Device-to-device (D2D) communication is deemed as a promising technology to improve the spectrum efficiency of the cellular systems. In this paper, we study a resource sharing scheme for the D2D ...communication underlaying cellular networks, where multiple D2D pairs can share subchannels with multiple cellular users (CUs). Our optimization task is to maximize the sum rate of D2D pairs while satisfying the rate requirements of all CUs. The formulated problem falls naturally into a mixed integer programming form that is intractable. We first develop a subchannel sharing protocol, by which we can determine whether or not a subchannel can be reused by two D2D pairs. Then, we prove that the problem can be well approximated by ignoring the mutual interference among the D2D pairs that share the same subchannels without deteriorating the performance of both the CUs and the D2D pairs. Based on the analysis results, we propose an efficient subchannel allocation scheme by employing a simple greedy strategy, as well as a power distribution algorithm that can work out almost the optimal solution to the original problem. Numerical results show that our proposal can significantly increase spectrum efficiency of the cellular system. Furthermore, our proposed subchannel sharing protocol is effective and efficient for practical communication scenarios.
In this letter the transmission power and interference threshold constraints for a cognitive OFDM system are converted to a normalized capacity of each OFDM subchannel. A simple but very efficient ...algorithm is proposed to allocate bits of all subchannels, which always picks the bit with the least cost. Simulation results show the proposed algorithm can obtain optimum solution in most cases. The remarkable characteristic of the algorithm is the computational complexity is very low and asymptotically constant for given radio scenarios, which meets the requirement of practical communication systems perfectly.
Multifunctional drug delivery and combined multimodal therapy strategies are very promising in tumor theranostic applications. In this work, a simple and versatile nanoplatform based on biologically ...inspired polydopamine capped gold nanorods (GNR-PDA) is developed. Dopamine, a well-known neurotransmitter associated with many neuronal disorders, can undergo self-polymerization on the surface of GNRs to form a stable PDA shell. Its unique molecular adsorption property, as well as its high chemical stability and biocompatibility, facilitate GNR-PDA as an ideal candidate for drug delivery. Methylene blue (MB) and doxorubicin (DOX) are directly adsorbed on GNR-PDA via electrostatic and/or π–π stacking interactions, forming GNR-PDA-MB and GNR-PDA-DOX nanocomposites, respectively. The GNR-PDA-MB can generate reactive oxygen species (ROS, from MB) or hyperthermia (from GNR-PDA) with high efficiency under deep-red/NIR laser irradiation, while the GNR-PDA-DOX exhibits light-enhanced drug release under NIR laser irradiation. The combined dual-modal light-mediated therapy, by using GNR-PDA-MB photodynamic/photothermal therapy (PDT/PTT) and GNR-PDA-DOX (Chemo/PTT), is carried out and shows remarkable cancer cell killing efficiency in vitro and significant suppression of tumor growth in vivo, which are much more distinct than any single-modal therapy strategy. Our work illustrates that GNR-PDA could be a promising nanoplatform for multifunctional drug delivery and multimodal tumor theranostics in the future.
In this paper, we propose a clustering-based resource allocation (RA) scheme for the multiuser orthogonal frequency division multiplexing (OFDM)-based cognitive radio network, where we aim to ...maximize the sum capacity of the secondary users (SUs) subject to practical constraints in wireless environment. Our general RA optimization task leads to a challenging mixed integer programming problem that is computationally intractable. We first introduce a simple and efficient clustering method to divide all the SUs into multiple groups based on their mutual interference degrees, where the SUs in different groups can share the same OFDM subchannels to improve spectrum utilization efficiency, while the SUs with heavy mutual interference cluster together in the same group and employ different subchannels to alleviate their mutual interference. Then we develop efficient radio RA algorithms to maximize the sum rate of the SUs in each cluster. A user-oriented subchannel assignment method is presented to remove the awkward integer constraints of the formulated RA problem, followed by a fast power distribution algorithm that can work out optimal solutions with an approximate linear complexity. Simulation results indicate that our proposed RA scheme can improve the throughput of the SUs significantly as compared with other methods. Moreover, our proposed RA algorithms converge stably and quickly.
