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Showing papers on "Communications system published in 2009"


Journal ArticleDOI
TL;DR: Simulation results show that the proposed schemes can maximize the number of served UE units and the overall throughput of a cell in a realistic multiple-RS-multiple-UE scenario and effectively improve service coverage and system throughput.
Abstract: Relay technologies have been actively studied and considered in the standardization process of next-generation mobile broadband communication systems such as 3GPP LTE-Advanced, IEEE 802.16j, and IEEE 802.16m. This article first introduces and compares different relay types in LTE-Advanced and WiMAX standards. Simulation results show that relay technologies can effectively improve service coverage and system throughput. Three relay transmission schemes are then summarized and evaluated in terms of transmission efficiency under different radio channel conditions. Finally, a centralized pairing scheme and a distributed pairing scheme are developed for effective relay selection. Simulation results show that the proposed schemes can maximize the number of served UE units and the overall throughput of a cell in a realistic multiple-RS-multiple-UE scenario.

670 citations


Book
26 Aug 2009
TL;DR: This text is geared towards students who already have a technical understanding of electrical engineering from their introductory years at university and who wish to focus on digital communications.
Abstract: Digital communications is the foundation of modern telecommunications and digital signal processing. The second edition of Digital Communications is updated to include current techniques and systems used in the rapidly expanding field of fixed and mobile communications. The text has comprehensive coverage of digital communications without going into unnecessary detail or irrelevant topics. Its main aims are to develop the mathematical theory behind signal processing and use this knowledge to develop fixed and mobile data communications systems. This text is geared towards students who already have a technical understanding of electrical engineering from their introductory years at university and who wish to focus on digital communications. It covers everything these students will need to know, including modern techniques.

628 citations


Journal ArticleDOI
TL;DR: In this paper, a high-speed visible light communications link that uses a white-light light-emitting diode (LED) was described, and a data rate of 100 Mb/s was achieved using on-off keying non-return-to-zero modulation.
Abstract: This letter describes a high-speed visible light communications link that uses a white-light light-emitting diode (LED). Such devices have bandwidths of few megahertz, severely limiting the data rates of any communication system. Here, we demonstrate that by detecting only the blue component of the LED, and using a simple first-order analogue equalizer, a data rate of 100 Mb/s can be achieved using on-off keying nonreturn-to-zero modulation.

547 citations


Journal ArticleDOI
TL;DR: Optical processing methodologies, based on filtering, are described that are applicable to transmission and/or data storage and the advantages and limitations of a set of optical compression and encryption methods are discussed.
Abstract: Over the years extensive studies have been carried out to apply coherent optics methods in real-time communications and image transmission. This is especially true when a large amount of information needs to be processed, e.g., in high-resolution imaging. The recent progress in data-processing networks and communication systems has considerably increased the capacity of information exchange. However, the transmitted data can be intercepted by nonauthorized people. This explains why considerable effort is being devoted at the current time to data encryption and secure transmission. In addition, only a small part of the overall information is really useful for many applications. Consequently, applications can tolerate information compression that requires important processing when the transmission bit rate is taken into account. To enable efficient and secure information exchange, it is often necessary to reduce the amount of transmitted information. In this context, much work has been undertaken using the principle of coherent optics filtering for selecting relevant information and encrypting it. Compression and encryption operations are often carried out separately, although they are strongly related and can influence each other. Optical processing methodologies, based on filtering, are described that are applicable to transmission and/or data storage. Finally, the advantages and limitations of a set of optical compression and encryption methods are discussed.

