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Orthogonal frequency-division multiplexing - Wikipedia, the free encyclopedia Orthogonal frequency-division multiplexing (OFDM), also sometimes called discrete multitone modulation (DMT), is a complex modulation technique for transmission based upon the idea of frequency-division multiplexing (FDM) where each frequency channel is modulated with a simpler modulation. In OFDM the frequencies and modulation of FDM are arranged to be orthogonal with each other which almost eliminates the interference between channels. OFDM modulation and demodulation are typically (as of 2001) implemented using digital filter banks generally using the Fast Fourier Transform (FFT). en.wikipedia.org /wiki/OFDM   (2671 words)

Frequency-division multiplexing - Wikipedia, the free encyclopedia The analog of frequency division multiplexing in the optical domain is known as wavelength division multiplexing. Frequency-division multiplexing (FDM) is a form of signal multiplexing where multiple baseband signals are modulated on different frequency carrier waves and added together to create a composite signal. Modern telephone systems employ digital transmission, in which time-division multiplexing (TDM) is used instead of FDM. en.wikipedia.org /wiki/Frequency-division_multiplexing   (278 words)

Coded Orthogonal Frequency Division Multiplexing (COFDM) This property is that the discrete frequency spectrum that is calculated by a DFT from a block of data samples has frequency samples that are all equally spaced in frequency, and this spacing equals 1/T, where T is the total duration of the time samples in the block. This means that the frequency spectrum of the transmitted signal is given by the values of the complex data symbols on the subcarriers. OFDM, as used on DAB and Freeview actually uses narrowband channels (subcarriers), but there are many of these narrowband channels transmitted in parallel, so the overall spectrum is wide (but this doesn't mean that it uses wideband transmission principles). www.digitalradiotech.co.uk /cofdm.htm   (4724 words)

OFDM - Orthogonal Frequency Division Multiplexing Orthogonal frequency-division multiplexing is a method of digital modulation in which a signal is split into several narrowband channels at different frequencies. Orthogonal Frequency Division Multiplexing: Divides a range of available bandwidth spectrum into a series of frequencies known as tones. Interference will degrade only a small portion of the signal and has no or little effect on the remainder of the frequency components; the overall benefit, greater throughput under more diverse situations. www.auditmypc.com /acronym/OFDM.asp   (357 words)

Orthogonal Frequency Division Multiplexing (OFDM) Forum Standards & Protocols The OFDM Forum is expecting 2003 to be an important year in the standardization of wireless equipment using OFDM (Orthogonal Frequency Division Multiplexing) technology. Membership in the OFDM Forum enables organizations to be involved in driving industry changes and setting the standards that affect their business, have access to industry trends and new developments of which they may otherwise be unaware, and have the opportunity to meet and develop relationships with industry leaders. The OFDM Forum is a voluntary association comprising dedicated leaders in the wireless industry who are committed to establishing a single, compatible global OFDM standard for delivering cost effective devices on all wireless networks and in related industries. www.caba.org /standard/ofdm.html   (605 words)

Radio - Wikipedia, the free encyclopedia Since the energy of an individual photon of radio frequency is too low to remove an electron from an atom, radio waves are classified as non-ionizing radiation. The next advance was continuous wave telegraphy, or CW (Continuous Wave), in which a pure radio frequency, produced by a vacuum tube electronic oscillator was switched on and off by a key. In frequency modulation, louder sounds at the microphone cause the transmitter frequency to fluctuate farther, the transmitter power stays constant. en.wikipedia.org /wiki/Radio   (4736 words)

DTTB: Orthogonal Frequency Division Multiplexing However, the frequency selective nature of the channel (due to both multipath and CCI) causes each of the OFDM carriers to be subject to a different signal-to-noise ratio. Since guard bands in the frequency domain are needed for filtering, a number of carriers at the edges of the 8 MHz channel are left unmodulated (virtual carriers). OFDM is proposed for DTTB transmission in Europe and Japan. wireless.per.nl /reference/chaptr01/brdcsyst/dttb/dttb1.htm   (835 words)

Globecom 2004 Orthogonal frequency division multiplexing (OFDM) has been shown to be an effective technique to combat multipath fading in wireless communications. In this context, he pioneered the application of Orthogonal Frequency Division Multiplexing to the emerging field of wireless communications. This tutorial presents the basic principles of OFDM and discusses the problems and some of the potential solutions to the practical issues in implementing such a system, including techniques for peak-to-average power ratio reduction, time and frequency synchronization, channel estimation, adaptive antenna arrays and transmitter diversity. www.ieee-globecom.org /2004/tu11.html   (560 words)

