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"Konsep Orthogonal Frequency Division Multiplexing ( OFDM) adalah membagi aliran data input serial ke dalam sejumlah aliran data paralel dan mengirimkan aliran data paralel dengan rate rendah tersebut secara bersamaan. Salah satu keuntungan penggunaan OFDM dibandingkan dengan jenis modulasi lain adalah penggunaan lebar pita yang tersedia dengan lebih efisien.Simulasi dan analisa dilakukan terhadap performansi sistem OFDM pada beberapa mapper modulasi 16-my pada kondisi kanal AWGN dan kanal fading lambat. Jenis konstelasi yang digunakan adalah 16-QAM rektangular, 16-QAM star dan 16-PSK.Hasil pada kondisi kanal AWGN memperlihatkan bahwa sistem OFDM yang menggunakan 16-QAM rektangular memberikan performansi BER terbaik dibandingkan penggunaan 16-QAM star atau 16-PSK.Performansi OFDM pada kanal fading multipath dianalisa menggunakan respons impuls kanal statik. Hasil pada kedua model kanal fading multipath yang digunakan menunjukkan performansi yang relatif buruk. Algoritma forward error correction atau estimasi kanal perlu digunakan untuk mengurangi probabilitas kesalahan bit.Hasil akhir pada penggunaan kedua algoritma tersebut membuktikan bahwa pengaruh fading kanal multipath dapat dihilangkan sehingga meningkatkan performansi BER sistem OFDM.

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The concept of OFDM is to divide the serial input data stream into a number of parallel streams and to transmit these low-rate parallel streams simultaneously. One advantage of using OFDM compared to other types of modulation is better use of the available bandwidth.

The performance of the OFDM system under various 16-ary modulation mappers in AWGN and slowly fading channels are analyzed. It considers three candidate constellations : 16 rectangular-QAM, 16 star-QAM and 16-PSK.

The results for AWGN channel shows that the OFDM system using 16 rectangular-QAM gives the best BER performance compared to the same system using 16 star-QAM or 16-PSK mapper.

The performance of OFDM on multipath fading channels is analyzed using static channel impulse responses. The results of system in the two models of multipath fading channels indicate a relatively poor performance. Forward error-correcting or channel estimation algorithm is necessary to reduce the bit error probability.

The final results obtained after the use of both algorithms : convolutional coding and channel estimation, prove that fading effects can be removed, reducing almost totally the effects of the multipath channel."

"This paper will analyze the performance of adaptive slotted ALOHA DS-CDM4 over multipath fading with capture eject to increase throughput transmit data when traffic condition in saturation. To divine intervention we use algorithm to control level change transmission rate use user based on trqffic condition. Adaptive slotted ALOHA DS-CDA/L4 technique is technique access can do adaptation level transmission rate based trams condition. Using protocol access channel adaptive slotted ALOHA DS-CDAM combine between slotted ALOHA and DS-CDMA in wireless communication system. This method may users to do access simultaneously and using efficient spectrum is providential from adaptive slotted ALOHA DS-CDMA Performance of S-ALOHA DS-CDMA decrease on channel fading. To handle throughput decrease because amount bit on transmit packet, so capture effect can use to handle this problem. So effective throughput depend capture probability and probability packet success. From that result throughput adaptive slotted ALOHA DS-CDMA with capture eject on multipath fading channel increase with decrease capture ratio length bit packet and different number of path."

"Kehadiran sistem UWB telah menawarkan potensi besar untuk desain komunikasi nirkabel jarak pendek berkecepatan tinggi dengan kapasitas transfer data yang sangat besar. Hal ini dapat dicapai dengan cara melakukan eksploitasi spasial dan perbedaan multipath melalui penggunaan sistem MIMO-OFDM dan teknik simbol yang tepat. Sistem tersebut mengkombinasikan antena MIMO dan teknik OFDM yang handal dalam mentransmisikan data berkecepatan tinggi, meski pada lingkungan multipath sekalipun. Juga dapat mengatasi distorsi delay spread dan unflat fading akibat kanal multipath, sehingga dapat dicapai efisiensi spektrum dan peningkatan throughput.Pada tesis ini dilakukan penelitian tentang MIMO OFDM berbasis SVD. Pemodelan kanalnya dilakukan dengan cara menerapkan konsep dekomposisi kanal frekuensi selektif fading ke bentuk kanal paralel flat fading dalam domain frekuensi. Model kanal domain frekuensi digunakan untuk menyajikan performansi kecepatan data yang berbeda. Kemudian mengembangkan konsep decouple kanal frekuensi selektif ke dalam domain spasial dengan cara mendekomposisi kanal MIMO flat fading ke dalam kanal domain spasial orthogonal menggunakan pendekatan berbasis SVD. Selanjutnya mengkom- binasikan decouple spasial berbasis SVD dengan decouple domain frekuensi berbasis FFT untuk mendapatkan model kanal paralel UWB MIMO OFDM. Akhirnya diharapkan bahwa analisa teoritis ini dapat diaplikasikan dalam sistem komunikasi nirkabel jarak pendek berkecepatan tinggi dengan menerapkan suatu cara untuk memilih kecepatan data yang berbasis pada kondisi kanal.The emerging UWB system offers a great potential for the design of high speed short range wireless communications which fully support high data streaming capacity. This can be achieved by exploiting both spatial and multipath diversity via the use of MIMO OFDM system and proper coding techniques. The systems combine MIMO antenna and OFDM technique which reliable in high data rate transmission even in multipath environment. It also overcomes delay spread distortion and unflat fading caused by multipath channels, thus high spectral efficiency and high throughput improvement can be achieved.