463 citations


Journal ArticleDOI
TL;DR: A new wideband multiple-input-multiple-output (MIMO) model for VTV channels based on extensive MIMO channel measurements performed at 5.2 GHz in highway and rural environments in Lund, Sweden is presented.
Abstract: Vehicle-to-vehicle (VTV) wireless communications have many envisioned applications in traffic safety and congestion avoidance, but the development of suitable communications systems and standards requires accurate models for the VTV propagation channel. In this paper, we present a new wideband multiple-input-multiple-output (MIMO) model for VTV channels based on extensive MIMO channel measurements performed at 5.2 GHz in highway and rural environments in Lund, Sweden. The measured channel characteristics, in particular the nonstationarity of the channel statistics, motivate the use of a geometry-based stochastic channel model (GSCM) instead of the classical tapped-delay line model. We introduce generalizations of the generic GSCM approach and techniques for parameterizing it from measurements and find it suitable to distinguish between diffuse and discrete scattering contributions. The time-variant contribution from discrete scatterers is tracked over time and delay using a high resolution algorithm, and our observations motivate their power being modeled as a combination of a (deterministic) distance decay and a slowly varying stochastic process. The paper gives a full parameterization of the channel model and supplies an implementation recipe for simulations. The model is verified by comparison of MIMO antenna correlations derived from the channel model to those obtained directly from the measurements.

414 citations


Journal ArticleDOI
TL;DR: It is proved that for Schur-concave objective functions, the optimal source precoding matrix and relay amplifying matrix jointly diagonalize the source-relay-destination channel matrix and convert the multicarrier MIMO relay channel into parallel single-input single-output (SISO) relay channels.
Abstract: In this paper, we develop a unified framework for linear nonregenerative multicarrier multiple-input multiple-output (MIMO) relay communications in the absence of the direct source-destination link. This unified framework classifies most commonly used design objectives such as the minimal mean-square error and the maximal mutual information into two categories: Schur-concave and Schur-convex functions. We prove that for Schur-concave objective functions, the optimal source precoding matrix and relay amplifying matrix jointly diagonalize the source-relay-destination channel matrix and convert the multicarrier MIMO relay channel into parallel single-input single-output (SISO) relay channels. While for Schur-convex objectives, such joint diagonalization occurs after a specific rotation of the source precoding matrix. After the optimal structure of the source and relay matrices is determined, the linear nonregenerative relay design problem boils down to the issue of power loading among the resulting SISO relay channels. We show that this power loading problem can be efficiently solved by an alternating technique. Numerical examples demonstrate the effectiveness of the proposed framework.

387 citations


Journal ArticleDOI
TL;DR: The state-of-the-art in V2V channel measurements and modeling is reviewed in vehicle-to-vehicle communications and some challenges are addressed for future studies.
Abstract: Vehicle-to-vehicle communications have recently received much attention due to some new applications, such as wireless mobile ad hoc networks, relay-based cellular networks, and intelligent transportation systems for dedicated short range communications. The underlying V2V channels, as a foundation for the understanding and design of V2V communication systems, have not yet been sufficiently investigated. This article aims to review the state-of-the-art in V2V channel measurements and modeling. Some important V2V channel measurement campaigns and models are briefly described and classified. Finally, some challenges of V2V channel measurements and modeling are addressed for future studies.

314 citations


Patent
29 Oct 2009
TL;DR: In this paper, the authors present an apparatus, system and method to dynamically manage an allocation of communication resources for direct device-to-device communications between a plurality of wireless communication devices in a wireless communication system.
Abstract: An apparatus, system and method to dynamically manage an allocation of communication resources for direct device-to-device communications between a plurality of wireless communication devices in a wireless communication system. In one embodiment, the apparatus (410) includes a communication resource allocator (420) configured to: (1) select a master communication device of a plurality of wireless communication devices that form a device-to-device group, (2) provide an allocation of communication resources for device-to-device group that facilitate direct device-to-device communications therebetween. The apparatus (410) also includes a message generator (430) configured to assemble messages that include the allocation of the communication resources.

