Scheduling and call admission control schemes in soft handoff for packet switched transmission in WCDMA networks

This article presents an overview of radio resource management schemes for supporting of multimedia applications in IP CDMA-based systems considering soft handoff (SHO). A collection of radio resource management (RRM) algorithms guarantees the stability of the radio path and the QoS of radio connection by efficient sharing and managing of the radio resources. Differentiated allocation of resources through power control, prioritized access to medium through packet scheduling and admission control (CAC) and performance guarantees during soft handoff are discussed related with mobility characteristics and traffic patterns associated to the new services. The paper focuses in the uplink. Although soft handoff has been shown to increase the uplink system capacity it requires a more complex control of mobile station (MS) transmissions in the packet level. Given that more than one base station (BS or node B) control the cells where MSs are presented, several alternatives could be considered as to the location of the scheduling entity that controls the MS transmissions. This paper presents a system performance evaluation when more than one cell could be considered as valid scheduling entities. In this case, it has been required the implementation of a decision procedure in the MS when it receives scheduling assignments from multiple BSs. On the other hand, performance of CAC strategies in soft handoff is evaluated and compared with hard handoff considering adaptive reservation CAC schemes in order to prevent forced termination of handoff calls. Comparison is performed considering both homogeneous and heterogeneous load distributions in cells.