Channel code trees are hierarchical structured code sequences that allow codes to be selected from a table that do not interfere with each other. By structuring the codes in a tree format, lower level codes (branches of the tree) are subsets of upper level codes. When lower level codes are selected, the upper level codes cannot be used.

Figure 1.10 shows how the WCDMA system uses a code tree to assign different data rates to different users. This example shows that upper level codes in the code tree can be used to provide higher data rates and that these upper level codes use a lower spreading factor that provides for the higher data rate. This diagram also shows that when lower level codes are used, the upper level codes above them cannot be used.

Figure 1.10: Channel Code Tree