Oversampling diversity versus dual antenna diversity for chip-level equalization on CDMA downlink

We examine through numerical simulations the performance of three equalizers for CDMA downlink in which the channel is frequency-selective: the traditional RAKE receiver, and chip-spaced MMSE (minimum mean square error) and ZF (zero-forcing) equalizers. These simulation results provide an upper-bound on average BER performance for users near a single transmitting base-station, in which the channel is assumed static and known. We present results for two channel models: a random 4-path multipath channel with delay spread of 10 micro seconds, and an empirically derived random multipath channel generated by the commercial software package SMRCIM. We compare the cases of diversity obtained by two spatially separated antennas to two "virtual channels" obtained through oversampling a single antenna's received signal. This simulation study has yielded the expected result that spatial diversity is preferable to diversity obtained via oversampling. Furthermore, the MMSE always out-performs both RAKE and ZF equalizers.

[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]  M. Latva-aho,et al.  Multiple access interference suppression with linear chip equalizers in WCDMA downlink receivers , 1999, Seamless Interconnection for Universal Services. Global Telecommunications Conference. GLOBECOM'99. (Cat. No.99CH37042).

[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]  T. Kailath,et al.  A least-squares approach to blind channel identification , 1995, IEEE Trans. Signal Process..

[5]  M.D. Zoltowski,et al.  Blind channel identification on CDMA forward link based on dual antenna receiver at handset and cross-relation , 1999, Conference Record of the Thirty-Third Asilomar Conference on Signals, Systems, and Computers (Cat. No.CH37020).

[6]  Thomas Kailath,et al.  Linear Systems , 1980 .

[7]  M.D. Zoltowski,et al.  Two-channel zero forcing equalization on CDMA forward link: trade-offs between multi-user access interference and diversity gains , 1999, Conference Record of the Thirty-Third Asilomar Conference on Signals, Systems, and Computers (Cat. No.CH37020).

[8]  J. Lilleberg,et al.  Downlink channel decorrelation in CDMA systems with long codes , 1999, 1999 IEEE 49th Vehicular Technology Conference (Cat. No.99CH36363).