By Topic

Date April 30 2007-May 2 2007

Filter Results

Displaying Results 1 - 25 of 97
  • Reconfigurable concurrent oscillators for multi-band multi-mode wireless communication systems

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3042 KB) |  | HTML iconHTML  

    The next generation of wireless communication is a ubiquitous radio system concept, providing wireless access from short-range to wide-area, with one single reconfigurable and adaptive system for all envisaged radio environments. This paper presents the design approach of RCO (reconfigurable concurrent oscillator) that simultaneously generates two or more signals of different frequencies that eliminate the need of lossy switches for switching the frequency band, thereby improves the system throughput. The measured phase noise for band#1 (2.3-2.6 GHz) and band#2 (4.6-5.2 GHz) are typically -130 dBc/Hz, and -120 dBc/Hz at 100 kHz offset from the carrier respectively; and to our knowledge, this is the best phase noise performance for this class of VCO (voltage controlled oscillators) by using MCPR (multi-coupled planar resonators) so far reported. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Mode-coupled stubs-tuned planar resonator based spectral pure signal source for wireless communication systems

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3762 KB) |  | HTML iconHTML  

    A novel compact coupled planar resonator (CCPR) based VCO (voltage controlled oscillator) using mode-coupling technique was developed in response to expensive high Ceramic and SAW resonators based signal source for wireless communications. One of the problems related to the conventional Ceramic/SAW based resonators (with high Q and low phase noise) is the challenge for integration in IC form. Instead of employing the distributed planar uncoupled transmission line resonator for integration that exhibits low Q and high phase noise, this work describes a CCPR based VCO that supports user-definable frequency band in compact size and amenable for integration in the IC form. The measured phase noise for a carrier frequency 622 MHz is better than -135 dBc/Hz at 10 kHz offset, and to our knowledge, this is the best phase noise performance for this class of VCOs using printed resonator in 0.5'times0.5' circuit board size so far reported. The reported topology is not limited to this frequency, can be extended for other higher frequency by incorporating mode-injection stubs across the CCPR for desired operating frequency. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Switching FET broadband DBM for wireless applications

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (487 KB) |  | HTML iconHTML  

    A high intercept points, cost-effective, and power-efficient switching FET double balanced mixer (DBM) is reported. The Switching FET DBM demonstrated in this work offers input intercept points (IIP3) and conversion loss typically 44 dBm and 8.5 dB respectively with 15 dBm LO power for the frequency band (RF: 900-2150 MHz, LO: 850-1950 MHz, IF: 50-200 MHz). The measured interport isolation is typically better than 30 dB for broadband applications, and the circuit topology is not limited to these frequencies, and can be easily extended for present and later generation of communication systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Performance analysis of a novel real-time closed-loop technique for non-linearity correction of power amplifiers

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB) |  | HTML iconHTML  

    In this paper we discuss performance results of a novel real-time closed-loop power amplifier (PA) linearization technique that has originally been proposed by Ahmed and Li. The novel approach performs on-the-fly prediction and measurement of the PA AM/AM and AM/PM non-linearity, stores such non-linear characteristics and calculates their inverse functions in order to pre-distort the base-band amplitude and phase signals modulating the PA such that the combination, or the resultant, of the pre-distorter and the PA leads to a linear behavior at the output of the PA. We present a model of our predictor based approach and evaluate its performance for an GSM/EDGE application. The key performance metrics we evaluate have been based on the GSM/EDGE requirements, such as the Error Vector Magnitude (EVM), Switching Transients (ST), Adjacent Channel Power Ratio (ACPR), transmit time mask, modulation spectrum and PAE. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microwave power amplifiers for satellite communication systems

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (747 KB) |  | HTML iconHTML  

    This paper provides a short review of radio frequency/microwave power amplifiers (PAs) and their critical role in a modern satellite communication system. Authorspsila original design contributions are also highlighted. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dynamic reflection of RF signals from fluorescent lights: Their spectral analysis and effects on backscattered RFID tag signals

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1202 KB) |  | HTML iconHTML  

    Radio frequency (RF) energy reflected from active power line ballast driven fluorescent tubes are known to be modulated at twice the line frequency. When the lamps are driven by electronic ballasts, it is found that the reflected (backscattered) RF wave is amplitude modulated with sidebands located at multiples of electronic ballast frequency components, extending to hundreds of kilohertz with significant power levels spread within this range. Detailed analysis of the measured sidebands spectrum indicated that the sidebands themselves are modulated at multiples of twice the power line frequency. Fluorescent lamps driven by different types of electronic ballasts operating at different unsynchronized frequencies exhibited different power levels. Consequently in an environment with abundance of active fluorescent lamps, the reflected RF signals can significantly affect the reception of modulated backscattered transponder RFID signals at UHF and higher bands. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Space-time adaptive processing in ESPAR antenna and adaptive arrays in CDMA systems; A comparison

