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    Orthogonal Frequency Division Multiplexing (OFDM) merupakan teknik mudulasi untuk komunikasi wireless broadband dimasa yang akan datang karena bisa bertahan melawan frekuensi selective fading dan interferensi narrowband dan efisien menghadapi multi-path delay spread. Untuk mencapai hal huawai, OFDM membagi aliran data high-rate mejadi aliran rate yang lebih rendah, yang kemudian dikirimkan secara bersama pada beberapa sub-carrier.


    Keuntungan


    Dengan melakukan hal tersebut, durasi symbol meningkat. Keuntungan dari hal tersebut adalah jumlah dispersi waktu yang disebabkan oleh multi-path delay spread menurun secara signifikan. Selain itu, pengenalan guard time pada setiap symbol OFDM meneliminasi Inter-Symbol Interference (ISI). Pada guard time, symbol OFDM secara siklus diperpanjang untuk mengurangi Inter-Carrier Interference (ICI). OFDM dapat dianggap baik sebagai metode multiplexing maupun metode modulasi.


    Definisi


    OFDM menggunakan sub-carrier yang banyak untuk mengirimkan aliran data low rate secara parallel. Sub-carrier dimodulasikan sendiri dengan menggunakan Phase Shift Keying (PSK) atau Quadrature Amplitude Modulation (QAM) dan dibawa pada microwave carrier berfrekuensi tinggi (5 GHz). Hal ini sama dengan Frequency Division Multiplexing (FDM) konvensional atau Sub-Carrier Multiplexing, kecuali untuk kebutuhan ke-orthogonal-an antara setiap sub-carrier. Sub-carrier secara orthogonal dapat dilihat dengan dua cara, dalam domain waktu dan frekuensi. Pada domain waktu, setiap sub-carrier harus berupa bilangan integer dari siklus selama tiap interval (durasi) symbol OFDM. Dengan kata lain, jumlah siklus antara sub-carrier berbeda yang bersebelahan berbeda seperti diganbarkan gambar 2.3a.
    Pada domain frekuensi, spectra amplituda dari masing-masing sub-carrier (baik modulasi PSK maupun QAM) overlap seperti digambarkan gambar 2.3b[6]. Bagaimanapun, pada setiap spektrum sub-carrier dalam keadaan maksimum, spectra sub-carrier lainnya berada pada nol. Penerima OFDM menghitung nilai spektrum pada titik maksimum dari masing-masing subcarrier, hal ini dapat memulihkan setiap sub-carrier tanpa interferensi ICI dari sub-carrier lainnya.

    Dasar sinyal OFDM dibentuk menggunakan Inverse Fast Fourier Transform (IFFT), penambahan cyclic extension dan menampilkan penjendelaan untuk mendapatkan roll off yang lebih curam. Pada penerima, sub-carrier dimodulasi dengan menggunakan Fast Fourier Transform (FFT). Jika dibandingkan dengan system modulasi single carrier, OFDM lebih sensitive terhadap frekuensi offset dan noise phasa. Selain itu OFDM relatif mempunyai rasio data peak-to-avarege yang lebih tinggi, yang mereduksi efisiensi daya RF amplifier.


    Referensi

Kata Kunci Pencarian:

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OFDM/OFDM_ process.m at master · 2417677728/OFDM · GitHub

OFDM/OFDM_ process.m at master · 2417677728/OFDM · GitHub

OFDM Basics

OFDM Basics

What does OFDM mean? - OFDM Definitions | Abbreviation Finder

What does OFDM mean? - OFDM Definitions | Abbreviation Finder

OFDM | PDF

OFDM | PDF

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PPT - OFDM PowerPoint Presentation, free download - ID:2392138

PPT - OFDM PowerPoint Presentation, free download - ID:2392138

Simplified OFDM system | Download Scientific Diagram

Simplified OFDM system | Download Scientific Diagram

Simplified OFDM system | Download Scientific Diagram

Simplified OFDM system | Download Scientific Diagram

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ofdm

Daftar Isi

OFDM | Cox Community

Do you mean upstream OFDMA or downstream OFDM? I thought most areas had at least 1 downstream OFDM channel to be compatible with DOCSIS 3.1 and 940Mbps (AKA Go Super Fast) speed tier.

Weird issue with OFDM channel causing disconnects

From what I understand, you want to see a lot of correctable errors on the OFDM channel because that means it's running at its maximum possible speed. When you start seeing uncorrectable errors, that's when you should worry. I think the messages you're seeing are just the modem shuffling around OFDM profiles for maximum performance.

List of all CM-STATUS event type codes with explanations

The Next Codeword Pointer (NCP) is a portion of the downstream OFDM channel which is dedicated to carry information about the mapping of FEC codewords to subcarriers within a symbol. NCP is generally considered a part of the Downstream Convergence Layer. [DOCSIS PHYv3.1] includes a detailed description of the NCP.

OFDM Channel not locked - Downstream light consistently …

dave9 would be the best source but I think the OFDM(A) channels are your overall circuits. These circuits are then divided into separate channels: 32 and 4. Therefore the overall circuits wouldn't be individually locked. I could be wrong and sure I am.

Upstream OFDM is coming | Cox Community - Cox Support Forums

Basically upstream OFDM is being enabled in some areas along with a extra downstream OFDM channel. No new upstream speeds have been announced but I predict they are coming. Seems if you have 8 upstream channels you are close to an upgrade.

OFDM PLC errors on MB8600. on Firmware 8600-19.3.15.

Only Channel 33 is an issue which is OFDM PLC. All other channels have no correctable or uncorrectable errors in the last 24 hours. There are about 43 0million correctable errors on Channel 33 in the last 36 hours, no uncorrectable errors. They climb at an astonishing rate. As you may be able to tell, signal is 10.8 dBmV, SNR is 45.1.

Continuous event code 16 OFDM Profile Failure | Cox Community

Jun 19, 2024 · But event log shows continuous type 16 FEC errors with around 1 - 2 min intervals. OFDM/OFDMA Profile ID ...

OFDM channels required for Gigablast? | Cox Community

I just signed up for Gigablast and I was checking speeds. I checked my modem page on my CM1000 and I'm not seeing any OFDM channels locked. I'm seeing ~340 mbps max download speeds when doing a controlled test from my laptop wired directly into the modem. On averaging it's usually about about 300 mbps-310mbps.

OFDM Channel not locked - Downstream light consistently …

Dec 13, 2021 · OFDM Channel not locked - Downstream light consistently blinking now Exact same was posted a few months ago but the thread is locked and it failed to highlight a tangible solution. We have the same Netgear Modem CM1200, the same symptoms of constantly blinking light, and massive amounts of disconnections and lost packets.

Getting "US profile assignment change" constantly causing …

Downstream Bonded Channels; Channel ID: Lock Status: Modulation: Frequency: Power: SNR/MER: Corrected: Uncorrectables: 21: Locked ...