This paper investigates the performance of trellis coding when it is applied to a spread-spectrum multiple-access system. A system model is proposed that allows one to apply both trellis coding and a PN spreading sequence to the data symbols to be transmitted. Rate n/n + 1, trellis codes employing 2n+ 1 point MPSK signal constellations are investigated when Gold sequences are employed for purposes of PN spreading. Performance in an additive white Gaussian noise (AWGN) channel is investigated, with 5-20 users transmitting simultaneously. Using criteria of equal complexity and throughput, the performance of the trellis codes in a SSMA environment is compared to that of medium to low rate convolutional codes through the use of a generalized transfer function bound. The average degradation due to the interuser interference is determined by employing the method of moments. The validity of approximating the interuser interference as a Gaussian random variable is also investigated. The numerical results illustrate that for a given complexity, chip rate and throughput, that low rate convolutional codes provide the best performance in a SSMA system. As lower rate convolutional codes are employed, there is an increase in the effective interuser interference due to the greater cross-correlation effects from using shorter PN sequences, or alternatively from the effects of partial cross-correlation. However, this increased degradation is more than overcome by the increased distance properties of the low rate codes. The coding gains for the codes that were considered range from 1-6 dB (depending on the type and complexity of the code) over the corresponding uncoded performances of SSMA in an AWGN channel.

Additional Metadata
Persistent URL
Journal IEEE Journal on Selected Areas in Communications
Boudreau, G.D. (Gary D.), Falconer, D.D, & Mahmoud, S.A. (1990). A Comparison of Trellis Coded Versus Convolutionally Coded Spread-Spectrum Multiple-Access Systems. IEEE Journal on Selected Areas in Communications, 8(4), 628–640. doi:10.1109/49.54459