In this paper, we study the theory of four-wave mixing type noises over multicore fiber (MCF) and analyze the impacts of the noises on quantum key distribution (QKD) in the quantum and classical coexistence system. The models about four-wave mixing type noises proposed in this paper include forward inter-core four-wave mixing (FIC-FWM), backward four-wave mixing (B-FWM) and backward inter-core four-wave mixing (BIC-FWM). a) The model of FIC-FWM based on discrete change model (FIC-FWM-DCM) is proposed to obtain the precise power of FIC-FWM. Simultaneously, we further propose the model of FIC-FWM based on extended coupled-power theory (FIC-FWM-ECPT) which can obtain similar results to FIC-FWM-DCM but with lower computational complexity. b) The generation mechanism of B-FWM is proposed, and the model is built by combining forward four-wave mixing and backward Rayleigh scattering. c) The generation mechanism of BIC-FWM is proposed, and the model is built by combining FIC-FWM and B-FWM. Based on the above three models of four-wave mixing type noises, we analyze the impacts of the noises on QKD in the quantum and classical coexistence systems over MCF. The results show that the proposed models of FIC-FWM can significantly improve the simulation accuracy in the coexistence system. B-FWM noise can generate a serious impact on QKD when the guard bandwidth between quantum and classical channels is less than 250 GHz with the launch power of 2 mW. BIC-FWM noise can generate a significant impact on QKD when the frequency spacing is less than or equal to 25 GHz and the launch power is larger than 2 mW. Finally, the experiments are carried out to measure FIC-FWM, and the results show the proposed model of FIC-FWM can obtain the consistent results with experiments.

We theoretically study the issues for long-distance transmission of quantum key distribution (QKD) coexisting with classical signals. The recently proposed phase-matching QKD protocol can drastically improve the transmission distance of QKD. However, in the coexistence system, the noise generated by classical signals, especially spontaneous Raman scattering noise, is a big challenge. Moreover, the classical optical amplifier, which is necessary for the realistic long-distance classical communication, makes the noise more serious. In view of this, we establish the unified Raman noise model for three discrete-variable QKD protocols (BB84, measurement-device-independent and phase-matching QKD protocols) in the presence of classical optical amplifiers, which can be applied to both single-core single-mode fiber and multicore fiber. Then, we derive the key rate of the three QKD protocols coexisting with classical signals using the proposed unified Raman noise model. Finally, simulation results show that multicore fiber is promising for simultaneous long-distance transmission of QKD and the dense wavelength division multiplexing system.

In the practical crowdsourcing systems, there exist many cooperative tasks, each of which requires a group of users to perform together, such as finding the shortest multi-hop path or obtaining the media resources from a set of hosts. In this paper, we tackle the problem of how to truthfully and fairly schedule or allocate sufficient users who join mobile crowd-sourcing applications with their smartphones. Moreover, the cooperation among users is taken into account. Thus, we present a novel Cooperative Crowdsourcing (C2) auction mechanism for crowdsourcing multiple cooperative tasks. C2 contains two parts: user selection and payment computation. In the first part, we first prove that users selection with the minimum social cost is NP hard problem and design a greedy algorithm to achieve near-optimal solution in polynomial time. The other part is that the server determines the payments of selected users to avoid the bidder's cheating behavior through a pricing algorithm that if and only if users honestly bid their cost, they can obtain the maximum utility. Both theoretical analysis and extensive simulations demonstrate that C2 auction achieves not only truthfulness, individual rationality and high computational efficiency, but also low overpayment ratio.

Direct reporting, partial nodes selection and compressive sensing are three common types of data gathering in wireless sensor networks. Integrating the above three techniques together for a better performance has been paid many attentions. Hybrid-CS is an effective way to save energy for data gathering, which adopts direct reporting method instead of compressive sensing in the area near the leaf nodes. This paper presents a higher-level hybrid scheme that integrates partial nodes selection into compressive sensing by using a threshold, so as to extend the area before compressive sensing. For this idea, we give a completed theoretical analysis of the relationship between energy consumption and different parameters settings, then we present the influence of different parameters acting on network performance under three general scenarios. At last, we run extensive simulations on the real data trace of Citysee system and the results show that the proposed integrating scheme can realize the purpose of network performance optimization.

In low-duty-cycle wireless sensor networks, wireless nodes usually have two states: active state and dormant state. The necessary condition for a successful wireless transmission is that both the sender and the receiver are awake. In this paper, we study the problem: How fast can raw data be collected from all source nodes to a sink in low-duty-cycle WSNs? To address this, we define the Minimum Data Collection Delay (MDCD) problem, and give both the lower and upper tight bounds on the minimum delay for data collection when interfering links are eliminated. Furthermore, a novel concept, Virtual Grid Network (VGN) is introduced to successfully convert the MDCD problem into max-flow problem, and present a MDCD algorithm enlightened by the Ford-fulkerson max-flow method, which is able to find an optimal solution in polynomial time and achieves the lower bound. Extensive simulations are conducted and the results show that the proposed MDCD algorithm significantly outperforms the Shortest Path Routing algorithm (up to 32%) and achieves the lower bound.

As a large scale real sensor network system, GreenOrbs reveals that locating sensor nodes in the forest still faces great challenges because of volatile and fluctuating environmental factors. In this paper, we present a novel localization scheme, EARL, which provides accurate reference nodes and good ranging quality. We exam the range quality along routing paths by taking complex environmental factors into account, such as forest density, temperature and humidity. To improve localization accuracy, we use power scanning technique to judge the accuracy reference nodes and further calibrate the bad nodes through reverse-localization. To overcome the error propagation, we assign different weights to the range measurement according to the ranging quality. We implemented our localization scheme in GreenOrbs testbed, and evaluate through extensive experiments. The results demonstrate that EARL outperforms the current localization approaches with better accuracy. The localization accuracy achieved by our method is around 20% higher than best existing methods.

Currently, Wireless Sensor Networks (WSN) mostly operate on the fixed and unlicensed Industrial, Scientific and Medical (ISM) spectrum. With the increasing spectrum shortage in WSN, the Cognitive Radio Sensor Networks (CRSN) is proposed to employ the Cognitive Radio (CR) technology to utilize the spectrum resources dynamically (i.e., Dynamic Spectrum Access, DSA). However, it's a challenge to increase the delivery rate and the throughput in the CRSN because of the power and process restrictions. In this paper, with the consideration of the spectrum idle condition and communication capability, a novel DSA strategy based on the Real-time Usability (DSARU) is presented. And the energy-saving updating algorithm of the spectrum real-time usability is proposed to sense the spectrum changes. Based on the IEEE 802.15.4, DSARU simulation model and experiment system are set up to evaluate the transmission performances. Both simulation and experiment results demonstrate that the DSARU strategy can efficiently increase the delivery rate and throughput, especially under the condition of spectrum interference.