Showing papers on "Frequency band published in 2009"

Optimal Multiband Joint Detection for Spectrum Sensing in Cognitive Radio Networks

Abstract: Spectrum sensing is an essential functionality that enables cognitive radios to detect spectral holes and to opportunistically use under-utilized frequency bands without causing harmful interference to legacy (primary) networks. In this paper, a novel wideband spectrum sensing technique referred to as multiband joint detection is introduced, which jointly detects the primary signals over multiple frequency bands rather than over one band at a time. Specifically, the spectrum sensing problem is formulated as a class of optimization problems, which maximize the aggregated opportunistic throughput of a cognitive radio system under some constraints on the interference to the primary users. By exploiting the hidden convexity in the seemingly nonconvex problems, optimal solutions can be obtained for multiband joint detection under practical conditions. The situation in which individual cognitive radios might not be able to reliably detect weak primary signals due to channel fading/shadowing is also considered. To address this issue by exploiting the spatial diversity, a cooperative wideband spectrum sensing scheme refereed to as spatial-spectral joint detection is proposed, which is based on a linear combination of the local statistics from multiple spatially distributed cognitive radios. The cooperative sensing problem is also mapped into an optimization problem, for which suboptimal solutions can be obtained through mathematical transformation under conditions of practical interest. Simulation results show that the proposed spectrum sensing schemes can considerably improve system performance. This paper establishes useful principles for the design of distributed wideband spectrum sensing algorithms in cognitive radio networks.

Observation of frequency band gaps in a one-dimensional nanostructured magnonic crystal

Abstract: We report the experimental observation of band gaps in a synthetic nanostructured magnonic crystal composed of two different magnetic materials. The sample, in the form of a one-dimensional periodic array comprising alternating Permalloy and cobalt nanostripes, has been fabricated using advanced lithographic techniques. Dispersion relations of spin waves in the magnonic crystal have been mapped by Brillouin spectroscopy. The center frequency and width of the band gaps observed are tunable by an applied magnetic field. Dispersion relations calculated based on the finite element method accord with the measured data.

Resource allocation in an OFDM-based cognitive radio system

Abstract: The problem of subcarrier, bit and power allocation for an OFDM based cognitive radio system in which one or more spectrum holes exist between multiple primary user (PU) frequency bands is studied. The cognitive radio user is able to use any portion of the frequency band as long as it does not interfere unduly with the PUs' transmissions. We formulate the resource allocation as a multidimensional knapsack problem and propose a low-complexity, greedy max-min algorithm to solve it. The proposed algorithm is simple to implement and simulation results show that its performance is very close to (within 0.3% of) the optimal solution.

Small Square Monopole Antenna for UWB Applications With Variable Frequency Band-Notch Function

Abstract: In this letter, a novel printed monopole antenna (PMA) for ultrawideband (UWB) applications with variable frequency band-notch characteristic is presented. The proposed antenna consists of a stepped square radiating patch with two U-shaped slots and a notched ground plane with a T-shaped sleeve that provides a wide usable fractional bandwidth of more than 140% (2.8516.73 GHz). By cutting two modified U-shaped slots with variable dimensions on the radiating patch, frequency band-stop performance is generated, and we can control its characteristics such as band-notch frequency and its bandwidth. The designed antenna has a small size of 12 times 19 mm2 while showing the band rejection performance in the frequency band of 5.02-5.97 GHz.

Coexistence Between UWB and Narrow-Band Wireless Communication Systems

Abstract: Ultra-wide-band (UWB) signals are suitable for underlay communications, over a frequency band where, possibly, other systems are active. Such coexistence of UWB and other systems is possible if the mutual interference has a small impact on their respective performance. This paper aims to present recent results on the interference and coexistence among UWB systems and other conventional narrow-band (NB) systems. Specifically, we consider a point-to-point UWB (NB) under the interference generated by a finite number of NB (UWB) radio transmitters. We consider channels including additive white Gaussian noise and multipath fading both for the victim and the interfering links, and different receiver architectures. While our main focus is on UWB systems based on impulse radio, wide-band systems employing carrier-based direct-sequence spread-spectrum and orthogonal frequency-division multiplexing are also considered.

