research centers


Search results: Found 17

Listing 1 - 10 of 17 << page
of 2
>>
Sort by

Article
ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING BASED ON MULTIWAVELETS

Authors: Dr. Walid A. Mahmoud --- Dr. Saad N. Abdul Majed
Journal: Journal of Baghdad College of Economic sciences University مجلة كلية بغداد للعلوم الاقتصادية الجامعة ISSN: 2072778X Year: 2008 Issue: 16 Pages: 328-339
Publisher: Baghdad College of Economic Sciences كلية بغداد للعلوم الاقتصادية

Loading...
Loading...
Abstract

n this paper a new proposed structure for the Orthogonal Frequency Division Multiplexing (OFDM) system will be studied, which will be based on a different approach, an OFDM system was modeled using MATLAB to allow various parameters of the system to be varied and tested. The aim of doing that simulation is to measure the performance of OFDM under different channel conditions.


Article
Mitigate PAPR Effect in Optical Orthogonal Frequency Division Multiplexing Using Companding Technique

Authors: Mohammed A. Husein --- Sinan M. Abdul Satar --- Ali n. Kareem
Journal: IRAQI JOURNAL OF COMPUTERS,COMMUNICATION AND CONTROL & SYSTEMS ENGINEERING المجلة العراقية لهندسة الحاسبات والاتصالات والسيطرة والنظم ISSN: 18119212 Year: 2018 Volume: 18 Issue: 3 Pages: 60-69
Publisher: University of Technology الجامعة التكنولوجية

Loading...
Loading...
Abstract

orthogonal frequency division multiplexing (OFDM) is emerging asthe leading technology for high data rates. The OFDM based on multicarriertransmission that transforms a wideband channel into a group of thin-bandchannels. The high peak to average power ratio (PAPR) considers the maindrawback factor in this system, so the companding technique modifies theamplitude of OFDM signal to reduce this factor. The proposed A-lawcompanding technique has been implemented in intensity modulation/directdetection optical orthogonal frequency division multiplexing (IM/DDOOFDM).The proposed companding scheme guarantees the improvedperformance in terms of bit error rate (BER) and quality factor (QF) whilereducing PAPR effectively and efficiently by modifying the amplitude of thetransmitted signals. Our results confirm that the suggested scheme exhibits agood ability to reduce PAPR and a good BER performance based on the use theA factor. At the complementary cumulative distribution function (CCDF) of 10-3, the PAPR value of our proposed scheme is about 4.4 dB lower than those ofun-companded signal at best control factor used of A at 87.6, accordingly theQF is 2.5 dB and the BER is 6.2×10-3 at a distance 900km without anyequalization technique or training sequence or any channel estimation.


Article
Performance Of Channel Estimation For (OFDM) System Based On Block-Type Pilot Arrangement In Rayleigh Fading Channel

Authors: Maha George Zia Maha George Zia Maha George Zia مها جورج زيا --- Fadia Noori Al-Nuaimy فادية نوري
Journal: Journal of Engineering and Sustainable Development مجلة الهندسة والتنمية المستدامة ISSN: 25200917 Year: 2011 Volume: 15 Issue: 1 Pages: 18-37
Publisher: Al-Mustansyriah University الجامعة المستنصرية

Loading...
Loading...
Abstract

Recently, the superimposed pilot channel estimation has been proposed for wireless communications, where the pilot symbol sequence is superimposed on a data symbol sequence and transmitted together, and thus it has higher spectral efficiency. The channel estimation for orthogonal frequency division multiplexing (OFDM) system based on pilot arrangement over frequency selective Rayleigh fading channel is presented. The estimation of the channel is based on least square (LS) and minimum mean square error (MMSE) estimators. In this work, two schemes of pilot arrangement are proposed; pilot aided form (3) and pilot aided form (1). The bit error rate (BER) performance of superimposed pilot channel estimation is compared with the two proposed schemes by simulation. The simulation results show that the superimposed pilot channel estimation outperforms pilot aided form (3), while pilot aided form (3) outperforms pilot aided form (1) under frequency selective fading channel for both MMSE and LS estimators.

