Fast OVSF Code Generation Method using Multi-Stage Spreading Scheme

This paper proposes the fast OVSF code generation method using the multi-stage spreading scheme based on the single code indexing scheme. The conventional OVSF indexing scheme based on the code-tree structure uses two numbers as the codeword indices, the layer number and the code number of the corresponding layer. However, the single code index number implicitly includes the information of the spreading factor as well as the code number. Since the binary representation of the single code indices shows the pattern of the codeword, the orthogonality between two different codewords can be determined by comparing their code indices instead of much longer codewords. The above useful property also makes the codeword can be generated directly kom its single code index. In this paper, the multi-stage spreading scheme is applied to generate the long code by spreading two shorter codewords with the appropriate code indices. The proposed fast code generation algorithm is designed for 3GPP UMTS systems and verified by the simulations.