Abstract
Data services with diverse rate and QoS requirements are going to be realized in 3G mobile networks. Due to the scarcity of bandwidth available in a wireless environment, the efficient use of the spectrum plays an important role in the overall system performance. In UMTS/W-CDMA, Orthogonal Variable Spreading Factor (OVSF) codes are used to achieve the separation between different physical channels, and they are considered an important and valuable wireless access resource. Currently there exist two types of problems when considering the channelization code assignment. In addition to the well-known call blocking problem that call requests are rejected due to insufficient code resource, a coarse use of these codes will incur the code blocking problem and result in poor call admission performance. Furthermore, due to the inherent tree properties of the OVSF codes, the amount of codes existing in the code tree drops significantly with the increase of their rate support, which made the admission of high-rate call requests much more difficult than low-rate ones. To address these problems, we propose an OVSF channelization code assignment scheme and a channelization code re-assignment scheme to efficiently utilize the OVSF codes. By simulations, we find that both of our proposed schemes exhibit superior performance in reducing the code blocking probability.