US Patent 7450491 Multicarrier and multirate CDMA system

In a multi-carrier and multi-rate CDMA system, a base station transmits an index tag to a number of mobile stations. The index tag has a length indicating a transmission rate and all index tags are nodes in a code tree. In the code tree, mother nodes and their child nodes block each other and are not assigned to the mobile stations at the same time. At the same time, index tags of nodes in the same level of the code tree map are orthogonal to each other. The mobile station constructs an index tag matrix according to the index tag. Then, the index tag matrix is multiplied with a generating matrix that is stored in every mobile station to generate a spreading factor matrix whose rows respectively correspond to different carriers.