Showing papers on "Communications system published in 2015"

A survey of millimeter wave communications (mmWave) for 5G: opportunities and challenges

Abstract: With the explosive growth of mobile data demand, the fifth generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mmWave) bands to greatly increase communication capacity. There are fundamental differences between mmWave communications and existing other communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage. These characteristics of mmWave communications pose several challenges to fully exploit the potential of mmWave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control. To address these challenges, we carry out a survey of existing solutions and standards, and propose design guidelines in architectures and protocols for mmWave communications. We also discuss the potential applications of mmWave communications in the 5G network, including the small cell access, the cellular access, and the wireless backhaul. Finally, we discuss relevant open research issues including the new physical layer technology, software-defined network architecture, measurements of network state information, efficient control mechanisms, and heterogeneous networking, which should be further investigated to facilitate the deployment of mmWave communication systems in the future 5G networks.

LED Based Indoor Visible Light Communications: State of the Art

Abstract: Visible Light Communication (VLC) is an emerging field in Optical Wireless Communication (OWC) which utilizes the superior modulation bandwidth of Light Emitting Diodes (LEDs) to transmit data. In modern day communication systems, the most popular frequency band is Radio Frequency (RF) mainly due to little interference and good coverage. However, the rapidly dwindling RF spectrum along with increasing wireless network traffic has substantiated the need for greater bandwidth and spectral relief. By combining illumination and communication, VLC provides ubiquitous communication while addressing the shortfalls and limitations of RF communication. This paper provides a comprehensive survey on VLC with an emphasis on challenges faced in indoor applications over the period 1979–2014. VLC is compared with infrared (IR) and RF systems and the necessity for using this beneficial technology in communication systems is justified. The advantages of LEDs compared to traditional lighting technologies are discussed and comparison is done between different types of LEDs currently available. Modulation schemes and dimming techniques for indoor VLC are discussed in detail. Methods needed to improve VLC system performance such as filtering, equalization, compensation, and beamforming are also presented. The recent progress made by various research groups in this field is discussed along with the possible applications of this technology. Finally, the limitations of VLC as well as the probable future directions are presented.

Device-to-Device Communication in LTE-Advanced Networks: A Survey

Abstract: Among the LTE-A communication techniques, Device-to-Device (D2D) communication which is defined to directly route data traffic between spatially closely located mobile user equipments (UEs), holds great promise in improving energy efficiency, throughput, delay, as well as spectrum efficiency As a combination of ad-hoc and centralized communication mechanisms, D2D communication enables researchers to merge together the long-term development achievements in previously disjoint domains of ad-hoc networking and centralized networking To help researchers to have a systematic understanding of the emerging D2D communication, we provide in this paper a comprehensive survey of available D2D related research works ranging from technical papers to experimental prototypes to standard activities, and outline some open research problems which deserve further studies

Design Guidelines for Spatial Modulation

Abstract: A new class of low-complexity, yet energy-efficient Multiple-Input Multiple-Output (MIMO) transmission techniques, namely, the family of Spatial Modulation (SM) aided MIMOs (SM-MIMO), has emerged. These systems are capable of exploiting the spatial dimensions (i.e., the antenna indices) as an additional dimension invoked for transmitting information, apart from the traditional Amplitude and Phase Modulation (APM). SM is capable of efficiently operating in diverse MIMO configurations in the context of future communication systems. It constitutes a promising transmission candidate for large-scale MIMO design and for the indoor optical wireless communication while relying on a single-Radio Frequency (RF) chain. Moreover, SM may be also viewed as an entirely new hybrid modulation scheme, which is still in its infancy. This paper aims for providing a general survey of the SM design framework as well as of its intrinsic limits. In particular, we focus our attention on the associated transceiver design, on spatial constellation optimization, on link adaptation techniques, on distributed/cooperative protocol design issues, and on their meritorious variants.

