For low cost and short distance wireless data communication systems in the THz frequency range, resonant tunneling diodes (RTDs) are very promising. To obtain a large signal-to-noise ratio, thus high data rate, the transmitter output power and receiver sensitivity have to be high.
In this paper, we discuss how to overcome the limitations of current RTD-based systems for wireless communication with respect to circuit design, showing our latest experimental results.
Small Satellites and especially CubeSat have received significant attention recently. The development of secondary launch systems to provide a reasonably priced ride to space has increased the number of small satellites in orbit. Recent subsystem developments have also supported this revolution. One area that has been slow to develop is high rate communications. Early CubeSat systems were built on the amateur satellite service, but the available data rates are low.
Efforts are evolving to develop high rate CubeSat transceivers. This paper will provide an overview of current CubeSat communication systemscapabilities in addition to details about an effort to develop a high rate CubeSat communication system that is compatible with the NASA Near Earth Network. The system includes a 200kbps S-Band receiver and a 12.5Mbps X-Band transmitter.
A novel synchronization technique is proposed for a heterogeneous cognitive radio combining a public safety mobile communication system (PMCS) with a commercial mobile wireless communicationsystem (CMWCS). Since the PMCS is crucial in public safety activities such as search-and-rescue operations, we have implemented a heterogeneous cognitive technique to improve the communicationquality of the PMCS. To combine the PMCS with the CMWCS properly, the proposed synchronization technique enables not only the co-synchronization between the PMCS and the CMWCS but also the self-synchronization of the PMCS.
In this paper, we especially focus on the PMCS’s self-synchronization that is one of the most difficult parts of our proposed cognitive radio system. The proposed technique is utilized for systems employing differentially encoded 7t/4-shift QPSK modulation. The synchronization can be achieved by correlating the envelopes calculated from the PMCS’s received signals with subsidiary information (SI) sent via the CMWCS. In this study, the performance of the proposed synchronization technique is evaluated by computer simulation.
This paper intends to give an overview about atmospheric propagation effects affecting millimeter and terahertz (THz) communication systems. The main focus is on attenuation caused by atmospheric gases and liquid water droplets, either in the form of suspended particles into clouds or rain falling hydrometeors.
Theoretical aspects about each of them are presented, emphasizing on those that deserve special attention as frequency increases. Statistics of attenuation estimated from meteorological data and some experimental results, as in the case of rain attenuation, obtained in Madrid, Spain, are presented throughout the paper, thus providing further insights about the phenomena discussed.
TDD (Time Division Duplex) is one of the two duplex modes. TD-SCDMA (Time Division Synchronous CDMA) is the first TDD-based cellular mobile system which is commercialized in wide area and large scale and TD-SCDMA is also the first cellular mobile system which adopted smart antenna technology (also called as beamforming). As the long term evolution of TD-SCDMA, TD-LTE(A) (Time Division-Long Term Evolution, and TD-LTE Advanced) introduced OFDM (Orthogonal Frequency Division Multiplexing) and enhanced smart antenna technology together with MIMO (Multiple Input Multiple Output), which are adopted by LTE FDD (Frequency Division Duplex) either. It is indicated that TD-SCDMA and TD-LTE(A) have opened a sustainable utilization era of TDD and smart antenna technologies in the wireless mobile communication.
This paper aims to present a systematic introduction to TDD-based mobile communications from TD-SCDMA to TD-LTE and beyond, with particular focuses on TDD key technologies, principles of TDD cellular mobile systems, TDD evolution path, and future TDD 5G directions. The comparisons between TDD and FDD are also included. We hope that this paper will provide a comprehensive overview of TDD technology upgrade and its standard evolution, and serve as a valuable reference for research on 5G mobile communicationsystems. It is believed that TDD will play more important role in 5G.
Various tele-communication systems have been spreading with advance of network technology in recent years. Teleconference system can realize interactive communication between remote locations via Internet. On the other hands, it is difficult for commonly-used teleconference systems to simultaneously display data and video images of users as increasing the number of remote users due to restriction of monitor size. The users cannot move freely with gestures while communicating each other. In addition, the realistic sensation such as user’s facial expression and gesture cannot be sufficiently transmitted.
