Control and quality-of-service provisioning in high-speed microcellular networks

Abstract

esign and implementation of broadband networks is one of the major focal areas in modern telecommunications. With recent developments in the field of wireless, hand-held terminals, as well as in personal communications services (PCS) [l-61, integration of mobile, wireless connections in a backbone broadband network is an essential and challenging task since mobile users may need to access the communication services offered by the fixed broadband network. This implies that wireless networks must provide packetbased t ransport and bandwidth-upon-demand, as well as support multimedia applications. Since the radio spectrum is limited, future wireless systems will have micro/picocellular architectures in order to provide the higher capacity needed to support broadband services [7-91. Due to the small coverage area of micro/picocells and characteristics of the multipath and shadow fading radio environment, hand-off events in future microcellular systemswill occur at a much higher rate as compared to today’s macrocellular systems, and control of such systems will introduce a new set of challenges. We canviewwirelessimobile connections as consisting of paths (or routes) through the broadband backbone network; and radio links between the mobile, wireless terminals and base stations (or access points) which are the interface of mobile users to the fixed backbone network. When the quality of a radio link between a wireless terminal and its access point degrades, a new access point with acceptable quality must be found (hand-off), and network control functions of both the fixed and wireless network need to be invoked. In the backbone network, hand-off requires the establishment of a new route, which transports the packets destined to (or originated from) the wireless terminal to (or from) the new access point. Here, network call processing functions need to be invoked in order to set up such a route and ensure that the newly established route maintains acceptable quality-of-service (QOS) to both the wireless connection and to pre-existing calls sharing links of the new route. Furthermore, to execute hand-off, the network call controller must first ensure that the new wireless connection does not overload the new access point and then create a radio link between the mobile terminal and the new access point. As one can see, a substantial number of call processing and control functions of the fixed and wireless network must be invoked to complete a hand-off event. If such control functions are performed in a centralized fashion, call processing of handoff events would impose a bottleneck on the capacity of future microcellular networks. In this article, we propose and study distributed control methodologies for high-speed microcellular networks based on a hierarchical grouping of backbone and wireless network resources. With our approach, a number of adjacent cells are grouped into a cell-cluster that is used for call setup and control of the radio links, and all access points in a cell-cluster belong to the same backbone network connection tree, to be used for call setup and control of the backbone portion of wireless connections.