Millimeter Wave Cellular Networks: A MAC Layer Perspective

Abstract: The millimeter-wave (mmWave) frequency band is seen as a key enabler of multigigabit wireless access in future cellular networks. In order to overcome the propagation challenges, mmWave systems use a large number of antenna elements both at the base station and at the user equipment, which leads to high directivity gains, fully directional communications, and possible noise-limited operations. The fundamental differences between mmWave networks and traditional ones challenge the classical design constraints, objectives, and available degrees of freedom. This paper addresses the implications that highly directional communication has on the design of an efficient medium access control (MAC) layer. The paper discusses key MAC layer issues, such as synchronization, random access, handover, channelization, interference management, scheduling, and association. This paper provides an integrated view on MAC layer issues for cellular networks, identifies new challenges and tradeoffs, and provides novel insights and solution approaches.

Energy-Efficient Information and Communication Infrastructures in the Smart Grid: A Survey on Interactions and Open Issues

Abstract: Smart grid has modernized the way electricity is generated, transported, distributed, and consumed by integrating advanced sensing, communications, and control in the day-to-day operation of the grid. Electricity is a core utility for the functioning of society and for the services provided by information and communication technologies (ICTs). Several concepts of the smart grid, such as dynamic pricing, distributed generation, and demand management, have significantly impacted the operation of ICT services, in particular, communication networks and data centers. Ongoing energy-efficiency and operational expenditures reduction efforts in communication networks and data centers have gained another dimension with those smart grid concepts. In this paper, we provide a comprehensive survey on the smart grid-driven approaches in energy-efficient communications and data centers, and the interaction between smart grid and information and communication infrastructures. Although the studies on smart grid, energy-efficient communications, and green data centers have been separately surveyed in previous studies, to this end, research that falls in the intersection of those fields has not been properly classified and surveyed yet. We start our survey by providing background information on the smart grid and continue with surveying smart grid-driven approaches in energy-efficient communication systems, followed by energy, cost and emission minimizing approaches in data centers, and the corresponding cloud network infrastructure. We discuss the open issues in smart grid-driven approaches in ICTs and point some important research directions such as the distributed renewable energy generation capability-coupled communication infrastructures, optimum energy-efficient network design for the smart grid environment, the impact of green communication techniques on the reliability and latency requirements of smart grid data, workload consolidation with smart grid-awareness, and many more.

Visible Light Communication

Abstract: Visible light communication (VLC) is an evolving communication technology for short-range applications. Exploiting recent advances in the development of high-power visible-light emitting LEDs, VLC offers an energy-efficient, clean alternative to RF technology, enabling the development of optical wireless communication systems that make use of existing lighting infrastructure. Drawing on the expertise of leading researchers from across the world, this concise book sets out the theoretical principles of VLC, and outlines key applications of this cutting-edge technology. Providing insight into modulation techniques, positioning and communication, synchronisation, and industry standards, as well as techniques for improving network performance, this is an invaluable resource for graduate students and researchers in the fields of visible light communication, optical wireless communication, and industrial practitioners in the field of telecommunications.

A Survey of Millimeter Wave (mmWave) Communications for 5G: Opportunities and Challenges.

Abstract: With the explosive growth of mobile data demand, the fifth generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mmWave) bands to greatly increase communication capacity There are fundamental differences between mmWave communications and existing other communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage These characteristics of mmWave communications pose several challenges to fully exploit the potential of mmWave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control To address these challenges, we carry out a survey of existing solutions and standards, and propose design guidelines in architectures and protocols for mmWave communications We also discuss the potential applications of mmWave communications in the 5G network, including the small cell access, the cellular access, and the wireless backhaul Finally, we discuss relevant open research issues including the new physical layer technology, software-defined network architecture, measurements of network state information, efficient control mechanisms, and heterogeneous networking, which should be further investigated to facilitate the deployment of mmWave communication systems in the future 5G networks

Secure and Green SWIPT in Distributed Antenna Networks With Limited Backhaul Capacity

