Region Division Assignment: A New OVSF Code Reservation and Assignment Scheme for Downlink Capacity in W-CDMA Systems

This work focuses on the efficient management of orthogonal-variable-spreading-factor (OVSF) codes for multimedia communications in the W-CDMA systems. Because these systems must assign only OVSF codes that are mutually orthogonal, even if they have sufficient transmission capacity they block connections for which no orthogonal OVSF codes are available. This code blocking can, with extra overhead, be eliminated by reassigning codes, but in this paper we propose an OVSF code management scheme designed to not reassign codes. This scheme, called Region Division Assignment, cannot eliminate code blocking but can reduce the overhead for code assignment. Computer simulations based on the multiple access protocol in UMTS/IMT-2000 show that the proposed scheme can efficiently provide variable-rate services as well as low-rate services.