288 citations


Proceedings ArticleDOI
01 Oct 2009
TL;DR: In this article, the authors discuss some of the smart grid applications and estimates the communication requirements of a medium data intensive smart grid device, and propose data communication enabled solutions and enhancements.
Abstract: The Smart Grid of the future, while expected to affect all areas of the Electric Power System, from Generation, to Transmission, to Distribution, cannot function without an extensive data communication system. Smart Grid has the potential to support high levels of Distributed Generation (DG); however the current standards governing the interconnection of DG do not allow the implementation of several applications which may be beneficial to the grid. This paper discusses some of the Smart Grid applications, and estimates the communication requirements of a medium data intensive Smart Grid device. Two issues that will become very important with the spread of DG are DG Islanding and DG Availability. For each issue, we propose data communication enabled solutions and enhancements.

261 citations


Journal ArticleDOI
TL;DR: MobEyes is described, which is an effective middleware that was specifically designed for proactive urban monitoring and exploits node mobility to opportunistically diffuse sensed data summaries among neighbor vehicles and to create a low-cost index to query monitoring data.
Abstract: Recent advances in vehicular communications make it possible to realize vehicular sensor networks, i.e., collaborative environments where mobile vehicles that are equipped with sensors of different nature (from toxic detectors to still/video cameras) interwork to implement monitoring applications. In particular, there is an increasing interest in proactive urban monitoring, where vehicles continuously sense events from urban streets, autonomously process sensed data (e.g., recognizing license plates), and, possibly, route messages to vehicles in their vicinity to achieve a common goal (e.g., to allow police agents to track the movements of specified cars). This challenging environment requires novel solutions with respect to those of more-traditional wireless sensor nodes. In fact, unlike conventional sensor nodes, vehicles exhibit constrained mobility, have no strict limits on processing power and storage capabilities, and host sensors that may generate sheer amounts of data, thus making already-known solutions for sensor network data reporting inapplicable. This paper describes MobEyes, which is an effective middleware that was specifically designed for proactive urban monitoring and exploits node mobility to opportunistically diffuse sensed data summaries among neighbor vehicles and to create a low-cost index to query monitoring data. We have thoroughly validated the original MobEyes protocols and demonstrated their effectiveness in terms of indexing completeness, harvesting time, and overhead. In particular, this paper includes (1) analytic models for MobEyes protocol performance and their consistency with simulation-based results, (2) evaluation of performance as a function of vehicle mobility, (3) effects of concurrent exploitation of multiple harvesting agents with single/multihop communications, (4) evaluation of network overhead and overall system stability, and (5) performance validation of MobEyes in a challenging urban tracking application where the police reconstruct the movements of a suspicious driver, e.g., by specifying the license number of a car.

250 citations


Journal ArticleDOI
TL;DR: This article provides a brief overview of signal processing methods and advances in underwater acoustic communications, discussing both single carrier and emerging multicarrier methods, along with iterative decoding and spatial multiplexing methods.
Abstract: The performance and complexity of signal processing systems for underwater acoustic communications has dramatically increased over the last two decades. With its origins in noncoherent modulation and detection for communication at rates under 100 b/s, phase-coherent digital communication systems employing multichannel adaptive equalization with explicit symbol-timing and phase tracking are being deployed in commercial and military systems, enabling rates in excess of 10 kb/s. Research systems have been shown to further dramatically increase performance through the use of spatial multiplexing. Iterative equalization and decoding has also proven to be an enabling technology for dramatically enhancing the robustness of such systems. This article provides a brief overview of signal processing methods and advances in underwater acoustic communications, discussing both single carrier and emerging multicarrier methods, along with iterative decoding and spatial multiplexing methods.

Journal ArticleDOI
TL;DR: These fading models describe the atmospheric turbulence because of its very good agreement with experimental measurement data and can be used as an alternative to time-consuming Monte-Carlo simulations.
Abstract: Turbulence fading is one of the main impairments affecting the operation of free-space optical (FSO) communication systems. The authors study the performance of FSO communication systems, also known as wireless optical communication systems, over log-normal and gamma-gamma atmospheric turbulence-induced fading channels. These fading models describe the atmospheric turbulence because of its very good agreement with experimental measurement data. Closed-form expressions for the average (ergodic) capacity and the outage probability are derived for both statistical models. Another contribution of this work is a study of how the performance metrics are affected by the atmospheric conditions and other parameters such as the length of the link and the receiver's aperture diameter. The derived analytical expressions are verified by various numerical examples and can be used as an alternative to time-consuming Monte-Carlo simulations.

