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An Adaptive Load Balance and Handoff Management Strategy for Hierarchical Infrastructure Networks

ABSTRACT Hierarchical cellular networks that employ microcells with overlaying macrocells have been proposed to increase the traffic-carrying capacity and circuit quality. Variations in the traffic loads among cells will lessen the traffic-carrying capacity. Moreover, the handoff procedure usually takes place when the call crosses the cell boundary. An ineffective management will increase the system overheads, such as channel switch, data switch, and even network switch. The investigation proposes an effective load balance and handoff management strategy. This strategy are implemented to solve traffic-adaption problem that can enhance the traffic-carrying capacity for variations in traffic. For the management of handoff procedure, our strategy considers the mobility of mobile hosts and the bandwidth utilization in macrocells. It can decrease the number of handoffs and, accordingly, lessen the system overhead. Furthermore, the simulation results are presented to confirm the efficiency of the proposed strategy. INTRODUCTION Hierarchical microcell/ macrocell architectures have been proposed [Byungchan 2001, Bo 2001, Chung 2005, Iera 2002, Liu 2005, Li2001, Mar 2000, Shan 2003, Zhao 2005] to increase the traffic-carrying capacity and circuit quality. However, a cellular system has a probability to experience variations in traffic. To provide a high quality communication service for mobile subscribers and to enhance a high traffic-carrying capacity when there are variations in traffic have received much attention [Huang 2004]. Moreover, the handoff procedure usually takes place when the call crosses the cell boundary. In general, the handoff procedure including data transmission, channel switching, and even network switching takes tens or hundreds ms. An effective decrease of the number of handoff procedures that can lessen the system overhead is meaningful. A geographical area is covered by both of a microcell and a macrocell, where each cell has a base transceiver station (BTS) in its center. Each BTS has a set of primary channels [Chen 2002, Cao 2003, Cao 2000, Katzela 1996]. When a call arrives at an area, this call is first handled by the BTS of a cell. If no primary channels are available in this cell to serve this call, the BTS of the overlaid cell is activated to handle this call. If an available primary channel can be found, this channel is assigned for establishing the communication session of this call. Otherwise, the call is blocked. Accordingly, the number of channels allocated to a BTS will affect the communication quality in this cell and the allocations of system channels among cells will affect the traffic-carrying capacity of a cellular system. A reasonable allocation should provide more channels to each cell with heavy traffic than with light traffic. Otherwise, it will experience that the heavy traffic cells do not have sufficient channels to carry their traffic loads but the light traffic cells have many available channels. Thus, the traffic-carrying capacity of a cellular system is reduced and the call blocking probability arises. To consider real-life networks, the traffic distributions among cells should be changeable according to various conditions. In order to achieve higher channel utilization, when there are variations in traffic, the channel allocations among cells should be effectively reallocated according to current traffic profile. Each service area is covered by both microcells and macrocells. When a call arrives at an area, the channels of the targeted microcell or the channels of targeted macrocell can be used to handle this call. Many cell selection strategies have been proposed to handle the handoff procedures. Micro-Macro strategy [Zhao 2005] that when a call arrive, the targeted microcell is first to handle this call, if no available channels in this microcell, the overlapped macrocell then are activated to handle this call. The strategy prioritizes the channels of microcells to be assigned to incoming calls. …