Abstract: This paper studies the resource allocation algorithm design for secure information and renewable green energy transfer to mobile receivers in distributed antenna communication systems. In particular, distributed remote radio heads (RRHs/antennas) are connected to a central processor (CP) via capacity-limited backhaul links to facilitate joint transmission. The RRHs and the CP are equipped with renewable energy harvesters and share their energies via a lossy micropower grid for improving the efficiency in conveying information and green energy to mobile receivers via radio frequency signals. The considered resource allocation algorithm design is formulated as a mixed nonconvex and combinatorial optimization problem taking into account the limited backhaul capacity and the quality-of-service requirements for simultaneous wireless information and power transfer (SWIPT). We aim at minimizing the total network transmit power when only imperfect channel state information of the wireless energy harvesting receivers, which have to be powered by the wireless network, is available at the CP. In light of the intractability of the problem, we reformulate it as an optimization problem with binary selection, which facilitates the design of an iterative resource allocation algorithm to solve the problem optimally using the generalized Bender's decomposition (GBD). Furthermore, a suboptimal algorithm is proposed to strike a balance between computational complexity and system performance. Simulation results illustrate that the proposed GBD-based algorithm obtains the global optimal solution and the suboptimal algorithm achieves a close-to-optimal performance. In addition, the distributed antenna network for SWIPT with renewable energy sharing is shown to require a lower transmit power compared with a traditional system with multiple colocated antennas.

Key techniques for 5G wireless communications:network architecture, physical layer, and MAC layer perspectives

Abstract: The fourth generation (4G) mobile communication systems are offering service worldwide steadily. Although 4G systems could be loaded with much more services and data than previous systems, there is still a dramatic gap between the peoples practical requirements and what can be offered by the 4G technologies. Consequently, the research and development for the fifth generation (5G) systems have already been started. This article presents an overview of potential network architecture and highlights several promising techniques which could be employed in the future 5G systems. These techniques include non-orthogonal multiple access (NOMA), massive multiple input and multiple output (MIMO), cooperative communications and network coding, full duplex (FD), device-to-device (D2D) communications, millimeter wave communications, automated network organization, cognitive radio (CR), and green communications. The state-of-art and implementation issue of these techniques are also addressed.

Quantized Massive MU-MIMO-OFDM Uplink

Abstract: Coarse quantization at the base station (BS) of a massive multi-user (MU) multiple-input multiple-output (MIMO) wireless system promises significant power and cost savings. Coarse quantization also enables significant reductions of the raw analog-to-digital converter (ADC) data that must be transferred from a spatially-separated antenna array to the baseband processing unit. The theoretical limits as well as practical transceiver algorithms for such quantized MU-MIMO systems operating over frequency-flat, narrowband channels have been studied extensively. However, the practically relevant scenario where such communication systems operate over frequency-selective, wideband channels is less well understood. This paper investigates the uplink performance of a quantized massive MU-MIMO system that deploys orthogonal frequency-division multiplexing (OFDM) for wideband communication. We propose new algorithms for quantized maximum a-posteriori (MAP) channel estimation and data detection, and we study the associated performance/quantization trade-offs. Our results demonstrate that coarse quantization (e.g., four to six bits, depending on the ratio between the number of BS antennas and the number of users) in massive MU-MIMO-OFDM systems entails virtually no performance loss compared to the infinite-precision case at no additional cost in terms of baseband processing complexity.

A Measurement Based Shadow Fading Model for Vehicle-to-Vehicle Network Simulations

Abstract: The vehicle-to-vehicle (V2V) propagation channel has significant implications on the design and performance of novel communication protocols for vehicular ad hoc networks (VANETs). Extensive research efforts have been made to develop V2V channel models to be implemented in advanced VANET system simulators for performance evaluation. The impact of shadowing caused by other vehicles has, however, largely been neglected in most of the models, as well as in the system simulations. In this paper we present a shadow fading model targeting system simulations based on real measurements performed in urban and highway scenarios. The measurement data is separated into three categories, line-of-sight (LOS), obstructed line-of-sight (OLOS) by vehicles, and non-line-of-sight due to buildings, with the help of video information recorded during the measurements. It is observed that vehicles obstructing the LOS induce an additional average attenuation of about 10 dB in the received signal power. An approach to incorporate the LOS/OLOS model into existing VANET simulators is also provided. Finally, system level VANET simulation results are presented, showing the difference between the LOS/OLOS model and a channel model based on Nakagami-m fading.

System for instant messaging the sender and recipients of an e-mail message

Abstract: Systems and techniques for transferring electronic data between users of a communications system include a host system structured and arranged to receive and deliver messages of various types between users of the communications system. The host system includes an instant messaging network; a mail gateway; and a configuring network in communication with both the instant messaging network and the mail gateway. The instant messaging network enables instant messaging communication between users of the communications system and has the capability to monitor whether a certain user is capable of receiving an instant message at a particular moment. The mail gateway receives and delivers e-mail messages to users of the communications system. The configuring network is dedicated to automatically configuring instant messaging communication between an intended recipient of an e-mail message and the sender of the e-mail message.

