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This paper describes several small printed circuit board planar antennas that can be integrated with amplifiers for short-range vehicle wireless communication. The antennas are designed for the 315-MHz frequency band, which is commonly used for control and security devices in the USA and Canada. Each antenna has dimensions of 50 × 70 mm (much less than the free-space wavelength λ = 0.95 m) and is implemented on FR-4 dielectric substrate. These investigated antennas were compared with respect to input impedance, radiation resistance, radiation efficiency, directivity, directionality, bandwidth, matching system complexity, and gain. This paper also includes experimental verification of the final antenna design in the vehicle. It is shown that the antenna diversity method can increase communication range for remote keyless entry systems. [ABSTRACT FROM AUTHOR]

There has been recent extensive research on integrating cellular networks and ad hoc networks to overcome the limitations of cellular networks. Although several schemes have been proposed to use such hybrid networks to improve the performance of individual multicast groups, they do not address quality of service (QoS) issues when multiple groups are present. This paper, on the other hand, considers an interesting scenario of hybrid networks when an ad hoc network cannot accommodate all the groups and a base station has to select a subset of groups to optimize its bandwidth savings and maximize the utilization of the ad hoc network while providing QoS support for multicast users. In this paper, a network model for multicast admission control that takes wireless interference into account is developed, the group selection problem is formulated as a multidimensional knapsack problem, and an integer linear programming (ILP) formulation and a polynomial-time dynamic algorithm are proposed. A distributed implementation of the dynamic algorithm in real systems is also examined. Simulation studies demonstrate that the dynamic algorithm is able to achieve very competitive performance under various conditions, in comparison with the optimal solution computed by the ILP approach. [ABSTRACT FROM AUTHOR]

Editorial. Reports on developments in the Wireless Information Technology and Networks initiative announced by the National Science Foundation (NSF) for research in wireless communication systems in the U.S. in 1999. Number of proposals received by the NSF; Information on the Wireless Grantees Workshop at the National Academy of Science in Washington D.C.; Organization of papers in the May 2002 issue of the periodical 'IEEE Transactions on Antennas and Propagation.'

Reverse link capacity of a direct-sequence code-division multiple-access (DS-CDMA) system in a multicell environment has been studied recently, and significant capacity improvements due to the use of beamforming have been observed. However, system performance with beamforming will be affected by several impairments, such as direction of arrival estimation errors, array perturbations, mutual coupling, and signal spatial spreads. In this paper, reverse link performance of CDMA systems with beamforming under these impairments (imperfect beamforming) is investigated. A simplified beamforming model is developed to evaluate the system performance in terms of user capacity, bit-error rates (BER), and outage probabilities. Both signal-to-interference-ratio-based power control and strength-based power control are considered in this paper. The capacity and BER degradations due to different impairments are shown, and outage probabilities under different power control schemes are examined. [ABSTRACT FROM AUTHOR]

In a mobile telecommunications network, the period when a mobile station (MS) resides in a cell (the radio coverage of a base station) is called the cell residence time of that MS. The period between when a call arrives at the MS and when the MS moves out the cell is called the excess life of the cell residence time for that MS. In performance evaluation of a mobile telecommunications network, it is important to derive the excess life distribution from the cell residence times. This distribution determines if a connected call will be handed over to a new cell, and therefore significantly affects the call dropping probability of the network. In mobile-telecommunications-network simulation, generating the excess-life random numbers is not a trivial task, which has not been addressed in the literature. This paper shows how to generate the random numbers from the excess life distribution, and develop the excess-life random number generation procedures for cell residence times with gamma, Pareto, lognormal, and Weibull distributions. This paper indicates that the generated random numbers closely match the true excess-life distributions. [ABSTRACT FROM AUTHOR]

A complete complementary code based direct sequence code division multiple access (CC/DS-CDMA) system has been proposed recently as a potential candidate for beyond third generation (B3G) wireless communications. This paper addresses the issues that design of efficient code assignment schemes should be based on a flexible physical layer support, which is extremely important for emerging cross-layer designs in future wireless applications. The study in this paper considers a CC/DS-CDMA system with multiple time slots, three traffic classes and two dynamic code-flock assignment schemes, namely random assignment (RA) and compact assignment (CA). Simulation results show that the CC/DS-CDMA system has variable capacity property (VCP), which is sensitively affected by different code-flock assignment schemes. In general, CA can offer lower blocking probability, whereas RA can offer a larger mean system capacity and higher throughput when offered traffic is heavy. [ABSTRACT FROM AUTHOR]

