No abstract

No abstract

No abstract

Cellular networks have been hierarchical so that mobility management have primarily been deployed in a centralized architecture. More flattened network architecture for the mobile Internet is anticipated to meet the needs of rapidly increasing traffic from the mobile users and to reduce cost in the core network. Distributing the mobility management functions as opposed to centralizing them at the root of the network hierarchy is more compatible with a flat network architecture. Mobility management may be distributed at different levels: core level, access router level, access level, and host level. It may also be partially distributed or fully distributed. A distributed mobility management architecture avoids unnecessarily long routes, is more scalable with the increasing number of mobile users, and is a convenient platform for dynamic mobility management which means providing mobility support to mobile users only when they need the support. Dynamic mobility management can avoid waste of resources and also reduce signaling overhead and network cost. The desired distributed and dynamic mobility management needs to solve existing problems, meet the needs of changes in traffic and network architecture, and be simple and inexpensive to deploy. This paper surveys existing mobility management solutions in mobile Internet, explains the limitations of a centralized mobility management approach, and discusses potential approaches of distributing mobility management functions. The issues and challenges in the design of distributed and dynamic mobility management are also described

Cognitive radio (CR) technology is regarded as a promising solution to the spectrum scarcity problem. Due to the spectrum varying nature of CR networks, unlicensed users are required to perform spectrum handoffs when licensed users reuse the spectrum. In this paper, we study the performance of the spectrum handoff process in a CR ad hoc network under homogeneous primary traffic. We propose a novel three dimensional discrete-time Markov chain to characterize the process of spectrum handoffs and analyze the performance of unlicensed users. Since in real CR networks, a dedicated common control channel is not practical, in our model, we implement a network coordination scheme where no dedicated common control channel is needed. Moreover, in wireless communications, collisions among simultaneous transmissions cannot be immediately detected and the whole collided packets need to be retransmitted, which greatly affects the network performance. With this observation, we also consider the retransmissions of the collided packets in our proposed discrete-time Markov chain. In addition, besides the random channel selection scheme, we study the impact of different channel selection schemes on the performance of the spectrum handoff process. Furthermore, we also consider the spectrum sensing delay in our proposed Markov model and investigate its effect on the network performance. We validate the numerical results obtained from our proposed Markov model against simulation and investigate other parameters of interest in the spectrum handoff scenario. Our proposed analytical model can be applied to various practical network scenarios. It also provides new insights on the process of spectrum handoffs. Currently, no existing analysis has considered the comprehensive aspects of spectrum handoff as what we consider in this paper.