Keping Long

Cooperative transmissions for secondary spectrum access in cognitive radios

In cognitive radio networks CRNs, the primary users PUs and secondary users SUs will interfere with each other, which may severely degrade the performances of both primary and secondary transmissions. In this paper, we propose a two-phase cognitive transmission TCT protocol for secondary spectrum access in CRNs, aiming at improving the secondary transmission performance while guaranteeing the quality-of-service QoS of primary transmissions. In TCT protocol, SUs gain the opportunities to access the licensed spectrum through assisting primary transmissions using superposition coding SC, where SUs limit their transmit power to satisfy a given primary QoS requirement and also employ interference cancelation technique to mitigate the interference from PUs. Under the constraint of satisfying a required primary outage probability, we derive the closed-form expressions of secondary outage probabilities over Rayleigh fading channels for proposed TCT protocol. Numerical and simulation results reveal that, with a guaranteed primary outage probability, TCT achieves better secondary transmission performance than traditional case. Copyright

Static weighted routing strategy on two-layer complex networks

The routing strategy is important to information dissemination and exchange in complex communication networks. The traditional routing strategies are often insufficient to alleviate congestion and enhance the utilization efficiency of two-layer complex networks. In this paper, a novel efficient static weighted routing strategy is proposed. The weight of the logical edges mapped on the hub nodes at the physical layer is assigned a higher weight according to the degree of nodes. Then packets choose the routing path with the minimum sum weight of logical edges. It is found that the average packet transmission time and average throughput have been improved greatly compared to the shortest path routing strategy in two-layer complex networks.

Power-efficient RWA in dynamic WDM optical networks considering different connection holding times

The challenges imposed by environmental issues, such as global warming and the energy crisis, are demanding more responsible energy usage, including in the optical networking field. In optical transmission networks, most of the electrical power is consumed by the optical-electrical-optical conversion in optical repeaters. Modern optical network control plane technologies allow idle optical repeaters to be put into a low-power sleep mode. Inspired by this, we propose a novel power-efficient routing and wavelength assignment (RWA) algorithm, called HTAPE. The HTAPE algorithm exploits the knowledge of the connection holding times to minimize the number of optical repeaters in the active mode, and hence reduce the total electricity consumption of the optical network. We test the new algorithm on the typical CERNET and USNET networks. Compared with traditional RWA algorithms without holding-time-awareness, it is observed that the HTAPE algorithm yields significant reductions in power consumption.

A new way to improve the robustness of complex communication networks by allocating redundancy links

We investigate the robustness of complex communication networks on allocating redundancy links. The protecting key nodes (PKN) strategy is proposed to improve the robustness of complex communication networks against intentional attack. Our numerical simulations show that allocating a few redundant links among key nodes using the PKN strategy will significantly increase the robustness of scale-free complex networks. We have also theoretically proved and demonstrated the effectiveness of the PKN strategy. We expect that our work will help achieve a better understanding of communication networks.

Efficient secondary access with intelligent spectrum sensing in cognitive radio networks

In cognitive radio networks, cooperative sensing can significantly improve the performance in detection of a primary user via secondary users SUs sharing their detection results. However, a large number of cooperative SUs may induce great sensing delay, which degrades the performance of secondary transmissions. In this paper, we jointly consider cooperative sensing and cognitive transmission in cognitive radio networks, aiming to achieve efficient secondary access with low sensing overhead under both the sensing time and reporting power limitations, where primary users are guaranteed to be sufficiently protected. We first propose an adaptive sensing scheme to lower the detection time while not degrading the detection probability. Then, based on the proposed adaptive sensing scheme, an efficient cognitive transmission protocol is well designed, which improves the throughput of secondary transmissions while ensuring the QoS of primary transmissions. We analyze the performance for the proposed secondary access framework in terms of misdetection probability, average detection time and normalized secondary throughput, respectively, and derive their closed-form expressions over Rayleigh fading channels with considering the reporting errors accordingly. We also study the problems of optimizing the number of cooperative SUs to minimize the misdetection probability and average detection time, and maximize the normalized secondary throughput for proposed framework. Simulation results reveal that the proposed framework outperforms the traditional case significantly. Copyright

