Active Communication Links Research Articles

Active Multiple Access Secure Communication Enabled by Graphene-Based Time-Modulated Metasurfaces

This article presents a technique for establishing active secure communication links over single and multiple orthogonal frequency channels via a reflective graphene-based time-modulated metasurface operating in the low terahertz frequency regime. For this purpose, the Fermi energy level of unit cells is modulated via pseudorandom radio frequency biasing signals whose dc offsets are set to steer the reflected beam toward the desired direction by imposing a spatial phase gradient profile across the surface, while their waveforms are engineered to spread the incident wave spectrum into a noise-like spectrum with a near-zero power spectral density via random modulation of the reflection phase of each element between 0 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> with respect to its offset phase. This allows for addressing a legitimate user in real-time who can retrieve the signal via synchronous demodulation with the pseudorandom key of the metasurface while camouflaging the signal from the adversary by lowering the probability of detection. The approach is extended to enable multichannel secure communication by dividing the metasurface into interleaved subarrays modulated with orthogonal pseudorandom keys, which provides simultaneous and independent control over multiple beams with nonoverlapping spread spectra which can be retrieved by independent legitimate users while rejecting unwarranted access by eavesdroppers.

Distributed constraint-coupled optimization via primal decomposition over random time-varying graphs

The paper addresses large-scale, convex optimization problems that need to be solved in a distributed way by agents communicating according to a random time-varying graph. Specifically, the goal of the network is to minimize the sum of local costs, while satisfying local and coupling constraints. Agents communicate according to a time-varying model in which edges of an underlying connected graph are active at each iteration with certain non-uniform probabilities. By relying on a primal decomposition scheme applied to an equivalent problem reformulation, we propose a novel distributed algorithm in which agents negotiate a local allocation of the total resource only with neighbors with active communication links. The algorithm is studied as a subgradient method with block-wise updates, in which blocks correspond to the graph edges that are active at each iteration. Thanks to this analysis approach, we show almost sure convergence to the optimal cost of the original problem and almost sure asymptotic primal recovery without resorting to averaging mechanisms typically employed in dual decomposition schemes. Explicit sublinear convergence rates are provided under the assumption of diminishing and constant step-sizes. Finally, an extensive numerical study on a plug-in electric vehicle charging problem corroborates the theoretical results.

Resilience in Multirobot Multitarget Tracking With Unknown Number of Targets Through Reconfiguration

We address the problem of maintaining resource availability in a networked multirobot team performing distributed tracking of an unknown number of targets in a bounded environment. Robots are equipped with sensing and computational resources, enabling them to cooperatively track a set of targets using a distributed probability hypothesis density (PHD) filter. We use the trace of a robot's sensor measurement noise covariance matrix to quantify its sensing quality. While executing the tracking task, if a robot experiences sensor quality degradation, the team's communication network is reconfigured such that the robot with the faulty sensor may share information with other robots to improve the team's target-tracking ability without enforcing a large change in the number of active communication links. A central system monitor executes the network reconfiguration computations. We consider two different PHD fusion methods and propose four different mixed-integer semi-definite programming (MISDP) formulations (two formulations for each PHD fusion method) to accomplish our objective. All MISDP formulations are validated in simulation.

SEEDRP: a Secure Energy Efficient Dynamic Routing Protocol in Fanets

Unmanned Aerial Vehicles (UAVs) are now used for both commercial and military purposes. This technology is not without its share of issues and challenges. The high mobility of UAVs leads to frequent topology changes which may lead to packet loss or routing path failure. The high mobility of the nodes poses a more significant challenge in maintaining active communication links between the nodes. Routing is an integral part of transmission as the establishment of an active route between the source node and the final destination node is vital. It becomes necessary to identify the most optimal path before transmission. To counter these challenges, a secure energy efficient dynamic routing protocol (SEEDRP), is proposed for reliable and secure transmission. The SEEDRP works on two phases (1) SEEDRP-Routing (2) SEEDRP-Security. The first phase implements a distinct dynamic routing algorithm that finds a cost-effective path between the source and the destination nodes. The second phase of the proposed work focuses on a Distinct Dynamic Key generation scheme that secures the transmitted data. The proposed technique is juxtaposed with other existing techniques using a network simulator. The results show that the proposed technique aims at maximizing the QoS standards and helping the nodes save their energy without undermining performance. The SEEDRP scheme helps FANETs achieve good throughput and an effective packet delivery ratio. The SEEDRP is assessed and analyzed using the NS3 simulator to compare its salient characteristics with the existing protocols for FANETs.

Efficient techniques for energy saving in data center networks

Data centers are constructed with a huge number of network devices to support the expanding cloud based services. These devices are used to achieve the highest performance in case of full utilization of the network. However, the peak capacity of the network is rarely reached. Consequently, many devices are set into idle state and cause a huge energy waste leading to a non-proportionality between the network load and the energy consumed. In this paper, we propose a new approach to improve the efficiency of data centers in terms of energy consumption. Our approach exploits the correlation in time of the inter-node communication traffic and some topological features to maximize energy saving with only a minor increase in the average path length. Our approach dynamically controls the number of active communication links by turning off and on ports in the network (switches ports and nodes ports). Simulations results confirmed the energy saving gain procured by the proposed approach with a low impact on the average path length.

