Assignment and reassignment schemes for OVSF codes in WCDMA

Abstract

OVSF codes are used as channelization codes in WCDMA. In this paper a number of OVSF code assignment and reassignment strategies are proposed. We can use these schemes in accordance to the benefit required. Leftmost code assignment (LCA) of OVSF scheme is first proposed which provides benefit of less code searches and no reassignments, saving extra overhead in transmission. Limitation of LCA scheme is code blocking which increases the blocking probability of calls. Code blocking can be avoided by using code reassignments. Ancestor cost assignment scheme is used to make assignment compact so that vacant codes are available for higher rate calls. This reduces the blocking compared to DCA scheme. Class partition assignment divides all OVSF codes into different sets. The users with different rates(classes) are assigned different sets. The class partition assignment scheme reduces number of code searches compared to DCA assignment and reassignment schemes. Blocking in class partition assignment scheme can be reduced by reserving some OVSF codes for reassignments. Matlab is as simulation tool used to demonstrate the results.