University of Minnesota

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Filterbanks in single- and multi-user communications

In this research we take a fresh look at single- and multi-user transmitters and receivers (transceivers) and model their discrete-time baseband equivalent communication systems using synthesis and analysis filterbanks. Transmit filterbanks offer (perhaps redundant) precoders that unify and generalize existing modulations including OFDM, DMT, FDMA, TDMA, WDMA, and CDMA schemes. We have derived sufficient conditions which guarantee that with FIR filterbank precoders FIR channels are equalized perfectly (in the absence of noise) by FIR zero-forcing equalizer filterbanks, *irrespective* of the channel zero locations. Multicarrier transmissions through frequency-selective channels can thus be recovered even when deep fades are present. We have also developed jointly optimal transmitter-receiver filterbank designs based on maximum output SNR and minimum mean-square error criteria under zero-forcing and fixed transmitted power constraints.

By exploiting input-redundancy, we have also derived blind channel estimators, block synchronizers, and direct self-recovering equalizing filterbanks. The resulting algorithms are computationally simple, require small data sizes, can be implemented online, and remain consistent even at low SNR colored noise. Analysis and simulations illustrate superior performance relative to CMA and existing output diversity techniques that rely on multiple antennas and/or fractional sampling. Our blind equalization results apply both to single-user block transmission systems as well as to the downlink multiuser scenario.

For the uplink multiuser setup, we have capitalized on our unifying filterbank framework to develop a family of codes for low complexity Quasi-Synchronous CDMA systems capable of eliminating multiuser interference (MUI) completely in the presence of unknown and even rapidly varying multipath. Our judiciously designed pre-computable symbol-periodic user codes, that we term Lagrange or Vandermonde, and the corresponding linear receivers offer a generalization of orthogonal frequency division multiplexing (OFDM) especially valuable when deep-fading, carrier frequency errors, and Doppler effects are present. We have also exploited the flexibility inherent to the designed transceivers to derive transmission strategies that cope with major impairments of wireless CDMA channels. We have also generalized our symbol-periodic code design to include the class of aperiodic spreading and orthogonal multi-rate codes for variable bit rate users. Performance analysis and simulations results have illustrated distinct advantages of our transceiver designs over competing alternatives.

Journal Papers:

  1. A. Scaglione, G. B. Giannakis, and S. Barbarossa, "Lagrange/Vandermonde MUI Eliminating User Codes for Quasi-Synchronous CDMA in Unknown Multipath," IEEE Trans. on Signal Processing, 1999 (submitted).
  2. A. Scaglione, G. B. Giannakis, and S. Barbarossa, "Redundant Filterbank Precoders and Equalizers, Part I: Unification and Optimal Designs," IEEE Trans. on Signal Processing, vol. 47, June 1999 (to appear).
  3. A. Scaglione, G. B. Giannakis, and S. Barbarossa, "Redundant Filterbank Precoders and Equalizers, Part II: Blind Channel Estimation, Synchronization, and Direct Equalization," IEEE Trans. on Signal Processing, 1999 (to appear).
  4. A. Scaglione, S. Barbarossa, and G. B. Giannakis, "Filterbank Transceivers Optimizing Information Rate in Block Transmissions over Dispersive Channels," IEEE Trans. on Information Theory, vol. 47, April 1999 (to appear).
  5. A. Scaglione, and G. B. Giannakis, "Design of user codes in QS-CDMA systems for MUI elimination in unknown multipath," IEEE Communication Letters, February 1999 (to appear).
  6. G. B. Giannakis, "Filterbanks for blind channel identification and equalization," IEEE Signal Processing Letters, vol. 4, pp. 184-187, June 1997.

Conference Proceedings:

  1. G. B. Giannakis, Z. Wang, A. Scaglione, S. Barbarossa, "Mutually Orthogonal Transceivers for Blind Uplink CDMA Irrespective of Multipath Channel Nulls," Proc. of ICASSP, Phoenix, AZ, March 15-19, 1999.
  2. A. Scaglione, S. Barbarossa, and G. B. Giannakis, "Fading-resistant and MUI-free codes for CDMA systems," Proc. of ICASSP, Phoenix, AZ, March 15-19, 1999.
  3. A. Scaglione, S. Barbarossa, and G. B. Giannakis, "Transmit-Filterbanks Optimizing Information Rate in Block Transmissions over Dispersive Channels," Proc. of GLOBECOM, vol. 6, pp. 3651-3656, Sydney, Australia, Nov. 9-11, 1998.
  4. A. Scaglione, G. B. Giannakis and S. Barbarossa, "Redundant filterbank precoders and equalizers: Unification and optimal designs," Proc. of ICC, vol. I, pp. 21-25, Atlanta, GA, June 7-11, 1998.
  5. A. Scaglione, G. B. Giannakis and S. Barbarossa, "Self-recovering multirate equalizers using redundant filterbank precoders," Proc. of ICASSP, vol. VI, pp. 3501-3504, Seattle, WA, May 12-15, 1998.
  6. G. B. Giannakis and A. Scaglione, "Designing user codes for MUI elimination and unknown multipath mitigation in asynchronous CDMA systems," Proc. of 35th Annual Allerton Conf. on Communication, Control, and Computing}, pp. 729-738, Univ. of Illinois at U-C, Monticello, Il, September 1997 (invited).
  7. A. Scaglione, G. B. Giannakis, and S. Barbarossa, "Redundant Filterbank Precoders and Equalizers: Optimal Designs and Blind Recovery," Proc. of 35th Annual Allerton Conf. on Communication, Control, and Computing}, pp. 385-394, Univ. of Illinois at U-C, Monticello, Il, Sept. 1997.

 

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