MC CDMA may stand for Multi carrier code division multiple access , a multiple access technology used in telecommunication systems based on OFDM . A variant of the mobile communication standard CDMA2000 , where three or more pairs of 1.25MHz radio channels are used together so that higher data rates can be achieved. disambig ... more details
Politics of Ethiopia The Oromo Federalist Democratic Movement lang am , OFDM is a political party in Ethiopia , created to further the interests of the Oromo people Oromo people. At the last legislative Ethiopian general elections, 2005 elections , on 15 May 2005, the party won 11 seats, all from the Oromia Region . The party Whip politics Whip is Mesfin Nemera Deriesa from the Mirab Welega Zone . ref http www.ethiopar.net English hopre hormemb.html Ethiopian House of Peoples Representatives Website ref The Chairman is Bulcha Demeksa . In the August 2005 Regional assembly elections, the party won 10 out of 537 seats in the Oromia Region . ref http africanelections.tripod.com et 2005state.html African Elections Database ref Bulcha Demeksa, announced in mid April that his party would boycott the second round of voting in the Ethiopian by elections, 2008 2008 Ethiopian local elections , joining a number of other opposition parties. ref http www.sudantribune.com spip.php?article26826 Ethiopia s local elections marred by opposition boycott Sudan Times website, published 21 April 2008 accessed 1 June 2008 ref Despite this, the OFDM picked up one seat in the 116 towns which held elections for their administrative councils. ref http www.waltainfo.com CurrentIssues ... 17 March 2009 ref Recent developments The OFDM recently joined forces with other Ethiopian opposition ... 2008, the OFDM accused the Ethiopian government of ignoring the ethnic conflict in western Ethiopia ... opposition calls for probe into massacre ref The OFDM called it a massacre and blamed the government as being at least an accomplice. ref http www.jimmatimes.com article.cfm?articleID 31292 OFDM Press Release The Massacre of May, 2008 , Jimma Times 21 June 2008 ref OFDM Secretary General Bekele ... which were denied by the OFDM. ref http www.amnesty.org en library info AFR25 012 2008 en Ethiopia ... been set for his trial. ref http www.jimmatimes.com article.cfm?articleId 31856 OFDM leader Bekele Jirata ... more details
Pre code may refer to Pre Hays code Hollywood film industry, see Pre Code Hollywood Pre Comics Code Authority , see also Golden Age of comics Zero forcing precoding Precoding in MIMO data transmission linearly precoded OFDM scheme, see Single carrier FDMA dab ... more details
Modulation techniques Orthogonal frequency division multiplexing OFDM is a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital .... OFDM is essentially identical to coded OFDM COFDM and discrete multi tone modulation DMT , and is a frequency ... advantage of OFDM over single carrier schemes is its ability to cope with severe channel communications ... because OFDM may be viewed as using many slowly modulated narrowband signals rather than one ... of applications The following list is a summary of existing OFDM based standards and products. For further ... by WiMedia Alliance . The OFDM based multiple access technology OFDMA is also used in several 4G ... High Speed OFDM Packet Access HSOPA , now named Evolved UMTS Terrestrial Radio Access E UTRA . Key features ..., OFDM is a specialized FDM, the additional constraint being all the carrier signals are orthogonal to each other. In OFDM, the sub carrier frequencies are chosen so that the sub carriers are orthogonality .... OFDM generally has a nearly white spectrum, giving it benign electromagnetic interference ... more sensitive to multipath interference. OFDM requires very accurate frequency synchronization ... increases, ref Robertson, P. Kaiser, S. The effects of Doppler spreads in OFDM A mobile radio systems ... Papers VTC99 Robertson Kaiser.ps Link ref and is an important factor limiting the use of OFDM ..., OFDM is popular for wideband communications today by way of low cost digital signal processing ... interference One key principle of OFDM is that since low symbol rate modulation schemes i.e., where ... of each symbol is long, it is feasible to insert a guard interval between the OFDM symbols, thus ... prefix , which is transmitted during the guard interval, consists of the end of the OFDM symbol copied into the guard interval, and the guard interval is transmitted followed by the OFDM symbol. The reason that the guard interval consists of a copy of the end of the OFDM symbol is so that the receiver ... more details
