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Topic: Frequency division multiplexing

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In the News (Wed 17 Jul 19)

  Adaptive antenna arrays for orthogonal frequency division multiplexing systems with co-channel interference - Patent ...
Orthogonal frequency division multiplexing systems may be subject to co-channel interference in a cellular mobile communications environment in which frequency reuse considerations result in the same carrier frequency being used for different communications in adjacent or nearby cells.
In an orthogonal frequency division multiplexing system, the received signals are correlated for different blocks and tones and the temporal estimation of instantaneous correlation between signals received by the ith and jth antennas, r.sub.ij [n,k], is defined as x.sub.i [n,k].cndot.x.sub.j *[n,k].
The frequency domain correlation matrix S.sub.f =WAW.sup.H, where W is a discrete Fourier transform matrix defined as shown in equation 19 and A is a diagonal matrix with the elements shown in equation 20; ##EQU9## where.times.
www.freepatentsonline.com /5973642.html   (5675 words)

  Frequency-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.
Where frequency division multiplexing is used as to allow multiple users to share a physical communications channel, it is called frequency division multiple access (FDMA).
The analog of frequency division multiplexing in the optical domain is known as wavelength division multiplexing.
www.ebroadcast.com.au /lookup/encyclopedia/fr/Frequency_division_multiplexing.html   (142 words)

 NationMaster - Encyclopedia: Frequency division multiplexing
The concept corresponding to frequency division multiplexing in the optical domain is known as wavelength division multiplexing.
Frequency Division Multiplexing FTTC Fiber To The Curb Network where an optical fiber runs from the telephone switch to a curbside distribution point close to the subscriber where it is converted to copper pair.
Frequency Division Multiplexing FTTC - Fiber To The Curb - Network where an optical fiber runs from the telephone switch to a curbside distribution point close to the subscriber where it is converted to copper pair.
www.nationmaster.com /encyclopedia/Frequency-division-multiplexing   (386 words)

 Data Communications - Frequency Division Multiplexing and Time Division Multiplexing
Multiplexing is a form of data transmission in which one communication channel carries several transmissions at the same time.
Frequency division multiplexing (FDM) is the technique used to divide the bandwidth available in a physical medium into a number of smaller independent logical channels with each channel having a small bandwidth.
The method of using a number of carrier frequencies each of which is modulated by an independent speech signal is in fact frequency division multiplexing.
www.ligaturesoft.com /data_communications/multiplexing.html   (805 words)

 Through the Wires: Compression and Multiplexing (pg. 2)
Multiplexing is a technique used in communications and input/output operations for transmitting a number of separate signals simultaneously over a single channel or line.
The device used to combine the signals is a multiplexer, and the separate signals are recovered at the end by a demultiplexer.
Multiplexing equipment is typically located in long distance companies, local telephone companies and at end-user premises, and is associated with both analog and digital services.
library.thinkquest.org /27887/gather/fundamentals/compression_and_multiplexing2.shtml   (1267 words)

 FDM: Frequency Division Multiplex and FDMA
Frequency Division Multiplexing (FDM) is a technique the carrier bandwidth is divided into sub-channels of different frequency widths, each carrying a signal at the same time in parallel.Each channel is 30 kHz.
Receivers at the receiving end separates the multiplexed signals by means of frequency passing or rejecting filters, and demodulates the results individually, each in the manner appropriate for the modulation scheme used for that band or group.
Wavelength Division Multiplex (WDM) and Frequency Division multiplex (FDM) are both based on the same principles but WDM applies to digitized wavelengths of light in optical fiber while FDM is used in analog transmission such as twisted pair telephone line, cable access, cellular, radio and TV communications.
www.networkdictionary.com /telecom/fdm.php   (267 words)

 Orthogonal Frequency-Division Multiplexing (OFDM)
The demodulation of the received radio signal to baseband, possibly via an intermediate frequency, involves oscillators whose frequencies may not be perfectly aligned with the transmitter frequencies.
Frequency offsets and symbol clock offsets, however, generally need to be tracked at the receiver.
From (16), (19) and (20), the frequency estimate is the argument of a sum of complex numbers.
www.s3.kth.se /signal/grad/OFDM/URSIOFDM9808.htm   (4617 words)

 Multiplexing Summary
Multiplexing (also MUXing) is a term used in electrical engineering to refer to a process where multiple sources of information are combined in order to ease the organization, conversion, and transportation of the material from one place to another.
Multiplexing can also be accomplished through alternating polarisation (horizontal/vertical or clockwise/counterclockwise) on each adjacent channel and satellite, however this is only applicable to wireless communications.
Multiplexing may also refer to a juggling technique where multiple objects are released from one hand at the same time.
www.bookrags.com /Multiplexing   (898 words)

 Multiplexing   (Site not responding. Last check: )
Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.
The carrier frequencies have to be different enough to accommodate the modulation and demodulation signals.
The multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.
williams.comp.ncat.edu /Networks/multiplexing.htm   (470 words)