Orthogonal Frequency-Division Multiplexing (OFDM) Furthermore, to preserve the orthogonality between subcarriers, the amplifiers need to be linear. OFDM is often motivated by two of its many attractive features: it is considered to be spectrally efficient and it offers an elegant way to deal with equalization of dispersive slowly fading channels. OFDM is a type of multichannel modulation that divides a given channel into many parallel subchannels or subcarriers, so that multiple symbols are sent in parallel. www.s3.kth.se /signal/grad/OFDM/URSIOFDM9808.htm   (4617 words)

Orthogonal Frequency Division Multiplexing (OFDM) OFDM’s high degree of spectral efficiency, resiliency to interference and multi-path distortion, and existing inclusions in the leading higher rate wireless LAN standards, provides a strong based for the development of newer broadband wireless networks. With 802.11a OFDM modulation, the binary serial signal is divided into groups (symbols) of 1, 2, 4, or 6 bits, depending on data rate chosen, and converted into complex numbers representing applicable constellation points. OFDM signals typically have a time guard of 800 ns, however, which provides very good performance on channels having delay spreads up to 250 ns. www.wireless-nets.com /papers/wireless_lan_ofdm.htm   (1654 words)

J.P. Linnartz: OFDM Orthogonal Frequency Division Multiplexing (OFDM) has become the technology of choice for broadband communication in a wireless multipath environment. OFDM is significantly less sensitive to intersymbol interference, because a special set of signals is used to build the composite transmitted signal. OFDM is used in HIPERLAN Phase II, which supports 20 Mbit/s in propagation environments with delay spreads up to 1 msecond. www.wireless.per.nl /wireless/mccdma/ofdm.htm   (485 words)

58496.981223&ELEMENT_SET=DECL In an orthogonal frequency division multiplexing (OFDM) transmitter, a device embodying the invention is provided for processing digital data bits for transmission thereof to a receiver. A device, for an orthogonal frequency division multiplexing (OFDM) transmitter, for processing digital data bits for transmission thereof to a receiver, the device comprising: an outer interleaver for processing the data bits; an encoder for encoding said processed bits. The modulation technique used in OFDM systems is referred to as quadrature amplitude modulation (QAM), in which both the phase and the amplitude of the carrier frequency are modulated. www.wipo.int /cgi-pct/guest/getbykey5?KEY=98/58496.981223&ELEMENT_SET=DECL   (4401 words)

IEC: OFDM for Mobile Data Communications Orthogonal frequency division multiplexing (OFDM) is a communications technique that divides a communications channel into a number of equally spaced frequency bands. OFDM, or multitone modulation as it is sometimes called, is presently used in a number of commercial wired and wireless applications. OFDM enables the creation of a very flexible system architecture that can be used efficiently for a wide range of services, including voice and data. www.iec.org /online/tutorials/ofdm   (373 words)

Wireless Technology Evaluation: Orthogonal Frequency Division Multiplexing (OFDM) The signaling frequencies used by neighboring carriers are orthogonal to each other, which minimizes false detection of a signal on a neighboring carrier frequency. OFDM is a spread spectrum flavor of modulation that uses a large number of discrete carriers within a given bandwidth. A recent demonstration of OFDM showed that even when using an antenna that was not optimally located, it was possible to receive multi-megabit data streams up to a couple of miles away while driving. www.dis.anl.gov /is/wireless_ofdm.htm   (437 words)

OFDM (Orthogonal Frequency Division Multiplexing) (Linktionary term) OFDM is a multicarrier modulation (MCM) scheme in which many parallel data streams are transmitted at the same time over a channel, with each transmitting only a small part of the total data rate. OFDM is a transmission technique that has been around for years, but only recently became popular due to the development of digital signal processors (DSPs) that can handle its heavy digital processing requirements. OFDM is being implemented in broadband wireless access systems as a way to overcome wireless transmission problems and to improve bandwidth. www.linktionary.com /o/ofdm.html   (350 words)

Orthogonal Frequency Division Multiplexing Coded Orthogonal Frequency Division Multiplexing (COFDM) has captured the imagination of the engineers who are defining the current generation of digital broadcast systems. The OFDM spectrum can be visualised as a grid with time along one axis and narrow frequency bands along the other. In practice each frequency band will have a single carrier that is modulated in amplitude and phase using schemes such as Quadrature Amplitude Modulation (QAM) and Phase Shift Keying (PSK). www.radioeng.co.uk /ofdm.html   (366 words)

