  Signal to Noise Ratio (SNR) is an important index for wireless
communications. There are many methods for increasing SNR. In CDMA systems,
spreading sequences are used. We consider the frequency-selective
wide-sense-stationary uncorrelated-scattering (WSSUS) channel and evaluate the
worst case of SNR. We construct the non-linear programing for maximizing the
lower bound of the average of SNR. This problem becomes the convex programming
if we did not take into account the norm constraint. We derive necessary
conditions for optimal spreading sequences for the problem.