Since the U.S. Federal Communications Commission (FCC) opened the spectrum from 3.1 to 10.6 GHz for unlicensed radio applications with an EIRP of up to -41.3 dBm/MHz, numerous papers have been published on ultrawideband (UWB) antennas. Often the goal in these publications is to present an antenna, which has a satisfactory input reflection coefficient and a reasonable, constant radiation diagram versus frequency. However, in the case of UWB, there are numerous additional critical characteristics, which must be considered in the proper wireless system design. The publications, which treat this topic with sufficient proficiency, use such quantities as transient gain, group delay, ringing, dispersion, signal fidelity, polarization, efficiency, and the peak value of the transient response. For practical applications based on signals with an UWB instantaneous bandwidth occupation, all criteria are of vital importance, because they determine the sensor resolution, accuracy, or increase the bit error rate in communications systems. This paper gives an overview of UWB antenna designs together with their suitability for different applications with respect to the aforementioned critical characteristics. Additionally, UWB antenna array design, polarization diversity, and application in body area network (BAN) will be discussed. In nearly all cases the time-domain characteristics are taken into account, as they are more intuitive to interpret and very convenient for time-domain UWB system design. [ABSTRACT FROM PUBLISHER]

This paper provides novel analysis methods and detailed simulations for determining the impact of out-of-band emissions (OOBE) of adjacent band wireless services on mobile receive-only wireless services. Using the interference from the adjacent cellular bands on an operational digital wireless receive-only system as an example, we demonstrate the impact of the interference from adjacent cellular band transmitters and determine the performance impact such as outage on satellite receivers in realistic roadway conditions. This paper presents new methods for determining appropriate OOBE spectral masks for use by new cellular subscriber transmitters. This paper considers realistic propagation and traffic conditions in five cities throughout the United States and offers approaches that the engineering community may use to determine interference conditions between new cellular and fixed broadband mobile services in adjacent spectrum bands to existing receive-only mobile receiver systems, such as satellite radio. [ABSTRACT FROM PUBLISHER]

A new algorithm of matrix spectral factorization is proposed which can be applied to compute an approximate spectral factor of any positive definite matrix function which satisfies the Paley-Wiener condition. ref refid="fnote1"/ id="fnote1" asterisk="no"paraThis paper includes the detailed proofs for an innovative method for matrix spectral factorization that can be used in numerous applications, including filtering, data compression, and wireless communications. A U.S. patent application has been submitted for this innovation through the Technology Commercialization Center, University of Maryland.para [ABSTRACT FROM AUTHOR]

Energy constraints have a significant impact on the design and operation of wireless sensor networks. This paper investigates the base station (BS) selection (or anycast) problem in wireless sensor networks. A wireless sensor network having multiple BSs (data sink nodes) is considered. Each source node must send all its locally generated data to only one of the BSs. To maximize network lifetime, it is essential to optimally match each source node to a particular BS and find an optimal routing solution. A polynomial time heuristic is proposed for optimal BS selection and anycast via a sequential fixing procedure. Through extensive simulation results, it is shown that this algorithm has excellent performance behavior and provides a near-optimal solution. [ABSTRACT FROM AUTHOR]

During the last several years, the interest in wireless networking has grown significantly due to the availability of many wireless products, such as cell phones, wireless enabled mice, keyboards, modems, and many other products. Bluetooth-enabled cell phones, personal digital assistance (PDAs), and laptops are becoming common. Wireless fidelity (Wi-Fi) products are growing at a rapid rate. Several companies have already started developing WiMax products. The reason for the rapid growth of wireless technology is that it provides the users with additional convenience over the wired technology. General Motors Corporation introduced a Bluetooth network in its 2003 Saab 9–3 model car. Having a wireless personal area network (WPAN) in a vehicle will allow the driver to control the various operations within the vehicle without taking his hands off the steering wheel. For example, the driver will be able to make a phone call through a Bluetooth-enabled headset and a Bluetooth-enabled cell phone using voice-activated dialing features. If the Bluetooth network is connected to the vehicle's wired network through an appropriate gateway device, then the driver will be able to control the lights, windshield wipers, air flow, heat, and various other features of the vehicle through a Bluetooth-enabled headset and voice-activated features. An in-vehicle WPAN will also allow the users to use their PDAs as electronic car keys. Though an in-vehicle WPAN can provide the users with many convenient features, it can also make the vehicle system vulnerable to many types of security attacks unless it is properly designed. In this paper, the authors present a technique for building an in-vehicle secure WPAN (SWPAN). The technique is user friendly and easy to use. [ABSTRACT FROM AUTHOR]

Energy-efficient routing is a critical problem in multihop wireless networks due to the severe power constraint of wireless nodes. Despite its importance and many research efforts toward it, a distributed routing algorithm that maximizes network lifetime is still missing. To address this problem, this paper proposes a novel utility-based nonlinear optimization formulation to the maximum lifetime routing problem. Based on this formulation, a fully distributed localized routing algorithm is further presented, which is proved to converge at the optimal point, where the network lifetime is maximized. Solid theoretical analysis and simulation results are presented to validate the proposed solution. [ABSTRACT FROM AUTHOR]

