In this paper, a novel location management scheme called Distributed Group Tracking (DGT) for group communications in Cellular IP networks is proposed. In DGT, Base stations track each member of a group and build a share multicast routing tree called DGT-Tree for the group in a distributed manner. Transmission of multicast packets among group members is along the group's DGT-Tree. Simulation study has demonstrated that a better performance can be achieved by DGT over the gateway-based counterpart in terms of transmission cost as well as link load balance. Moreover, the average number of DGT operations decreases as the group size increases, showing the good scalability of the DGT scheme, and the average number of control packets as well as the cache requirement for performing DGT operations demonstrate the moderate overhead introduced by DGT.

As one of the promising techniques in Broadband Wireless Access (BWA), IEEE 802.16 also namely WiMax provides wide-area, high-speed, and non-line-of-sight wireless transmission to support multimedia services. Four service types are defined in the specification of IEEE 802.16 for QoS support. In order to achieve end-to-end multimedia services, 802.16 QoS must be well integrated with IP QoS. In this paper, we propose a framework of cross-layer QoS support in the IEEE 802.16 network. Two novel mechanisms are proposed in the framework for performance improvement: Fragment Control and Remapping. Fragment Control handles the data frames that belong to the same IP datagram in an atomic manner to reduce useless transmission. Remapping is concerned with the mapping rules from IP QoS to 802.16 QoS and is designed to reduce the impact of traffic burstiness on buffer management. Simulation study has shown that the proposed scheme has higher goodput and throughput, and lower delay than the contrast.