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (197 KB) |  | HTML iconHTML  

    In this paper the performance of the ESPAR (electronically steerable passive array radiator) antenna in suppressing both the co-channel and inter-symbol interferences is compared with the conventional circular and linear arrays. For this purpose, the STAP (space-time adaptive processing) is implemented in both arrays with equal elements. Simulation results show that when the pattern of the ESPAR antenna in not formed, the conventional arrays have about 4.5 dB better performances in their cost function. However, by forming the pattern of the ESPAR, its cost function is comparable or even better than the linear and circular arrays. Since the ESPAR antenna has only one active element, its implementation cost is very low in comparison with the linear and circular arrays whose all elements are active. Therefore, the ESPAR can be a frugal replacement for conventional arrays with the same performance. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Modified antenna effective gain in multiple-cluster 3D channel model

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1121 KB) |  | HTML iconHTML  

    This paper investigates the effective gain of antennas in indoor channels. A metric called instantaneous effective gain is proposed, and a multiple-cluster 3D channel model is used to facilitate the proposed antenna effective gain. In the multiple-cluster channel model, Laplacian and double exponential distribution are utilized to model azimuth and elevation signal power distribution respectively, and multiple clusters are built to describe the instantaneous channel power distribution. The modified antenna effective gain and multiple-cluster channel model are suitable for evaluating the antennas in antenna switching system. By using the proposed metric and the channel model, it is also found by simulation that the elevation mismatch of antenna patterns with indoor channels reduces the effective gain in the antenna switching system. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Stochastic optimization methods for angle of arrival estimation

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (207 KB) |  | HTML iconHTML  

    The difficulty for accurate determination of the angles of arrival (AOA) of signals arises from the optimization of likelihood functions of high dimension. Usually, a gradient-based technique is employed to find the optimum of the function. However, this method requires heavy computational work and the differentiability of the likelihood function. This paper presents two gradient-free methods: One is based on the Markov Chain Monte Carlo (MCMC) method and the other applies particle swarm optimization (PSO) to estimate the AOA. The main difference between the two methods is that the PSO-based method exploits multiple random search paths, while the MCMC-based method only employs undirected random search along a single path. A practical search space is also proposed for the case of symmetric objective functions to reduce the computational work in a manner that the traditional PSO stopping criteria is still applicable. To illustrate these techniques, a uniform linear antenna array is considered under the influence of additive complex Gaussian noise. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • SC/FDE combined with MIMO: An improved out of band power and performance via tamed frequency modulation

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (333 KB) |  | HTML iconHTML  

    Correlative minimum shift keying (MSK), a second order polynomial modulation scheme known as tamed frequency modulation (TFM), is a constant envelope type of modulation with a perfect peak to average power ratio (PAPR), besides the property of low out of band power. We apply the linearized TFM to the single carrier transmission with frequency domain equalization (SC/FDE) concept. We then obtain a power and bandwidth efficient broadband technique for the SISO and MIMO multipath channels. Finally we present simulation results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Adaptive reactance parasitic antenna array

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1236 KB) |  | HTML iconHTML  

    This paper presents initial experiences with the design and implementation of a low-cost beam steering antenna for long-distance WIFI applications. The antenna system has three components: (1) an adaptive parabolic reflector constructed from an array of passive scatterers with tunable reactive loads, (2) an optimizer that runs on a host computer that adjusts the phases and amplitudes of their currents based on received signal strengths, and (3) a minimal hardware controller that interfaces to an array of digital-to-analog converters and varactor bias voltage logic. Experimental measurements confirm electrodynamics simulations and show that highly directional patterns can be realized while controlling orientation in azimuth and elevation. Initial results achieve 18 dBi of gain across an operational 50 degrees of azimuth with a beam width of 10 degrees. Higher gains of 22 dBi or more are possible with reduced range of steerability. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Unequal error protection with eigen beamforming for partial channel information MIMO-OFDM

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (399 KB) |  | HTML iconHTML  

    Some communication applications, like multimedia, deliver data of different importance classes allowing unequal error protection (UEP) levels. In this paper, a multiple-input multiple-output (MIMO) system using orthogonal frequency division multiplexing (OFDM) is considered with a new UEP bit-loading algorithm based on the non-UEP algorithm by Chow, Cioffi, and Bingham. In the proposed bit-loading algorithm, bits are distributed across the unitarily transformed eigenbeams in case of partial channel information (CSI) knowledge. However, ideal performance can not withstand the rapid wireless channel variation unless a restricted beamforming is used. For the case of partial CSI, we proposed a switched beamforming technique that can maintain the required performance protection levels. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Short length CDMA codes for wireless sensor networks

