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Topic: COFDM

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	Coded Orthogonal Frequency Division Multiplexing (COFDM)
		COFDM uses a very different method of transmission to older digital radio modulation schemes and has been specifically designed to combat the effects of multipath interference for mobile receivers.
		The type of error correction coding that is used in COFDM is convolutional coding and the effect of convolutional coding is that for every one bit input to the error correction encoder, more than one bit is output depending on the "code rate" being used.
		COFDM also allows different groups of bits to be protected with a different strength code rate because some bits are more important for the correct reproduction of the audio than some of the other bits.
	www.digitalradiotech.co.uk /cofdm.htm (4740 words)

	Explaining some of the magic of COFDM
		COFDM is particularly well matched to these applications, since it is very tolerant of the effects of multipath (provided a suitable guard interval is used).
		If two synchronised COFDM transmitters operate on a common frequency there will some- where be locations where the two signals will be received at equal strength (and with a relative delay, depending on the geometry of the situation, which we assume to be within the system limits).
		COFDM is a modulation scheme which is especially tailored to work well with selective channels and isolated CW (or analogue TV) interferers.
	www.bbc.co.uk /rd/pubs/papers/paper_15/paper_15.html (0 words)

	COFDM Digital Video DTC Communications
		COFDM systems have become the standard for transmission in Europe.
		COFDM transmitters involves three major components: A signal encoder, a modulator, and an RF transmitter.
		COFDM receivers act in the reverse, relying on an RF receiver, COFDM demodulator, and an MPEG 2 decoder.
	www.dtccom.com /cofdm-digital-video.html (324 words)

	OFDM (Site not responding. Last check: )
		COFDM is particularly well matched to these applications, since it is very tolerant of the effects of multipath (provided a suitable guard interval is used).
		If two synchronised COFDM transmitters operate on a common frequency there will some- where be locations where the two signals will be received at equal strength (and with a relative delay, depending on the geometry of the situation, which we assume to be within the system limits).
		COFDM is a modulation scheme which is especially tailored to work well with selective channels and isolated CW (or analogue TV) interferers.
	www.rfengineer.cc /magic_cofdm.htm (4022 words)

	COFDM Digital Microwave
		Pacific Microwave Research, Inc. is the leader in digital microwave video systems for law enforcement, first responder, Unmanned Aerial Vehicle (UAV) and Unmanned Ground Vehicle (UGV) applications where performance and reliability are critical requirements.
		uses COFDM modulation coding, which provides link performance that is superior to traditional analog systems.
		Digital microwave video is ideal for video applications where signal reflections are numerous, such as an urban environment.
	www.pmicrowave.com (0 words)

	COFDM VS 8-VSB
		In summary it would appear that the poltical legs are weakened for COFDM in the United States, and one can add to this speculation that other regions of the world seeking affiliations with a large manufacturing base to lower the cost of their own DTV decisions must now reconsider their modulation choices.
		The parameters of the COFDM system were chosen to yield the same approximate net data rate as the VSB system (19.76 Mb/s for COFDM compared to the 8VSB net data rate of 19.39 Mb/s).
		The 8VSB and COFDM receivers selected for use in the comparative field tests were carefully evaluated for typical performance areas to insure that they were the best receivers available for the test program and represented the current available state-of-the-art in DTV technology.
	www.hdtvmagazine.com /archives/mstvtestsum.html (3355 words)

	COFDM performance expectations
		For a COFDM system, assuming multipath delay is less than the guard interval, a frequency domain one-tap equalizer could be used for each subchannel to correct the amplitude and phase distortions.
		COFDM is more immune to impulse noise than single carrier system, because a COFDM signal is integrated over a long symbol period and the impact of impulse noise is much less than that for single carrier systems.
		Since COFDM signal can be treated as a series of independent and identically distributed carriers, the central limiting theorem implies that the COFDM signal distribution should tend to be Gaussian when the number of carriers, N, is large.
	wireless.per.nl /reference/chaptr05/ofdm/ofdmperf.htm (1237 words)

	8-VSB - MythTV
		COFDM needs to deal with this type of noise as well but offers a range of inner codings to deal with more disperate environments, and because of the multiple carriers the COFDM outer coding can help deal with the low level noise problem better so long as it is not spread over the whole spectrum.
		ATSC and COFDM use an outer coding which compensates for short bursts of high power noise, but the COFDM standard allows a range of codings which can be tailored to the local environment while ATSC only allows a single outer coding.
		COFDM has this problem as well, but because it uses multiple carriers and each carrier is reflected differently by each reflector the outer coding can compensate for a portion of the problem as if it were a long bursts of high power noise which covered only a portion of the channel's bandwidth.
	www.mythtv.org /wiki/index.php/8-VSB (847 words)

	DBS Adds COFDM Microwave
		The ChannelMASTER approach also adds built-in capabilities that better facilitate set-up time, particularly for portable application, by including bar/tone generators with ID and multiple inputs to allow for digital or composite video input.
		COFDM brings several advantages to microwave transmission, notably self-correction of artifacts associated with multipath resulting from reflected signals.
		So effective is this correction that COFDM is touted for use from moving vehicles.
	www.directbroadcast.com /pr27.htm (175 words)