Spin-wave propagation in a microstructured magnonic crystal

Abstract: Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a Permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatially resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.

Pulse propagation in a linear and nonlinear diatomic periodic chain: effects of acoustic frequency band-gap

Abstract: One-dimensional nonlinear phononic crystals have been assembled from periodic diatomic chains of stainless steel cylinders alternated with Polytetrafluoroethylene spheres. This system allows dramatic changes of behavior (from linear to strongly nonlinear) by application of compressive forces practically without changes of geometry of the system. The relevance of classical acoustic band-gap, characteristic for chain with linear interaction forces and derived from the dispersion relation of the linearized system, on the transformation of single and multiple pulses in linear, nonlinear and strongly nonlinear regimes are investigated with numerical calculations and experiments. The limiting frequencies of the acoustic band-gap for investigated system with given precompression force are within the audible frequency range (20–20,000 Hz) and can be tuned by varying the particle’s material properties, mass and initial compression. In the linear elastic chain the presence of the acoustic band-gap was apparent through fast transformation of incoming pulses within very short distances from the chain entrance. It is interesting that pulses with relatively large amplitude (nonlinear elastic chain) exhibit qualitatively similar behavior indicating relevance of the acoustic band gap also for transformation of nonlinear signals. The effects of an in situ band-gap created by a mean dynamic compression are observed in the strongly nonlinear wave regime.

Vibration and Wave Propagation Control of Plates with Periodic Arrays of Shunted Piezoelectric Patches

Abstract: Periodic arrays of shunted, piezoelectric patches are employed to control waves propagating over the surface of plate structures, and corresponding vibrations. The shunted, piezoelectric patches act as sources of impedance mismatch, which gives rise to interference phenomena resulting from the interaction between incident, reflected and transmitted waves. Periodically distributed mismatch zones, i.e., the piezo patches, produce frequency dependent, wave-dynamic characteristics, which include the generation of band gaps, or stop bands in the frequency domain. The extent of induced band gaps depends on the mismatch in impedance generated by each patch. The total impedance mismatch, in turn, is determined by the added mass and stiffness of each patch as well as the shunting electrical impedance. Proper selection of the shunting electric-circuit thus provides control over the attenuation capabilities of the piezo-plate structure, as well as the ability to adapt to changing excitation conditions. Control of wave-propagation attenuation and vibration reduction for plates with periodic, shunted, piezoelectric patches is demonstrated numerically, employing finite-element models of the considered structures.

Radio Link Budgets for UHF RFID on Multipath Environments

Abstract: Radio frequency identification (RFID) applications are growing rapidly, especially in the UHF frequency band, which is being used in inventory management. Passive UHF tags are preferred for this application. However, the read range is often overestimated using free space calculations. This paper presents a method to estimate the read range in multipath environments. Other effects with a direct impact on read range as the effect of materials on tag performance are also addressed. Using the proposed model and the ray trace method a RFID system simulator is presented.

Spin-wave propagation in a microstructured magnonic crystal

Abstract: Transmission of microwave spin waves through a microstructured magnonic crystal in the form of a permalloy waveguide of a periodically varying width was studied experimentally and theoretically. The spin wave characteristics were measured by spatially-resolved Brillouin light scattering microscopy. A rejection frequency band was clearly observed. The band gap frequency was controlled by the applied magnetic field. The measured spin-wave intensity as a function of frequency and propagation distance is in good agreement with a model calculation.