Directional MAC protocol for IEEE 802.11ad based wireless local area networks

IEEE 802.11ad defines a new physical and medium access control layer for IEEE 802.11 networks to operate in the unlicensed 60 GHz millimeter wave spectrum for multi-gigabit wireless communications. Higher frequency waves have higher propagation loss but smaller antenna size. Hence, for millimeter wave networks, higher number of antennas can be packed together, enabling beamforming with very large gains. In this paper, we propose a novel Directional MAC protocol for Basic Stations (DMBS) with the goal of fully leveraging spatial reusability, and limiting deafness and hidden terminal problems with minimal overhead, and without using any complicated hardware for localization. The distinguishing features of DMBS are threefold. First, DMBS extends the association beamforming training time (A-BFT) of IEEE 802.11ad, during which the stations perform initial beamforming training with the access point (AP), by an intelligent listening mechanism. This mechanism allows the stations to passively learn about the best direction of the neighboring stations, decreasing the associated beamforming training overhead. Second, DMBS determines the best transmission direction by using multi-directional sequential (circular) RTS/CTS (Request To Send/ Clear To Send) (CRTS/CCTS) packets, and tracks the best direction by updating its beamforming table upon reception of every RTS/CTS packet, without requiring any additional hardware for localization. If the location information of the destination is up-to-date, the source station only transmits directional RTS/CTS (DRTS/DCTS) in the known direction. Third, DMBS uses two network allocation vectors (NAVs). The first NAV, denoted by NAV1, is used to reduce deafness by determining the busy nodes upon the reception of every RTS/CTS packet. The second NAV, called NAV2, is used to limit hidden terminal problem while maximizing spatial reusability by determining whether a transmission can interfere with active communication links. If NAV2 is set, then the node defers its multi-directional communication but still communicates directionally. We provide a novel Markov chain based analytical model to calculate the aggregate network throughput of DMBS. We demonstrate via extensive simulations that DMBS performs better than existing directional communication protocols in terms of throughput for different network sizes, mobilities and number of receivers.

Data Traffic Scheduling for Cyber Physical Systems With Application in Voltage Control of Distributed Generations: A Hybrid System Framework

The design of the communication infrastructure in cyber physical systems (CPSs) is of key importance since it conveys information from sensors to controllers. Scheduling in the medium access control layer, i.e., the selection of active communication links, plays an important role in improving efficiency of communication in CPS. Different from traditional scheduling algorithms designed for pure data communication networks, the scheduling in CPS is for the purpose of optimizing the physical dynamics and needs to be designed with awareness of the dynamics. In this paper, the scheduling problem in CPS is fitted into the framework of the hybrid systems, in which different selections of links correspond to different dynamic modes. Both centralized and distributed scheduling algorithms are designed. The proposed algorithms are also applied in the background of voltage control of distributed generations (DGs). Numerical simulations show that the proposed framework and algorithms achieve good performances.

Nonlinear Formation Guidance Law with Robust Disturbance Observer

Many formation guidance laws have been proposed for VAV formation flight. Since most autonomous formation flight methods require various active communication links between the vehicles to know motion information of other vehicles, damage to the receiver or the transmitter and communication delay are critical problem to achieve a given formation flight mission. Therefore, in this point of view, the method that does not need an inter-vehicle communication is preferred in the autonomous formation flight. In this paper, we first summarize the formation guidance law without an inter-vehicle communication using feedback linearization and sliding mode control proposed in previous study. We also propose the modified formation guidance law with robust disturbance observer, which can provide significantly better performance than previously mentioned guidance law in case that other vehicles maneuver with large accelerations. The robust disturbance observer can estimate uncertainties generated by acceleration of leader vehicle. By eliminating the uncertainties using the estimated uncertainties, VAVs are able to achieve the tight formation flight. The performance of the proposed approach is validated by numerical simulations.

Entropic analysis of the information rate density of broadband active fiber-optic communication links

The maximum transfer rate characteristics of broadband active fiber-optic communication links are considered within the model of filling numbers. It is established that, for active information transmission systems, in contrast to passive ones, not only the parameters of the line itself are significant but also the input signal-to-noise ratio. It is shown that the classical approach underestimates considerably the value of the maximum information rate density of erbium fiber amplifiers. In lengthy communication links with erbium amplifiers, the value of the information rate density may reach ∼12–15 (bit/s)/Hz, which is more than one order of magnitude higher than the values achieved currently.

Otimum Transmitter Power Control In Celiular Radio Systems

In cellular radio systems, transmitter power controls aim at achieving acceptable carrier-to-interference (C/I) ratios in all active communication links. All of the existing power control schemes focus on single channel control, which could not guarantee optimal performance if applied to the whole system containing multiple channels. This paper presents a full optimization model for the transmitter power control problem which deals with all channels and cells in the system simultaneously. With the limitations of computational speed and data updating ability, our model, at this moment, may not be appropriate for real-time power control. Rather, our model provides a performance standard that various practical real-time power control methods can achieve. This is important information in the design of a practical real-time system. To solve the optimization model, we use the Lagrangian relaxation technique. Our computational result shows that it is possible to reduce the overall blocking probability by 20 – 50% over the existing power control schemes.

Performance of optimum transmitter power control in cellular radio systems

Most cellular radio systems provide for the use of transmitter power control to reduce cochannel interference for a given channel allocation. Efficient interference management aims at achieving acceptable carrier-to-interference ratios in all active communication links in the system. Such schemes for the control of cochannel interference are investigated. The effect of adjacent channel interference is neglected. As a performance measure, the interference (outage) probability is used, i.e., the probability that a randomly chosen link is subject to excessive interference. In order to derive upper performance bounds for transmitter power control schemes, algorithms that are optimum in the sense that the interference probability is minimized are suggested. Numerical results indicate that these upper bounds exceed the performance of conventional systems by an order of magnitude regarding interference suppression and by a factor of 3 to 4 regarding the system capacity. The structure of the optimum algorithm shows that efficient power control and dynamic channel assignment algorithms are closely related.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>