Image cyclic delay.jpg thumb right Cyclic Delay Diversity Cyclic Delay Diversity Cyclic Delay Diversity CDD is a diversity scheme used in OFDM based telecommunication systems, transforming spatial diversity into frequency diversity avoiding intersymbol interference . CDD was introduced in 2001 and can gain frequency diversity at the receiver without changing the Single Input and Single Output SISO receiver structure. The idea of CDD for OFDM had previously also been submitted as a patent application in September 2000. References Louay M.A. Jalloul and Sam. P. Alex, Evaluation Methodology and Performance of an IEEE 802.16e System , Presented to the IEEE Communications and Signal Processing Society, Orange County Joint Chapter ComSig , December 7, 2006. Available at http chapters.comsoc.org comsig meet.html A. Dammann and S. Kaiser. Performance of low complex antenna diversity techniques for mobile OFDM systems. In Proceedings 3rd International Workshop on Multi Carrier Spread Spectrum & Related Topics MC SS 2001 , Oberpfaffenhofen, Germany, pages 53 64, Sept. 2001. http www.springer.com dal home generic search results?SGWID 1 40109 22 33345316 0 ISBN 0 7923 7653 6. P. Larsson, Cyclic Delay Diversity for Mitigating ISI in OFDM systems , filed 22nd of September 2000 http www.wipo.int patentscope search docservicepdf pct 090063618006bee2?download First filed patent application , PCT Biblio. data from http www.wipo.int patentscope search en detail.jsf?docId WO2002025857&recNum 1&docAn SE2001001703&maxRec 1&office &prevFilter &sortOption &queryString FP 3A 28peter larsson 22cyclic delay diversity 22 29&tab PCT Biblio. Data WIPO . See also OFDM diversity scheme Category Radio resource management telecomm stub ... more details
Characteristics and principles of operation section. See also the list of OFDM Key features OFDM Key features . Claimed advantages over CDMA OFDM can combat multipath interference with more robustness ... users connect. Claimed advantages over OFDM with time domain statistical multiplexing Allows simultaneous ... multiple access collision avoidance is simplified. Further improves OFDM robustness to fading and interference ... simultaneously at low constant data rate. The complex OFDM electronics, including the FFT algorithm ... from power consumption point of view, while OFDM combined with data packet scheduling may allow FFT algorithm to hibernate during certain time intervals. The OFDM diversity gain, and resistance to frequency ... carrier is used in every OFDM symbol. Adaptive sub carrier assignment based on fast ... with co channel interference from nearby cells is more complex in OFDM than in CDMA. It would ... fast, this further improves the OFDM robustness to fast fading and narrow band cochannel ... user. OFDMA can be seen as an alternative to combining OFDM with time division multiple access ... space, and slots are assigned along the OFDM symbol index as well as OFDM sub carrier index. OFDMA ... broadband standard. The radio interface was formerly named High Speed OFDM Packet Access HSOPA , now ... OFDM the now defunct Qualcomm 3GPP2 Ultra Mobile Broadband UMB project, intended as a successor of CDMA2000 ... Carrier and Spread Spectrum Systems From OFDM and MC CDMA to LTE and WiMAX , 2nd Edition, John Wiley ..., India. http www.supelec.fr d2ri flexibleradio cours ofdmtutorial.pdf Short Introduction to OFDM Tutorial ... more details
, gives regular OFDM without spreading. However, it is advantageous to identify spreading code matrices ... is an NxN DFT matrix. This Circulant Identity case is a simple form of CI. Since OFDM s over sampled ... each data symbol to a cyclically shifted orthogonally positioned superposition of OFDM subcarriers. The actual ... more details
cell is a group of base stations sending using the same spreading code, or a group of OFDM transmitters .... See also Antenna diversity Cooperative diversity Macro diversity OFDM Single Frequency Networks ... more details
alliance known as Medrek. Bulcha resigned from his OFDM party s chairmanship in late 2010 but continues as an adviser for the leadership. His retirement from OFDM and his harsh criticism of Prime Minister ... more details
