Reduced-rank adaptive MMSE equalization for high-speed CDMA forward link with sparse multipath channels

This paper deals with adaptive reduced-rank, chip-level MMSE estimation for the forward link in CDMA based on the multi-stage nested Wiener filter (MSNWF). We first examine through simulations the convergence of 'block-adaptive' MSNWF based on training by pilot symbols; MSNWF operates in a low-rank subspace facilitating faster convergence than LMS and RLS. We then describe a "semi-blind" approach which exploits the underlying channel structure, specifically the fact that the channel impulse response is sparse, to adapt a much lower-dimensional equalizer. Our simulations show this low-rank MMSE equalizer converges very quickly to the asymptotic SINR.

[1]  D. Slock,et al.  Linear receivers for the DS-CDMA downlink exploiting orthogonality of spreading sequences , 1998, Conference Record of Thirty-Second Asilomar Conference on Signals, Systems and Computers (Cat. No.98CH36284).

[2]  Dirk T. M. Slock,et al.  Structured estimation of sparse channels in quasi-synchronous DS-CDMA , 2000, 2000 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings (Cat. No.00CH37100).

[3]  Michael D. Zoltowski,et al.  Simple MMSE equalizers for CDMA downlink to restore chip sequence: comparison to zero-forcing and RAKE , 2000, 2000 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings (Cat. No.00CH37100).

[4]  Louis L. Scharf,et al.  A Multistage Representation of the Wiener Filter Based on Orthogonal Projections , 1998, IEEE Trans. Inf. Theory.

[5]  David Gesbert,et al.  A semi-blind approach to structured channel equalization , 1998, Proceedings of the 1998 IEEE International Conference on Acoustics, Speech and Signal Processing, ICASSP '98 (Cat. No.98CH36181).

[6]  J. S. Goldstein,et al.  Adaptive reduced-rank residual correlation algorithms for DS-CDMA interference suppression , 1998, Conference Record of Thirty-Second Asilomar Conference on Signals, Systems and Computers (Cat. No.98CH36284).

[7]  Michael D. Zoltowski,et al.  Reduced-rank adaptive MMSE equalization for the forward link in high-speed CDMA , 2000, Proceedings of the 43rd IEEE Midwest Symposium on Circuits and Systems (Cat.No.CH37144).

[8]  Yung-Fang Chen,et al.  Joint angle and delay estimation for DS-CDMA with application to reduced dimension space-time RAKE receivers , 1999, 1999 IEEE International Conference on Acoustics, Speech, and Signal Processing. Proceedings. ICASSP99 (Cat. No.99CH36258).