ. Press, 1998.
4. H. V. Poor, and G. W. Wornell, Eds., Wireless Communications: Signal Processing Perspectives, Englewood Cliffs, NJ: Prentice-Hall, 1998.
5. U. Madhow, "Blind adaptive interference suppression for direct-sequence CDMA", Proc. IEEE, vol. 86, pp.  2049 -2069, Oct.  1998.
6. G. Woodward and B. Vucetic, "Adaptive detection of DS-CDMA", Proc. IEEE , vol. 86, pp.  1413-1434, July  1998.
7. I. Ghauri and D. T. M. Slock, "Blind channel and linear MMSE receiver determination in DS-CDMA systems", in Proc. ICASSP'99, Mar. 1999, pp.  2699-2702. 
8. M. K. Tsatsanis and Z. Xu, "Performance analysis of minimum variance CDMA receivers", IEEE Trans. Signal Processing, vol. 46, pp.  3014-3022, Nov.  1998.
9. X. Wang and H. V. Poor, "Blind adaptive multiuser detection in multipath CDMA channels based on subspace tracking", IEEE Trans. Signal Processing, vol. 46, pp.  3030-3044, Nov.  1998.
10. H. Liu and M. D. Zoltowski, "Blind equalization in antenna array CDMA systems", IEEE Trans. Signal Processing, vol. 45, pp.  161-172, Jan  1997.
11. T. F. Wong, T. M. Lok, J. S. Lehnert and M. D. Zoltowski, "A linear receiver for direct-sequence spread-spectrum multiple-access systems with antenna arrays and blind adaptation", IEEE Trans. Inform. Theory, vol. 44, pp.  659 -676, Mar.  1998.
12. A. M. Sayeed, "Canonical multipath-Doppler coordinates in wireless communications", in 36th Annu. Allerton Conf. Communication, Control and Computing, Monticello, IL, 1998, pp.  536-545. 
13. A. M. Sayeed and B. Aazhang, "Joint multipath-Doppler diversity in mobile wireless communications", IEEE Trans. Commun., vol. 47, pp.  123-132, Jan.  1999.
14. A. M. Sayeed, A. Sendonaris and B. Aazhang, "Multiuser detection in fast fading multipath environments", IEEE J. Select. Areas Commun., vol. 16, pp.  1691-1701,  Dec.  1998.
15. P. A. Bello, "Characterization of randomly time-variant linear channels", IEEE Trans. Commun. Technol., vol. COM-11, pp.  360 -393, Nov.  1963.
16. T. Kailath, "Sampling models for linear time-variant filters", MIT Res. Lab. of Electron., Tech. Rep. 352, May 1959.
17. G. H. Golub and C. F. Van Loan, Matrix Computations, 2nd ed.   Baltimore, MD: Johns Hopkins Univ. Press, 1989.
18. U. Madhow and M. L. Honig, "MMSE interference suppression for direct-sequence spread-spectrum CDMA", IEEE Trans. Commun., vol. 42, pp.  3178-3188, Dec.  1994.
19. X. Wang and H. V. Poor, "Blind multiuser detection: A subspace approach", IEEE Trans. Inform. Theory, vol. 44, pp.  677 -690, Mar.  1998.
20. H. V. Poor and S. Verdu, "Probability of error in MMSE multiuser detection", IEEE Trans. Inform. Theory, vol. 43, pp.  858 -871, May  1997.
21. S. Haykin, Adaptive Filter Theory, 3rd ed.   Englewood Cliffs, NJ: Prentice-Hall, 1996.
22. S. Verdu, "Optimum multi-user asymptotic efficiency", IEEE Trans. Commun., vol. 38, pp.  496-508, Apr.  1990.
23. S. Bhashyam, A. M. Sayeed and B. Aazhang, "Time-selective signaling and reception for communication over multipath fading channels", IEEE Trans. Commun. , pp.  83-94, Jan.  2000.
24. A. M. Sayeed, E. N. Onggosanusi and B. D. Van Veen, "A canonical space-time characterization of mobile wireless channels", IEEE Commun. Lett., vol. 3, pp.  94-96, Apr.  1999.
25. E. N. Onggosanusi, A. M. Sayeed and B. D. Van Veen, "Canonical space-time coordinates for multiuser wireless communications", in Proc. 2nd IEEE Workshop on Signal Processing Advanced Wireless Communications (SPAWC), 1999.