Journal ArticleDOI
TL;DR: The most effective training sequence interval for channel estimation in a mobile environment is elucidate and it is shown that the adaptive equalization system with the effectual interval alleviates the influence of shadowing.
Abstract: White LEDs were invented the 1990's. Since then they have been extensively researched and applied in various ways. Compared with conventional lighting devices, the white LED has lower power consumption, lower voltage requirements, longer lifetime, smaller size, faster response, and cooler operation. The white LED will eventually replace incandescent or fluorescent lights in offices and homes. We have proposed an indoor visible light wireless communication system that utilizes multiple white LED lighting equipment. In this system, the equipment is used not only for illuminating rooms but also for an optical wireless communication system. The system has significantly higher power levels than infrared wireless communication systems, since it also functions as the main lighting equipment. One problem is we tend to install many lighting sources on a ceiling in order to illuminate the room as evenly as possible. While the number of sources permits site diversity transmission over LOS links, the optical path difference between the multiple sources triggers intersymbol interference (ISI), which significantly degrades system performance. This paper overcomes the ISI problem by proposing an adaptive equalization system. We elucidate the most effective training sequence interval for channel estimation in a mobile environment. And we show that the adaptive equalization system with the effectual interval alleviates the influence of shadowing.

Journal ArticleDOI
TL;DR: This work extracts closed form mathematical expression for the evaluation of the average (ergodic) capacity of such a system, using the log-normal and gamma-gamma distribution, in order to model the atmospheric turbulence conditions and to study the influence of the above parameters on it.
Abstract: The optical wireless communication systems are rapidly gaining popularity as effective means of transferring data at high rates over short distances. These systems facilitate rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs. On the other hand, the performance of this new technology depends strongly on the atmospheric conditions and the parameters of the link such as the length and the operation wavelength. In this work, we extract closed form mathematical expression for the evaluation of the average (ergodic) capacity of such a system, using the log-normal and gamma-gamma distribution, in order to model the atmospheric turbulence conditions and we study the influence of the above parameters on it.

Proceedings ArticleDOI
04 Oct 2009
TL;DR: This paper thoroughly examines the crucial communication and sharing behaviour of these future applications, encompassing coherence protocols, network-on-chip and thread mapping, and aims to support the design of future communication systems for CMPs.
Abstract: Recent benchmark suite releases such as Parsec specifically utilise the tightly coupled cores available in chip-multiprocessors to allow the use of newer, high performance, models of parallelisation. However, these techniques introduce additional irregularity and complexity to data sharing and are entirely dependent on efficient communication performance between processors. This paper thoroughly examines the crucial communication and sharing behaviour of these future applications. The infrastructure used allows both accurate and comprehensive program analysis, employing a full Linux OS running on a simulated 32-core x86 machine. Experiments use full program runs, with communication classified at both core and thread granularities. Migratory, read-only and producer-consumer sharing patterns are observed and their behaviour characterised. The temporal and spatial characteristics of communication are presented for the full collection of Splash-2 and Parsec benchmarks. Our results aim to support the design of future communication systems for CMPs, encompassing coherence protocols, network-on-chip and thread mapping.