Actual Diversity Performance of a Multiband Diversity Antenna With Hand and Head Effects

Abstract: Using the metric actual diversity gain (ADG), diversity performance is investigated for a compact mobile terminal prototype with two internal, triple frequency band antennas in four different cases of user interaction. ADG is presented as a preferred alternative to apparent diversity gain and effective diversity gain. Absorption due to user proximity causes degradation and imbalance in mean effective gain of the antennas over the frequency bands, contributing to a degradation in diversity performance. However, user-induced changes in the antenna patterns cause a decrease in correlation in the low frequency band, which facilitates increased diversity gain. The study reveals that a significant net diversity gain, i.e., ADG of 5-8 dB compared to a single antenna prototype, can be achieved using multiband antennas in the proximity of a user, even at low frequencies for antennas with high mutual coupling.

A tunable multi-band metamaterial design using micro-split SRR structures

Abstract: This paper presents the results of a feasibility study for the design of multi-band tunable metamaterials based on the use of micro-split SRR (MSSRR) structures. In this study, we have designed and constructed a conventional split-ring resonator (SRR) unit cell (type A) and two modified SRR unit cells having the same design parameters except that they contain two (type B) or four (type C) additional micro-splits on the outer square ring, along the arm having the main split. Transmission characteristics of the resulting MSSRR cells are obtained both numerically and experimentally and compared to those of the ordinary SRR unit cell. It is observed that the presence of the additional micro-splits leads to the increase of resonance frequency by substantial amounts due to the series capacitance effect. Next, we have designed and constructed 2×2 homogeneous arrays of magnetic resonators which consist of the same type of cells (either A, or B, or C). Such MSSRR blocks are found to provide only a single frequency band of operation around the magnetic resonance frequency of the related unit cell structure. Finally, we have designed and constructed 2×2 and 3×2 inhomogeneous arrays which contain columns of different types of metamaterial unit cells. We have shown that these inhomogeneous arrays provide two or three different frequency bands of operations due to the use of different magnetic resonators together. The number of additional micro-splits in a given MSSRR cell can be interactively controlled by various switching technologies to modify the overall metamaterial topology for the purpose of activating different sets of multiple resonance frequencies. In this context, use of electrostatically actuated RF MEMS switches is discussed, and their implementation is suggested as a future work, to control the states of micro-splits in large MSSRR arrays to realize tunable multi-band metamaterials.

A harmonic bandwidth extension method for audio codecs

Abstract: Today's efficient audio codecs for low bitrate application scenarios often rely on parametric coding of the upper frequency band portion of a signal while the lower frequency band portion of the same is conveyed by a waveform preserving coding method. At the decoder, the upper frequency signal is approximated from the lower frequency data using the upper frequency band parameters. However, commonly used methods of bandwidth extension almost inevitably suffer from a sensation of unpleasant roughness, which is especially present for tonal music items. In this paper we expose the origin of the roughness and propose a bandwidth extension method, which does not introduce roughness into the reconstructed audio signal. A listening test demonstrates the advantage of the proposed method compared to a standard bandwidth extension.

Modeling of two-dimensional nanoscale Y-bent plasmonic waveguides with cavities for demultiplexing of the telecommunication wavelengths

Abstract: Numerical simulations, based on a finite-difference-time-domain (FDTD) method, of infrared light propagation for add/drop filtering in two-dimensional (2D) metal–insulator–metal (Ag–SiO2–Ag) resonators are reported to design 2D Y-bent plasmonic waveguides with possible applications in telecommunication wavelength demultiplexing (WDM). First, we study optical transmission and reflection of a nanoscale SiO2 waveguide coupled to a nanocavity of the same insulator located either inside or on the side of a linear waveguide sandwiched between Ag. According to the inside or outside positioning of the nanocavity with respect to the waveguide, the transmission spectrum displays peaks or dips, respectively, which occur at the same central frequency. A fundamental study of the possible cavity modes in the near-infrared frequency band is also given. These filtering properties are then exploited to propose a nanoscale demultiplexer based on a Y-shaped plasmonic waveguide for separation of two different wavelengths, in selection or rejection, from an input broadband signal around 1550 nm. We detail coupling of the 2D add/drop Y connector to two cavities inserted on each of its branches. Selection or rejection of a pair of different wavelengths depends on the inside or outside locations (respectively) of each cavity in the Y plasmonic device.

