Dianjie Lu

Connectivity of large-scale Cognitive Radio Ad Hoc Networks

Connectivity of large-scale wireless networks has received considerable attention in the past several years. Different from traditional wireless networks, in Cognitive Radio Ad-hoc Networks (CRAHNs), primary users have spectrum access priority of the licensed bands over secondary users. Therefore, the connectivity of the secondary network is affected by not only the density and transmission power of secondary users, but also the activities of primary users. In addition, the number of licensed bands also has impact on the connectivity of CRAHNs. To capture the dynamic characteristics of opportunistic spectrum access, we introduce the Cognitive Radio Graph Model (CRGM) which takes into account the impact of the number of channels and the activities of primary users. Furthermore, we combine the CRGM with continuum percolation model to study the connectivity in the secondary network. We prove that secondary users can form the percolated network when the density of primary users is below the critical density. Then, the upper bound of the critical density of the primary users in the percolated CRAHNs is derived. Simulation results show that both the number of channels and the activities of primary users greatly impact the connectivity of CRAHNs.

Adaptive Power Control Based Spectrum Handover for Cognitive Radio Networks

This paper focuses on spectrum handover in cognitive radio networks where secondary users (SUs) opportunistically use licensed channels as long as the aggregate interference at the primary users (PUs) does not exceed a certain threshold. We incorporate power control into the proposed spectrum handover scheme to reduce the number of spectrum handovers and enhance the spectral efficiency. In our work, when a PU arrives, an SU first calculates the maximum transmission power that the SU does not interfere with the PU. If the SU can still reach its receiver, it lowers its power and continues to transmit; otherwise it switches to an idle band. Analysis results show that our proposed scheme can substantially reduce the spectrum handover ratio and improve the effective data rate by up to 30%.

Channel model for wireless sensor networks in forest scenario

Wireless sensor network (WSN) technology is a new and modern technology that has already been implemented in a wide variety of scenarios and its applications are growing every day. In this paper we present a measurement campaign to obtain more accurate small-scale near ground channel model to feed realistic simulation for the forest environment monitoring and control using WSN technology. This may also contribute to obtain more reliable results and conclusions of protocol performance in WSN applications.

Channel capacity optimization via exploiting multi-SU coexistence in Cognitive Radio Networks

In Cognitive Radio Networks (CRNs), when the Primary Users (PUs) appear, the SUs have to evacuate the licensed spectrum in use or reduce the transmit power so that no harmful interference is introduced to the PUs. In this paper, we explore the multiple Secondary Users (SUs) coexistence system in CRNs based on power control mechanism and interference temperature model. We propose an optimal solution that can maximize the channel capacity and minimize the spectrum handover overhead, constrained by the accumulated interference of both the SUs-to-PU and SUs-to-SUs. We formulate this problem as a non-linear optimization problem and propose a heuristic algorithm to solve it efficiently. Experimental results show that compared with two alternative approaches, our algorithm can improve the usage of the spectrum by up to 51% (with a random approach) and up to 278% (with a conservative approach).

A novel multi-channel access scheme in cognitive ad hoc networks

Multi-channel access is often used to improve the throughput and spectral efficiency of cognitive ad hoc networks. However, there have been few methods for satisfying the requirements of secondary users while using multiple channels simultaneously. In this paper, we propose a novel multi-channel access scheme for QoS supporting. Considering the time-varying channel characteristics, we propose to calculate the Expected Transmission Time (ETT) of each secondary user based on the channel status estimate. Then, the spectrum access problem is formulated as a constrained optimization problem. The solution gives the optimal multi-channel spectrum access under the QoS constraints of secondary users. Experiment results show that our method meets the requirements of secondary users while effectively improving the stability of channel access.

Clustering based spectrum allocation scheme using spectral graph partitioning

Efficient spectrum allocation in Open Spectrum Management is a challenging problem. In this paper, we propose a novel scheme to promote the spectrum utilization by decomposing the second users into non-overlapping clusters. To accomplish the partitioning, we employ a technique from algebraic graph theory known as Spectral Graph Partitioning (SGP). Based on this iterative method, the secondary users can be divided with the balanced radio resource. Then, the spectrum allocation algorithm can be performed distributively. Experiment result shows that our method effectively improves the performance of spectrum allocation.