Patent
Xiang Guang Che1, Troels Kolding1
28 Oct 2009
TL;DR: In this paper, the authors propose a dynamic allocation of subframes as downlink or uplink resources in a time division duplexed over the air (TDD) communications system.
Abstract: Systems and methods for enabling the dynamic allocation of certain sub frames as downlink or uplink resources in a time division duplexed over the air communications system. A base station or eNB may allocate certain subframes within a repeating radio frame of a TDD configuration as either DL or UL subframes for communicating to user equipment or UE devices to increase efficient use of system resources based on the data to be transmitted. Methods for determining the capabilities of a selected UE and based on the determining step, dynamically allocating certain subframes are disclosed. The methods and systems are compatible with user equipment that does not support the dynamic allocation of subframes.

Journal ArticleDOI
R.D. Pascoe1, T.N. Eichorn1
TL;DR: This article addresses various types of traditional train control systems relative to train location, speed determination, and enforcement, and compares these functions to a communication based train control (CBTC) system.
Abstract: This article addresses various types of traditional train control systems relative to train location, speed determination, and enforcement, and compares these functions to a communication based train control (CBTC) system.

Patent
25 Mar 2009
TL;DR: In this paper, a wireless communication apparatus which can simultaneously conduct communication on at least two frequency channels is described, which includes a communication unit which refers to a connection management table to determine a communication system which can be used by a WSN using an identifier of the wireless communication terminal, and conducts communication with the WSN on a second frequency channel using the communication system.
Abstract: A wireless communication apparatus which can simultaneously conduct communication on at least two frequency channels is described. The apparatus includes a communication unit which refers to a connection management table to determine a communication system which can be used by a wireless communication terminal using an identifier of the wireless communication terminal, and conducts communication with the wireless communication terminal on a second frequency channel using the communication system, when a request from the wireless communication terminal to change the first frequency channel to the second frequency channel is permitted.

Journal ArticleDOI
TL;DR: In this article, a conventional microstrip array constructed with e-textiles is shown to have robust performance with moderate amounts of bending, similar to that which might be seen with body-worn arrays.
Abstract: Support of ever increasing applications for wireless data and communications on a body-centric platform requires novel antenna systems that can be integrated with the body-worn environment, while maintaining free-range of movement and minimal mass impact. E-textile antennas show great promise due to their ease of integration with other textile materials, and they are inherently low-mass and flexible relative to conventional antenna materials. Much attention has been given recently to multiple-antenna communication systems due to the increased performance compared to conventional single-antenna systems. For body-centric applications, the low-mass, flexibility, and integration simplicity of e-textile antennas can enable multiple-antenna systems, which otherwise would be precluded by the rigidity and mass of conventional antenna materials. Several examples of this are considered here with e-textile antennas in an array environment. A conventional microstrip array constructed with e-textiles is shown to have robust performance with moderate amounts of bending, similar to that which might be seen with body-worn arrays. In addition to the conventional array, a wideband multiple-antenna system to support a variety of wireless communication protocols, while maintaining polarization diversity and excellent coverage over a majority of the radian sphere is demonstrated.

Patent
13 May 2009
TL;DR: In this article, the authors present a data communication system in which a communication scheme is switched without a decrease in communication efficiency, where the first and second devices select either a full-duplex communication scheme or a half-duplication communication scheme depending on the first-and second communication flags in compliance with a procedure predetermined between the devices.
Abstract: The object of the present invention is to provide a data communication system in which a communication scheme is switched without a decrease in communication efficiency. In a data communication system including first and second devices that are capable of performing full-duplex communication and half-duplex communication via a set of channels connecting the first and second devices, the first device transmits, via the set of channels, to the second device a first communication flag indicating whether half-duplex communication is to be specified in accordance with a communication processing capability of the first device, the second device transmits, via the set of channels, to the first device a second communication flag indicating whether half-duplex communication is to be specified in accordance with a communication processing capability of the second device, and the first and second devices select either a full-duplex communication scheme or a half-duplex communication scheme depending on the first and second communication flags in compliance with a procedure predetermined between the devices and perform data communication in the selected communication scheme, the selected communication scheme conforming to the communication processing capability of each device.