A new multicarrier system, termed multisymbol encapsulated orthogonal frequency division multiplexing (MSE-OFDM), is proposed, in which one cyclic prefix (CP) is used for multiple OFDM symbols. The original motivation for the MSE-OFDM proposal is to reduce the redundancy due to the CP in static-channel environments. The authors then found that an alternative implementation of the system can be used to improve the robustness to frequency offset and reduce the peak-to-average power ratio (PAPR). Equalization and demodulation algorithms for the MSE-OFDM system are proposed. A new preamble and the corresponding frequency-offset and channel estimation techniques are studied for the MSE-OFDM system. Using the proposed MSE-OFDM preamble, the joint maximum likelihood (ML) estimation of the frequency offset and the channel impulse response (CIR) is investigated in this paper. Possible ways to reduce the joint estimation complexity, including exploitation of the preamble structure, approximation of the joint ML estimator, and fast Fourier transform (FFT) pruning, are discussed. The performance of the proposed MSE-OFDM systems and channel estimators are analyzed and verified through numerical simulations. An analysis on the bandwidth efficiency, the performance with frequency offset, and the PAPR of the MSE-OFDM system are also presented. [ABSTRACT FROM AUTHOR]

This paper presents a coherent demodulation scheme that reduces the multiple-access interference (MAI) considerably in a band-limited direct-sequence code-division multiple-access system. The despreading signal is obtained from a combination of the conventional despreading signal and its weighted early and late versions that are used in the delay-locked loop (DLL). It is shown that with appropriate choice of the weighting parameter of the early-late signals of the DLL, the signal-to-interference-plus-noise ratio of the decision variable is increased, which leads to improvement in the bit-error performance and hence the potential increase in the system capacity by about 25%. The analyses are performed in the frequency domain. The effect of imperfect synchronization on the system performance is also analyzed. [ABSTRACT FROM AUTHOR]

This paper considers a realistic evaluation of the power mobile handsets are able to transmit and receive. It has been suggested to use the so-called total radiated power (TRP) and the total isotropic sensitivity (TIS) for the uplink and downlink, respectively, which may be seen as special cases of the general mean-effective-gain (MEG) measure. These measures are computed from the spherical radiation pattern of the handset and the different measures are obtained by using different models of the mobile propagation environment. In this paper, the results obtained via the spherical radiation patterns are compared with the equivalent performance obtained in a live Global System for Mobile Communications (GSM) network using data from the Abis network interface. This method does not require altering of the handsets and the testing uses normal calls in the network. The investigation is based on measurements with four different commercially available handsets carried out in two different indoor environments and involving 22 test users. In addition, a series of measurements were also made with a phantom simulating the handset user, allowing a test of how well the phantom represents the average user. [ABSTRACT FROM AUTHOR]

In this paper, a novel multihop virtual multiple-input-multiple-output (MIMO) communication protocol is proposed by the cross-layer design to jointly improve the energy efficiency, reliability, and end-to-end (ETE) QoS provisioning in wireless sensor network (WSN). In the protocol, the traditional low-energy adaptive clustering hierarchy protocol is extended by incorporating the cooperative MIMO communication, multihop routing, and hop-by-hop recovery schemes. Based on the protocol, the overall energy consumption per packet transmission is modeled and the optimal set of transmission parameters is found. Then, the issues of ETE QoS provisioning of the protocol are considered. The ETE latency and throughput of the protocol are modeled in terms of the bit-error-rate (BER) performance of each link. Then, a nonlinear constrained programming model is developed to find the optimal BER performance of each link to meet the ETE QoS requirements with a minimum energy consumption. The particle swarm optimization (PSO) algorithm is employed to solve the problem. Simulation results show the effectiveness of the proposed protocol in energy saving and QoS provisioning. [ABSTRACT FROM AUTHOR]

A network of sensors can be used to obtain state-based data from the area in which they are deployed. To reduce costs, the data, sent via intermediate sensors to a sink, are often aggregated (or compressed). This compression is done by a subset of the sensors called ‘aggregators.’ Inasmuch as sensors are usually equipped with small and unreplenishable energy reserves, a critical issue is to strategically deploy an appropriate number of aggregators so as to minimize the amount of energy consumed by transporting and aggregating the data. In this paper, the authors first study single-level aggregation and propose an Energy-Efficient Protocol for Aggregator Selection (EPAS) protocol. Then, they generalize it to an aggregation hierarchy and extend EPAS to Hierarchical EPAS. The optimal number of aggregators with generalized compression and power-consumption models was derived, and fully distributed algorithms for aggregator selection were presented. Simulation results show that the algorithms significantly reduce the energy consumption for data collection in wireless sensor networks. Moreover, the algorithms do not rely on particular routing protocols and are thus applicable to a broad spectrum of application environments. [ABSTRACT FROM AUTHOR]