 Method of receiving orthogonal frequency division multiplexing signal and receiver thereof - Patent 5771223
A Fourier transform circuit in a receiver performs a Fourier transform on a orthogonal frequency division multiplexing signal received through a transmission channel for each symbol to sequentially reproduce a received reference vector sequence and a received vector sequence.
Fourier transforming the orthogonal frequency division multiplexed signal obtained from the transmission channel for each of the at least one precedent symbol so as to produce a received vector sequence and a received reference vector sequence in frequency domains which correspond to those of the transmission vector sequence and the transmission reference vector sequence, respectively;
Therefore, it is an object of the present invention to provide a method of receiving an orthogonal frequency division multiplexing signal, and a receiver thereof, which can prevent the increase of errors of a branch metric even if a transmission characteristic of a transmission channel is degraded.
www.freepatentsonline.com /5771223.html   (3143 words)

 Coded Orthogonal Frequency Division Multiplexing (COFDM)
Therefore, a good way to model a carrier signal is to ignore the low frequency modulating signal and just assume that the multipaths are each high frequency sinusoids with different amplitudes due to the different distances covered (the amplitude reduces the further it travels) and relative phase angle due to the different delay.
This means that the frequency spectrum of the transmitted signal is given by the values of the complex data symbols on the subcarriers.
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.
www.digitalradiotech.co.uk /cofdm.htm   (4740 words)

 OER 166 - Wavelength division multiplexing
For example, if the multiplexer uses single-mode entrance fibers and a multimode output fiber, the coupling losses would be excessive in the reversed use.
Simultaneous multiplexing of input channels and demultiplexing of output channels can be performed by the same component: the multi/demultiplexer.
However, wavelength division multiplexers using interference filters cannot be used when the number of channels is too high or when the wavelengths are too close.
www.spie.org /web/oer/october/oct97/multiplex.html   (1826 words)

 30. Multiplexing (cont'd)   (Site not responding. Last check: )
Frequency Division Multiplexing (FDM) is an analog technique where each communications channel is assigned a carrier frequency.
FDM does not require all channels to terminate at a single location.
FDM is an analog and slightly historical multiplexing technique.
www.techbooksforfree.com /intro_to_data_com/page98.html   (151 words)

 An Overview of Multiplexing   (Site not responding. Last check: )
Multiplexing is the process where multiple channels are combined for transmission over a common transmission path.
FDM was the first multiplexing scheme to enjoy widescale network deployment, and such systems are still in use today.
A TASI multiplexer is interconnected between the PBX and the trunk facilities.
telecom.tbi.net /mux1.html   (2046 words)

 Theory of Frequency Division Multiplexing- Developer Zone - National Instruments
Frequency division multiplexing (FDM) means that the total bandwidth available to the system is divided into a series of nonoverlapping frequency sub-bands that are then assigned to each communicating source and user pair.
Disadvantages of FDM include the need for bandpass filters, which are relatively expensive and complicated to construct and design (remember that these filters are usually used in the transmitters as well as the receivers).
Another disadvantage of FDM is that in many practical communication systems, the power amplifier in the transmitter has nonlinear characteristics (linear amplifiers are more complex to build), and nonlinear amplification leads to the creation of out-of-band spectral components that may interfere with other FDM channels.
zone.ni.com /devzone/cda/ph/p/id/269   (844 words)

 OFDM Tutorial
Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system.
Multiple Input, Multiple Output Orthogonal Frequency Division Multiplexing is a technology developed by Iospan Wireless that uses multiple antennas to transmit and receive radio signals.
This process, called spatial multiplexing, proportionally boosts the data-transmission speed by a factor equal to the number of transmitting antennas.
www.wave-report.com /tutorials/OFDM.htm   (526 words)

 Frequency-Division Multiplexing   (Site not responding. Last check: )
Each analog signal can be modulated by a separate frequency (called a carrier frequency) that makes it possible to recover that signal during the demultiplexing process.
FDM can be used in broadband LANs (a standard for Ethernet also exists).
One advantage of FDM is that it supports bidirec-tional signaling on the same cable.
www.measureup.com /testobjects/MS_NetEss/5a672df.htm   (87 words)

Frequency division multiplexing (FDM) is a process that allows each signal to travel on its own unique frequency, the individual signals are then modulated by data type and are combined to form a single signal.
Frequency division multiplexing was first employed in the 1930s in telephone systems to combine multiple conversations onto one single line.
FDM has taken a backseat to time division multiplexing (TDM) with the emergence of digital telephone systems.
www.timbercon.com /Frequency-Division-Multiplexing/index.html   (106 words)