Proceedings ArticleDOI
05 Apr 2009
TL;DR: The results indicate that with practical signal-to-noise ratio values, the full-duplex mode is preferable in terms of capacity.
Abstract: We study the fundamental capacity trade-off between full-duplex and half-duplex transmission modes in a twohop communication system with a fixed infrastructure-based amplify-and-forward relay. First, we derive closed-form expressions for the average end-to-end capacity in the relay link. We show that it may be better to tolerate some loop interference with the full-duplex mode than to consume channel resources by allocating two orthogonal channels with the half-duplex mode. Furthermore, we evaluate the maximum loop interference power levels that still allow the full-duplex mode to achieve the same capacity as the half-duplex mode. Our results indicate that with practical signal-to-noise ratio values, the full-duplex mode is preferable in terms of capacity.

Patent
24 Jul 2009
TL;DR: In this paper, a system, method and device for providing a power line communication system via an ad hoc network protocol is provided, which includes transmitting and receiving Alive Notifications via the power line.
Abstract: A system, method and device for providing a power line communication system via an ad hoc network protocol is provided. In one embodiment, the method includes transmitting and receiving Alive Notifications via a power line. Each Alive Notification may include data identifying an interface of the transmitting power line node and information identifying an interface of one or more other power line nodes from which the transmitting node has previously received an Alive Notification and reliability information all such nodes. The method may further include regularly transmitting and receiving topology information and routing information via the power line and updating topology and routing information in memory. The method may further include selecting a route to a network for transmission of data based on the routing information stored in memory, wherein the selected route includes the fewest hops and satisfies reliability requirements. The method may further include identifying a first power line node that comprises the first hop of the selected route and transmitting data to the first power line node.

Journal ArticleDOI
TL;DR: This work proposes an empirical channel path loss model for outdoor non-line-of-sight deep ultraviolet (UV) solar blind communications at ranges up to 100 m, and fits the model based on extensive measurements, and provides guidelines to system design.
Abstract: We consider outdoor non-line-of-sight deep ultraviolet (UV) solar blind communications at ranges up to 100 m, with different transmitter and receiver geometries. We propose an empirical channel path loss model, and fit the model based on extensive measurements. We observe range-dependent power decay with a power exponent that varies from 0.4 to 2.4 with varying geometry. We compare with the single scattering model, and show that the single scattering assumption leads to a model that is not accurate for small apex angles. Our model is then used to study fundamental communication system performance trade-offs among transmitted optical power, range, link geometry, data rate, and bit error rate. Both weak and strong solar background radiation scenarios are considered to bound detection performance. These results provide guidelines to system design.

Journal ArticleDOI
TL;DR: This letter shows that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system and develops a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.
Abstract: This letter studies the collaborative use of amplify-and-forward (AF) relays to form a virtual multiple-input single-output (MISO) beamforming system with the aid of perfect channel state information (CSI) in a flat-fading channel. In particular, we optimize the relay weights jointly to maximize the received signal-to-noise ratio (SNR) at the destination terminal with both individual and total power constraints at the relays. We show that the optimal collaborative-relay beamforming (CRB) solution achieves the full diversity of a MISO antenna system. Another main contribution of this letter is a distributed algorithm that allows each individual relay to learn its own weight, based on the Karush-Kuhn-Tucker (KKT) analysis.

Journal ArticleDOI
TL;DR: In this survey, undergroundMine communication is investigated and major issues which underground mine communication systems must take into account are discussed.
Abstract: After a recent series of unfortunate underground mining disasters, the vital importance of communications for underground mining is underlined one more time. Establishing reliable communication is a very difficult task for underground mining due to the extreme environmental conditions. Until now, no single communication system exists which can solve all of the problems and difficulties encountered in underground mine communications. However, combining research with previous experiences might help existing systems improve, if not completely solve all of the problems. In this survey, underground mine communication is investigated. Major issues which underground mine communication systems must take into account are discussed. Communication types, methods, and their significance are presented.

