A new frequency-time-spreading code for MC/DS-CDMA wireless systems over Rayleigh fading channels

While two-dimensional (2-D) orthogonal variable spreading factor (OVSF) codes were proposed for multicarrier direct-sequence code-division multiple-access (MC/DS-CDMA) systems in order to eliminate multiple-access interference, the number of orthogonal sequences (or code cardinality) was restricted by the number of carrier frequencies. Non-orthogonal 2-D frequency-time-spreading (FTS) codes were then proposed to increase the code cardinality by sacrificing some code performance. To improve the code performance, we here propose a modified 2-D FTS code. We also evaluate the performance of the new code in the MC/DS-CDMA system over a non-fading additive white Gaussian noise channel and a Rayleigh fading channel, and compare with those of the 2-D OVSF, random and original FTS codes.