Joint scheduling and power control schemes have previously been proposed to reduce power dissipation in wireless ad hoc networks. However, instead of power consumption, throughput is a more important performance concern for some emerging multihop wireless networks, such as wireless mesh networks. This paper examines joint link scheduling and power control with the objective of throughput improvement. The MAximum THroughput link Scheduling with Power Control (MATH-SPC) problem is first formulated and then a mixed integer linear programming (MILP) formulation is presented to provide optimal solutions. However, simply maximizing the throughput may lead to a severe bias on bandwidth allocation among links. To achieve a good tradeoff between throughput and fairness, a new parameter called the demand satisfaction factor (DSF) to characterize the fairness of bandwidth allocation and formulate the MAximum Throughput fAir link Scheduling with Power Control (MATA-SPC) problem is defined. An MILP formulation and an effective polynomial-time heuristic algorithm, namely, the serial linear programming rounding (SLPR) heuristic, to solve the MATA-SPC problem are also presented. Numerical results show that bandwidth can be fairly allocated among all links/flows by solving the MILP formulation or by using the heuristic algorithm at the cost of a minor reduction of network throughput. In addition, extensions to end-to-end throughput and fairness and multiradio wireless multihop networks are discussed. [ABSTRACT FROM AUTHOR]

Impulse radio (IR) and especially time-hopping IR (TH-IR) systems have attracted considerable attention since their introduction in the context of ultra wideband (UWB) systems in the early 1990s. Recently, with the U.S. Federal Communications Commission actions allowing for the wide-spread use of UWB radio systems, the interest in these systems has grown further. These systems promise to deliver high data rates in multiple access communication channels with very simple transmitter and receiver designs. The importance of multiuser detection for achieving high data rates with these systems has already been established in several studies. This paper studies several low-complexity multiuser detectors specifically designed for TH-IR radio systems. It is demonstrated that many multiuser detectors developed primarily for direct-sequence code division multiple access (DSCDMA) systems can be used essentially without any change in TH-IR receivers. Further, several novel, low-complexity multiuser detectors that exploit the special signal structure used for transmission by TH-LR systems are developed. These novel detectors are analyzed both theoretically and via simulations. It is shown that a very simple iterative multiuser detector yields performance that is similar to that of a single-user system. [ABSTRACT FROM AUTHOR]

Recent mine disasters in the U.S. exposed various inadequacies and gaps in mine-safety technology. Congress responded to these tragedies by enacting the Mine Improvement and New Emergency Response Act of 2006 (MINER Act), which resulted in the most significant change to mine-safety laws in 30 years. To help meet the requirements of the MINER Act and to help eliminate future tragedies, the National Institute for Occupational Safety and Health initiated aggressive research programs for developing new, and enhancing existing, mine-safety technologies. A major research emphasis addressed the lack of postaccident communications, which surfaced as a critical deficiency in some disasters. As a result, three communications approaches emerged as viable technologies—enhanced leaky-feeder, wireless-mesh, and medium-frequency systems. This paper describes the operation, application, advantages, and disadvantages of each system, as well as the challenges associated with underground wireless communications. [ABSTRACT FROM AUTHOR]

In this paper, the authors propose a node-cooperative automatic repeat request (ARQ) scheme for wireless ad hoc networks, which is suitable for mobile wireless channels with high and correlated frame-error profile. An analytical model based on a two-state Markovian process is proposed to describe the behavior of the proposed retransmission scheme and to obtain its throughput, average delay, and delay jitter. The results of Monte Carlo simulations are included to demonstrate the efficacy of the proposed scheme and to verify the accuracy of the analytical models. Results show that a cooperation among a small number of nodes can significantly improve the performance of the retransmission process in terms of throughput, average delay, and delay jitter by reducing the average duration of retransmission trials. [ABSTRACT FROM AUTHOR]

In this paper, the authors study the performance of scheduling algorithms exploiting the multiuser selection diversity. Schedulers with affordable-rate transmission and adaptive transmission based on the absolute signal-to-noise ratio (SNR) and the normalized SNR are considered. In contrast to previous studies on the multiuser-diversity systems, the channel dynamics is taken into consideration in this paper by a novel formulation based on the level crossing analysis of stochastic processes. Then, the authors make the connection between the Doppler frequency shift, which indicates the channel temporal correlation, and the average (channel) access time, the average waiting time (AWT) between accesses, and the average access rate (AAR) of active users. These properties are important for the scheduler design, especially for applications where delay is a concern. In addition, analytical expressions for the system throughput and the degree of fairness (DOF) when users have nonidentical average channel conditions are presented. These expressions quantify the effect of disparateness in users' average channel conditions on the system performance. [ABSTRACT FROM AUTHOR]