 OFDM, VOFDM, COFDM, Orthogonal Frequency Division Multiplexing
OFDM Receivers for Broadband-Transmission OFDM and the orthogonality principle, The general problem: Data transmission over multipath channels, Single carrier approach, Multi carrier approach, Orthogonal Frequency Division Multiplexing, An OFDM receiver for DVB-T, Tasks of the inner receiver and receiver structure, Channel estimation for OFDM, Performance of the complete receiver...
OFDM Tutorial Frequency division multiplexing (FDM) is a technology that transmits multiple signals simultaneously over a single transmission path, such as a cable or wireless system.
Orthogonal FDM's (OFDM) spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies.
www.palowireless.com /ofdm/tutorials.asp   (585 words)

802.11a uses orthogonal frequency division multiplexing as opposed to FHSS or DSSS.
Due to higher frequency, range is less than lower frequency systems (i.e., 802.11b and 802.11g) and can increase the cost of the overall solution because a greater number of access points may be required.
A transmission system involving modulation techniques in which several data streams are each modulated onto a different frequency, the frequencies are mixed to create a composite, and the composite signal containing all component data streams placed on the transmission medium.
www.wlandscape.net /glossary.html   (2407 words)

DWDM is a modification of TDM and FDM.
It is sometimes called wave division multiplexing It performs the same function of multiplexing data, but it uses different colored lasers to send multiple channels over the same physical line.
A multiplexer is the device that performs the actual "data compression." It works much like a switch does on a regular LAN.
www.skullbox.net /multiplexing.php   (497 words)

 CHAPTER 1   (Site not responding. Last check: )
In frequency - division multiplexing (FDM) transmission a number of baseband channels are sent over a common wideband transmission path by using each channel to modulate a different carrier frequency.
In FDM telephone systems is used SSBSC amplitude modulation to translate the signal spectrum of each baseband channel in a well-defined position of the line useful bandwidth.
At the receiving end, the incoming wideband signal is applied to a bank of band - pass filters, each of, which selects the frequency band containing the signal of one channel.
www.dsp.pub.ro /leonardo/ipa/Chapter1/Level1/SubChapter1.6/Subchapter1_6.htm   (642 words)

 [No title]
Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier transmission technique, which divides the available spectrum into many carriers, each one being modulated by a low rate data stream.
Orthogonal frequency division multiplexing (OFDM) is a special case of multicarrier transmission, where a single datastream is transmitted over a number of lower rate subcarriers.
In this paper, the maximum likelihood (ML) estimation algorithm of the integer frequency offset is derived under the assumption that the channel impairments only consist of additive noise.
www.lycos.com /info/orthogonal-frequency-division-multiplexing.html   (611 words)

CDMA is a form of multiplexing, allowing numerous signals to use a single transmission channel, optimizing the use of available bandwidth.
The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code.
FDMA is the division of the frequency band allocated for wireless cellular telephone communication into 30 channels, each of which can carry a voice conversation or, carry data of a digital service.
www.andreas-schwope.de /ASIC_s/Schnittstellen/Data_Lines/body_multiplexing.html   (1113 words)

 Orthogonal Frequency division Multiplexing (OFDM)
Orthogonal Frequency Division Multiplexing (OFDM) is a technique with a long history in multicarrier communication.
Frequency and timing synchronization are two important practical considerations in the implementation of an OFDM system.
Frequency synchronization is required to preserve the orthogonality of the subchannels and timing estimation is required for identification of the start of every new frame.
www.deas.harvard.edu /hbbcl/ofdm.html   (241 words)

 Orthogonal frequency division multiplexing/modulation communication system for improving ability of data transmission ...
Though similar to the conventional FDM (Frequency Division Multiplexing) scheme, the OFDM scheme is characterized in that it can obtain optimal transmission efficiency during high-speed data transmission by maintaining orthogonality among a plurality of sub-carriers.
In addition, the OFDM scheme has excellent frequency efficiency and is resistant to multi-path fading, thus making it possible to obtain optimal transmission efficiency during high-speed data transmission.
Further, since the OFDM scheme uses overlapped frequency spectrums, it has excellent frequency utilization efficiency, is resistant to frequency selective fading, is resistant to multi-path fading, can reduce the effects of ISI (Inter-Symbol Interference) using the guard interval, can simply design the hardware structure of an equalizer, and is resistant to impulse noises.
www.freshpatents.com /Orthogonal-frequency-division-multiplexing-modulation-communication-system-for-improving-ability-of-data-transmission-and-method-thereof-dt20060817ptan20060184862.php   (2170 words)

 [No title]   (Site not responding. Last check: )
Hence, OFDM signals are more sensitive to carrier frequency offset than the single carrier modulation signals.
In the frequency domain, multipath propagation leads to the attenuation of some of the OFDM carriers and in general, adjacent carriers may be attenuated to almost the same degree.
The time and frequency interleaving procedure ensures that bits which are adjacent in time in the sub-channel bit stream are not adjacent in time and frequency when coded onto the 1536 carrier of digital radio signal.
www.lycos.com /info/orthogonal-frequency-division-multiplexing--carriers.html?page=2   (462 words)

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