The performance of code division multiple access system depends on the correlation of the employed spreading code. Low cross-correlation values between spreading sequences are desired to suppress multiple access interference. An auto-correlation function with with a distinct peak enables proper synchronization and suppresses intersymbol interference. However, these requirements contradict each other and a trade-off needs to be established. In this paper, a global two dimensional optimization method is proposed to minimize auto-correlation with cross-correlation being allowed to lie within a fixed region. This approach is applied to design a set of complex valued spreading sequences.