UMTS無線電資源分配之研究

Abstract

The {it Universal Mobile Telecommunications System} (UMTS) adopts WCDMA as the air interface to provide variable data rate services. In WCDMA, Orthogonal Variable Spreading Factor (OVSF) codes are assigned to different users to preserve the orthogonality among users' physical channels. The data rate supported by an OVSF code depends on its Spreading Factor ($SF$). An OVSF code with smaller $SF$ can support higher data rate services than that with larger $SF$s. Four classes of traffics are identified in UMTS, which are conversational, streaming, interactive, and background traffics. The traffic for the conversational and streaming classes has the fairly constant characteristics. The dedicated physical channels (DPCHs) are preferred channels to serve these two classes of traffics. The interactive traffic is highly dependent on request-response patterns of end users, which has the bursty characteristics, and the applications with the background traffic does not request stringent response-time. To efficiently utilize the radio bandwidth, the shared channel technology is proposed to deliver interactive and background traffics. In this dissertation, we study the radio resource allocation for UMTS, where the dedicated and shared channel approaches are considered. For the dedicated code channel assignment, we propose two OVSF code assignment schemes, CADPB1 (Code Assignment with Dynamic Partition and Buffering 1) and CADPB2. Both schemes are simple and only incur low system overhead. The analytic model and simulation experiments are conducted to evaluate the performance of the two schemes. For the shared channel approach, we propose a Shared-Channel Assignment and Scheduling (SCAS) algorithm to allocate shared code channels to interactive and background connections, which incurs low complexity and is considered practical. We formally prove the correctness of the SCAS and also conduct simulation experiments to investigate the performance of the SCAS algorithm.