Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Orthogonal Frequency Division Multiplexing
Post: #1


Multi Carrier Modulation is a technique for data transmission by dividing a high ]bit rate data stream is several parallel low bit ]rate data streams and using these low bit rate data streams to modulate several carriers. Multi Carrier Transmission has a lot of useful properties such as delay spread tolerance and spectrum efficiency that encourage their use in untethered broadband communications. OFDM is a multi carrier modulation technique with densely spaced sub carriers that has gained a lot of popularity among the broadband community in the last few years. It has found immense applications in communication systems. This report is intended to provide a tutorial level introduction to OFDM Modulation, its advantages and demerits, and some applications of OFDM.

History Of OFDM

The concept of using parallel data transmission by means of frequency division multiplexing (FDM) was published in mid 60s. Some early development can be traced back in the 50s. A U.S. patent was filled and issued in January, 1970. The idea was to use parallel data streams and FDM with overlapping sub channels to avoid the use of high speed equalization and to combat impulsive noise, and multipath distortion as well as to fully use the available bandwidth. The initial applications were in the military communications. In the telecommunications field, the terms of discrete multi tone (DMT), multichannel modulation and multicarrier modulation (MCM) are widely used and sometimes they are interchangeable with OFDM. In OFDM, each carrier is orthogonal to all other carriers. However, this condition is not always maintained in MCM. OFDM is an optimal version of multicarrier transmission schemes.

For a large number of sub channels, the arrays of sinusoidal generators and coherent demodulators required in a parallel system become unreasonably expensive and complex. The receiver needs precise phasing of the demodulating carriers and sampling times in order to keep crosstalk between sub channels acceptable. Weinstein and Ebert applied the discrete Fourier transform (DFT) to parallel data transmission system as part of the modulation and demodulation process. In addition to eliminating the banks of subcarrier oscillators and coherent demodulators required by FDM, a completely digital implementation could be built around special purpose hardware performing the fast Fourier transform (FFT). Recent advances in VLSI technology enable making of high speed chips that can perform large size FFT at affordable price.

In the 1980s, OFDM has been studied for high speed modems, digital mobile communications and high density recording. One of the systems used a pilot tone for stabilizing carrier and clock frequency control and trellis coding was implemented. Various fast modems were developed for telephone networks.
In 1990s, OFDM has been exploited for wideband data communications over mobile radio FM channels, high bit rate digital subscriber lines (HDSL, 1.6 Mb/s), asymmetric digital subscriber lines (ADSL, 1,536 Mb/s), very high speed digital subscriber lines (VHDSL, 100 Mb/s), digital audio broadcasting (DAB) and HDTV terrestrial broadcasting.

Important Note..!

If you are not satisfied with above reply ,..Please


So that we will collect data for you and will made reply to the request....OR try below "QUICK REPLY" box to add a reply to this page
Popular Searches: code division multiplexing access, seminar on orthogonal frequency division, time division multiplexing, orthogonal matrix calculator, training report civil enggcommunication system ofdm orthogonal division multiplexing technique, time microkernel with orthogonal persistence, project matlab orthogonal laplacianfaces,

Quick Reply
Type your reply to this message here.

Image Verification
Image Verification
(case insensitive)
Please enter the text within the image on the left in to the text box below. This process is used to prevent automated posts.

Possibly Related Threads...
Thread: Author Replies: Views: Last Post
  dense wavelength division multiplexing full report project reporter 3 3,338 16-06-2014 07:00 PM
Last Post: seminar report asees
  Dense Wavelength Division Multiplexing computer science crazy 3 3,029 02-02-2013 02:20 PM
Last Post: seminar details
Music Optical Networking and Dense Wavelength Division Multiplexing Computer Science Clay 1 1,117 24-12-2012 11:21 AM
Last Post: seminar details
  OECD Policy Guidance on Radio Frequency Identification computer girl 0 411 04-06-2012 04:34 PM
Last Post: computer girl
  radio frequency identification full report computer science technology 1 1,206 14-03-2012 10:18 AM
Last Post: seminar paper
  radio frequency light sources full report project report tiger 3 5,402 06-10-2011 10:03 AM
Last Post: shibu4cool81
  Orthogonal Frequency Division Multiplexing Frequency Offset Correction full report project topics 5 3,560 19-08-2011 12:00 AM
Last Post: amadkki
Tongue Code Division Duplexing Computer Science Clay 6 3,940 16-08-2011 09:56 AM
Last Post: seminar addict
  Discrete Variable Frequency Soft Starting on DSP-based Voltage Controller-Fed seminar class 0 991 05-05-2011 11:15 AM
Last Post: seminar class
  A 130nm CMOS to Minimize area and quantization noise in frequency synthesizer seminar class 0 494 02-05-2011 02:22 PM
Last Post: seminar class