Peak to Average Power Ratio (PAPR) is one of the serious problems in any wireless communication system using multi carrier modulation technique like OFDM, which reduces the efficiency of the transmit high power amplifier. In this paper, proposed scheme will be introduced that combine interleaving method with peak windowing. Simulation results show that our technique simultaneously decrease Bit Error Rate (BER), reduce the PAPR by 3.5 dB and improve out-of- band radiation, in presence of nonlinear power amplifier model.
The effect of cold plasma beam on electromagnetic whistler wave with perpendicular AC electric field has been studied by using the unperturbed Lorentzian (Kappa) distribution in the Earth's atmosphere for relativistic plasma. The cold plasma has been described by a simple Maxwellian distribution where as Lorentzian (Kappa) distribution function has been derived for relativistic plasma with temperature anisotropy in the presence of a perpendicular AC electric field to form a hot/warm background. The dispersion relation is obtained by using the method of characteristic solutions and kinetic approach. An expression for the growth rate of a system with added cold plasma injection has been calculated. Results for representative values of parameters suited to the Earth's magnetosphere has been obtained. It is inferred that in addition to the other factors, the relativistic plasma modifies the growth rate and it also shifts the wave band significantly. The relativistic electrons by increasing the growth rate and widening the bandwidth may explain a wide frequency range of whistler emissions in the Earth's magnetosphere.
Forward scattering from a finite, right-circular cylinder is analyzed as a function of size. Both axial and broadside incidence are treated. Predictions based upon combinations of Physical Optics, Wu's series, and empirical formulas are compared with numerical results from the moment method. The analysis examines cylinders that vary between 1 to 20 wavelengths in radius and 0 to 20 wavelengths in length. Approximate formulas accurately model the RCS of cylinders as small as one wavelength in radius. Accuracy of predictions improves with increase in cylinder size.
In this paper two-dimensional problem of plane-wave diffraction by a "fractional strip" is studied. "Fractional strip" is introduced as a strip with fractional boundary conditions (FBC) involving fractional derivatives of the field components. FBC describe intermediate boundary between perfect electric conductor (PEC) and perfect magnetic conductor (PMC). It is shown that "fractional strip" has scattering properties similar to the well-known impedance strip. For one important case of fractional order equal to 0.5 the solution of the wave diffraction problem by a "fractional strip" can be found analytically. Detailed comparison analysis of the physical characteristics of the scattered fields for both fractional and impedance strips is presented. The relation between the fractional order and the value of impedance is derived. It is shown that in a wide range of input parameters the physical characteristics of the "fractional strip" are similar to the strip with pure imaginary impedance.
In this paper we evaluate the potential of a 5-element monopole array incorporated into a handheld device for beamforming in the 5.0-GHz band. The geometry of the handset consists of a 5-element array: four elements located at the handset corners and the fifth-element located at the center. Also, the interaction of the antenna array, mounted on a mobile handset, with a human head phantom is investigated. Firstly, the spatial peak specific absorption rate (SAR) values of 5-element array antennas for mobile handsets in the vicinity of a spherical phantom of a human head are evaluated numerically as a function of the distance between the handset and the head phantom for two different scenarios. Next, the effect of the human head on the handset radiation pattern is studied. The effect of different handset positions on the radiation pattern is also considered. The particle swarm optimization (PSO) algorithm is used to optimize the complex excitations of the adaptive arrays elements in a mutual coupling environment for beamforming synthesis. All numerical simulations are performed using the FEKO Suite 5.3 software. To validate the numerical simulations, we first perform two validation tests and compare the numerical results with published simulated and measurement results.
A new multi-layer planar array architecture to achieve multi-polarized radiation is developed in this paper. The design concept is based on embedding U-shaped coupling slots in the ground plane to extend the bandwidth. The proposed antennas have two feed ports, by adjusting the feeding properly, the antennas can transmit arbitrary elliptic polarized signal theoretically. Return loss and radiation patterns are measured for the 1-element, 2-element, 4- element, 16-element antenna arrays at 12.5 GHz. Radiation patterns of the antenna arrays show close agreement to the predicted ones in the shape of the main beam. By further incorporating properly designed feed networks, the -20 dB return-loss bandwidth of the proposed antenna arrays can cover the 12.5 GHz frequency band (12.25-12.75 GHz). Design details and experimental results are presented and discussed.