Rf front-end module and antenna systems

Abstract: Architectures and implementations of a transceiver system for wireless communications are presented, the system including one or more antennas supporting a single frequency band or multiple frequency bands, a transmit circuit, a receive circuit, and an isolation circuit that is coupled to the one or more antennas and the transmit and receive circuits and provides adequate isolation between the transmit circuit and the receive circuit.

Method and apparatus for communicating in a dominant interference scenario

Abstract: Techniques for supporting communication in a dominant interference scenario are described. A user equipment (UE) may communicate with a first base station and may observe high interference from and/or may cause high interference to a second base station. In one design, the first base station may use a first frequency band, which may overlap at least partially with a second frequency band for the second base station and may further extend beyond the second frequency band. The first base station may send at least one synchronization signal and a broadcast channel in a center portion of the first frequency band for use by UEs to detect the first base station. The second frequency band may be non-overlapping with the center portion of the first frequency band. The first base station may also communicate with at least one UE on the first frequency band.

Two port frequency reconfigurable antenna for cognitive radios

Abstract: A two port frequency reconfigurable antenna for cognitive radios is presented. It is composed of a disc monopole with two ports that excite at opposite sides; one port is very wideband and consists of a coplanar feed line and the other port is tunable narrowband and consists of a microstrip feed line with defect slots in its ground plane. The slots act as a filter that suppresses frequencies outside the desired band, its operating frequency band can be tuned by varying the length of the slots. The two ports are decoupled by at least 10 dB through the considered frequency range. It is believed that the proposed antenna can be a good candidate for cognitive radios in generic small base stations where the narrowband port is used for operation and the wideband one is used for sensing the spectrum. For accuracy, it is important that the sensing (measurement of the interference noise) is made with the same polarisation as the operation and the proposed antenna achieves this by having the two collinear ports. To examine the presented approach, simulated and measured results are presented and good agreement is reported.

Base station device, mobile station device, communication system and communication method

Abstract: A communication system which performs communication between a base station device configuring at least one cell and a mobile station device, wherein: the base station device includes: a synchronization signal generation unit which generates a synchronization signal corresponding to a cell identity for identifying a cell; and a transmission unit which generates a first transmission signal including the synchronization signal using a first parameter obtained from the cell identity, generates a second transmission signal excluding the synchronization signal using a second parameter obtained from a virtual cell identity different from the cell identity, transmits the first transmission signal using a first frequency band, and transmits the second transmission signal via a second frequency band different from the first frequency band. The mobile station device includes: a reception unit which receives a first reception signal including the synchronization signal using the first parameter obtained from the cell identity via the first frequency band and receives a second reception signal using the second parameter obtained from the virtual cell identity via the second frequency band.

A Practical Simple Geometry and Gain/Phase Calibration Technique for Antenna Array Processing

Abstract: A calibration technique is proposed in this paper for an arbitrary array. This technique estimates the array sensor gain/phase and geometry with a set of simultaneous equations formed by using the MUSIC null spectrum property. Note that the technique does not use iterative calculation in estimating the array parameters and hence it has no convergent problem; however, it requires that n directions of arrival (DOAs) of signal sources to be known to calibrate the array which is perturbed n-dimensionally. The efficacy of the method is demonstrated by means of simulations and on experimental data collected with an antenna array operating in high-frequency radio band.

Frequency hopping pattern and arrangement for sounding reference signal

Abstract: A method, an apparatus, and a computer program that includes forming frequency hopping position of the sounding reference signal is based on a hopping pattern. The hopping pattern of the sounding reference signal is configured to utilize a tree assignment for a frequency allocation of the sounding reference signal and to support at least one frequency band branch per layer. The hopping pattern of the sounding reference signal is also configured to provide consecutive sounding reference signals on widely separated frequency allocations.

