Electronics and Communications

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Published Research Papers from Vol. 1 (2005) to Vol. 9 (2013) ISSN: 1744-2400

Mediterranean Journal of Electronics and Communications covers all areas of applications in electronics, and communications engineering. Its scope encompasses cutting-edge research and development, education and applications.
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IMPULSE NOISE MITIGATION TECHNIQUES FOR OFDM RECEIVERS AND THEIR APPLICATION IN DIGITAL VIDEO BROADCASTING

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 J. Armstrong, H. A. Suraweera, C. Chai, M. Feramez
 Although multicarrier communication systems are inherently more resistant to impulse noise than single carrier systems, impulse noise is still a significant problem in many multicarrier applications. It is a major limitation in digital video broadcasting (DVB) systems which use orthogonal frequency division multiplexing (OFDM). This paper describes two different approaches which can be used in OFDM receivers to reduce the effect of impulse noise. The simplest approach is to try to identify received time domain samples which are affected by impulse noise, and to clip or null these samples. This is shown to be ineffective except in cases of extremely impulsive noise. A decision directed impulse mitigation scheme is then described. In this algorithm the noise component in each received input sample is estimated based on preliminary decisions on the transmitted data. When the estimate is large enough to indicate that impulse noise is present in the sample, the estimated noise component is subtracted from the input sample before final demodulation. Simulation results are presented for the DVB parameters showing that the technique is very effective for a wide range of levels of impulse noise. The algorithm involves non linear processing in both the time and frequency domains. This paper presents results showing how performance depends on the threshold levels for impulse noise detection.

BASELINE WANDER EFFECT ON INDOOR WIRELESS INFRARED LINKS OPERATED BY DUAL HEADER PULSE INTERVAL MODULATION

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 Z. Ghassemlooy, N. Aldibbiat
In indoor infrared wireless environment the system performance is affected by the presence of interference from artificial light sources, which can be reduced by employing an electrical high pass filter (HPF). But filtering will result in an interference known as baseline wander. The severity of baseline wander highly depends on the type of modulation technique. This paper discusses the effect of artificial light sources on indoor infrared systems employing dual-header pulse interval modulation (DH-PIM). The paper examines the effect of changing the cut-on frequency of the HPF on the optical power requirement and penalty of diffuse and non-diffuse infrared wireless links for different bit rates. Results presented are compared with other modulation techniques. It is shown that DH-PIM is more susceptible to the effects of baseline wander than pulse position modulation (PPM) and digital pulse interval modulation (DPIM). This is because DH-PIM power spectral density is higher at DC and low frequency region. However, compared with on-and off keying (OOK), DH PIM offers improved performance.

IMPROVING PRE-POST RAKE SCHEMES FOR DS/CDMA MOBILE COMMUNICATIONS

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G. Giunta, L. Vandendorpe, F. Benedetto
A technique known as Pre-Post-Rake has been recently proposed in the field of mobile communications. It provides a capacity increase in the downlink by means of alternative solution to the standard Rake processing and to the Pre-Rake approach. In this paper we focused our work on the Pre-Post-Rake and presented a new Pre-Post-Rake scheme that acts as a multi-path channel equalizer. Compared with conventional methods, it reduces the effect of interferences and further improves the performance, in both single user and multi-user environments. The penalizing of this new method is just little extra computational complexity which can be compensated by a reasonable capacity gain.

DESIGN OF A HIGH-SPEED WLAN ADAPTIVE EQUALIZER: IMPLEMENTATION ISSUES

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G. Caffarena, A. Fernández, C. Carreras, J. A. Lopez, O. Nieto-Taladriz

In this paper we address the implementation of a time-varying channel equalizer for Orthogonal Frequency-Division Multiplexing (OFDM) based Wireless Local Area Network (WLAN) systems on Field-Programmable Gate Array (FPGA) devices. A Recursive Least-Squares (RLS) equalizer working in conjunction with Adaptive Bit-Loading (ABL) pre-equalization is designed for a 200 Mbps WLAN system. We present a design methodology that allows efficiently traversing the path from specification to implementation. This methodology is strongly based on the introduction of target technology information at early stages of the design process, thus reducing the size of the design space and achieving good results in standard times. Special attention is given to the quantization process, being one of the main goals to reduce its computation time. Moreover, implementation results on Xilinx Virtex-II devices are provided.