مؤخرا,تخمين القناة لترتيب الحاملات نوع (superimposed ) قد قدمت للاتصلات اللاسلكية, وان ترتيب رموز الحاملات الموجهه نوع(superimposed ) ورموز البيانات ترسل سوية وتكون ذات كفاءة طيفية عالية. تخمين القناة بنظام التقسيم الترددي المضاعف المتعامد والمستند على ترتيب الحاملات الموجهه قد اظهرت في قناة الخفوت الانتقائية التردد نوع (Rayleigh ) . ان تخمين القناة استند على استخدام خوارزمية التخمين التربيعي الضئيل (LS) والتخمين باقل معدل خطاء تربيعي (MMSE). في هذا العمل ,تم اقتراح تشكيلين مختلفين من ترتيب الرموز الموجهه الاول يسمى التشكيل الثالث للرموز الموجهه (form3) والثاني يسمى التشكيل الاول للرموز الموجهه (form1) وقد تم اختبار اداء نسبه معدل الخطاء (BER) في ترتيب الحاملات الموجهه لتخمين القناة نوع (superimposed) وقورنت مع التشكيلن المقترحين بواسطة نظام التحليل. ان تحليل النتائج اظهر ان تخمين القناة باستخدام ترتيب الحاملات الموجهه نوع (superimposed) يكون افضل بالاداء عن التشكيل الثالث, وان التشكيل الثالث كان افضل بالاداء عن التشكيل الاول في قناة الخفوت الانتقائية التردد بواسطة استخدام خوارزميتي النخمين(LS) وكذالك (MMSE).


Article
DESIGN OF COFDM SYSTEM IN DIGITAL MOBILE COMMUNICATION
للاتصالات الرقمية المتنقلة COFDM تصميم نظام

Author: Ahmed Obaid Aftan احمد عبيد عفتان
Journal: Al-Qadisiyah Journal for Engineering Sciences مجلة القادسية للعلوم الهندسية ISSN: 19984456 Year: 2010 Volume: 3 Issue: 4 Pages: 413-424
Publisher: Al-Qadisiyah University جامعة القادسية

Loading...
Loading...
Abstract

In this paper I proposed a model for COFDM (coded orthogonal frequency division multiplexing) based on OFDM structure with TCM coding block and with Higher constellation modulation schemes (BPSK, QPSK, 16-QAM, QASK)
Computer simulation models with Matlab system for performance assessment over the effects of channel like noise (AWGN) and multi-path fading channel such as (Rayleigh distribution)
As a result these models of proposed COFDM have better gains in dB at the receiver output under ideal and Rayleigh fading channel and some features like high data rate up to 20MHz at carrier frequency 1GHz, robust to channel propagation effects, increasing resistance to types of interferences, and provide the security by hid the signal from eavesdropper.
These features make the proposed model more suitable to use with wireless communication for 4G (fourth generation) digital mobile communication

في هذه البحث, اقترحت نموذج COFDM ترميز التقسيم الترددي المتعامد والمستند على تقنية OFDM بتشفير الكتلة مضافا الى ذلك الترميز نوع TCM للنموذج المقترح واستخدمت في هذا النموذج المقترح عدة انواع من تقنيات التضمين الرقمي هـــــــي ((BPSK, QPSK, 16-QAM, QASK .تم إعتماد برنامج MATLAB لمحاكاة وإختبار أداء النموذج المقترح COFDMفي هذا البحث وملاحظة تأثيرات القناة عليها مثل , الضوضاء البيضاء AWGN وتأثيرات توهين تعدد المسار Multi-Path Fading Channel مثل ( Rayleigh distribution) حيث بينت النتائج ان النموذج COFDM وباستخدام نوع التضمين QPSK ونظام الترميز TCM code هو الافضل والاقوى في العمل ويعطي معامل ربح للنظام اكثر من غيرة تحت تأثيرات القناة المتعددة والتداخلات وبالنتيجة فان تقنية COFDM تمتلك بعض المميّزات منها القدرة العالية على نقل البيانات تقدر حوالي 20MHz فما فوق , متانة تجاه تاثيرات القناة , ممانعة عالية لانواع التداخلات وتزودنا كذلك بإمكانية الحماية الامنية للمعلومات وذلك بإخفاء الاشارة عن المتنصتين. هذه المميّزات تجعل النموذج المقترح مناسباَ بشكل كبير لغرض الاستعمال في انظمة الجيل الرابع 4G للاتصالات اللاسلكية النقالة .


