Code placement and replacement strategies for wideband CDMA OVSF code tree management

Yu-Chee Tseng, Chih Min Chao, Shih Lin Wu

Research output: Contribution to journalArticlepeer-review

66 Scopus citations


The use of OVSF codes in WCDMA systems has offered opportunities to provide variable data rates to flexibly support applications with different bandwidth requirements. Two rarely addressed issues on such environment are the code placement problem and code replacement problem. The former may have significant impact on code utilization and thus code blocking probability, while the latter may affect the code reassignment cost if dynamic code assignment is to be conducted. The general objective is to make the OVSF code tree as compact as possible in order to support new calls, either with less blocking or with less reassignment cost. This paper is perhaps the first one which addresses these issues on WCDMA. Three simple strategies, which can be adopted by both code placement and code replacement, are proposed: random, leftmost, and crowded-first. Among them the crowded-first strategy looks most promising, which is shown to be able to reduce, for example, the code blocking probability by 77% and the number of reassignments by 81% as opposed the random strategy when the system is 80% fully loaded and the max SF=256.

Original languageEnglish
Pages (from-to)562-566
Number of pages5
JournalConference Record/IEEE Global Telecommunications Conference
StatePublished - 1 Jan 2001


  • 3G
  • OVSF
  • Personal communication services
  • Wireless communication

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