In order to support multi - rate transmission in ds - cdma , many cdma techniques such as multi - code ( mc ) scheme , orthogonal variable spreading factor ( ovsf ) and variable modulation have been used 在ds - cdma系统中多速率传输的方法有很多种,例如多码方案( mc - cdma ) ,正交可变扩频增益方案( ovsf )和多调制方案等。