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (246 KB) |  | HTML iconHTML  

    Wireless sensor networks consist of a large number sensors spread across a given geographical area. Each sensor has its own communication capability as well as certain level of intelligence for signal processing and networking. As the sensor nodes are densely populated, communication range requirement for these nodes is smaller. After signal detection, a number of sensor nodes communicate over the same wireless multiuser channel. This necessitates the use of orthogonal codes with good cross correlation properties to mitigate multi access interference (MAI). In sensor networks, due to the dense placement of nodes, limited availability of power brings different metrics for optimality where short length spreading codes might be utilized for coding purposes. In this paper, a design methodology for the generation of such short length varying power orthogonal code sets with multiple levels of chip values is presented. BER characteristics of these short length codes are presented for two user and multiuser scenarios in AWG noise environment. As dynamic utilization of spreading code libraries consisting of multiple orthogonal sets brings additional network security at the code level, we expect spreading code rich system solutions in the future. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Distributed fermat-point location estimation for wireless sensor network applications

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (883 KB) |  | HTML iconHTML  

    This paper presents a distributed fermat-point range estimation strategy, which is important in the moving sensor localization applications. The fermat-point is defined as a point which minimizes the sum of distances from three sensors inside a triangle. This point is indeed at the trianglepsilas center of gravity. We solve the problems of large errors and poor performance in the bounding box algorithm. We obtain two results by performance analysis for a deployed environment with 200 sensor nodes. First, when the number of sensor nodes is below 150, the mean error decreases rapidly as the node density increases, and when the number of sensor nodes exceeds 170, the mean error stays below 1%. Second, when the number of beacon nodes is below 60, the normal nodes do not have sufficient number of accurate beacon nodes to help them estimate their locations. However, when the number of beacon nodes exceeds 60, the mean error changes slightly. Simulation results indicated that the proposed algorithm for sensor position estimation is more accurate than existing algorithms and improves on existing bounding box strategies. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • RDM+: a new Mac layer real-time communication protocol

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (175 KB) |  | HTML iconHTML  

    Many real-time communication protocols have been studied to guarantee the communication requirements of distributed real-time systems. But, current techniques lack all or most of these requirements specially bounded message delivery time. In this paper we have proposed a Mac layer protocol called RDM+ with concepts similar to Round Data Mailer multi layer protocol. Our simulation results show that this new protocol has the potential to be used in todaypsilas automotive systems. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Reduced-complexity bandwidth-constrained distributed estimation for wireless sensor networks

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (329 KB) |  | HTML iconHTML  

    While elegant in form, the maximum likelihood estimator (MLE) for heavily bandwidth-constrained distributed estimation in Gaussian noise is computationally expensive to implement. We consider an alternative estimator for this case which requires far less computational complexity, yet performs close to the MLE under the same operating conditions. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Cluster-grid structure routing protocol for sensor mobility management

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1120 KB) |  | HTML iconHTML  

    Sink mobility has become an increasingly important requirement of various sensor network applications. Handling such mobile sink conditions brings new challenges to large-scale sensor networking. This investigation proposed a hybrid-structure routing protocol (HSRP) that combines the benefits of grid-based and cluster-based structures. Grid-based structure is designed to solve the cluster head selection problem. A virtual cluster structure based on grid structure information is also built. The hybrid-structure can establish a local shortest routing path from mobile sink toward to source. Simulation results indicate that the proposed HSRP mechanism reduces about 28% energy consumption than other approach. Moreover, HSRP mechanism reduces average delay time, increases higher success ratio, and has a longer network lifetime. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Designing efficient and resilient tactical sensor network neighborhood keying algorithms

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB) |  | HTML iconHTML  

    This paper discusses the problem of achieving bandwidth and energy-efficient neighborhood group key distributions (NGKD) in tactical wireless sensor networks (TWSNs). We present new techniques that improve NGKD performance while also improving the resilience of TWSNs against attacks that combine node capture with message interception. This is accomplished without introducing additional communications or heavy-weight cryptographic computations that would degrade sensor network performance and reduce node lifetime. Our iterated keying algorithm allows networks to initialize and add new members as rapidly as any algorithm available, but with substantially greater deletion efficiency than in current practice. Our simulations demonstrate that, compared to techniques currently used in DoD research prototypes, our algorithm can reduce deletion bandwidth and energy costs by nearly 50 percent. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A Wavelet based Filtered Multi-Tone