Patent
10 Jun 2009
TL;DR: In this paper, a hierarchical communication system is described in which two wireless local area networks exhibiting substantially different characteristics are employed to link inherently portable or mobile computer devices, and the communication in each local area network is controlled by a reservation access protocol.
Abstract: A hierarchical communication system is described in which two wireless local area networks exhibiting substantially different characteristics are employed to link inherently portable or mobile computer devices. A series of radio base stations make up a infrastructure network. The infrastructure network and at least one portable computer device make up the first local area network. The communication on the first local area network is accomplished by spread spectrum frequency hopping communication A second local area network allows for radio communication between a portable computer device and peripheral devices with built-in transceivers utilized by the portable computer device. The communication in each local area network is controlled by a reservation access communication protocol. The communication protocol facilitates frequency hopping synchronization and supports adaptive data rate selection based upon the quality of communication on the communication channel. The communication protocol prevents interference between communication on the first local area network and communication on the second local area network. In a premises LAN, a series of radio base stations and a backbone LAN make up an infrastructure network. The infrastructure network and at least one mobile computing device make up a higher-power LAN, utilizing a frequency hopping protocol. A lower-power LAN allows for radio communication between a mobile computing device and peripheral devices, utilizing a single-frequency spread spectrum protocol. A vehicular LAN provides for short-range communication between a vehicle terminal and a portable terminal. When out of direct RF range of the premises LAN, the vehicle terminal maintains indirect communication when necessary with the premises LAN via one of several alternate RF channels. A microprocessor, located inside radio units which participate in multiple LAN's, selects the appropriate protocol, frequency band and power level for communicating through the network.

Journal ArticleDOI
TL;DR: This article discusses resource efficiency in relay systems, particularly in two-way and full-duplex relay systems that utilize multiple antennas and improved duplexing to enhance system efficiency.
Abstract: In spite of their potential to improve the performance of wireless communication systems, relay-based communication systems face significant challenges, resource wastage. In this article we discuss resource efficiency in relay systems, particularly in two-way and full-duplex relay systems that utilize multiple antennas and improved duplexing to enhance system efficiency. We compare in detail the features, frame structures, performances, advantages and disadvantages, and technical challenges associated with TWRs and FDRs. Using illustrations of quantitative performance, we demonstrate that both of these approaches can efficiently reduce resource wastage in relay-based communication systems.

Patent
27 Feb 2009
TL;DR: In this article, a communications system may include at least one mobile wireless communications device for storing personal interest information for respective contacts and for storing calendar event data, and the system may further include a notification server communicating with the mobile wireless communication device via a wireless communications network.
Abstract: A communications system may include at least one mobile wireless communications device for storing personal interest information for respective contacts and for storing calendar event data. The system may further include a notification server communicating with the at least one mobile wireless communications device via a wireless communications network and configured to access the personal interest information and calendar event data from the at least one mobile wireless communications device, and send notifications to the at least one mobile wireless communications device based upon the personal interest information and the calendar event data.

Journal ArticleDOI
TL;DR: A 14 February 2002 report and order by the federal communications commission authorizes the unlicensed use of UWB in 3.1--10.6 GHz to provide an efficient use of scarce radio bandwidth while enabling both high data rate personal area network (PAN) wireless connectivity and longer-range, low data rate applications as well as radar and imaging systems.
Abstract: Ultra-wideband (UWB) wireless communication is a revolutionary technology for transmitting large amounts of digital data over a wide frequency spectrum using short-pulse, low powered radio signals. UWB commonly refers to a signal or system that either has a large relative bandwidth (BW) that exceeds 20% or a large absolute bandwidth of more than 500 MHz. A 14 February 2002 report and order by the federal communications commission (FCC) authorizes the unlicensed use of UWB in 3.1--10.6 GHz. This is intended to provide an efficient use of scarce radio bandwidth while enabling both high data rate personal area network (PAN) wireless connectivity and longer-range, low data rate applications as well as radar and imaging systems.