This paper deals with channel acquisition and tracking in the uplink of a multicarrier code division multiple access (MC-CDMA) system. The transmission medium is characterized by multipath propagation, and the goal is to estimate the channel frequency response and the noise-power of each active user. Channel acquisition is performed jointly with the noise-power estimation following two different approaches. The first assumes independently faded subcarriers, while the second exploits the fading correlation across the signal bandwidth to improve the system performance. Both schemes are based on the maximum likelihood (ML) criterion and exploit some training blocks carrying known symbols. Channel tracking is pursued through least mean square (LMS) techniques using data decisions provided by a partial parallel interference cancellation (PPIC) receiver. Numerical results are given to highlight the effectiveness of the proposed methods and to present comparisons with other existing solutions. [ABSTRACT FROM AUTHOR]

In this paper, a new cross-layer communication protocol for vehicular Internet access along highways is introduced. The objective of the new Controlled Vehicular Internet Access (CVIA) protocol is to increase the end-to-end throughput while achieving fairness in bandwidth usage between road segments. To achieve this goal, the CVIA protocol eliminates contention in relaying packets over long distances. CVIA creates single-hop vehicle clusters and mitigates the hidden node problem by dividing the road into segments and controlling the active time of each segment. Using an analytical throughput estimation model, the protocol parameters are flue-tuned to provide fairness among road segments. Simulation results confirm that the proposed CVIA protocol provides higher throughput and better fairness in multihop data delivery in vehicular networks when compared with purely IEEE 802.11-based protocols. [ABSTRACT FROM AUTHOR]

This paper examines the problem of quality-of-service group communications in a heterogeneous network, which consists of multiple mobile ad hoc networks attached to the backbone Internet. A heuristic multicast algorithm named delay and delay variation multicast algorithm (DDVMA) is proposed. DDVMA is designed for solving the delay- and delay-variation-bounded multicast tree problem, which has been proved to be NP-complete. It can find a multicast tree satisfying the multicast end-to-end delay constraint and minimizing the multicast delay variation. Two concepts, which can help the DDVMA achieve better performance in terms of multicast delay variation than the delay and delay variation constraint algorithm that is known to be the most efficient so far, are proposed, namely, 1) the proprietary second shortest path and 2) the partially proprietary second shortest path. An analysis is given to show the correctness of DDVMA, and simulations are conducted to demonstrate the performance improvement of DDVMA in terms of multicast delay variation. It is also shown that the strategy employed by DDVMA is also applicable to handling the mobility of mobile hosts in a heterogeneous network. [ABSTRACT FROM AUTHOR]

Referring received signal strength (RSS) to a signal propagation model to find user location is one of the most promising strategies in wireless communications. This paper develops a simple method based on relative signal-strength measurements, that is, the differences in stationary signal strength measured at the user location from multiple base transceiver stations (BTSs). The stationary signal strength is the averaged RSS and also is a stationary Gaussian process. In using this method, it is vitally important to confirm that some uncertain propagation parameters can be canceled out while a signal propagation model is merged into our method for locating users. In this way, the differences in stationary signal strength lead to two solutions: One is the distance difference between pairs of BTSs, and the other is the distances from the user location to the multiple BTSs. Consequently, the hyperbolic positioning algorithm due to the distance-difference solution and the circular positioning algorithm due to the distances solution can be presented, respectively. Afterward, some experimental results were drawn from a field trial in a real propagation environment. Results show that the hyperbolic and circular positioning algorithms can locate the user to within about 350 and 300 m in 67 percentile, respectively. Compared with the numerical result reported in the literature on existing methods based on RSS only, our method is superior. Despite the result not meeting Federal Communications Commission (FCC) requirements, this method proved to be sufficiently simple and efficient in terms of the computation at burden and network signaling load. [ABSTRACT FROM AUTHOR]

The authors examine the need for wireless and pervasive communications for improved healthcare services in the U.S. They call for innovation in information and communications technology in order to facilitate reliable, comprehensive and high quality clinical care service. They highlight the use of mobile software services in mobile phones and personal digital assistants (PDAs) to track the health conditions of patients.

