In this paper, we propose an efficient technique to mitigate the effects of both multiple access interference (MAI) and intersymbol interference (ISI) in downlink wireless CDMA systems. A hybrid scheme comprising beamforming at the base station and a regularized zero forcing equalizer at the mobile unit is suggested and studied. The proposed scheme uses the beamforming to reduce the effect of the MAI. Then, the regularized zero forcing equalizer is used to reduce the effect of ISI and provide a better estimate of the data. The performance of the proposed scheme is studied and compared with traditional schemes. Our simulation results show a noticeable performance improvement by using the proposed scheme with low complexity at the mobile unit.
A compact elliptic-function low pass filter using microstrip stepped-impedance modified-hairpin resonators is developed and a multiple cascaded filter using semi-hairpin resonators is designed, analyzed and tested. Sharpness of cut off frequency, low insertion-loss, enhancement of bandwidth and very compact size are features of the proposed low-pass filter. Size reduction of this filter is reported about 62% with 13% enhancement of bandwidth respects to the conventional filter with comparable performance. The measurement results are in good agreement with the theoretical ones.
At WRC-07, the frequency band 3500 MHz has been allotted for the next generation of mobile International Mobile Telecommunication-Advanced (IMT-Advanced). Meanwhile this band is already in used by fixed services, which means that harmful interference probability may be transpired. In this paper, the coexistence between the two services in various geographical deployment areas (dense urban, urban, suburban, and rural areas) will be analyzed. Spectrum emission mask is an effective interference model will be invested and interference to noise ratio of -6 dB is the used coexistence criteria. Co-channel, zero-guard band, and adjacent channel are three Intersystem interference scenarios will be investigated. The analysis will focus on determine required minimum separation distance and frequency separation under different attenuation due to local clutter and height of antennas at fixed channel bandwidth.
In this study, a wireless bio-radar sensor was designed to detect a human heartbeat and respiration signals without direct skin contact. In order to design a wireless bio-radar sensor quantitatively, the signal-to-noise ratio (SNR) in the baseband output of a sensor should be calculated. Therefore, we analyzed the SNR of the wireless bio-radar sensor, considering the signal power attenuation in a human body and all kinds of noise sources. Especially, we measured a residual phase noise of a typical free-running oscillator and used its value for the SNR analysis. Based on these analysis and the measurement results, a compact, low-cost 2.4 GHz direct conversion bio-radar sensor was designed and implemented in a printed circuit board. The demonstrated sensor consists of two printed antennas, a voltage-controlled oscillator, an I/Q demodulator, and analog circuits. The heartbeat and respiration signals acquired from the I/Q channel of the sensor are applied to the digital signal processing circuit using MATLAB. ECG (electrocardiogram), and reference respiration signals are measured simultaneously to evaluate the performance of the sensor. With an output power of 0dBm and a free running oscillator without a phase locked loop circuits, a detection range of 50 cm was measured. Measurement results show that the heart rate and respiration accuracy was very high. Therefore, we verified that a wireless bio-radar sensor could detect heartbeat and respiration well without contact and our SNR analysis could be an effective tool to design a wireless bio-radar sensor.
A novel method for direction-of-arrival (DOA) estimation is proposed. This technique employs the excellent performance of Bartlett method in coherent environments as well as high resolution and low computational complexity of Beamspace MUSIC. Simulation results show that the use of Beamspace MUSIC with Bartlett yields significantly improved performance compared to the original MUSIC especially in highly correlated situations.
The WIMAX technology based on air interface standard 802-16 wireless MAN is configured in the same way as a traditional cellular network with base stations using point to multipoint architecture to drive a service over a radius up to several kilometers. The range and the Non Line of Sight (NLOS) ability of WIMAX make the system very attractive for users, but there will be slightly higher BER at low SNR. In this paper, a comparison between the performance of wimax using convolutional code and convolutional product code (CPC) [1] is made. The CPC enables reducing BER at different SNR values compared to the convolutional code. For example, at BER equals 10-3 for 128 subcarriers, the amount of improvements in SNR is more than 2 dB. Several results are obtained at different modulating schemes (16QAM and 64QAM) and different numbers of sub-carriers (128 and 512).
Multicarrier Phase-Coded signals have been recently introduced to achieve high range resolution in radar systems. As in single carrier phase coded radars, the conventional method for compression of these signals is based on using matched filter or direct computation of autocorrelation function. In this paper we propose a new method based on Discrete Fourier Transform (DFT) that has lower computational complexity compared to the conventional approach. It has been proved that the proposed method is mathematically equivalent to matched filtering, so there is no processing loss. Also the effect of sampling frequency on compression loss has been investigated and for the oversampled matched filter of MCPC signals, a computational efficient algorithm based on polyphase implementation has been proposed.