Beam-searching and transmission scheduling in millimeter wave communications

Abstract: Millimeter wave (mmWave) wireless networks rely on narrow beams to support multi-gigabit data rates. Nevertheless, the alignment of transmitter and receiver beams is a timeconsuming operation, which introduces an alignment-throughput tradeoff. A wider beamwidth reduces the alignment overhead, but leads also to reduced directivity gains. Moreover, existing mmWave standards schedule a single transmission in each time slot, although directional communications facilitate multiple concurrent transmissions. In this paper, a joint consideration of the problems of beamwidth selection and scheduling is proposed to maximize effective network throughput. The resulting optimization problem requires exact knowledge of network topology, which may not be available in practice. Therefore, two standardcompliant approximation algorithms are developed, which rely on underestimation and overestimation of interference. The first one aims to maximize the reuse of available spectrum, whereas the second one is a more conservative approach that schedules together only links that cause no interference. Extensive performance analysis provides useful insights on the directionality level and the number of concurrent transmissions that should be pursued. Interestingly, extremely narrow beams are in general not optimal.

Channel optimization in half duplex communications systems

Abstract: Channel Optimization in Half Duplex Communications Systems is provided herein. Methods may include obtaining at a first terminal, radio frequency (RF) spectral information local to the first terminal, analyzing at the first terminal, RF spectral information for a second terminal that is not co-located with the first terminal, transmitting data to the second terminal on a second terminal optimal frequency band, and receiving data from the second terminal on the first terminal optimal frequency band, where the first terminal optimal frequency being based upon the RF spectral information local to the first terminal.

Device-to-device communication in 5G cellular networks

Abstract: Device-to-device (D2D) communication commonly refers to a type of technology that enable devices to communicate directly with each other without communication infrastructures such as access points (APs) or base stations (BSs). Bluetooth and WiFi-Direct are the two most popular D2D techniques, both working in the unlicensed industrial, scientific and medical (ISM) bands. Cellular networks, on the other hand, do not support direct over-the-air communications between users and devices. However, with the emergence of context-aware applications and the accelerating growth of Machine-to-Machine (M2M) applications, D2D communication plays an increasingly important role. It facilitates the discovery of geographically close devices, and enables direct communications between these proximate devices, which improves communication capability and reduces communication delay and power consumption. To embrace the emerging market that requires D2D communications, mobile operators and vendors are accepting D2D as a part of the fourth generation (4G) Long Term Evolution (LTE)-Advanced standard in 3rd Generation Partnership Project (3GPP) Release 12.

Apparatus and method for adjusting beam pattern in communication system supporting beam division multiple access scheme

Abstract: A method for adjusting a beam pattern in a beam pattern adjusting apparatus in a communication system supporting a Beam Division Multiple Access (BDMA) scheme is provided. The method includes determining whether a Voltage Standing Wave Ratio (VSWR) value for each antenna included in an antenna array included in the beam pattern adjusting apparatus is greater than or equal to a threshold VSWR value, if it is determined that an antenna of the antenna array has a VSWR value that is greater than or equal to the threshold VSWR, detecting whether each of the antenna elements is operable, and if it is determined that at least one of the antennas is inoperable, adjusting a beam pattern of at least one of the antennas that is operable.

RollingLight: Enabling Line-of-Sight Light-to-Camera Communications

Abstract: Recent literatures have demonstrated the feasibility and applicability of light-to-camera communications. They either use this new technology to realize specific applications, e.g., localization, by sending repetitive signal patterns, or consider non-line-of-sight scenarios. We however notice that line-of-sight light-to-camera communications has a great potential because it provides a natural way to enable visual association, i.e., visually associating the received information with the transmitter's identity. Such capability benefits broader applications, such as augmented reality, advertising, and driver assistance systems. Hence, this paper designs, implements, and evaluates RollingLight, a line-of-sight light-to-camera communication system that enables a light to talk to diverse off-the-shelf rolling shutter cameras. To boost the data rate and enhance reliability, RollingLight addresses the following practical challenges. First, its demodulation algorithm allows cameras with heterogeneous sampling rates to accurately decode high-order frequency modulation in real-time. Second, it incorporates a number of designs to resolve the issues caused by inherently unsynchronized light-to-camera channels. We have built a prototype of RollingLight with USRP-N200, and also implemented a real system with Arduino Mega 2560, both tested with a range of different camera receivers. We also implement a real iOS application to examine our real-time decoding capability. The experimental results show that, even to serve commodity cameras with a large variety of frame rates, RollingLight can still deliver a throughput of 11.32 bytes per second.