Ultrawideband (UWB) is defined by the Federal Communications Commission (FCC) for short-range high-capacity wireless communications. We propose and numerically demonstrate a novel scheme of all-optical UWB pulse generation based on parametric processes in cascaded periodically poled lithium niobate (PPLN) waveguides. The commonly used UWB pulses known as derivatives of the Gaussian pulse are considered to be the combination of overshoots and undershoots. As parametric amplification produces overshoots and parametric attenuation creates undershoots, it is expected that UWB pulses can be generated in the optical domain based on parametric processes. By use of sum-frequency generation (SFG) providing parametric attenuation and cascaded second-harmonic generation and difference-frequency generation (SHG + DFG) offering parametric amplification, PPLN-based UWB pulse generation is suggested and implemented. In addition to UWB monocycle and doublet, UWB triplet, quadruplet, and quintuplet are also obtained. The waveforms and radio frequency (RF) spectra of all generated UWB pulses are calculated, with the results showing that all obtained RF spectra meet the UWB definition (FCC, part 15). The operation performance is studied, indicating that the proposed PPLN-based UWB pulse generation has good stability to the UWB pulse wavelength. [ABSTRACT FROM AUTHOR]

A hybrid wireless network is an extension of an infrastructure network, where a mobile host may connect to an access point (AP) using multihop wireless routes, via other mobile hosts. The APs are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select its operating channel dynamically through channel switching. In this environment, a routing protocol that finds routes to balance load among channels while maintaining connectivity was proposed. The protocol works with nodes equipped with a single network interface, which distinguishes the work with other multichannel routing protocols that require multiple interfaces per node. The protocol discovers multiple routes to multiple APs, possibly operating on different channels. Based on a traffic load information, each node selects the ‘best’ route to an AP and synchronizes its channel with the AP. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The protocol assures every node has at least one route to an AP, where all intermediate nodes are operating on the same channel. The simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a multichannel protocol with no load balancing. [ABSTRACT FROM AUTHOR]

Scheduling plays an important role in providing quality of service (QoS) support to multimedia communications in various kinds of wireless networks, including cellular networks, mobile ad hoc networks, and wireless sensor networks. The authors propose a scheduling algorithm at the medium access control (MAC) layer for multiple connections with diverse QoS requirements, where each connection employs adaptive modulation and coding (AMC) scheme at the physical (PHY) layer over wireless fading channels. Each connection is assigned a priority, which is updated dynamically based on its channel and service status; the connection with the highest priority is scheduled each time. The authors' scheduler provides diverse QoS guarantees, uses the wireless bandwidth efficiently, and enjoys flexibility, scalability, and low implementation complexity. Its performance is evaluated via simulations. [ABSTRACT FROM AUTHOR]

Highlights the 2005 Design Automation Conference in the United States. Wireless systems; Sessions on power and other topics; Hands-on tutorials that show designers real tools and flows.

An overview of the articles published within the issue is presented. They include a paper which points to an opportunity to create a more open and competitive U.S. market as the 700 MHz ultra-high frequency band for wireless and mobile communications emerges. Another paper discusses the two main applications for wireless electronic devices, namely wireless sensor networks (WSN) and a subset of WSN called body sensor networks. A paper suggests employing the nonequilibrium Green's function (NEGF) formalism in modeling nanoscale devices.

Wireless communications play a critical role in national security and disaster relief and are extensively utilized by first responder teams, such as police officers, firefighters, and ambulances. The first responders in emergency situations need to always be connected with one another and with the remote service centers for effective cooperation and coordination. However, the existing public safety (PS) services fail to satisfy the PS user requirements in many emergency scenarios, which usually leads to exceptionally high traffic loads. As a result, increasing the network capacity is one of the primary concerns, and spectrum sharing has been deemed the key solution. With appropriate spectrum sharing partnerships among PS agencies and commercial networks, PS users can access licensed PS spectrum, shared spectrum, as well as commercial networks when the need arises. In this article we present different initiatives undertaken by Wireless @ Virginia Tech toward the next generation PS network. We also discuss our vision of a flexible, rapidly deployable, and reconfigurable PS system to meet imminent and future demands on critical communications infrastructure and discuss the value of spectrum sharing for supporting this long-term vision. [ABSTRACT FROM AUTHOR]

Next-generation public safety communications (PSC) systems must sustain high-speed, ultra reliable wireless data transmissions. Moving toward this next generation of PSCs warrants a new perspective of increased heterogeneity in emerging wireless architectures and increased multiplexing of wireless spectrum. To realize this vision, models that incentivize users to opportunistically share their spectrum as substrates over possibly multiple hops, and decentralized and open techniques that seamlessly exploit these substrates for public safety applications are much needed. The value of such multihop and multi-technology pervasive spectrum sharing (PSS) is more pronounced for application scenarios in which the need for spectrum access is vital, and infrastructure-less operation is necessary. This article introduces PSS as a new architecture where sharing is the norm, and outlines its vision, principles, and technical challenges. [ABSTRACT FROM AUTHOR]

