CAC for Multibeam Opportunistic Schemes in Heterogeneous WiMax Systems Under QoS Constraints

Abstract

Spatial scheduling in a heterogeneous WiMax Downlink channel, based on partial channel state information at the transmitter (CSIT), is carried out through a multibeam opportunistic beamforming technique. In contrast to existing literature, this paper considers a more practical perspective and presents a strategy where a minimum rate per user is required, which can only be guaranteed under a certain system outage restriction. Within this scenario, the paper then formulates the minimum rate and maximum/mean delay expressions in closed form expressions. Furthermore, in opportunistic schemes a high number of users is required to improve the sum rate system performance, but for practical considerations, a large number of available users induces a large service delay. A dynamic call admission control (CAC) is then proposed to regulate the number of users, and to guarantee the service to all the users in the cell under rate and delay requirements. The derived expressions are then tested via simulations in several transmission scenarios, where users running delay-constrained (DC) and delay-tolerant (DT) applications coexist.