	Media Visions - iTV \| COFDM Test
		Outdoor reception for 8VSB and COFDM were comparable, the study reported, yet 8VSB and COFDM also were about the same, which meant the COFDM receiver did not perform indoors as well as advocates predicted.
		COFDM may not be better than 8VSB, in other words, but 8VSB has big problems.
		Further COFDM study is now moot, he says, but no decision has been made if or how the remaining balance of about $1.2 million will be applied toward the "urgent" 8VSB improvements.
	www.media-visions.com /itv-cofdmtest.html (1216 words)

	Technical Articles \| COFDM vs VSB (Site not responding. Last check: )
		The discussion of COFDM versus VSB is not new to TV broadcasters in the US or in Europe, who have already rebuilt their transmission plants, or soon will, to support on-the-air digital broadcasting.
		In light of the original discussions relative to COFDM and VSB, there is still a tendency among broadcast engineers to view the two as competitive forms of modulation for ENG, which is not at all the case.
		The COFDM and single carrier QPSK/QAM values are based on an MRC CodeRunner 2 ENG van transmitter and CodeRunner 4 central receiver with the capability of switching from COFDM to an SCM4000 single carrier system.
	www.mrcbroadcast.com /tech_services/COFDM%20vs%20VSB.html (1150 words)

	Wireless Ethernet - The Next Generation
		COFDM is the basis of the new European (and soon Australian) High Definition TV broadcast standard, the European Digital Audio Broadcasting (DAB) standard, and the new 802.11-a 5 GHz band wireless LAN standard.
		The origins of COFDM go back to 1971, when a pair of very clever research engineers, Paul Ebert and S. Weinstein, both working for Bell Labs in New Jersey, discovered a curious relationship between the Fourier transform, beloved by engineers, and the behaviour of coherent FDM systems using large numbers of subcarriers.
		The FDM signal, made up of a large number of coherent (ie having a fixed frequency relationship) subcarriers, could be shown to be the Fourier transform of the digital data stream, and that the behaviour of the stack of coherent demodulators could be described by the inverse Fourier transform.
	www.ausairpower.net /OSR-0301.html (2786 words)

	COFDM
		COFDM is a spectrum efficient digital modulation scheme employing equally spaced carriers and has become the standard method for digital broadcasting.
		Individual COFDM carriers are spread across the radio channel but not all of the carriers transmit data.
		The carrier spacing is equal to the inverse of the symbol duration.
	www.drmradio.co.uk /html/cofdm.html (623 words)

	Digital Modulation
		It is because of these properties that COFDM is being exploited for other applications like wireless cameras and mobile vision links.
		COFDM spreads the digital information over a large number of orthogonal carriers, using Frequency Division Multiplex.
		COFDM does not rely on the vulnerability of a single carrier but spreads the digital information over many narrow band carriers using Frequency Division Multiplex (FDM).
	www.gigawave.co.uk /cofdm.html (1496 words)

	ISP Planet - Fixed Wireless - Technology - Broadband Mobile Wireless using COFDM
		With COFDM, the terminal device will be locked on to several cell sites at the same time, all delivering the same signal at the same frequency.
		COFDM is designed to operate in the licensed 2.3 to 2.4MHz band reserved for digital broadcast and multimedia applications.
		Dolgonos' idea is that COFDM will deliver the bandwidth to a vehicle—with the modem possibly mounted outside where reception will be better anyway—and some other wireless medium (Bluetooth?) will deliver the signal to the laptop or PDA inside.
	www.isp-planet.com /fixed_wireless/technology/mobile_broadband.html (824 words)

	What is COFDM? - a definition from Whatis.com - see also: coded orthogonal frequency division multiplexing
		COFDM is used predominately in Europe and is supported by the Digital Video Broadcasting (DVB) set of standards.
		When a signal is transmitted, it is met with obstructions such as canyons, buildings, and even people, which scatter the signal causing it to take two or more paths to reach its final destination, the television.
		COFDM is resistant to multipath effects because it uses multiple carriers to transmit the same signal.
	searchnetworking.techtarget.com /sDefinition/0,,sid7_gci331325,00.html (568 words)

	COFDM
		Realistically, COFDM ENG Systems have about half the range as analog systems, but provide a much cleaner picture, with virtually no chroma amplitude or phase changes.
		High signal levels at the receiver result in intermod between the many COFDM carriers present in a single channel COFDM Channel.
		Many times the "C" is dropped, and COFDM is referred to as OFDM.
	www.tvtower.com /COFDM.html (440 words)