Wireless-Powered Communications: Performance Analysis and Optimization

Abstract: This paper investigates the average throughput of a wireless-powered communications system, where an energy constrained source, powered by a dedicated power beacon (PB), communicates with a destination. It is assumed that the PB is capable of performing channel estimation, digital beamforming, and spectrum sensing as a communication device. Considering a time-splitting approach, the source first harvests energy from the PB equipped with multiple antennas, and then transmits information to the destination. Assuming Nakagami- $m$ fading channels, analytical expressions for the average throughput are derived for two different transmission modes, namely, delay tolerant and delay intolerant . In addition, closed-form solutions for the optimal time split, which maximize the average throughput are obtained in some special cases, i.e., high-transmit power regime and large number of antennas. Finally, the impact of cochannel interference is studied. Numerical and simulation results have shown that increasing the number of transmit antennas at the PB is an effective tool to improve the average throughput and the interference can be potentially exploited to enhance the average throughput, since it can be utilized as an extra source of energy. Also, the impact of fading severity level of the energy transfer link on the average throughput is not significant, especially if the number of PB antennas is large. Finally, it is observed that the source position has a great impact on the average throughput.

Adaptive Beamforming With Resource Allocation for Distance-Aware Multi-User Indoor Terahertz Communications

Abstract: Terahertz (THz) communication is envisioned as a key technology for next-generation ultra-high-speed wireless systems. In this paper, we study an indoor multi-user THz communication system with multiple antenna subarrays. To capture the distance-frequency-dependent characteristics of THz channels, we design a hybrid beamforming scheme with distance-aware multi-carrier transmission, including analog beamforming for user grouping and interference cancellation in radio-frequency (RF) domain and digital beamforming with dynamically selected subarrays at baseband. Specifically, an adaptive power allocation and low-complexity antenna subarray selection policy is developed to serve different users at different distances and reduce the cost of active RF circuits simultaneously, where two greedy subarray selection algorithms are proposed. The effectiveness of the proposed adaptive hybrid beamforming and antenna subarray selection algorithms is verified through simulation results, which achieves significant gains over other nonadaptive and non-distance-aware schemes.

Chirp signal-based aerial acoustic communication for smart devices

Abstract: Smart devices such as smartphones and tablet/wearable PCs are equipped with voice user interface, ie, speaker and microphone Accordingly, various aerial acoustic communication techniques have been introduced to utilize the voice user interface as a communication interface In this paper, we propose an aerial acoustic communication system using inaudible audio signal for low-rate communication in indoor environments By adopting chirp signal, which is widely used for radar applications due to its capability of resolving multi-path propagation, the proposed acoustic modem supports long-range communication independent of device characteristics over severely frequency-selective acoustic channel We also design a backend server architecture to compensate for the low data rate of chirp signal-based acoustic modem Via extensive experiments, we evaluate various characteristics of the proposed modem including multi-path resolution and multiple chirp signal detection We also verify that the proposed chirp signal can deliver data at 16 bps in typical indoor environments, where its maximum transmission range is drastically extended up to 25 m compared to the few meters of the previous research

Coupling Coefficients Estimation of Wireless Power Transfer System via Magnetic Resonance Coupling Using Information From Either Side of the System

Abstract: Wireless power transfer via magnetic resonance coupling method has opened a new possibility to the electric vehicle system. It allows the wireless charging system of moving vehicles, using charging lanes. However, although the efficiency of power transmission is relatively high, the efficiency still depends on displacement of coils. There have been several researches on methods to maintain power transmission at the highest efficiency. However, in such systems, the information on system parameter especially coupling coefficients is needed, and in the charging lane system, such information is unlikely to be obtainable without a communication system. Therefore, it has come to attention that parameter estimation is a crucial factor to implement a charging lane system. This paper presents derivations of equations for estimating coupling coefficients in several configurations of wireless power transfer system, using information from only one side, either the transmitting side or the receiving side, of the system. The presented equations are both applicable to the case of single receiving coil and are also generalized for the case of multiple receiving coils. Each equation is verified by both simulations and experiments. An experimental system of the coupling coefficient estimation system is constructed for estimation from the receiving side using a dc/dc converter.