622-Mbps Orthogonal Frequency Division Multiplexing Modulator As part of the continuing effort to advance the state-of-the-art in satellite communications and remote sensing systems, Lewis is developing a programmable Orthogonal Frequency Division Multiplexing (OFDM) modulator card for high-data-rate communication links. The Communications Technology Division at the NASA Lewis Research Center is developing advanced electronic technologies for the space communications and remote sensing systems of tomorrow. The OFDM modulator is particularly suited to high-data-rate downlinks to ground terminals or direct data downlinks from near-Earth science platforms. www.grc.nasa.gov /WWW/RT1998/5000/5650nguyen.html   (208 words)

OFDM Orthogonal frequency-division multiplexing (OFDM) is a multi-carrier technique for simultaneously transmitting digitally modulated signals over several parallel channels. L.J. Cimini, Jr., “Analysis and simulation of a digital mobile channel using orthogonal frequency division multiplexing,” IEEE Trans. S.B. Weinstein and P.M. Ebert, “Data transmission by frequency-division multiplexing using the discrete Fourier transform,” IEEE Trans. www.csee.wvu.edu /wcrl/ofdm.htm   (236 words)

Title page for ETD etd-11132004-013015 For MIMO-OFDM systems, we propose a subspace tracking based approach that can exploit the frequency correlations of the OFDM system to reduce the feedback rate. OFDM is a promising technique for high-data-rate wireless communications because it can combat inter-symbol interference (ISI) caused by the dispersive fading of wireless channels. To calculate weights for interference suppression, we propose a polynomial-based parameter estimator to combat the severe leakage of the DFT based estimator due to the small size of the cluster. etd.gatech.edu /theses/available/etd-11132004-013015   (351 words)

OFDM definition - Wi-FiPlanet.com (pronounced as separate letters) Short for Orthogonal Frequency Division Multiplexing, an FDM modulation technique for transmitting large amounts of digital data over a radio wave. OFDM works by splitting the radio signal into multiple smaller sub-signals that are then transmitted simultaneously at different frequencies to the receiver. OFDM reduces the amount of crosstalk in signal transmissions. wi-fiplanet.webopedia.com /TERM/8/OFDM.html   (133 words)

Electronic News: A Rare Opportunity - Orthogonal Frequency Division Multiplexing WIDESPREAD DEVELopment of Orthogonal Frequency Division Multiplexing(OFDM) technology for application in the 5GHz Unlicensed National Information Infrastructure (UNII) bands, combined with a recent Federal Communications Commission (FCC) decision affecting the 2.4GHz ISM band, has created a unique opportunity for the wireless LAN industry. The industry may be converging on OFDM as the technology-of-choice for high-rate WLAN applications in both the 2.4GHz and 5GHz bands. OFDM systems are now poised to launch at 5GHz. www.findarticles.com /p/articles/mi_m0EKF/is_38_47/ai_78437256   (421 words)

IRL - Communication system using Orthogonal Frequency Division Multiplexing (OFDM) Orthogonal frequency division multiplexing (OFDM) is a communications modulation technique of increasing importance on which many existing and emerging standards are based. Communication system using Orthogonal Frequency Division Multiplexing (OFDM) IRL - Communication system using Orthogonal Frequency Division Multiplexing (OFDM) www.irl.cri.nz /productsandservices/products-ip/IRL-220-communication-system-using-orthogonal-frequency-division-multiplexing.aspx   (211 words)

MB-OFDM RF Design - multiband-orthogonal frequency-division multiplexing system - MB-OFDM The chosen architecture for the frequency synthesizer uses two quadrature I and Q PLLs, one generating a local oscillator frequency for the middle sub-band (3960 MHz) while the other generates a frequency equal to the sub-band spacing (528 MHz). The filter is needed to suppress the third harmonic that is generated in the 528 MHz PLL's frequency divider, which could otherwise result in in-band spurious signals being generated after downconversion in the presence of a strong interferer such as an 802.11a signal. After mixing the RF input with the local oscillator signals in the Gilbert mixer, the quadrature IF frequency outputs are filtered in a fully differential low-pass Chebyshev active filter with a nominal gain of 45 dB and a passband ripple of 2.8 dB. rfdesign.com /mag/radio_lowpower_receiver_architecture/index.html   (1740 words)