4G wireless networks are receiving a lot of attention from researchers, wireless carriers, device manufacturers, and mobile users. This survey compares the original vision with current 4G offerings and considers future prospects. [ABSTRACT FROM AUTHOR]

The Federal Communications Commission (FCC) Phase II enhanced 911 (E-911) requirements have motivated increased interest in the challenge of localizing mobile sources in urban environments. The FCC E-911 Phase-II requires wireless carriers to provide the location of a 911 caller with accuracy of 100 meters in 67% of cases and 300 meters in 95% of cases. This work proposes an information theoretic bound on mobile station (MS) localization performance in urban environments that provides an alternative criterion for the MS localization performance evaluation. The proposed lower bound provides necessary, but not sufficient conditions for achieving arbitrary small probability of the localization error. The MS localization problem is modeled in the framework of communication via channels where the source location is modeled as a transmitted message which is encoded by the propagation conditions. The bound is evaluated for variety of propagation conditions predicted by a recently proposed statistical model of urban propagation conditions. The bound is demonstrated to apply to urban scenes of interest, and the sensitivity of the bound to changes in propagation conditions is discussed. [ABSTRACT FROM AUTHOR]

The article discusses the history of communications and the life of Edouard Branly in the U.S. It notes that Branly constantly denied being the inventor of radio and claims that as a scientist should be discovered an effect allowing others to develop wireless transmission. He was the first to publish the effect of a spark or of the electromagnetic wave. It points out that the Branly effect refers to a set of phenomena.

The article reports on the study conducted by Radu Stoleru of Texas A&M University and John A. Stankovic and Sang H. Son of the University of Virginia on node localization in wireless sensor networks and the potential of localization protocol composability in the U.S. There are several wireless sensor network (WSN) systems are developed for several domains including military surveillance, environmental monitoring, habitat monitoring and structural monitoring. When researchers studied how one can effectively locate sensor nodes at low cost, they failed because despite the myriads of schemes available in the market, no robust localization system has potential to provide the solution needed. Presented are the details of the research.

The article offers information on the routing challenges associated with the implementation of multichannel wireless mesh networks (WMN) in the U.S. According to the author, WMN is regarded as the most efficient and cost effective approach in addressing network congestion and capacity degradation in multihop communication infrastructure. In addition, the availability and capacity of multiple channel, routing algorithm nodes and traffic load distribution must be examined to assert the appropriate measures as well as load control for the optimization of channel diversity. It also highlights the design problems of WMN infrastructure as well as the solutions, including radio interference, load assignment and routing metrics.

Cognitive radios have been advanced as a technology for the opportunistic use of underutilized spectrum wherein secondary devices sense the presence of the primary user and use the spectrum only if it is deemed empty. Spectral cognition of this form can also be used by regulators to facilitate the dynamic coexistence of different service types. An example of this is the operation of ultra-wideband devices in WiMAX bands: UWB devices must detect and avoid WiMAX devices in certain regulatory domains. In this article we start by discussing various options for detection and avoidance. We then describe the obstacles faced in achieving robust detection and avoidance with an on-chip implementation of basic DAA functionality. Finally, we present measurement results for operation of a single UWB device with a WiMAX system. This interaction also highlights the problem of dealing with listen before speak primaries where secondary transmission could interfere by blocking the primary's access to the medium. [ABSTRACT FROM AUTHOR]

Growing needs for suitable spectrum sought by wireless service providers has led the Federal Communications Commission to propose sharing of broadcast spectrum by unlicensed transmitters. Such transmitters could operate on any locally unused TV channel. Signals from nearby transmitters may cause interference to DTV receiver operation. [ABSTRACT FROM AUTHOR]

The standard approach to radio-spectrum allocation in the US posits three alternative models from which regulators choose (on a case-by-case basis) to impose basic rules for coordinating wireless activities. However, this regulatory framework often yields anticonsumer outcomes. The author argues that public policy should instead permit competitive market forces to allocate airwave rights among rival users. One mechanism for accomplishing this shift is to move away from administrative allocations to a general regime of exclusive property rights. [ABSTRACT FROM AUTHOR]

An adaptive carrier interferometry (CI) scheme is proposed for multicarrier code-division multiple-access (MC-CDMA) systems where it is assumed that there is a feedback channel between the receiver and the transmitter. By exploiting the additional degree of freedom in selecting the amplitudes of the subcarriers in accordance with the channel condition, the proposed scheme attains a significant performance gain over the conventional CI-MC-CDMA systems in which a constant amplitude is set for all the carriers. Two adaptation strategies, namely 1) local adaptation and 2) global adaptation, are considered for estimating the appropriate subcarrier amplitudes at the receiver in the proposed systems. Both single-user adaptation, where the other users do not adapt, and multiuser adaptation, in which all users adapt, are investigated. A further advantage of the proposed scheme is that it eliminates the peak-to-average power ratio problem present in the conventional CI-MC-CDMA systems. [ABSTRACT FROM AUTHOR]