In this paper, in order to resolve such problems, we focus on tiled display technology which has featured large display size and high resolution, and can configure various display sizes to solve these problems in remote communication. In this paper, we propose a configuration and an architecture of tele-communication system to obtain video image of multiple users by using multiple cameras based on tiled display environment and construct a prototype system. We describe multi-camera function, life-size display function and background switching function which are required to communicate with higher presence.
With the extensive use of information technology in AAL communication systems, a data management model has recently embodied the 3-V characteristics of big data: volume, velocity, and variety. A lot of work has been done on volume and velocity, but not as much has been reported on variety. To handle the variety of data, universal solutions with acceptable performance are usually much more cost effective than customized solutions. To achieve universality, a basic idea is to first define a universal abstraction that covers a wide range of data types, and then build a universal system for universal abstraction.
Traditional database management systems commonly use a multidimensional data type, or feature vectors, as a universal abstraction. However, many new data types in AAL systems cannot be abstracted into multidimensional space. To find a more universal data abstraction and build more universal systems, we propose the concept of big data abstraction, with metric space as a universal abstraction for AAL data types. Furthermore, to demonstrate how metric-space data abstraction works, we survey the state of the art in metric space indexing, a fundamental task in data management. Finally, open research issues are discussed.
Visible-light communication (VLC) will be deployed in various indoor environments, including those requiring different lighting colors, which imposes the needs for transmission optimization under certain lighting constraints. This work establishes a framework for the transmission power and rate optimization, for light emitting diode (LED)-based VLC systems under lighting constraints. We describe the system model of LED-based color-division VLC system, which incorporates the transmission power spectral density, the receiving optical filters, the human eye perception, and the lighting constraints. Then, we formulate the corresponding power and rate optimization problems, for both point-to-pointcommunication system and broadcast communication system.
More specifically, for a point-to-pointcommunication system, it maximizes the transmission rate subject to the transmission power constraint and the lighting constraint; and for a broadcast system, it minimizes the total transmission power subject to some quality of service (QoS) constraint across all receivers. Various convex optimization problems have been formulated and solved analytically or using standard convex optimization solutions. It is obsesrved that the optimal symbol modulation power allocation scheme significantly outperforms the equal power allocation scheme.
Multi-radio access technology (RAT) cellular communication systems limit connected users to utilizing a single RAT even when employing multi-mode user equipment (UE) capable of utilizing multi-RATs. Single-mode access, combined with static spectrum partitioning between co-deployed RATs and independent resource allocation for employed RATs, results in suboptimal spectrum utilization in multi-RAT systems.
This paper models user access in multi-RAT systems and proposes enabling multi-mode UE to simultaneously utilize multiple RATs, using multi-RAT carrier aggregation, to improve the performance and spectrum utilization of multi-RAT systems. Several realizations of multi-mode access with varying implementation requirements are presented and discussed. Detailed system-level simulations, for a system co-deploying High Speed Packet Access (HSPA) and Long-Term Evolution (LTE), are performed to investigate the gains and limitations of different user access configurations in multi-RAT systems.
This paper provides a survey and tutorial of electromagnetic (EM) radiation exposure and reduction in mobile communication systems. EM radiation exposure has received a fair share of interest in the literature; however, this work is one of the first to compile the most interesting results and ideas related to EM exposure in mobile communication systems and present possible ways of reducing it. We provide a comprehensive survey of existing literature and also offer a tutorial on the dosimetry, metrics, international projects as well as guidelines and limits on the exposure from EM radiation in mobilecommunication systems.
Based on this survey and given that EM radiation exposure is closely linked with specific absorption rate (SAR) and transmit power usage, we propose possible techniques for reducing EM radiation exposure in mobile communication systems by exploring known concepts related to SAR and transmit power reduction in mobile systems. Thus, this paper serves as an introductory guide to EM radiation exposure in mobile communication systems and provides insights toward the design of future low-EM exposure mobile communication networks.