	Despite FCC Rulings, US TV Stations Still Interested in COFDM
		Considering the fact that the largest supporters of COFDM own a considerable number of stations (e.g.: Sinclair 60+), mostly in markets 100 or smaller, it is easy to see how these numbers stack up.
		Each modulation system has its own merits: COFDM appears to work better close-in to the transmitter and in places where there is highly reflective structures or terrain; where as 8-VSB appears to work better at distances away from the transmitter and over longer distances.
		Last, but not least, the additional cost of a dual standard (8-VSB & COFDM) digital television receiver to a potential purchaser could stand as an additional deterrent in a marketplace where DTV receivers are already considered rather pricey.
	www.digitalbroadcasting.com /read/nl20010921/464495 (528 words)

	Digital TV.com.au :: How it Works
		Accordingly, as shown in figure 1, the COFDM implements a partitioning of the terrestrial transmission channel both in the time domain and in the frequency domain, to organise the RF channel as a set of narrow « frequency sub-bands » and as a set of small contiguous « time segments ».
		That's because the COFDM is able to use the « positive echoes » (i.e.: the ones which increase the received power), and is able to bypass the negative effects of the others.
		Accordingly, COFDM offers to the broadcasters a new way to operate their terrestrial networks : to increase the number of co-channel signal sources to improve the quality of services, inside the transmission cell.
	www.digital-tv.com.au /howitworks.html (5791 words)

	FCC Office of Engineering and Technology Issues Report on Transmission Standards for Digital Television
		They generally stated that all of the factors that have been identified regarding COFDM performance in the Sinclair demonstrations were well understood and considered at the time the DTV transmission system decision was made.
		The COFDM system, on the other hand, has better performance in dynamic and high level static multipath situations, and offers advantages for single frequency networks and mobile reception.
		In this analysis, COFDM was assumed to have an advantage in urban areas close to a station's transmitter and 8-VSB was assumed to have an advantage in fringe area coverage.
	www.fcc.gov /Bureaus/Engineering_Technology/News_Releases/1999/nret9004.html (1387 words)

	dVMo COFDM digital video radio link (Site not responding. Last check: )
		COFDM also provides a dramatically enhanced link performance in the presence of multipath signals making it highly suited to mobile applications.
		Use of a COFDM modulation scheme with a MPEG CODEC results in a multipath immune spectrally efficient signal of only 7MHz occupied bandwidth.
		Because of the nature of the COFDM signal, any amplification of the modulated signal must be very linear in its characteristics.
	www.woodanddouglas.co.uk /products/securit/dvmogen.htm (513 words)

	Army Technology - Enterprise Control Systems - COFDM Microwave Link and RF Inhibition Systems
		The benefits of COFDM technology are well known and have been acknowledged as a major step forward in video transmission.
		Having pioneered COFDM transmission from air-borne platforms in the late 1990’s ECS is now supplying fourth generation downlink systems for police and military surveillance forces.
		The COFDM mini-surveillance transmitter is a miniature, ruggedised, 1W unit designed to be easily deployed and used for street surveillance in metropolitan areas.
	www.army-technology.com /contractors/navigation/enterprise-control (715 words)

	COFDM Revisited
		This issue became a topic of discussion at the conference call of the APTS Engineering Advisory Group in mid-July where testimonials from engineers who eyewitnessed the tests confirmed that the 8-VSB transmission could not be received in densely populated areas just a few miles from the transmitter.
		The difference in quality between the COFDM and analog reception was so dramatic that if I was a viewer having the same conditions, I would gladly pay for a COFDM receiver to achieve that level of picture quality.
		There were trees in the direction of the transmitter about 200 to 300 ft away and there were airplanes crossing the RF signal path.
	www.sbe36.org /1999/0903_cofdm.html (1238 words)

	TVTechnology - RF Technology
		Because COFDM uses multiple carriers, it is possible to use channel-state information such as the signal-to-noise ratio for each carrier, for example, to determine how much weight to give the data from that carrier.
		If COFDM is so robust, why don't we just scrap 8-VSB, ignore the years of development and field-testing, and switch to DVB-T? As you may suspect, the robustness of COFDM comes at a price.
		The COFDM parameters were described as 1,705 carriers (the "2k" mode) modulated with 64 QAM, coded with 3/4 forward error correction and a 1/8 guard interval.
	www.tvtechnology.com /features/On-RF/dl_8VSB_vs_cofdm_part1.shtml (2334 words)

	Tests support 8VSB
		COFDM appears to have lost a significant battle according to a report presented in early January to a closed industry meeting sponsored by NAB and MSTV.
		COFDM signals were less receivable, scoring only 48 percent in the Washington/Baltimore area and 60 percent in Cleveland.
		At seven locations, using a COFDM signal from WBAL-DT, Ostroff reported that the COFDM receivers were easily overloaded and desensitized by 3dB to 7dB at all seven test sites.
	broadcastengineering.com /mag/broadcasting_tests_support_vsb_2 (801 words)

	smartBridges :: Wireless Network Products
		With modulation techniques like COFDM and OFDM however, most of these challenges can be solved.
		COFDM resistance to multi-path effects enables the wireless equipment to be used for wireless coverage in urban and suburban areas
		COFDM is the key feature for any wireless equipment that ensures the most benefits for the wireless service providers and enterprises.
	www.smartbridges.com /education/articles.asp?id=407 (644 words)

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