To meet the ever increasing demand of wireless services for high data rates and mobility, mobile communication systems have evolved from the first generation cellular network to the current 4G one. ...The core purpose of a cellular network is to provide users with guaranteed QoS and seamless coverage throughout the service area. In the early stage, this task is achieved by installing cells at candidate sites and configuring their parameters as optimally as possible. Generally, each cell is assigned a dedicated operating frequency, and its adjacent cells operate on different frequencies to avoid inter-cell interference. As the evolution of the cellular network proceeds, advanced signal processing techniques, such as coordinated multipoint transmission and reception, and inter-cell interference coordination, are rising as promising solutions to improve the system performance, which on the other hand inevitably increase the CAPEX and OPEX of the cellular system. Besides, as the deployment of cells becomes denser and denser, it is more and more difficult and expensive to obtain capacity or QoS gains with these signal processing techniques. In this article, we rethink the cellular network planning issue in the context of heterogeneous networking, which is widely accepted as a cost-efficient paradigm to enhance the performance of the cellular system. We point out that the essential objectives of designing a cellular network, coverage and capacity, can also be achieved in heterogeneous networking scenarios using a cutting-edge territory division technique, which divides a service region into multiple subregions with almost equal traffic loads. We develop a dynamic cellular network planning framework that can significantly reduce the CAPEX and OPEX of the system. The QoS for users can also be enhanced while shifting away from employing complex and costly signal processing techniques.
In this letter, we study the resource allocation in cellular networks with device-to-device (D2D) communication enhancement, where multiple D2D pairs can share subchannels with cellular users (CUs). ...Our optimization task is to maximize the sum rate of the cellular system while satisfying the rate requirements of all CUs. We propose an alternating optimization method to address the formulated problem efficiently. Numerical results show that our proposal can significantly increase the throughput of the cellular network.
Stability analysis of double-diffusive convection for viscoelastic fluid with Soret effect in a porous medium is investigated using a modified-Maxwell–Darcy model. We use the linear stability ...analysis to investigate how the Soret parameter and the relaxation time of viscoelastic fluid effect the onset of convection and the selection of an unstable wavenumber. It is found that the Soret effect is to destabilize the system for oscillatory convection. The relaxation time also enhances the instability of the system. The effects of Soret coefficient and relaxation time on the heat transfer rate in a porous medium are studied using the nonlinear stability analysis, the variation of the Nusselt number with respect to the Rayleigh number is derived for stationary and oscillatory convection modes. Some previous results can be reduced as the special cases of the present paper.
In this paper, we investigate the energy consumption issue in cognitive radio (CR) networks. We aim to maximize the energy efficiency of the CR network while considering practical restrictions, ...including the power budget of the system, the interference thresholds of the primary users (PUs), the rate requirements of the secondary users, and the fairness among them. Particularly, due to the lack of explicit support from the PU system, perfect channel state information may not be acquired. Thus, the interference constraint is posed as chance-constrained form and tackled by Bernstein approximation. Then, we convert the optimization task into a quasi-convex problem via relaxing the integer variables, followed by a simple rounding technique to yield feasible subchannels assignment. We derive a fast algorithm to distribute power among subchannels by exploiting the structure of the power-allocation problem. Moreover, we give an efficient heuristic algorithm for subchannels assignment, which reduces the computation load dramatically. Simulation results show that both our proposed resource allocation schemes perform well in practical scenarios. The energy efficiency obtained by the integer subchannels assignment and the fast power distribution achieves more than 98% of the upper bound. On the other hand, the proposed heuristic subchannels assignment with optimal power allocation achieves a good tradeoff between computation complexity and energy efficiency.
Structural colors are colors generated by the interaction between incident light and nanostructures. Structural colors have been studied for decades due to their promising advantages of long-term ...stability and environmentally friendly properties compared with conventional pigments and dyes. Previous studies have demonstrated many artificial structural colors inspired by naturally generated colors from plants and animals. Moreover, many strategies consisting of different principles have been reported to achieve dynamically tunable structural colors. Furthermore, the artificial structural colors can have multiple functions besides decoration, such as absorbing solar energy, anti-counterfeiting, and information encryption. In the present work, we reviewed the typical artificial structural colors generated by multilayer films, photonic crystals, and metasurfaces according to the type of structures, and discussed the approaches to achieve dynamically tunable structural colors.
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•Structural colors are colors generated by the interaction between incident light and nanostructures•High-resolution and long-term stable structural colors, can be designed as functional devices•Structural colors have application prospects in many fields, such as high-resolution printing and anti-counterfeiting
In this paper, we investigate the energy-efficient resource allocation in orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) networks, where we try to maximize the system ...energy-efficiency under the consideration of many practical limitations, such as transmission power budget of the CR system, interference threshold of primary users and traffic demands of secondary users. Our general objective formulation leads to a challenging mixed integer programming problem that is hard to solve. To make it computationally tractable, we employ a time-sharing method to transform it into a non-linear fractional programming problem, which can be further converted into an equivalent convex optimization problem by using its hypogragh form. Based on these transformations, it is possible to obtain (near) optimal solution by standard optimization technique. However, the complexity of the standard technique is too high for this real-time optimization task. By exploiting the structure of the problem extensively, we develop an efficient barrier method to work out the (near) optimal solution with a reasonable complexity, significantly better than the standard technique. Numerical results show that our proposal can maximize the energy efficiency of the CR system, whilst the proposed algorithm performs quickly and stably.
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