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB) |  | HTML iconHTML  

    This paper discusses the performance of the wavelet based filtered multi-tone (WFMT) modulation. The novel WFMT modulation was proposed in 2003 for improving characteristics of wireless and DSL multicarrier systems. In this paper we describe a main idea of WFMT and discuss the advantages of this novel modulation. The WFMT modulation in comparison with OFDM and DMT has low level of out-of-band side lobes, low sensitivity to narrowband RF interference, lower number of frequency sub-channels and correspondently lower peak-to-average power ratio for the same size of FFT/IFFT core. The number of the frequency sub-channels in WFMT system is small (about 5~50). The attractive feature of WFMT is its low implementation complexity compared with known multicarrier architectures, that are based on FIR synthesis and analysis filter-banks. Several main characteristics of the WFMT are illustrated by simulation results. The practically realized WFMT system is described followed by the test results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the minimization of the total generalized squared correlation of synchronous DS-CDMA

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (831 KB) |  | HTML iconHTML  

    We characterize the total generalized squared correlation (TGSC) for a given signature sequence set used in uplink synchronous code division multiple access (S-CDMA) when channel state information is known perfectly at both transmitter and receiver. We give a definition of the TGSC based on the eigenvalues of Gram matrix associated to signature sequences set for multipath channels in the presence of the colored noise. Total squared correlation (TSC) and total weighted squared correlation (TWSC) measures are particular cases of TGSC. Modified alternating projection method and gradient flow method for minimizing TGSC (TSC, TWSC) in multipath channels and in the presence of the colored noise are investigated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Coherent versus differential mobile OFDM with application to DVB-H

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB) |  | HTML iconHTML  

    Orthogonal frequency division multiplexing (OFDM) is the modulation scheme of choice for digital video broadcasting-handheld (DVB-H), which is required to operate under high mobility conditions resulting in significant Inter-carrier Interference (ICI). To mitigate ICI, several cancellation schemes have been proposed but they require reliable channel information at the receiver which is quite challenging and costly under high mobility. To overcome these challenges, we investigate non-coherent detection as an alternative for the DVB-H system, and combine it with different ICI mitigating techniques that do not require channel information. Our simulation results show that the proposed non-coherent environment schemes outperform the coherent schemes in typical DVB-H scenarios. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new frequency-time-spreading code for MC/DS-CDMA wireless systems over Rayleigh fading channels

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB) |  | HTML iconHTML  

    While two-dimensional (2-D) orthogonal variable spreading factor (OVSF) codes were proposed for multicarrier direct-sequence code-division multiple-access (MC/DS-CDMA) systems in order to eliminate multiple-access interference, the number of orthogonal sequences (or code cardinality) was restricted by the number of carrier frequencies. Non-orthogonal 2-D frequency-time-spreading (FTS) codes were then proposed to increase the code cardinality by sacrificing some code performance. To improve the code performance, we here propose a modified 2-D FTS code. We also evaluate the performance of the new code in the MC/DS-CDMA system over a non-fading additive white Gaussian noise channel and a Rayleigh fading channel, and compare with those of the 2-D OVSF, random and original FTS codes. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Study of MFSK/FH-CDMA wireless communication systems without symbol-synchronous assumption

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (386 KB) |  | HTML iconHTML  

    We propose a more accurate method to analyze multilevel frequency-shift-keying frequency-hopping code-division multiple-access (MFSK/FH-CDMA) wireless communication systems using ldquoone-hitrdquo FH patterns, instead of random FH patterns. By also removing the over-optimistic symbol-synchronous assumption, the new method provides a more realistic performance analysis as the MFSK modulation may result in two hits even when one-hit FH patterns are used if symbol transmissions are not synchronized. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comparison of time and frequency domain single and double differential schemes for OFDM UWB systems

    Page(s): 1 - 5
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    Ultra-wideband (UWB) systems possess several distinct features such as very high data rate, large multipath or frequency diversity and improved ranging precision while requiring low-power low-complexity transceivers. Among the different modulation schemes, differential PSK is an attractive option because it does not require channel estimation, and hence reduces implementation complexity. This paper investigates an OFDM UWB receiver based on both time and frequency-domain differential PSK modulation and compares the performances of single and double differential schemes in the presence of frequency offset. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Distributed spectrum and power control in cognitive radio based wireless ad hoc networks

    Page(s): 1 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (233 KB) |  | HTML iconHTML  

    In this paper, we propose a cognitive radio-based multi-user resource allocation framework for mobile ad hoc networks using multi-carrier DS CDMA modulation over a frequency-selective fading channel. In particular, given pre-existing communications in the spectrum where the system is operating, in addition to potential narrow-band interference, a channel sensing and estimation mechanism is provided to obtain information such as subcarrier availability, noise power and channel gain. Both frequency spectrum and power are allocated to emerging new users (i.e., cognitive radio users), based on the distributed multi-user resource allocation framework, in order to satisfy the target data rate and the power constraint of each cognitive radio user, while attempting to avoid interference to the existing users as well as minimize total power consumption of the network. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.