Article
A New Technique for PAPR Reduction in OFDM System

Author: Ahmed K. Abed احمد كريم عبد
Journal: University of Thi-Qar Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 26645564/26645572 Year: 2011 Volume: 2 Issue: 2 Pages: 41-51
Publisher: Thi-Qar University جامعة ذي قار

Loading...
Loading...
Abstract

Orthogonal frequency division multiplexing (OFDM) is an attractive technique for modern wireless communication. One major drawback of orthogonal frequency division multiplexing schemes is the high peak to average power ratio (PAPR) of the output signal. Selecting mapping (SLM) and partial transmit sequences (PTS) are two important techniques for reducing PAPR, but they need to transmit side information to indicate how the transmitter generates the signals. In this paper, we proposed an efficient technique to reduce PAPR in OFDM system. For this technique, circular shifter used to produce K cyclic sequences from the same information sequence. These sequences XOR with K randomly generated keys, the same keys used in receiver side to detect data. The sequence with the lowest PAPR among K sequences is chosen for transmission. Side Information (SI) is coded using Hamming code and embedded into the information sequence. Computer simulation tests have been applied on BPSK and N= 64 subcarriers OFDM system with the proposed method. Moreover, this system will be evaluated under the effect of AWGN channel. The results exhibit the ability of such technique to reduce the PAPR without major effect on the system performance as compared with the conventional OFDM technique. The PAPR of OFDM signal is further reduced by 4–5 dB by this technique.


Article
Partial Transmission Sequence of Multi-Carrier Modulation

Author: Abdulgaffar S. M. عبد الغفار سويلم مهوس
Journal: University of Thi-Qar Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 26645564/26645572 Year: 2011 Volume: 2 Issue: 2 Pages: 87-92
Publisher: Thi-Qar University جامعة ذي قار

Loading...
Loading...
Abstract

Partial Transmission Sequence (PTS) method proposed is one of the methods to reduce the Peak to Average Power Ratio (PAPR) of Orthogonal Frequency Division Multiplexing (OFDM) system. In which each symbol of OFDM in the frequency domain is divided into sub blocks and each one, multiplied by a phase factor to rearrange the origin symbol to a version with the lowest PAPR. This method is based on changing the phase of each sub blocks to reduce the probability of occurrence high PAPR. The nonlinear behavior of the phase affect's the accuracy of reduction which makes it different as compared with this method.
In this paper, a proposed method is suggested to reduce the complexity of such method


Article
Design of Space Time Trellis Coded OFDM

Authors: Ismael Shenan Dshar --- S. M. Abbas
Journal: Journal of Engineering مجلة الهندسة ISSN: 17264073 25203339 Year: 2008 Volume: 14 Issue: 3 Pages: 2684 -2698
Publisher: Baghdad University جامعة بغداد

Loading...
Loading...
Abstract

Space Time Trellis Code (STTC) is a technique that can be used to improve the performance of the Orthogonal Frequency Division Multiplexing (OFDM) system over wireless channels by providing both coding gain and diversity gain. STTC is combined from two codes, Trellis Code Modulation (TCM) as an inner code and Space Time Block Code (STBC) as an outer code. TCM which combines the choice of a modulation scheme with that of a convolutional code provides the coding gain, and the other code provides the diversity gain. Simulation is done over flat fading and frequency selective Rayleigh fading channel for Eight Phase Shift Keying (8-PSK) TCM. It found that the best results are obtained for the case of two transmitters and three receivers which have a gain of about 18dB over that without STBC.

نظام الترميز الشعيري الزماني المكاني (STTC) هو تقنيه يمكن استخدامها لتحسين فعالية الاتصالات اللاسلكية خلال قنوات اللاسلكية بتزويد النظام بكل من ربح الترميز و ربح التنوع. STTC يتركب من نظامين ترميزيين، التضمين ألترميزي الشعيري (TCM) كترميز داخلي و الترميز المكاني الزماني (STBC) كترميز خارجي. التضمين ألترميزي الشعيري (TCM)والذي يتم الحصول عليه بجمع عمليتي التضمين (Modulation) و الترميز الشعيري (Convolutional code) يزود النظام بربح الترميز و الترميز الآخر يزود النظام بربح التنوع. استخدمت المحاكاة عبر قناة استواء اخفاتي وقناة اختيار اخفاتي نوع (Rayleigh) ل (8-PSK) TCM. وجدت أفضل النتائج في حالة استخدام جهازي إرسال و ثلاثة أجهزة استلام (2TX-3RX) والتي تحتوي على 18ديسيبل.