Orthogonal Frequency Division Multiplexing Popular for wireless modulation, orthogonal frequency division multiplexing (OFDM) is used in broadcast applications and "last-mile" connectivity applications such as multichannel multipoint distribution systems (MMDS) and wireless local area networks. OFDM is a multi-carrier modulation scheme that sends multiple high-speed signals concurrently on different frequencies. APEX™ devices combined with signal processing intellectual property functions are ideal for the high-throughput requirements of wireless OFDM applications. www.altera.com /products/ip/altera/s-alt-ofdm.html   (318 words)

Siemens AG - Mobile communication speed record: One gigabit per second over the air The Orthogonal Frequency Division Multiplexing (OFDM) transmission method that it employs protects the signals against most types of interference, such as the echoes that are produced when the signals reflect off buildings. In contrast to conventional individual antennas, which each transmit on a separate frequency, the MIMO method enables data rates to be multiplied by making significantly more efficient use of the costly frequency band resource. By the time the next generation of mobile communication debuts, which is expected to occur beginning in the year 2015, the need for transmission capacities for voice, data, image and multimedia is conservatively anticipated to rise by a factor of 10. www.siemens.com /index.jsp?sdc_p=cz3s3uo1232024pnflmi1218535&sdc_sid=32379314396&sdc_bcpath=1156112.s_3,&   (947 words)

Orthogonal Frequency Division Multiplexing By using an IFFT for modulation we implicitly chose the spacing of the subcarriers in such a way that at the frequency where we evaluate the received signal (indicated as arrows) all other signals are zero. all reflections of previous symbols are removed and the orthogonality is preserved. In OFDM the subcarrier pulse used for transmission is chosen to be rectangular. www.ert.rwth-aachen.de /Projekte/Theo/OFDM/node6.html   (482 words)

An Equalization Technique for Orthogonal Frequency-Division Multiplexing Systems in Time-Variant Multipath Channels A loss of subchannel orthogonality due to time-variant multipath channels in orthogonal frequency-division multiplexing (OFDM) systems leads to interchannel interference (ICI) which increases the error floor in proportion to the Doppler frequency. J. Ahn and H. Lee, "Frequency domain equalization of OFDM signals over frequency nonselective Rayleigh fading channels," Electron. In this technique, the equalization of the received OFDM signal is achieved by using the assumption that the channel impulse response (CIR) varies in a linear fashion during a block period and by compensating for the ICI terms that significantly affect the bit-error rate (BER) performance. www.comsoc.org /comm/private/1999/jan/27_47comm01-jeon.html   (325 words)

Welcome to SkyDSP, OFDM systems, telemetry, software radio OFDM allows different modulations to be used on each of the carriers in the system. This paper is an introduction to the use of OFDM in multiuser applications and some of the potential techniques that can be used to make a multiuser OFDM system a highly robust, high spectral efficient communication system. OFDM waveforms tend to have a high Peak to Average Power Ratio (PAPR). www.skydsp.com /publications   (276 words)

OFDM, VOFDM, COFDM Resources OFDM (orthogonal frequency division multiplexing) has been suggested to combat this ISI problem with reasonable complexity. High-Throughput, High-Performance OFDM via Pseudo-Orthogonal Carrier Interferometry Coding (PDF) OFDM is susceptible to poor probability of error performance in fading channels. Frequency Domain Equalization for 2-11 GHz Broadband Wireless Systems (1/2001, 304Kb, PDF) Broadband wireless systems deployed in outdoor non-line of sight environments may encounter delay spreads of over 5 to 10 us - which can cause potential intersymbol interference over 50 or more data symbol intervals. www.palowireless.com /ofdm/resources.asp   (313 words)

Amazon.com: Orthogonal Frequency Division Multiplexing for Wireless Communications (Signals and Communication Technology): Books: Ye (Geoffrey) Li,Gordon L. Stuber Orthogonal Frequency Division Multiplexing for Wireless Communications is an edited volume with contributions by leading authorities in the subject of OFDM. Orthogonal Frequency Division Multiplexing for Wireless Communications provides a comprehensive introduction of the theory and practice of OFDM. Chapter 1, by G. Stüber, briefly introduces the history of OFDM or multicarrier modulation and basic concepts of OFDM, Chapter 2, by Y. (G.) Li, presents design of OFDM systems for wireless communications, various impairments caused by wireless channels, and some other types of OFDM related modulation. www.amazon.com /exec/obidos/tg/detail/-/0387290958?v=glance   (639 words)

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