Network controlled cell selection for the high speed downlink packet access in UMTS

An expanded effort is underway to support the evolution of the UMTS standard to meet the rapidly developing needs associated with wireless Internet applications. The support of high speed downlink packet access (HSDPA) is provided by means of a new, shared channel called high speed downlink shared channel (HS-DSCH) which is enabled by a number of performance enhancing technologies such as adaptive modulation and coding (AMC), hybrid ARQ (HARQ), fat-pipe scheduling, fast cell selection (FCS) and multiple input multiple output (MIMO) antenna techniques. In this paper, the advantage of FCS is investigated. To avoid the difficulty in HARQ transmission-state synchronization, FCS is allowed only among the cells (sectors) belonging to the same base station. Two FCS approaches are compared in this paper. The user controlled cell selection (UCCS) selects the serving cell based only on the channel quality seen by the user. While a new-network controlled cell selection (NCCS) approach jointly considers channel quality and network loading. It is shown that FCS significantly improves the HSDPA performance at low mobility. Among the FCS schemes, NCCS is superior to UCCS when the load among the cells in the active set is unbalanced.