Orthogonal variable spreading factor (OVSF) is an implementation of Code division multiple access (CDMA) where before each signal is transmitted, the spectrum is spread through the use of a user's code. User's codes are carefully chosen to be mutually orthogonal to each other.
These codes are derived from an OVSF code tree, and each user is given a different, unique code. An OVSF code tree is a complete binary tree that reflects the construction of Hadamard matrices.