This paper is intended to the analysis of adaptive radar detectors for partially correlated χ2 targets. This important class of targets is represented by the so-called moderately fluctuating Rayleigh targets, which, when illuminated by a coherent pulse train, return a train of correlated pulses with a correlation coefficient in the range 0 < ρ < 1 (intermediate between SWII and SWI models). The detection of this type of fluctuating targets is practically of great importance. Since the CFAR detectors represent an attractive class of schemes that can be used to overcome the problem of clutter by adaptively setting their threshold based on local information of total noise power, they are commonly used to decide the presence or absence of the radar target of interest, which is of partially correlated χ2 type. In addition, the OS based algorithms are chosen to carry out this task owing to their immunity to outlying targets which may be present amongst the contents of the reference window. Moreover, since the large processing time of the single-window OS detector limits its practical applications, our scope here is to analyze the performance of OS modified versions for moderately fluctuating Rayleigh targets in nonideal situations. This analysis includes the single-window as well as the double-window OS detection schemes for the case where the radar receiver postdetection integrates M square-law detected pulses and the signal fluctuation obeys χ2 statistics with two degrees of freedom. These detectors include the mean-level (ML-), the maximum (MX-) and the minimum (MN-) OS algorithms. Exact formulas for their detection probabilities are derived, in the absence as well as in the presence of spurious targets. The primary and the secondary interfering targets are assumed to be of the moderately fluctuating Rayleigh targets. Swerling's well known cases I and II represent the cases where the signal is completely correlated and completely decorrelated, respectively, from pulse to pulse. Under the multiple-target operations, the ML-OS detector has the best homogeneous performance, the MN processor has the best multitarget performance when a cluster of radar targets appears in the reference window, while the MX scheme doesn't offer any excessive merits, neither in the absence nor in the presence of outlying targets, as expected.
The characteristics impedance of the fundamental mode in a rectangular waveguide is computed using finite element method. The method is validated by comparison with the theoretical results. In addition to this, we have considered the problem of determining the modes of propagation of electromagnetic waves in a rectangular waveguide for the simple homogeneous dielectric case. The starting point is Maxwell's equations with an assumed exponential dependence of the fields on the Z-coordinates. From these equations we have arrived at the Helmholtz equation for the homogeneous case. Finite-element- method has been used to derive approximate values of the possible propagation constant for each frequency.
A composite right/left-handed transmission line resonator with 3 unit cells is fabricated and its radiation loss is investigated. At the zeroth order resonance state, the resonator shows radiation loss, which is dominant over other conductor and dielectric losses. This paper investigates the radiation loss of zeroth order resonators from a quality-factor point of view. With the use of a metal shield, the quality factor is considerably increased through a reduction of the radiation loss. The increase in the quality factor is explained by means of the extracted parameters of the equivalent circuit model.
This paper presents an exact performance analysis for the evaluating a mean acquisition time in a cellular code division multiple access system. New expressions for the probabilities of detection, miss, and false alarm are derived in a frequency-selective Rician fading channel. From the numerical results, it is shown that our formula gives the accurate results of the mean acquisition time in the performance analysis of the parallel acquisition system with the reference filter.