Compact high-temperature superconducting filters have high selectivity and sensitivity. Combined with a cryocooled low-noise amplifier, they significantly reduce the effective noise factor of a cellular base-station receiver. Their impact on wireless code-division multiple-access networks is examined using an analytical analysis and numerical simulations. Potential benefits of the superconducting technology include increased capacity utilization and coverage efficiency. Numerical simulations also address the question of how the network should be optimized to realize these benefits. [ABSTRACT FROM AUTHOR]

In this study, a new method for digitizing a combination of different analog signals occupying significantly different bandwidths and having a very high dynamic range is proposed and analyzed. Since it is based upon signal-prediction/cancellation principles, it is referred to as adaptive prediction and cancellation digitization (APCD) method and is applied to various families of signals simultaneously received by a multistandard software radio (SWR) base-station receiver. It is shown theoretically and by means of computer simulations that the APCD method can effectively reduce the high dynamic range of the signals before digitization takes place. Hence, the stringent analog-to-digital-converter (ADC) resolution requirements imposed by the operation of such SWR base-station receivers can be significant relaxed. The signal dynamic-range reduction is achieved by applying appropriate signal processing techniques, e.g., autoregressive (AR) and periodic autoregressive (PAR) prediction. Such techniques allow accurate prediction and subsequent cancellation of high-power narrowband signals present among the composite received analog signal. As these signals usually have cyclostationary statistical characteristics, analysis and performance evaluation of AR and PAR predictors, when used to predict cyclostationary signals, were presented. A new adaptive algorithm for implementing the PAR predictor is also proposed, and its validity is justified by theoretical analysis as well as by various performance evaluation results obtained by means of computer simulations. [ABSTRACT FROM AUTHOR]

This study deals with the effects of the cross/intermodulation (CM/IM) on the communication performance when both Tx (transmit) leakage and external single tone interference pass through LNA in code division multiple access (CDMA)/frequency division duplex (FDD) transceiver. The CM/IM powers happen because of the nonlinearity of the LNA and these get work as interference to the desired signal. The CM/IM interference powers are analyzed with the frequency change of external single tone interference in Rx (receive) band. The relationship between these interference powers, input third-order intercept point (IIP3), and the dependence of the allowable noise figure (NFallowable) on the IIP3 are presented in this study. If IIP3 is large enough for CM/IM interference power spectrum slightly to overlap with the Rx band, the interference power in Rx band gets smaller but NFallowable increases as IIP3 is increased. Thus, the bit-error-rate (BER) performance is degraded. On the other hand, when the interference power spectrum largely overlaps with the Rx band, it is important to increase the IIP3 to get the better BER performance since the performance improvement by the linearity growth is larger than the performance degradation caused by the increment of NFallowable. [ABSTRACT FROM AUTHOR]

The authors consider multiaccess control for the uplink in orthogonal-frequency-division-multiple-access wireless networks, where subcarriers are grouped into clusters. A multi-channel random access, based on local channel state information (CSI), was investigated, and an opportunistic muitichannel Aloha (OMC-AIoha) was proposed accordingly. A key step is to build a mapping from a user's CSI to its transmission probability and subcarrier allocation. For the sake of comparison, the throughput of the optimal centralized scheduling was also characterized by using the Extreme-Value Theory of order statistics. The authors show that the OMC-Aloha is asymptotically order optimal, in the sense that the only performance loss compared to the optimal centralized scheduling is due to the contention inherent in random access. In addition, they examine the proportional fairness in heterogeneous systems. [ABSTRACT FROM AUTHOR]

Different ways to simultaneously control event sensing reliability and device utilization in a beacon-enabled IEEE 802.15.4 sensor cluster are investigated. Activity management is achieved through probabilistic control of the duration of active and inactive (i.e., service and sleep) periods. The probabilistic control parameters are derived as functions of the required event sensing reliability, device utilization, medium access control and physical layer parameters, and network size. [ABSTRACT FROM AUTHOR]

Wireless network access technology in the U.S. raises new concerns when it comes to security. Those who manage wireless networks must ensure that these networks don't introduce new vulnerabilities into the corporate network. The threat of unauthorized access in wireless LAN, for instance, is significant because of uncontrolled signal propagation. This means that potential intruders physically located outside a company could access the company's internal information and network services. It is the aim of this article to discuss many options network administrators can do in defending against unauthorized access in wired or wireless networks.