Article
The Relationship between Data Transfer Rate and Distance in Power Networks Modems

Author: Salih H. Mahmood
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2018 Volume: 36 Issue: 6 Part (A) Engineering Pages: 620-627
Publisher: University of Technology الجامعة التكنولوجية

Loading...
Loading...
Abstract

With the rapid growth of communication networks, reliable and economical communication systems are needed and can be implemented in buildings. PLC uses electrical wiring to transmit information and provides high-speed and cheap data communications, such as home networks and Internet access. PLC is a hostile environment for communication, making communication signals spread difficult and experiencing significant challenges such as noise, attenuation and interference. This research focus on the challenges of communications via power lines such as distance and stability. Performance factors are tested and studied through the actual application of communication networks by connecting modems and computers in the network via power sockets to test the impact of distance on information transmission. The low data transfer rate when increasing the distance was clear, which means that the data transfer is inversely proportional to the distance, there was also a difference in stability when actual data are transferred and in the case of non-actual data transfer, as described later in the practical part. In order to reduce the effect of long distances and to overcome attenuation requires the use of high-speed modems and implements advanced modulation technique such as OFDM that applied in the PLC systems.Keywords: Local area


Article
Efficient T-OOFDM System to Mitigate the Dispersion of Long-Haul Optical Fiber Channel at WANs

Author: Mohammed Shweesh Ahmed
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 3 Pages: 5-11
Publisher: Tikrit University جامعة تكريت

Loading...
Loading...
Abstract

Due to its attractive features, the utilization of fiber optics as a transmission medium with various applications is increased rapidly. In despite, when signals are transmitted with high data rates through ultra-long haul distances of single-mode fiber (SMF), which is usually used at wide area networks (WANs), the nonlinear dispersion of signals is raised. This phenomenon leads digital pulses to interfere with the adjacent pulses. In this paper, an optical orthogonal frequency division multiplexing based T-transform (T-OOFDM) system is proposed to mitigate the effect of fiber dispersion significantly and reduce the peak-to-average power ratio (PAPR) of the transmitted signal when compared with conventional optical OFDM (OOFDM) system. Simulations results confirmed by the analytical analysis demonstrated that the detrimental effects arising from fiber channel dispersion on the subcarrier orthogonality of the transmitted signals can be efficiently minimized by using T-OOFDM system. Moreover, the peak of the transmitted signal will be considerably reduced whilst preserving the average power of signals.


Article
Performance Evaluation of DHT Based Optical OFDM for IM/DD Transmission Over Diffused Multipath Optical Wireless Channel

Author: Hussein A. Leftah
Journal: Iraqi Journal for Electrical And Electronic Engineering المجلة العراقية للهندسة الكهربائية والالكترونية ISSN: 18145892 Year: 2019 Volume: 15 Issue: 1 Pages: 72-75
Publisher: Basrah University جامعة البصرة

Loading...
Loading...
Abstract

Optical OFDM based on discrete Hartley transform(DHT-O-OFDM) has been proposed for large-size data mappingintensity modulation direct detection (IM/DD) scheme as an alternativeto the conventional optical OFDM. This paper presents aperformance analysis and evaluation of IM/DD optical DC-biasedDHT-O-OFDM over diffused multipath optical wireless channels.Zero-padding guard interval along with minimum mean-squareerror (MMSE) equalizer are used in electrical domain after thedirect detection to remove the inter-symbol interference (ISI)and eliminate the deleterious effects of the multi-path channels.Simulation results show that the ZP-MMSE can effectively reducethe effects of multi-path channels. The results also show that theeffects of optical wireless multi-path channel become more seriousas the data signaling order increases.

Listing 1 - 10 of 17 << page
of 2
>>
Sort by
Narrow your search

Resource type

article (17)


Language

English (16)

Arabic and English (1)


Year
From To Submit

2019 (2)

2018 (4)

2017 (1)

2015 (1)

2014 (1)

More...