BUILDING SPACE-TIME TRELLIS CODES BY SET-PARTITIONING : (TURBO) SUPER ORTHOGONAL SPACE TIME TRELLIS CODES

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 G. Ferre, J. P. Cances, V. Meghdadi, J. M. Dumas
This paper introduces new variations about the codes recently introduced by Jafarkhani et al. named Super Orthogonal Space Time Trellis Codes (SOSTTC). Using powerful set partitioning rules, these codes are able to combine the coding advantage of STTC’s together with the advantage diversity of STBC. This partitioning is based mainly on the determinant criterion introduced first by Tarokh. Jafarkhani proposed, in the case of two transmit antennas, a general framework for the construction of SOSTTC with maximum coding rate equal to 1. The obtained results are quite outstanding with simple trellises. Recently, he extended his previous results to the case of four transmit antennas with a quasi orthogonal Hadamard based Space Time Block Code. In this paper we propose a new application field of these codes in the context of turbo encoding schemes with parallel concatenation. We obtain excellent performances since the turbo codes enable to work within 1.2-1.3 dB from the theoretical outage capacity.

THE GENERALIZED MAX-MIN FAIRNESS POLICY BASED ON LINEAR PROGRAMMING

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M. Logothetis, I. Moscholios, G. Kokkinakis
Most of elastic traffic calls require rates between certain limits, while it is essential for a bandwidth allocation mechanism to allocate the available bandwidth in a fair manner among elastic calls. Therefore, the minimum and maximum bandwidth requirements of calls have to be taken into account in a bandwidth allocation process. Such a process is the Generalized Max-Min Fairness policy (GMM). The GMM policy has been described without mathematical support in a five-step procedure, in which the fairness criteria are given without coming into details as far as its computer implementation is concerned. In this paper, we present the GMM policy in a clear mathematical way, based on Linear Programming (LP). The proposed new algorithm is directly convertible into computer software. Due to its high complexity, we proceed to a simplified version of it, which is suitable for real-time applications. By the simplified version the resultant bandwidth allocation does not always meet the GMM fairness criteria and therefore is characterized near optimal. To clarify the proposed new (optimal) GMM algorithm, we present selected numerical examples on well-established testbed networks. The near optimal GMM algorithm is evaluated by comparing its results with the results of the GMM algorithm.

ON THE USE OF CYLINDRICAL REFLECTORS TO IMPROVE THE PERFORMANCE OF 3-D CORNER REFLECTOR ANTENNA

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 S. M. Alhossin, B. S. Sharif, E. G. Chester
This paper reports on the improvement achieved in antenna gain by incorporating three cylindrical reflectors within a V-shaped corner reflector antenna (V-SCRA). Two reflector antennas are reported. The first is created by replacing the corner with a three cylindrical reflecting surface. Simulation results demonstrate a 5 dB increase in gain, low input reactance and very low sidelobes. The same approach is also applied to the three dimensional corner reflectors antenna. In this case, simulations demonstrate 4 dB gain improvements and lower sidelobes with reference to single cylindrical corner reflector. The input impedance is compatible with 50-75 Ohm coaxial cables.

TELETRAFFIC MODEL OF MOBILE RADIO NETWORKS WITH OVERLAPPING MICROCELLS

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L. Badia, M. Zorz
Overlapping coverage of nearby base stations is exploited in order to improve the performance of micro-cellular mobile radio networks. A teletraffic model is developed and the performance is analyzed for the network scenarios when overlapping coverage is and is not utilized. Furthermore, several handover priority policies are considered in the analysis. The grade of service of the network is gauged in terms of the estimation of call blocking rate as well as handover failure probability. Numerical results show that overlapping increases network capacity and improves its performance.

ERROR RECONSTRUCTION FUNCTIONS OF RESONANT GAUSSIAN PROCESSES WITH JITTER SAMPLING

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 V. A. Kazakov , D. Rodriguez
In this paper, the Sampling-Reconstruction Procedure of some Gaussian processes with an arbitrary number of samples is investigated. The models of the Gaussian processes represent principally the features of the processes with simple and double resonance. All or some samples can have the independent jitter. The probability density function of the jitter is characterized by the Beta-distribution and by some discrete laws. The method of the investigation is based on the conditional mean rule. The types of the covariance functions and the types of the Beta distributions are changed. The minimum error reconstruction functions are calculated for some new examples.

A NEW FRAMEWORK FOR DESIGNING LINEAR-PHASE FIR FILTERS BASED ON EXTENDED LEAST SQUARE ERRORS

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M. Saadatmand-Tarzjan, K. Mohamedpour

In this paper a new iterative algorithm based on least square error method (LS) called extended LS (ELSE) is proposed to automatically design linear-phase FIR filters with any desired frequency response (DFR) and limited deviations. Minimizing a cost function that is defined based on the desired filter specifications including DFR and threshold of acceptable deviations (TAD), is the main idea of ELSE. In contrast to the other typical filter designing methods, defining the transition bands is not necessary in ELSE. Moreover, ELSE regulates the convergence rate by an automated approach that was utilized in neural networks; and it approximates the filter degree using an increasing-decreasing approach. In simulations, ELSE shows significant performance compared to LS though it may be more computationally complex. Also, it supplies the application demands in all of the case studies.