Performance of multirate techniques in W-CDMA

We analyze and compare the error performances of two multirate transmission schemes in W-CDMA: multicode (MCD) and variable spreading gain (VSG). First, we show that in an AWGN channel, the VSG data user performs better than the MCD user if the number of in-cell voice users are low and the background noise is weak. However, as the noise power or the number of voice subscribers increases, the performances of the two schemes become similar. We then show that in a multipath fading channel, the two schemes achieve very similar error performances as long as their receivers are able to track all resolvable signal paths. However, when the receiver can only track multipath components within the current symbol interval, the VSG user yields a much worse error probability than the MCD user. This is because the VSG data user has a much shorter symbol interval. Simulation results are illustrated to support the analysis.

[1]  S. Ramakrishna,et al.  A comparison between single code and multiple code transmission schemes in a CDMA system , 1998, VTC '98. 48th IEEE Vehicular Technology Conference. Pathway to Global Wireless Revolution (Cat. No.98CH36151).

[2]  Ramjee Prasad,et al.  Wideband CDMA for third generation mobile communications , 1998 .

[3]  T. Wada,et al.  A constant amplitude coding for orthogonal multi-code CDMA systems , 1997 .

[4]  Erik Dahlman,et al.  Wide-band services in a DS-CDMA based FPLMTS system , 1996, Proceedings of Vehicular Technology Conference - VTC.

[5]  Fumiyuki Adachi,et al.  Wideband DS-CDMA for next-generation mobile communications systems , 1998, IEEE Commun. Mag..

[6]  F. Gourgue,et al.  Comparison between multicode with fixed spreading and single code with variable spreading options in UTRA/TDD , 1999, 1999 2nd IEEE Workshop on Signal Processing Advances in Wireless Communications (Cat. No.99EX304).

[7]  Dilip V. Sarwate,et al.  Partial Correlation Effects in Direct-Sequence Spread-Spectrum Multiple-Access Communication Systems , 1984, IEEE Trans. Commun..

[8]  L. B. Milstein,et al.  Using higher order constellations with minimum mean square error (MMSE) receiver for severe multipath CDMA channel , 1998, Ninth IEEE International Symposium on Personal, Indoor and Mobile Radio Communications (Cat. No.98TH8361).

[9]  T. Ottosson,et al.  Multi-rate schemes in DS/CDMA systems , 1995, 1995 IEEE 45th Vehicular Technology Conference. Countdown to the Wireless Twenty-First Century.

[10]  Jack M. Holtzman,et al.  A simple, accurate method to calculate spread-spectrum multiple-access error probabilities , 1992, IEEE Trans. Commun..

[11]  Anthony Ephremides,et al.  Cellular multicode CDMA capacity for integrated (voice and data) services , 1999, IEEE J. Sel. Areas Commun..

[12]  G.L. Turin,et al.  Introduction to spread-spectrum antimultipath techniques and their application to urban digital radio , 1980, Proceedings of the IEEE.

[13]  Qiang Wang,et al.  Concatenated Orthogonal/PN Spreading Sequences and Their Application to Cellular DS-CDMA Systems with Integrated Traffic , 1996, IEEE J. Sel. Areas Commun..

[14]  John G. Proakis,et al.  Digital Communications , 1983 .

[15]  Dan Keun Sung,et al.  Capacities of single-code and multicode DS-CDMA systems accommodating multiclass services , 1999 .

[16]  William C. Y. Lee.  Mobile Communications Engineering: Theory and Applications , 1997 .