Optimized Multiple Microgrid-Based Clustering of Active Distribution Systems Considering Communication and Control Requirements

Abstract: An optimized communication and control infrastructure, based on the microgrid building block concept, for active distribution systems is essential to facilitate powerful control framework under the smart grid paradigm. In this paper, a novel methodology for designing a communication and control infrastructure is presented. The new design takes into account both communication system and distribution system-related aspects. The proposed design facilitates systematic and optimized clustering of the distribution system into a set of virtual microgrids with optimized communication requirements while considering the power quality aspects, characteristics of distributed generation units, distributed energy storage units, and distributed reactive sources. The new design facilitates robust infrastructure for smart distribution systems operation and control, e.g., self-healing control and optimized system-level operation, by using virtual microgrids as building blocks in future distribution systems. The motivations, conceptual design, problem formulation and solution algorithms are presented in this paper. The well-known PG&E 69-bus distribution system is selected as a test case and through several sensitivity studies, the effect of optimization coefficients on the design, and the robustness of the algorithm are investigated. Finally, the algorithm is tested on the IEEE 123-bus distribution system.

Communication method and apparatus using beamforming

Abstract: The present disclosure relates to a pre-5 th -generation (5G) or 5G communication system to be provided for supporting higher data rates beyond 4 th -generation (4G) communication system such as long term evolution (LTE). A communication method and apparatus using beamforming are provided. The method includes acquiring transmission beam specific, measurement information of a base station (BS) and measuring a reference signal (RS) transmitted through transmission beams of the BS according to the transmission beam specific, measurement information. The measurement information on each transmission beam is determined according to at least one of an elevation angle of the corresponding transmission beam, an azimuth of the corresponding transmission beam, a handover urgency, information on a handover failure, and information on a radio link failure (RLF). A mobile station (MS) may perform a measurement report or a handover process according to a result of the measurement.

Survey on optical camera communications: challenges and opportunities

Abstract: Wireless technologies based on radio frequencies (RFs) have always dominated other types of wireless technologies up until now. However, the recent proliferation of media-rich smart devices has pushed the RF spectrum usage to its limit. Therefore RF band expansion towards the optical spectrum is imminent in commercial scale. Indeed, the research on wireless communications using the optical spectrum has gained tremendous ground during the past couple of decades and standardised, respectively, by infrared data association for infrared communication and IEEE 802.15.7 for visible light communication. However, only few shortcomings of the IEEE 802.15.7 standard have led to the development of a revised version, called IEEE 802.15.7r1. This article provides an insight on the activity of the proposed revision of IEEE 802.15.7r1. The proposed revision version targets communication systems that mainly use either image sensors or cameras, known as the optical camera communications (OCC). Leveraging the existing infrastructure, OCC systems will be able to provide ubiquitous coverage in both indoors and outdoors. The authors present their survey focusing on the key technology consideration in IEEE 802.15.7r1, current research status, impairments, enhancements and futuristic application scenarios of the OCC systems.

Networked-Based Hybrid Distributed Power Sharing and Control for Islanded Microgrid Systems

Abstract: Distributed generation (DG) microgrid systems are forming the building blocks for smart distribution grids. Enhanced networked-based control structure is needed not only to eliminate the frequency deviations, power-sharing errors, and stability concerns associated with conventional droop control in microgrids but also to yield: 1) improved microgrid dynamic performance, 2) minimized active/reactive power-sharing errors under unknown line impedances, and 3) high reliability and robustness against network failures or communication delays. This paper proposes a new hybrid distributed networked-based power control scheme that addresses the aforementioned problems in a distributed manner. The new method consists of a set of distributed power regulators that are located at each DG unit to ensure perfect tracking of the optimized set points assigned by the centralized energy management unit (EMU). The average power measurements are transmitted to the EMU to calculate the share of each unit of the total power demand based on real-time optimization criteria; therefore, a low-bandwidth communication system can be used. In the proposed method, the distributed nature of the power regulators allows them to adopt the delay-free local power measurements as the required feedback signals. Therefore, the proposed structure provides great robustness against communication delays. Further, this paper presents a generalized and computationally efficient modeling approach that captures the dominant dynamics of a microgrid system. The model can be used to study the impact of power-sharing controllers and delays in microgrid stability. Comparative simulation and experimental results are presented to show the validity and effectiveness of the proposed controller.