this property in the part of the symbol after the cyclic prefix. Use in OFDM Cyclic Prefixes are used in OFDM in order to combat multipath by making channel estimation easy. As an example, consider an OFDM ... . The message symbol can be written as math mathbf d d 0, d 1, ldots d N 1 T math The OFDM symbol is constructed ... 1 math , the OFDM symbol obtained is math mathbf x x N L 1 , ldots x N 2 , x N 1 , x 0 , x 1 , ldots ... University Press 2005 . A short tutorial on http sites.google.com site mdanishnisar pubs 01 OFDM Tutorial Nisar.pdf the significance of cyclic prefix in OFDM systems . Category Quantized radio modulation ... more details
that while in OFDM the transmit symbols directly modulate the multiple sub carriers, in SC FDMA ..., Finland, Sep. 2006 ref In OFDM as well as SC FDMA, equalization is achieved on the receiver side ... SC FDMA and OFDM employ no IFFT or FFT at transmitter, but introduce the cyclic prefix to transform ..., and Thomas Hindelang, http sites.google.com site mdanishnisar pubs 16 DFT Spread OFDM Nisar IST 2007.pdf On Performance Limits of DFT Spread OFDM Systems , in Sixteenth IST Mobile Summit, July 2007 ... Performance Evaluation of DFT Spread OFDM Based SC FDMA for UTRA LTE Uplink , IEEE Vehicular Technology ... between OFDM and single carrier modulation with a DFE using a frequency domain feedforward ... more details
Unreferenced date December 2009 Image Radio propagation noise.jpg 300px thumb right Selective fading causes a cloudy pattern to appear on a spectrogram display. Selective fading or frequency selective fading is a radio propagation anomaly caused by partial cancellation of a radio Signalling telecommunication signal by itself &mdash the signal arrives at the receiver by Multipath propagation two different paths , and at least one of the paths is changing lengthening or shortening . This typically happens in the early evening or early morning as the various layers in the ionosphere move, separate, and combine. The two paths can both be skywave or one be groundwave . Selective fading manifests as a slow, cyclic disturbance the cancellation effect, or null , is deepest at one particular frequency, which changes constantly, sweeping through the received Sound audio . The effect can be counteracted by applying some diversity scheme , for example OFDM with subcarrier interleaving and forward error correction , or by using two receiver radio receivers with separate antenna radio antenna s spaced a quarter wavelength apart, or a specially designed diversity reception diversity receiver with two antennas. Such a receiver continuously compares the signals arriving at the two antennas and presents the better signal. See also Attenuation distortion Fading Diversity scheme s OFDM DEFAULTSORT Selective Fading Category Radio frequency propagation fading ko ... more details
In optical communications , intensity modulation IM is a form of modulation in which the optical Power physics power output of a source is varied in accordance with some characteristic of the modulating Signal information theory signal . The envelope of the modulated optical signal is an analog of the modulating signal in the sense that the instantaneous power of the envelope is an analog of the characteristic of interest in the modulating signal. Recovery of the modulating signal is by direct detection, not Heterodyne heterodyning . References FS1037C MS188 Further reading William Shieh, Ivan Djordjevic, OFDM for Optical Communications , Academic Press, 2009 ISBN 0123748798. Optical communication Category Optical communications ... more details
Multi Carrier Code Division Multiple Access MC CDMA is a multiple access scheme used in OFDM based telecommunication systems, allowing the system to support multiple users at the same time. MC CDMA spreads each user symbol in the frequency domain. That is, each user symbol is carried over multiple parallel subcarriers, but it is phase shifted typically 0 or 180 degrees according to a code value. The code values differ per subcarrier and per user. The receiver combines all subcarrier signals, by weighing these to compensate varying signal strengths and undo the code shift. The receiver can separate signals of different users, because these have different e.g. orthogonal code values. Since each data symbol occupies a much wider bandwidth in hertz than the data rate in bit s , a signal to noise plus interference ratio if defined as signal power divided by total noise plus interference