Reliable Fast Frequency Sweep for Microwave Devices via the Reduced-Basis Method

Abstract: In this paper, a reduced-basis-approximation-based model-order reduction for fast and reliable frequency sweep in the time-harmonic Maxwell's equations is detailed. Contrary to what one may expect by observing the frequency response of different microwave circuits, the electromagnetic field within these devices does not drastically vary as frequency changes in a band of interest. Thus, instead of using computationally inefficient, large dimension, numerical approximations such as finite- or boundary-element methods for each frequency in the band, the point in here is to approximate the dynamics of the electromagnetic field itself as frequency changes. A much lower dimension, reduced-basis approximation sorts this problem out. Not only rapid frequency evaluation of the reduced-order model is carried out within this approach, but also special emphasis is placed on a fast determination of the error measure for each frequency in the band of interest. This certifies the accurate response of the reduced-order model. The same scheme allows us, in an offline stage, to adaptively select the basis functions in the reduced-basis approximation and automatically select the model-order reduction process whenever a preestablished accuracy is required throughout the band of interest. Finally, real-life applications will illustrate the capabilities of this approach.

Antenna impedance stabilization with stabilization load in second antenna circuitry

Abstract: There are first and second antennas proximally disposed and configured to resonate within respective first and second frequency bands, which may overlap. An impedance stabilization circuitry is coupled to ground. There is a selective coupler (for example, diplexer, directional coupler, switch) interfacing the second antenna selectively with the impedance stabilization circuitry and with radio circuitry. The selective coupler comprises a first port coupled to the second antenna, a second port coupled to the impedance stabilization circuitry, and a third port configured to couple with radio circuitry that is configured to operate in the second frequency band. The selective coupler provides a predetermined impedance to signals within the first frequency band and a low insertion loss to signals within the second frequency band, thus providing a stable impedance for the first antenna's view of the second antenna.

Performance of a Novel $\Psi$ -Shape Microstrip Patch Antenna With Wide Bandwidth

Abstract: In this letter, a novel Psi-shape microstrip patch antenna that provides wide-impedance bandwidth performance in addition to the acceptable radiation patterns is presented. The substrate is a foam material, and for ease of fabrication, the patch is etched on a thin dielectric layer, which is placed over the foam and fed by a coaxial probe. The simulated and measured 2:1 VSWR impedance bandwidths are 55% and 54%, respectively. The measured and simulated radiation patterns are in acceptable agreement as well. The measured front-to-back (F/B) ratio is better than 20 dB throughout the frequency band.

A unified model for interference analysis in unlicensed frequency bands

Abstract: This paper presents a unified framework for interference characterizations and analysis in the unlicensed frequency bands and the like, where many narrowband heterogeneous terminals coexist and share a common wideband channel using less-restrictive transmission etiquettes. Here, each transmitter/receiver pair makes his own decision regarding when to access the channel without any direct coordination with the other users. This is usually based on the local channel conditions at the receiver or/and the transmitter. Due to the nature of the wireless channel, communication in such environments is usually prone to arbitrary partial-band interference which can be generated anywhere in the space and frequency domains. In this paper, a new spatial-spectral interference model is introduced, where interferers can be of any power spectral density and are distributed according to a Poisson process in space and frequency domains. This basic model is extended to include the effects of channelization, where users are allowed only to transmit at a preassigned set of discrete frequencies. This is further extended to include also the effects of spectral-spatial guard zones, where the interferers can not exist in a given band nearby the victim receiver. Based on this multidimensional spatial-spectral Poisson model and the accurate conditional Gaussian analysis, explicit expressions are derived for average error rates of different communication systems.

