Security, flexibility, and scalability are critical to the success of wireless communications. Wireless networks with movable base stations combine the advantages of mobile ad hoc networks and wireless LAN to achieve these goals. Hierarchical mobile wireless network (HMWN) is proposed for supporting movable base stations. In such a system, mobile hosts are organized into hierarchical groups. The group agents serve as a distributed trust entity. A secure packet forwarding algorithm and an authentication and key exchange protocol are developed to protect the network infrastructure. A roaming support mechanism and the associated mutual authentication protocol are proposed to secure the foreign group and the mobile host when it roams within the network. The computation overhead of secure packet forwarding and roaming support algorithms is studied via experiments. The results demonstrate that these two security mechanisms only require, respectively, less than 2% and 0.2% to 5% CPU time in a low-end 700 MHz PC.

In a fixed-channel-allocation (FCA) cellular network, a fixed number of channels are assigned to each cell. However, under this scheme, the channel usage may not be efficient because of the variability in the offered traffic. Different approaches such as channel borrowing (CB) and dynamic channel allocation (DCA) have been proposed to accommodate variable traffic. Our work expands on the CB scheme and proposes a new channel-allocation scheme--called mobile-assisted connection-admission (MACA) algorithm--to achieve load balancing in a cellular network, so as to assure network communication. In this scheme, some special channels are used to directly connect mobile units from different cells; thus, a mobile unit, which is unable to connect to its own base station because it is in a heavily-loaded "hot" cell, may be able to get connected to its neighboring lightly-loaded cold cell's base station through a two-hop link. Research results show that MACA can greatly improve the performance of a cellular network by reducing blocking probabilities.