Our scope in this paper is to provide a complete analysis of CFARdetection of fluctuating targets when the radar receiver incoherently integrates M returned pulses from a chi-squared fluctuating targets with two and four degrees of freedom and operates in a multitarget environment. Since the Swerling models of fluctuating targets represent a large number of such type of radar targets, we restrict our attention here to this interesting class of fluctuation models. There are four categories of such representation; namely SWI, SWII, SWIII, and SWIV. SWI and SWIII represent scan-to- scan fluctuating targets, while SWII and SWIV represent fast pulse-to-pulse fluctuation. Exact expressions are derived for the probability of detection of all of these models. A simple and an effective procedure for calculating the detection performance of both fixed-threshold and adaptive-threshold algorithms is obtained. The backbone of this procedure is the ω-domain representation of the cumulative distribution function of the test statistic of the processor under consideration. In the CFARcase, the estimation of the noise power levels from the leading and the trailing reference windows is based on the OS technique. The performance of this detector is analyzed in the case where the operating environment is ideal and where it includes some of extraneous targets along with the target under test. The primary and the secondary outlying targets are assumed to be fluctuating in accordance with the four Swerling's models cited above. The numerical results show that, for large SNR, the processor detection performance is highest in the case of SWIV model while it attains its minimum level of detection in the case of SWI model. Moreover, SWII model has higher performance than the SWIII representation of fluctuating targets. For low SNR, on the other hand, the reverse of this behavior is occurred. This observation is common either for fixed-threshold or for adaptive-threshold algorithm.
Wireless technology offers new found freedom and the potential for 'anytime, anyplace' communications. Communication technology requires being sustainable in the sense of efficiency, not only to preserve the information within the quality requirements, but also to express the same contents with the minimum resources. The Code Division Multiple Access (CDMA) is an emerging technology for next generation multimedia information of real-time and non real-time traffic and various multi-source multi-traffic communication environments. Multiple inputs multiple output (MIMO) as an adaptive antenna based technology which can improves the capacity of wireless mobile communication. The combined technique has both the advantages of CDMA and MIMO systems. Below the jamming margin CDMA alone works up to satisfactory level but above jamming margin CDMA along with MIMO may be a better proposition for anytime-anywhere communication.
This article aims to provide a novel and efficient technique for pattern shaping and null steering in the environment of unwanted interferences. This paper presents a DSP based method, where at first DFT coefficients are obtained from spatial domain sampling and then operating by suitable window function gives new set of DFT coefficients. IFFT(IDFT) over these coefficients provide complex weights which adaptively introduces null in the direction interference while keeping the main beam toward desired signal.
Broadband single carrier modulated signals experience severe multipath distortion scrambling & ISI when propagating through physical medium. Correcting the distortion with channel equalization is the foremost task of the detector. Prior information about the transmitted signals in the form of channel decoder feedback can significantly enhance equalization accuracy. An algorithm that iteratively performs channel decoding and equalization with prior information is generally denoted turbo-equalizer. Turbo-Equalizer uses prior information & the principle of interference cancellation by MMSE criterion. Here we have tested Adaptive Turbo Equalization with least Mean Square Algorithm (LMS) & modified normalized LMS algorithm & Turbo-Decoding with a Log-Map. Consequently the Mean Square Error analysis, Stability analysis and convergence analysis are provided and its shown if the system is sparse, then the system will converge faster for a given total asymptotic MSE, though the choice of initialization is important. Here all the Implementation concepts have been verified in MATLAB platform and evaluation of the proposal is presented. The measurement for the performance is displayed as bit error rates (BER) in comparison to SNR of the Channel.
New fractal geometry for microstrip antennas is presented in this paper. This fractal structure is implemented on hexagonal and several iteration is applied on initial shape. This antenna has lowprofile, lightweight and is easy to be fabricated and has successfully demonstrated multiband and broadband characteristics. The simulated results showthat proposed antenna has very good performance in impedance bandwidth and radiation pattern.
A novel co-planar waveguide (CPW) ultra-wideband (UWB) aperture antenna is presented. The antenna consists of a rectangular aperture on a printed circuit board ground plane and a mushroom-shaped exciting stub. The mushroom-shaped stub is simple and has less parameter, which is convenient to analyze and optimize. The antenna has a compact aperture size 22 × 13mm2, fabricated on FR4 substrate with dielectric constant of 4.3, thickness of 1.5 mm. The antenna is successfully implemented and measured, which has 8.3 GHz match bandwidth (VSWR < 2), and stable radiation patterns.
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