Design and Realization of a Linearly Polarized Eleven Feed for 1-10 GHz

Abstract: A new linearly polarized eleven feed for operation between 1 and 10 GHz is presented. This frequency band is higher than the realized before, and the input reflection coefficient is better than ${-}8$ dB over the frequency range, which also is an improvement over previous models. The log-periodic dipole petals have been designed by using a simple one-by-one parameter optimization scheme with a simulation tool based on moment method. The final analysis has been improved by applying an finite-difference time-domain (FDTD)-based solver for the central part of the feed and then a circuit network program to combine the results of the center part with the result of the dipole panels. The antenna has been manufactured by printed circuit board (PCB) technology on a metalized Kevlar sheet in order to obtain better tolerances and smaller dimensions than in previous models. Measurements show agreement with the analysis.

A 1.94 to 2.55 GHz, 3.6 to 4.77 GHz Tunable CMOS VCO Based on Double-Tuned, Double-Driven Coupled Resonators

Abstract: This paper presents a multi-band CMOS VCO using a double-tuned, current-driven transformer load. The dual frequency range oscillator is based on enabling/disabling the driving current in the secondary port of the transformer. This approach eliminates the effect of switches connected directly to the VCO tank whose capacitance and on-resistance affect both the tuning range and the phase noise of a typical multi-band oscillator. The relation between the coupling coefficient of the transformer load, selection of frequency bands, and the resulting quality factor at each band is investigated. The concept is validated through measurement results from a prototype fabricated in 0.25 ?m CMOS technology. The VCO has a measured tuning range of 1.94 to 2.55 GHz for the low frequency range and 3.6 to 4.77 GHz for the high frequency range. It draws a current of 1 mA from 1.8 V supply with a measured phase noise of -116 dBc/Hz at 1 MHz offset from a 2.55 GHz carrier. For the high frequency band, the VCO draws 10.1 mA from the same supply with a phase noise of -122.8 dBc/Hz at 1 MHz offset from a 4.77 GHz carrier.

Ultrawideband Composite Cavity-Backed Folded Sectorial Bowtie Antenna With Stable Pattern and High Gain

Abstract: A composite cavity-backed folded sectorial bowtie antenna (FSBA) is proposed and investigated in this paper, which is differentially fed by an SMA connector through a balun, i.e. a transition from a microstrip line to a parallel stripline. The composite cavity as a general case, consisting of a conical part and a cylindrical rim, can be tuned freely from a cylindrical to a cup-shaped one. Parametric studies are performed to optimize the antenna performance. Experimental results reveal that it can achieve an impedance bandwidth of 143% for SWR les 2, a broadside gain of 8-15.3 dBi, and stable radiation pattern over the whole operating band. The total electrical dimensions are 0.66lambdam in diameter and 0.16lambdam in height, where lambdam is the free-space wavelength at lower edge of the operating frequency band. The problem about the distorted patterns in the upper frequency band for wideband cavity-backed antennas is solved in our work.

A Dual-Band CMOS Voltage-Controlled Oscillator Implemented With Dual-Resonance LC Tank

Abstract: A new fully integrated, dual-band CMOS voltage controlled oscillator (VCO) is presented. The VCO is composed of n-core cross-coupled Colpitts VCOs and was implemented in 0.18 mum CMOS technology with 0.8 V supply voltage. The circuit allows the VCO to operate at two resonant frequencies with a common LC tank. The VCO has two control inputs, one for continuous control of the output frequency and one for band switching. This VCO is configured with 5 GHz and 12 GHz frequency bands with differential outputs. The dual-band VCO operates in 4.78-5.19 GHz and 12.19-12.61 GHz. The phase noises of the VCO operating at 5.11 and 12.2 GHz are -117.16 dBc/Hz and -112.15 dBc/Hz at 1 MHz offset, respectively, while the VCO draws 3.2/2.72 mA and 2.56/2.18 mW consumption at low/high frequency band from a 0.8 V supply.