Optimizing client association for load balancing and fairness in millimeter-wave wireless networks

Abstract: Millimeter-wave communications in the 60-GHz band are considered one of the key technologies for enabling multigigabit wireless access. However, the special characteristics of such a band pose major obstacles to the optimal utilization of the wireless resources, where the problem of efficient client association to access points (APs) is of vital importance. In this paper, the client association in 60-GHz wireless access networks is investigated. The AP utilization and the quality of the rapidly vanishing communication links are the control parameters. Because of the tricky nonconvex and combinatorial nature of the client association optimization problem, a novel solution method is developed to guarantee balanced and fair resource allocation. A new distributed, lightweight, and easy-to-implement association algorithm, based on Lagrangian duality theory and subgradient methods, is proposed. It is shown that the algorithm is asymptotically optimal, that is, the relative duality gap diminishes to zero as the number of clients increases .

Indoor Terahertz Communications: How Many Antenna Arrays Are Needed?

Abstract: Terahertz (THz) communications promise to be the next frontier for wireless networks. Novel solutions should be explored to overcome the hardware constraints and the severe path loss. In this paper, we study a low-complexity indoor THz communication system with antenna subarrays. The Saleh-Valenzuela (S-V) channel model is modified to characterize the THz channel. By exploiting the hybrid beamforming with multiple subarrays, we analyze the ergodic capacity of the system and obtain an upper bound. Furthermore, with the analysis of performance degradation for the uncertainty in THz phase shifters, we provide a guidance on the design of antenna subarray size and number for certain long-term data rate requirements with different distances. Simulation results validate the effectiveness of the ergodic capacity upper bound, and show that the proposed THz system and antenna array structure can efficiently achieve capacity gains and support THz communications.

FPGA realization of a chaotic communication system applied to image processing

Abstract: The hardware realization of a chaotic communication system from the description of continuous-time multi-scroll chaotic oscillators is introduced herein by using field-programmable gate arrays (FPGA). That way, two multi-scroll chaotic oscillators generating 2 and 6 scrolls are synchronized by applying Hamiltonian forms and observer approach. The synchronized master-slave topology is used to implement a secure communication system by adding chaos to an image at the transmission stage and by subtracting chaos at the recover stage. The FPGA realization begins by applying numerical methods to solve the system of equations describing the whole chaotic communication system. Further, the replacement of multipliers by single constant multiplication blocks reduces the use of hardware resources and accelerates the processing time as well. Using chaotic oscillators with 2 and 6 scrolls, three kinds of images are processed: one in black and white and two in gray tones. Finally, the experimental results confirm the appropriateness on realizing chaotic communication systems for image processing by using FPGAs.

Radar waveform design in spectrum sharing environment: Coexistence and cognition

Abstract: The proliferation of mobile devices of late has been exponential in numbers as well as heterogeneity, which gives rise to a great increase in the demand of spectral resources. Researchers have suggested that in order to solve the spectrum crisis, future spectrum users will be required to be frequency-flexible and cognitive, and spectrum sharing protocols on communication system have thus been studied. Radars, in the present form, are spectrum users which have fixed operating frequencies, high power and tendency to interfere with other users. Because of these characteristics, conventional radar will have difficulty in cooperating with spectrum sharing communication systems. Though the idea of combining radar and communication has been around for a long time, few have considered operating a radar in the communication band until recently. In order to make radar and communication systems coexist in the same band, one must maintain the quality of communication links. Additionally, radar should also be cognitive to benefit from the knowledge provided by the communication systems. In this paper, we investigate how future radars respond to spectrum sharing environment and derive optimal waveforms satisfying the spectral requirement.