power in the entire transmission band of less than 0 dB is feasible. One way of interpreting MC CDMA is to regard it as a direct sequence CDMA signal DS CDMA which is transmitted after it has been fed through an inverse FFT Fast Fourier Transform Rationale Wireless radio links suffer from frequency selective ... sub freq sub is the PN code length. Once frequency domain spreading has taken place and the OFDM subcarriers have all been allocated values, OFDM modulation then takes place using the Fast Fourier Transform IFFT to produce an OFDM symbol the OFDM guard interval is then added and if transmission is in the downlink ... OFDM is used as the modulation scheme, the data symbols on the individual subcarriers are spread ... will then be multiplied by the length 4 time domain PN code and transmitted on OFDM symbols 0, 1, 2 ... and L. Papke, On the performance of convolutionally coded CDMA OFDM for mobile communication system .... Fazel and S. Kaiser, Multi Carrier and Spread Spectrum Systems From OFDM and MC CDMA to LTE and WiMAX ... OFDMA , an alternative multiple access scheme for OFDM systems, where the signals of different users ... more details
Multiple Access OFDM system. DVB RCT can serve large cells, up to 65km radius, providing a typical ... generation OFDM technology for broadband portable and mobile services, Multiple Access OFDM included ... that the coverage area of the Multiple Access OFDM signals can be designed to closely match the service ... class wikitable Downstream Channel DS OFDM, ETS 300 744 DVB T compliant Return Interaction Channel Multiple Access OFDM MA OFDM Forward Interaction Channel US Embedded in DS, compliant with ETS 300 744 DVB T OFDM Carrier set 1024 1K , 2048 2K OFDM Carrier spacing CS 1K, 2K, 4K Transmission modes ... more details
wiktionary DMT DMT may refer to In chemical substances Dimethyltryptamine , a psychedelic tryptamine Dimethyl terephthalate , a polyester precursor Desoxymethyltestosterone , a designer anabolic steroid DMT1 DMT1 Divalent Metal Transporter 1 a transporter involved in human iron metabolism. In other uses Digital Monetary Trust , an anonymous internet banking system using electronic money Discrete multitone modulation Discrete multi tone modulation , a form of orthogonal frequency division multiplexing OFDM D mt , a historical kingdom in what is now Eritrea and northern Ethiopia Diver Medic Technician, a certification offered by the National Board of Diving and Hyperbaric Medical Technology Dreamtime , a creation belief from the Australian Aborigines See also disambig de DMT et DMT es DMT fr DMT hr DMT it DMT hu DMT egy rtelm s t lap ja DMT no Dmt pl DMT pt DMT sr DMT fi DMT ... more details
In telecommunications , a carrier wave or carrier is a waveform usually sinusoidal that is Modulation modulated modified with an signal electrical engineering input signal for the purpose of conveying information. ref citeweb title Carrier wave with no modulation transports no information. url http www.utexas.edu research cemd nim Agif CarrWave.html publisher University Of Texas accessdate 2008 05 30 ref This carrier wave is usually a much higher frequency than the input signal. The purpose of the carrier is usually either to transmit the information through space as an electromagnetic wave as in radio communication , or to allow several carriers at different frequencies to share a common physical transmission medium by frequency division multiplexing as, for example, a cable television system . Frequency modulation FM and amplitude modulation AM are common modes of modulating the carrier. In the case of single sideband modulation SSB , the carrier is suppressed and in some forms of SSB, eliminated . The carrier must be reintroduced at the receiver by a beat frequency oscillator BFO . The frequency of a radio or television station is actually the carrier wave s center frequency . Definition In telecommunication s, the term carrier cxr or carrier wave has the following meanings ref Federal Standard 1037C and MIL STD 188 ref A waveform suitable for modulation by an information bearing Signalling telecommunication signal An unmodulated Emission electromagnetic radiation emission . Carrierless modulation systems Newer forms of radio communication such as spread spectrum and ultra wideband do not transmit a conventional carrier wave, nor does Orthogonal frequency division multiplexing OFDM which is used in Digital subscriber line DSL and in the European standard for High definition television HDTV . Orthogonal frequency division multiplexing OFDM may be thought of as an array of symmetrical carrier waves. The rules governing carrier wave propagation affect OFDM different ... more details