This thesis studies MIMO OFDM techniques base on singular value decomposition. The channel modeling is done by applying the concept of decomposition of frequency selective fading channel into parallel flat fading channel in the frequency domain. This frequency domain channel model is used to present the performance for different data rates. Then develops the concept of decoupling of frequency selective channel into spatial domain by presenting SVD based approach to decouple flat fading MIMO channels to orthogonal spatial channels. At least, the SVD based spatial domain decoupling is combined with FFT based frequency domain decoupling to obtain UWB MIMO OFDM parallel channel model. It is finally expected this theoretical analysis can be implemented in high speed short range wireless communication systems by applying a rate selection technique base on channel condit."

"Orthogonal Frequency Division Multiplexing (OFDM) memberikan efisiensi bandwidth yang lebih tinggi daripada Frequency Division Multiplexing (FDM) biasa. Pada komunitas wireless, sistem OFDM biasanya diterapkan dengan menggunakan Discrete Fourier Transform (DFT) untuk membentuk sinyal OFDM. Akan tetapi, sistem OFDM yang menggunakan transformasi DFT (DFT-OFDM) ini mudah mengalami intersymbol interference (ISI) pada kanal multipath fading. Untuk mengurangi terjadinya ISI pada DFT-OFDM maka digunakan teknik yang disebut dengan cyclic prefix, akan tetapi penggunaannya membutuhkan bandwidth yang lebih lebar sampai 25% dan akan menambah delay. Untuk meningkatkan efisiensi bandwidth dan mengatasi ISI yang terdapat pada sistem DFT-OFDM, maka digunakanlah sistem OFDM menggunakan Discrete Wavelet Transform (DWT-OFDM). Unjuk kerja DFT-OFDM dan DWT-OFDM pada kanal AWGN dan Rayleigh fading dianalisa dalam skripsi ini. Didapatkan bahwa sistem DWT-OFDM memberikan unjuk kerja yang lebih baik dari DFT-OFDM."

"ABSTRAKSkema multipath routing dapat digunakan untuk meningkatkan toleransi terhadap fault serta meningkatkan tingkat keandalan dari jaringan. Penggunaan tingkat keandalan selama ini cenderung difokuskan sebagai sebuah target yang harus dicapai dengan level setinggi-tingginya. Penggunaan sifat path disjointness yang merepresentasikan kemiripan jalur-jalur anggota dari himpunan jalur hasil algoritma pencarian jalur multipath dapat mempengaruhi tingkat keandalan dari himpunan jalur yang dihasilkan. Pemanfaatan tingkat keandalan dan derajat divergensi yang merepresentasikan tingkat kemiripan dari jalur-jalur yang ada bisa digunakan sebagai basis untuk menghasilkan algoritma pencarian jalur yang menghasilkan himpunan jalur yang menggunakan sumber daya secara tepat guna

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ABSTRACTMultipath routing scheme can be used to improve the fault tolerance and increase the reliability level of a network. The utilization of reliability level to this date tends to be focused as a target that have to be achieved as high as possible. The use of path disjointness properties that represent similarity level in a set of path in a paths synthesis algorithm can affect the overall reliability level of the set of paths generated. Utilization of the level of reliability and the degree divergence of a set of paths can be used as a basis to develop a paths synthesis algorithm that generate a set of paths that use network resource efficiently"

"Semakin besarnya peran teknologi informasi dalam proses bisnis, menuntut semakin tingginya kebutuhan ketersediaan dan kehandalan infrastruktur jaringan, termasuk jaringan Wide Area Networking (WAN) yang mengintegrasikan jaringan kantor cabang dengan kantor pusat atau pusat data. Untuk meningkatkan ketersediaan jaringan WAN diperlukan lebih dari satu jalur koneksi (link), sehingga ketika terjadi gangguan pada link utama, jaringan WAN pada kantor cabang tersebut masih dapat berjalan. Konfigurasi pada jaringan WAN umumnya bersifat aktif-standby sehingga hanya satu link yang aktif digunakan sehingga kurang optimal. Pada jaringan WAN yang memiliki bandwidth terbatas, congestion sangat mungkin terjadi sehingga dapat menyebabkan penurunan performansi jaringan yang dapat mengganggu aplikasi kritis yang penting bagi proses bisnis di kantor cabang. Tesis ini mengimplementasikan dan menganalisis performansi jaringan WAN berbasis arsitektur jaringan SDWAN dengan simulasi menggunakan Ryu controller dan Mininet. Aplikasi sederhana link monitoring dan QoS monitoring ditambahkan untuk dapat memilihkan jalur menyesuaikan dengan kondisi performansi link. Hasil simulasi menunjukkan bahwa arsitektur SDWAN dengan multipath memiliki total throughput yang lebih tinggi dibanding dengan satu link. Dengan bandwidth pada tiap link sebesar 10 Mbps maka total throughput yang didapat mendekati 20 Mbps, 2 kali lipat dibanding ketika menggunakan satu link. Arsitektur SDWAN dengan aplikasi link monitoring dapat mendeteksi terjadinya congestion pada jaringan sehingga packet loss dan jitter yang tinggi terjadi dalam kurun waktu yang singkat (kurang dari 5 detik). Jika tanpa link monitoring packet loss dan jitter yang tinggi terjadi selama congestion berlangsung. Tanpa adanya konfigurasi QoS, aplikasi kritis mengalami peningkatan packet loss dan jitter pada saat terjadi penggunaan bandwidth yang tinggi. Adanya konfigurasi Quality of Services (QoS) dan aplikasi QoS monitoring pada jaringan SDWAN dapat menjamin aplikasi yang kritis dapat berjalan dengan baik walaupun terjadi kondisi utilitas link yang tinggi serta mengurangi waktu terjadinya penurunan throughput dan peningkatan jitter pada aplikasi biasa menjadi kurang dari 5 detik.

