Wireless Personal Communications (2006) 36: 59–67 DOI: 10.1007/s11277-006-7680-6 C  Springer 2006 Handover Optimization in Wireless Microcellular ATM Networks S. LOUVROS, D. KARABOULAS and S. KOTSOPOULOS Wireless Telecommunications Laboratory, Department of Electrical and Computer Engineering, University of Patras, Hellas E-mail: splouvros@hotmail.com; slouvros@cosmote.gr Abstract. Microcellular solutions in wireless ATM networks increase the network traffic control as a result of frequent handover requests. The blocking probability or the forced termination probability presents a quality of service criterion for evaluation of certain handover techniques. This paper presents a handover protocol that can avoid cell loss and guarantee cell sequence, and a two layer wireless call admission control is studied, using Markov state diagrams, in order to optimize the performance of wireless ATM networks. Keywords: handover, Markov state diagrams, microcellular, wireless ATM networks 1. Introduction The future of mobile communications promise constantly increasing subscriber number, which puts demand on more capacity in cellular networks around the world. While small cells relieve the capacity problem, frequent movements of mobile users poses a big network control chal- lenge called handover. When the handover rate increases, the probability of an ongoing session to be dropped due to a lack of free channel is high. In wireless ATM networks where rerouting, terminating and establishing connections are involved, they result in time consumption during the handover process. Other problems that result from the handover process are cell losses and cells out of sequence [1]. Several handover algorithms have been proposed aiming a single problem: either support- ing microcell architecture or guaranteeing transmission quality. In a traditional wire line ATM network, the user is stationary; however in a wireless ATM environment the connection must be rerouted in every handover. Because of the frequent handovers, the call processor may need to become involved many times during a mobile connection lifetime, and it would cause a considerable burden on the processing of cellular controllers [2]. In [3, 6] a model for frequent handovers in microcellular ATM networks is proposed. In this model, a mobile connection call setup procedure creates a virtual connection tree and covers a large geographical region. Be- cause of the pre-established connection path at call setup time, the mobile user does not need to demand a rerouting procedure during the handover process each time. However, it cannot han- dle misrouted cells and cell out-of-sequence problems [10]. References [11, 12] adopt a Base Station (BS) group to ensure that a mobile subscriber can move rapidly between radio cells. All messages terminated to a mobile subscriber are multicasted to all the BSs of the group. How- ever this approach consumes a large volume of network bandwidth to ensure that messages are not lost. Finally to prevent handover dropping, some radio channel assignment schemes [13–16], such as fixed channel assignment and dynamic channel assignment, and wireless call