Design and analysis of QoS supported frequent handover schemes in microcellular ATM networks

Wireless information networks need to employ small radio cells to support large user populations. However, this will impose extra burden on network traffic control as a result of frequent handover behavior. Existing approaches to support a high handover rate still have cell loss and cell out-of-sequence penalty while the handover is in progress. This paper proposes a novel handover protocol that can avoid cell loss and guarantee cell sequence. It can enhance the performance of a microcellular asynchronous transfer mode network. By multicasting cells to a new base station before handover, our scheme can avoid cell loss and support a nonoverlapping microcell environment as well. The multicast of signaling messages during handover is to coordinate the cell transmission order between the old base station and the new base station to guarantee cell sequence. A formal representation of the handover protocol using finite-state diagrams has been developed to specify and verify the protocol. To guarantee quality of service, we present a hierarchical wireless call admission control to limit the number of in-progress connections and to prevent radio channel congestion. Mathematical models have been developed to analyze two quality-of-service parameters: handover dropping probability and forced termination probability. Experimental results show that our hierarchical wireless call admission control can effectively lower the handover dropping probability and the forced termination probability in comparison with the single-layer wireless call admission control.