Volume 15, Issue 2, August 2012

HDBMn: A Novel Line Coding Scheme with Re-encoding Detection Assistance [Full Text]

Christos S. Koukourlis

Abstract— In this paper an alternative Line Coding technique is described. This technique belongs to the general family of modified AMI (Alternate Mark Inversion) line coding, like the HDB3 (High Density Bipolar of order 3). The name given to the proposed technique is HDBMn, i.e. High Density Bipolar Manchester of order n. For simplification purposes, it will be referred as HDBM3, i.e. n=3. The proposed scheme uses a much simpler decoder while maintains the number of transitions in the transmitted waveform. Due to the simplified receiver design a reduced BER (Bit Error Rate) is expected. One of the motivations is to show that the HDB3 coding scheme, which was adopted by the industry in RZ format during the last decades, was not optimally implemented. It will be shown that almost in all cases where an error gets in to the stream, the proposed method is superior compared to the ubiquitous HDB3, because of the straightforward decoding of the incoming signal and the error detection capability of AMI which is preserved. An additional feature here is the clock recovery at the receiver which is extracted by re-encoding the decoded data and comparing the re-encoded waveform with the input waveform in order to reduce any phase ambiguity of the recovered clock. 


Fuzzy Models for Educational Data Mining [Full Text]

Ashraf Darwish and Olga Poleshchuk

Abstract- Models of educational information processing based on semantic spaces are developed in this paper. The first model allows formalizing the results of expert evaluation of students’ qualitative characteristic with the help of fuzzy sets. The second model is developed to determine rating psoints of students in the frame of qualitative characteristics and to assign one of qualification levels to each student. The obtained rating points are used to develop a model for students’ clusterization based on the expert opinions regarding the importance of certain characteristics for the corresponding cluster. The fourth model is proposed to predict the characteristics of students and to study the relationship between these characteristics. The method of regression’s creation is based on the transformation of the input and output fuzzy numbers into intervals, which are called weighted intervals. 


NMEA-0183 sentences analysis tool from the GPS system to increase the positional accuracy [Full Text]

Juan Toloza and Nelson Acosta

Abstract—The Global Positioning System (GPS) allows locating an object in any part of the World with a certain degree of accuracy. Some precision farming activities need to operate with a sub-metric level of accuracy. This type of applications cannot work with the standard system without some prior data treatment. In this article, it is introduced a data analysis tool, either “on- line” or “off-line”, from the GPS system with the aim at assisting an user in application requiring greater accuracy that the originally provided. It is achieved a positional accuracy of ± 1 meter.


Digital terrestrial television: a golden or a missing opportunity?  
A reflection on the introduction of DTT in Portugal [Full Text]

Raquel Castro Madureira, A. Manuel de Oliveira Duarte and Raquel Matias-Fonseca

Abstract— A few months after the introduction of the digital television in Portugal, this paper intends to do a reflection on the impact of the digital terrestrial television (DTT) in the Portuguese society. Comparing in terms of broadcast TV services it analyzes the state of the country in the time immediately before and after the transition to DTT. The analysis covers such aspects as the profile of the free TV audience, the legislation associated with the implementation of DTT and the impact of that process in Portuguese society. This analysis is then contrasted with the potential alternative technological solutions that current DTT standards accommodate but that political and regulatory authorities in Portugal decided not to consider. 


Scrambling based on 2D-Compersed Wavelet Transform and permutation Matrix in Communications Systems [Full Text]

Laith Ali Abdul-Rahaim and Hussein A.Lafta

Abstract - Since a Discrete Wavelet Transformation (DWT) domain based speech scrambler retains a considerable residual intelligibility in the scrambled speech; this paper proposes a new speech-scrambling technique using compression of the o/p of DWT matrix to remove the residual intelligibility from the scrambled speech. The proposed new technique, based on the combination of an appropriate QPSK mapping method and compression wavelet transform (DWTCS). The scramble speech will be without residual intelligibility by permuting several frequency components of wavelet transform. Without residual intelligibility in the scrambled speech, the proposed QPSK system is secure from frequency domain attacks by eavesdroppers. In addition, the speech scrambler system needs only two 2D-DWT operations instead of the four required by the 1D-(DWT)-based speech scrambler in system structure. Simulation results are also presented to show the effectiveness of this proposed technique.


Carrier Sense Multiple Access/Collision Detection-Teaching Model (CSMA/CD-TM): A Step-by-Step Demonstration of the Collision Detection Mechanism [Full Text]

Jameson Mbale

Abstract—Carrier Sense Multiple Access/Collision Detection (CSMA/CD) is a mechanism used to detect and resolve collisions when multiple nodes are trying to send frames simultaneously across a network. This particular method has been difficulty to teach students in a traditional lecture format used in sub-Saharan Africa, because it is difficult to visualize. The author developed a software simulation, called Carrier Sense Multiple Access/Collision Detection – Teaching Model (CSMA/CD-TM) to visualize this mechanism. The teaching model was shown to be effective in practice, with ninety three percent (93%) of a group of forty (40) students taught with it reporting saying that the CSMA/CD mechanism was clear or very clear to them, versus only ten percent (10%) of a control group of students who were taught without the model. This was due to the fact that in this region there were not enough available tangiable resources. Much of teaching was in theory in which learners could not figure out the movement of frames, struggling to use a single medium. The students learnt most of the concept in paper and had hardly seen the infrastructure taught. The concept of detecting and resolving had been an obsolete to the learners. The demonstration further illustrated the system releasing a jamming signal to resolve the eminent collision likely to be caused by multiple frames. 


Planar Monopole CPW Fed Slot Antenna with  
Modified H-Shaped Slot for RFID, WiMAX and WLAN Applications [Full Text]

Laxmi Ray, Chiranjib Goswami, Manimala Pal and Rowdra Ghatak

Abstract— In this paper a planar monopole antenna with dual wideband resonance characteristics is presented that simultane- ously satisfies RFID and Wi-MAX applications. The proposed antenna structure consists of a rectangular monopole bevelled at the base with an offset H shaped slot and occupies an area of 32×47 mm2. The measured realized gain is about 2.4dBi in the lower band (2.38 GHz -2.72 GHz) and about 3.8 dBi in the upper band (3.63 GHz – 6.15 GHz).