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The increasing digital transformation in business processes demands higher network infrastructure availability and reliability, including in wide area networks (WAN). To achieve higher availability on WAN infrastructure, organizations need multiple links from each branch to headquarter. WAN multiple links commonly are configured as an active-standby mode. The secondary link will be used in case of the occurrence of failure in the primary link. Congestion or bottleneck is a common problem in WAN infrastructure due to bandwidth limited that causes the critical application from the branch office cannot run properly. This research implements and analyzes the performance Software-Defined Wide Area Network (SDWAN) architecture in terms of throughput, delay, and packet loss from headquarter to a branch office of an organization. We proposed simple application link monitoring and QoS monitoring to do dynamic path selection based on performance link measurement. We simulated the SDWAN architecture performance using the Ryu controller and Mininet in virtual environment. The results showed that SDWAN architecture with the multipath link would increase the total throughput of users compared to using a single link. For 10 Mbps bandwidth in each link, the total throughput is almost 20 Mbps, instead of 10 Mbps in a single link. SDWAN architecture with the link monitoring application improve the performance on jitter and packet loss in a branch office when congestion occurred. The high packet loss and high jitter that lasted during the congestion only lasted in few seconds (around 5 seconds) with link monitoring. The QoS configuration can guarantee the critical applications running normally in case of high utilization or bottleneck link. The Qos monitoring reduces the duration of degradation throughput and high packet loss become less than 5 seconds. "

"Cognitive radio networks (CRN) will be widely deployed in the near future, and this SpringerBrief covers some important aspects of it, as well as highlighting optimization strategies in Resource Allocation and Spectrum Sensing in CRNs. The cognitive approach in radio access is introduced in the first part of this SpringerBrief, and then next the benefits of cooperative spectrum sensing are highlighted and a framework for studying it under realistic channel conditions is described. New exact closed-form expressions for average false alarm probability and average detection probability are derived in this scenario. A novel approximation to alleviate the computational complexity of the proposed models are also discussed.Once the spectrum opportunities are identified, efficient and systematic resource allocation (RA) shall be performed. The second part of this SpringerBrief describes the taxonomy for the RA process in CRN. A comprehensive overview of the optimization strategies of the CRN RA is also provided. The device-to-device (D2D) communication scenario is discussed, then as a case study and various optimization strategies for the application of the CR technology in the D2D realm is studied. The application of advanced geometric water-filling (GWF) approach in CRN D2D environment for optimum resource allocation is presented in detail. Numerical results provide more insight quantitatively. Overall, this book is suitable for a wide audience that include students, faculty and researchers in wireless communication area and professionals in the wireless service industry."

"This book offers students, scientists and engineers an extensive introduction to the theoretical fundamentals of digital communications, covering single input single output (SISO), multiple input multiple output (MIMO), and time-variant systems. Further, the main content is supplemented by a wealth of representative examples and computer simulations.The book is divided into three parts, the first of which addresses the principles of wire-line and wireless digital transmission over SISO links. Digital modulation, intersymbol interference, and various detection methods are discussed; models for realistic time-variant, wireless channels are introduced; and the equivalent time-variant baseband system model is derived.Since not all readers may be familiar with this topic, Part II is devoted to the theory of linear time-variant systems. The generalized convolution is derived and readers are introduced to impulse response, the delay spread function, and system functions in the frequency domain. In addition, randomly changing systems are discussed.In turn, Part III deals with MIMO systems. It describes MIMO channel models with and without spatial correlation, including the Kronecker model. Both linear and nonlinear MIMO receivers are investigated. The question of how many bits per channel use can be transmitted is answered and maximizing channel capacity is addressed. Principles of space–time coding are outlined in order to improve transmission quality and increase data rates. In closing, the book describes multi-user MIMO schemes, which reduce interference when multiple users in the same area transmit their signals in the same time slots and frequency bands."