Unreferenced date December 2009 About radio frequencies the band Broadcast band A Broadcast band is a segment of the radio spectrum used for broadcasting . border 1 Common name Frequencies Modulation Frequency range Notes Longwave 148.5 and 283.5 kHz Amplitude Modulation AM Low frequency LF Mostly used by Europe , North Africa and Asia . Mediumwave AM radio 535 to 1700 kHz Amplitude Modulation AM Medium frequency Medium Frequency MF Usually speech and news, where a lower bandwidth will suffice. Long range at night due to the ionosphere increasing in altitude. Shortwave 5.9 to 26.1 MHz Mostly AM and Single sideband modulation single sideband SSB modes. High Frequency HF Very long range through radio propagation skipping . Radio clock Standard time frequencies can be heard here. VHF low Broadcast television TV 54 to 88 MHz Single sideband modulation Vestigial sideband VSB vestigial sideband modulation for analog signal analog video , and FM for analog Sound audio 8 VSB or OFDM for digital broadcast Very high frequency Very High Frequency VHF band I Television channel Channels 2 through 6 are from 54 to 88 MHz, except 72 to 76. FM broadcast band FM radio 87.5 to 108 MHz , 76 to 90 in Japan Frequency Modulation FM VHF band II Usually music, due to the clarity and high Bandwidth signal processing bandwidth of FM. Relatively short range. VHF high TV 174 to 216 MHz Single sideband modulation Vestigial sideband VSB vestigial sideband modulation for analog signal analog video , and FM for analog Sound audio 8 VSB or OFDM for digital broadcast VHF band III Television channel Channels 7 through 13 are from 174 to 216 MHz. UHF TV 470 to 806 MHz Single sideband modulation Vestigial sideband VSB vestigial sideband modulation for analog signal analog video , and FM for analog Sound audio 8 VSB or OFDM for digital broadcast Ultra high frequency Ultra High Frequency UHF Channels 14 through 69 are from 470 to 806 MHz, except 608 to 614 radio astrono ... more details
band Orthogonal Frequency Division Multiplexing MB OFDM . The solution enables shortrange multimedia ... Orthogonal frequency division multiplexing OFDM architecture proposed by Texas Instruments and eventually ... SIG for high speed Bluetooth. This merged proposal became known as the MB OFDM proposal and was sponsored by Texas Instruments as a member of the Multi Band OFDM Alliance, which is now part of WiMedia ... proposal, which never happened. In the first round of down selection, the MB OFDM proposal was selected ... MB OFDM and DS UWB, with neither being able to achieve technical confirmation. There were several ... the MB OFDM and DS UWB radios to communicate with each other and share spectrum. Based on a concept ... supporting the MB OFDM proposal insisted that a common signaling mode was not needed or technically ... as a bridge between the two proposals, the lack of acceptance by MB OFDM supporters killed what turned ... Frequency Division Multiplexing MB OFDM UWB, supported by the WiMedia Alliance, then adopted ... more details
can be avoided by means of diversity scheme s and equalization filter s. OFDM and COFDM In wideband digital broadcasting, self interference cancellation is facilitated by the OFDM or COFDM modulation method. OFDM uses a large number of slow low bandwidth modulator s instead of one fast wide band modulator ... portion of the sub carriers are exposed to too much fading to be correctly demodulated. OFDM ... and ISDB T used in Japan and Brazil . OFDM is also widely used in digital radio systems, including ... in ATSC. Alternative modulations Alternatives to using OFDM modulation in SFN self interference ... diversity Digital Video Broadcasting , ISDB T , ATSC OFDM , guard interval External links http www.enensys.com ... more details
to the square of the signal frequency. On the other hand, OFDM has fundamental propagation advantages ..., and very close in price to b g only devices. Technical description Of the 52 OFDM subcarriers .... The advantages of using OFDM include reduced multipath effects in reception and increased spectral ... 3 4 216 0 224 See also List of WLAN channels OFDMOFDM system comparison table OFDM system comparison ... more details