In this paper, a novel structure for Ka-band micro electromechanical switches with low actuation voltage is proposed. In this structure, the membrane of the switch is chosen to be a Koch fractal. We have analyzed these switches in order to extract their parameters such as insertion loss, return loss and deformation posture. The effect of the actuation voltage on the deformation of the bridge has been analyzed and the results are compared with simple rectangular bridges. It is shown that bias voltage of these kinds of switches is remarkably lower than that of its other counterparts. This switch may be used as a low loss and effective element for more complicated systems such as distributed phase shifters and phased arrays.
In this paper, we present an improved Coulombianbased analytical calculation of magnetic fields created by permanentmagnetic rings. The 3 dimensional (3D) components of two types of magnetized rings (axially and radially) were analytically evaluated. The obtained components of the magnetic field are expressed over complete elliptical integrals of the first and second kind, as well as by Heuman's Lambda function. These expressions permit fast and accurate calculations of the magnetic field at any point of interest, for both regular and singular cases. The presented method gives an improvement of already known expressions for calculating the magnetic fields of the aforementioned magnetized rings, and we consider that these improved analytical expressions are more extendable to numerical applications.
This paper presents a broad-band technique for measuring the dielectric permittivity of isotropic nonmagnetic film-shaped materials at low microwave frequencies. The material under test is the substrate of an open-end coplanar waveguide (CPW) used as sample-cell. The dielectric permittivity is extracted from S11 reflection parameter measurement of the open-end CPW cell using analytical relationships, which allow to decrease the computation time with respect to any full-wave electromagnetic method. Vector network analyzer (VNA) and high-quality on-coplanar test fixture are used for the measurements between 300 kHz and 3 GHz. Measured εr data for several nonmagnetic low-loss materials are presented. This technique shows a good agreement between measured and predicted data for the real permittivity over 0.05 GHz-3GHz frequency range.
In this paper, a broadband bandpass filter (BPF) with superior spurious suppression over a wide frequency range at least up to 20 GHz at −20 dB has been designed. The proposed broadband bandpass filter has designed using quarter-wavelength short stubs alternating with branch stubs co-via structure, and inserting the bandstop filters to substitute for redundant connecting lines. Compare with some traditional co-via structure, this work by using the branch stubs to construct the co-via structure, not only reduce the size around 70% but also decrease the radiation loss due to some complex meander configurations occurring in the connecting lines. For the prototype broadband filter, center frequencies around 4 GHz were selected. The bandwidth of passband was between 1.95 GHz and 6.25 GHz, in which the insertion-loss amounts to around −1.5 dB. The suppression range of stopbandis between 8.2-20.3 GHz, in which the insertion-loss amounts to around −20 dB.
Based upon developed radial FDTD-method, used for solution of Maxwell equations in cylindrical coordinates and implemented in Matlab-7.0 environment, we simulated focusing of the annular Gaussian beam with radial polarization by conical microaxicon with numerical aperture 0.60. It is shown that the area of focal spot (defined as area where intensity exceeds half of its maximum) can be 0.096λ2, and focal spot diameter equals to 0.35λ.
A He's Energy balance method (EBM) is used to calculate the periodic solutions of nonlinear oscillators with fractional potential. Some examples are given to illustrate the effectiveness and convenience of the method. We find this EBM works very well for the whole range of initial amplitudes, and the excellent agreement of the approximate frequencies and periodic solutions with the Exact or other analytical solutions has been demonstrated and discussed. Comparison of the result obtained using this method with that obtained by Exact or other analytical solutions reveal that the EBM is very effective and convenient and can therefore be found widely applicable in engineering and other science.
In this paper,a novel compact monopole ultra-wideband (UWB) antenna with a notched ground is presented. To increase the impedance bandwidth,a notched ground is introduced. The parameters and the characteristics of the antenna are given. It shows good characteristics for UWB,and it satisfies the VSWR requirement of less than 2.0 in the frequency band from 2.55 GHz to more than 13 GHz. The measured radiation patterns show good omnidirectional performance and antenna gains across the operation bandwidth.
The speedy dissemination of digital consumer electronics devices within personal area causes increments of multimedia communication and advent of entertainment networking. This feature of communication requires high data-rate transmission. In order to meet the demand, in this paper, we apply multiple antenna schemes to MB-OFDM UWB system. And to use the UWB system with multiple antennas for various channel environment, some adaptive MIMO schemes are considered for multiple antenna MB-OFDM system. The first investigated technique is adaptive antenna selection which selects the proper number of transmitting antennas using estimated SNR. And the second technique is adaptive modulation which can be used after the adaptive antenna selection is executed. By using these adaptive techniques, the reliable and high data-rate communications which are well adapted to the various user's demands and channel conditions are achieved.
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