A Fast Code-Assignment Strategy for a WCDMA Rotated-OVSF Tree with Code-Locality Capability

In this paper, a new channelization code tree structure, namely an ROVSF (rotated-orthogonal variable spreading factor) code tree, is defined and investigated. Most existing code assignment schemes are investigated on the OVSF (orthogonal variable spreading factor) code tree in WCDMA systems. The main work of this investigation is to exploit and justify the new properties of the ROVSF code tree. We show that the ROVSF code tree offers the same code capability to that of the conventional OVSF code tree, but our ROVSF code tree additionally has the code-locality capability. With the code-locality capability, a fast code-assignment strategy is developed on the ROVSF code tree. Compared to existing code assignment schemes on OVSF code trees, a fast code assignment scheme is developed with lower search costs and a low blocking rate, due to its code-locality capability. Finally, the simulation results illustrate that our proposed scheme on the ROVSF code tree actually has lower search costs and a better blocking rate.