CDD may mean Capability Development Document , a document used by military of the United States when making decisions about equipment. Conserved domain database , a collation of protein structural and functional motifs from several independent databases. Centre for Democracy and Development , a non government organization in Africa Water purification Chlorine dioxide disinfection Chlorine dioxide disinfection , a fast acting process to disinfect water Cidade de Deus Rio de Janeiro , a neighbourhood in Rio de Janeiro, Brazil Congregatio Discipulorum Domini , a Catholic order founded in China. Collaborative Drug Discovery , a private software company with a web based platform for managing drug discovery data. Cooling degree day, a qualitative index used to reflect the demand for energy to cool a business see heating degree day . Customer Due Diligence . Craniodiaphyseal dysplasia , a bone disorder causing calcium build up in the skull. Cats Don t Dance , a 1997 animated film. Cyclic delay diversity , a diversity scheme used in OFDM based telecommunication systems. Childhood disintegrative disorder , a rare condition that causes late onset developmental delays. Cardenden railway station , a railway station in Scotland. C Drone Defect , a solo project of Marc Horstmeier. disambig fr CDD it CDD ... more details
Other uses Interference disambiguation Unreferenced date December 2009 Merge from Interference in mobile communications discuss Talk Interference communication Merger proposal date December 2011 listen filename Mobile phone interference.ogg title Sample of effects of interference mobile phone format Ogg In communication s and electronics , especially in telecommunications , interference is anything which alters, modifies, or disrupts a Signal electrical engineering signal as it travels along a channel communications channel between a communication source source and a receiver. The term typically refers to the addition of unwanted signals to a useful signal. Common examples are Electromagnetic interference EMI Co channel interference CCI , also known as Crosstalk electronics crosstalk Adjacent channel interference ACI Intersymbol interference ISI Inter carrier interference ICI , caused by doppler shift in OFDM modulation multitone modulation . Common mode interference CMI Conducted interference Interference is typically but not always distinguished from electronic noise noise , for example white noise white thermal noise . Radio resource management aims at reducing and controlling the co channel and adjacent channel interference. See also Distortion Signal to Interference Ratio SIR Signal to noise plus interference SNIR Inter flow interference Intra flow interference DEFAULTSORT Interference Communication Category Noise Category Interference fa fr Interf rence tr Enterferans ... more details
The UWB Forum was an industry organization dedicated to ensuring that Ultra wideband Ultra Wideband UWB products from multiple vendors are truly interoperable. The majority members Motorola and Freescale left the group in 2006 and the UWB Forum is now defunct. ref name motorola http www.eetimes.com news latest showArticle.jhtml jsessionid XBBESWEJN5N42QSNDLPSKHSCJUNN2JVN?articleID 184429508&printable true&printable true Freescale, Motorola pull out of UWB Forum ref IEEE IEEE 802.15 IEEE 802.15.3a was an attempt to provide a higher speed Ultra wideband UWB PHY enhancement amendment to IEEE 802.15.3 for applications which involve imaging and multimedia. IEEE 802.15.3a UWB standardisation attempt failed due to contrast between Wimedia WiMedia Alliance and UWB Forum. On January 19, 2006 IEEE 802.15.3a task group TG3a members voted to withdraw the December 2002 project authorization request PAR that initiated the development of high data rate Ultra wideband UWB standards. The IEEE 802.15.3a most commendable achievement was the consolidation of 23 Ultra wideband UWB PHY specifications into two proposals using Multi Band Orthogonal Frequency Division Multiplexing MB OFDM UWB, supported by the WiMedia Alliance, and Direct Sequence UWB DS UWB , supported by the UWB Forum. Notes references External links http www.uwbforum.org UWB Forum DEFUNCT this link does not work nowadays, April 2010 http www.wimedia.org WiMedia Alliance DEFAULTSORT Uwb Forum Category Standards organizations Category Article Feedback 5 ... more details
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