Cognitive radio has received great attention recently for its ability to improve spectrum efficiency by letting secondary users to access spectrum resource that is unoccupied by primary users. However, cognitive radio also brings new challenges in the design of future wireless networks. In this paper, we investigate the problem of resource allocation in cognitive radio networks. Specifically, we consider the problem of proportional fair scheduling in cognitive radio relay networks. Our problem formulation takes into account the fluctuations of usable spectrum resource, channel quality variations caused by frequency selectivity, and interference caused by different transmit power levels. We prove that the problem is NP-hard and is computationally infeasible to be solved in a timely manner by using brute force algorithms. An easy-to-compute upper bound for the formulated problem is also derived. We then propose two heuristic algorithms that are easy-to-implement, yet achieve performance close to the upper bound. The proposed algorithms can be executed and finished within 1 millisecond. Thus, they can meet the requirement of real-time scheduling. Simulation experiments verify that the proposed algorithms can achieve good proportional fairness among users and enhance system throughput by proper power control.

In this paper, we propose a peer-to-peer service discovery protocol specially designed for mobile ad-hoc network (MANET) environment. The proposed mobile service discovery protocol (MSDP) uses a dynamic clustering algorithm to group nodes in a MANET, and utilizes distributed hash tables (DHTs) to efficiently cache service information in a peer-to-peer manner. Simulation results under different scenarios show that MSDP has steady performance and is able to reduce message overhead efficiently

This paper presents the dynamic external home agent (x-HA) assignment, fast authentication, and pre-authentication in mobile virtual private networks (VPNs). The proposed architecture is based on the mobile VPN proposed by the IETF, which adopts mobile IP and IPsec. The IETF solution, however, leads to two questions: where should we put the x-HA and how should we trust the x-HA? We propose to assign the x-HA dynamically so the hand-off latency and end-to-end latency could be reduced significantly. By using diameter mobile IPv4 application, we also propose a technique such that the x-HA can be associated with the VPN securely. In addition, we also propose fast authentication and pre-authentication to further reduce hand-off delay. The proposed technique has been implemented in a mobile VPN testbed. Performance analysis based on empirical experiments is discussed.