Improving the attack tolerance of scale-free networks by adding and hiding edges

An edge compensatory model with the tunable parameter α to guide the process of enhancing the robustness of scale-free (SF) networks by adding new edges is presented. In addition, the ability of the model with different α to resist intentional attacks, simulated as the breakdown of a group of network nodes chosen according to degree, is explored. Simulations show that the robustness against intentional attack can be improved when α< 2. Once α is decreased to − 2, reducing α further does little to enhance the robustness of SF networks. Moreover, a novel edge information protection strategy is proposed. Empirical results have demonstrated how robustness is affected by the strategy. We find that hiding a small quantity of new edges contributes to the improvement of SF networks on attack tolerance. Due to the low cost of hiding edge information and the strongly improved network robustness, the strategy is a cost-efficient enhancement of robustness.

An enhanced backward recursive PCE-based computation scheme for end-to-end disjoint paths in multi-domain networks

To efficiently provide two disjoint end-to-end paths for working and protecting in multi-domain networks is challenging the network industry. The Backward Recursive PCE-based parallel approach (PA) for disjoint paths can achieve best computation performance at high cost of computation complexity and communication overhead. In this paper, we propose an enhanced PA (EPA), based on a no-differentiated in-BNs pair strategy to decrease the computation complex and communication overhead. The simulation results show that the EPA scheme can effectively reduce the computation and communication overhead.

A novel segment-shared protection algorithm based on dynamic domain-sequencing scheme for multi-domain optical mesh networks

Survivability has been widely recognized as an important design issue for optical networks. In practice, as the network scale keeps expanding, this design problem becomes more critical. Due to scalability and domain privacy, designing the protection scheme in multi-domain networks is more difficult than that in single domain networks. The path computation element (PCE) is known as an efficient architecture to compute optimal traffic engineering (TE) paths in multi-domain multilayer networks. Based on the PCE architecture, we first propose a new dynamic domain-sequencing scheme that considers the load balance of inter-domain links and then propose an improved segment-shared protection approach called DDSP. It can provide 100% protection ability for multiple failures that each single domain has only one failed link. Finally, the protection based on the optimal dynamic domain-sequencing scheme, called OPT, is designed, to evaluate performance of our algorithm and to provide the good bounding for the dynamic domain-sequencing scheme with limited intra TE information. Simulation evaluation shows that the proposed scheme is effective in multi-domain path protection with more efficient resource utilization, lower blocking probabilities and less inter-domain cost. Furthermore, the performance of it is near to OPT.

p-RWBO: a novel low-collision and QoS-supported MAC for wireless ad hoc networks

QoS supported MAC mechanism is a key issue for supporting QoS in wireless ad hoc networks. A new backoff algorithm, named RWBO+BEB, was proposed previously to decrease the packet collision probability significantly. In this paper, it is explored how to make RWBO+BEB support service differentiation in wireless ad hoc networks, and a novel proportional service differentiation algorithm, named p-RWBO, is proposed to allocate the wireless bandwidth according to the bandwidth ratio of each station. In p-RWBO, station n’s walking probability (pw,n) is selected according to its allocated bandwidth ratio. An analytical model is proposed to analyze how to choose pw,n according to the bandwidth ratios of station n. The simulation results indicate that p-RWBO can differentiate services in terms of both bandwidth and delay.

Chaos generator for secure transmission using a sine map and an RLC series circuit

This paper deals with the model analysis of a chaos generator for secure transmission. In this proposed system discrete value signals and continuous value signals are used together and are interacting one another. The main advantage of this system is that a discrete chaotic map can be implemented in the digital circuit with many parameters, and initial condition can be set with a great accuracy. Also, the problem of periodicity which is always encountered in any fully discrete systems can be avoided. A chaotic behavior study of the system is then provided, in which bifurcation phenomena are explained and chaotic attractors are shown. Finally, an asymptotic chaotic behavior of the proposed system is derived.