84:
456:
1267:
598:
3392:
498:
394:
154:
3402:
406:
43:
3381:
366:
3412:
1724:
471:. These ghosts are particularly bothersome since they move and behave like the normal targets (which they echo), and so the receiver has difficulty in isolating the correct target echo. These problems can be minimized by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below the ground or above a certain height (altitude).
1560:
409:
In this illustration, an object (in this case an aircraft) pollutes the system by adding a second path. The signal arrives at receiver (RX) by means of two different paths which have different lengths. The main path is the direct path, while the second is due to a reflection from the
451:
and ghosting, seen as a faded duplicate image to the right of the main image. Ghosts occur when transmissions bounce off a mountain or other large object, while also arriving at the antenna by a shorter, direct route, with the receiver picking up two signals separated by a delay.
509:, multipath effects can cause a stationary receiver's output to indicate as if it were randomly jumping about or creeping. When the unit is moving the jumping or creeping may be hidden, but it still degrades the displayed accuracy of location and speed.
1274:
In practical conditions and measurement, the multipath time is computed by considering as last impulse the first one which allows receiving a determined amount of the total transmitted power (scaled by the atmospheric and propagation losses), e.g. 99%.
815:
1345:
674:
At the receiver, due to the presence of the multiple electromagnetic paths, more than one pulse will be received, and each one of them will arrive at different times. In fact, since the electromagnetic signals travel at the
381:
whereby a wave from a source travels to a detector via two or more paths and the two (or more) components of the wave interfere constructively or destructively. Multipath interference is a common cause of
1728:
1628:
1576:); it can be shown that, on average, the distance (in Hz) between two consecutive valleys (or two consecutive peaks), is roughly inversely proportional to the multipath time. The so-called
1633:
For example, with a multipath time of 3 μs (corresponding to a 1 km of added on-air travel for the last received impulse), there is a coherence bandwidth of about 330 kHz.
1261:
571:
to avoid ISI. Because multipath propagation behaves differently in each kind of wire, G.hn uses different OFDM parameters (OFDM symbol duration, guard interval duration) for each media.
942:
1163:
1111:
1059:
2309:
669:
351:
distribution. All of these descriptions are commonly used and accepted and lead to results. However, they are generic and abstract/hide/approximate the underlying physics.
1565:
where the last right-hand term of the previous equation is easily obtained by remembering that the
Fourier transform of a Dirac pulse is a complex exponential function, an
865:
895:
1199:
1338:
1305:
1004:
975:
838:
689:
679:, and since every path has a geometrical length possibly different from that of the other ones, there are different air travelling times (consider that, in
2656:
1555:{\displaystyle H(f)={\mathfrak {F}}(h(t))=\int _{-\infty }^{+\infty }{h(t)e^{-j2\pi ft}dt}=\sum _{n=0}^{N-1}{\rho _{n}e^{j\phi _{n}}e^{-j2\pi f\tau _{n}}}}
1009:
More in general, in presence of time variation of the geometrical reflection conditions, this impulse response is time varying, and as such we have
1170:
304:
from water bodies and terrestrial objects such as mountains and buildings. When the same signal is received over more than one path, it can create
421:
The interference will arise owing to the two (or more) components of the wave having, in general, travelled a different length (as measured by
113:
316:; this may cause a radio signal to become too weak in certain areas to be received adequately. For this reason, this effect is also known as
3364:
3336:
3331:
2356:
1772:
2074:
1824:
1673:
1278:
Keeping our aim at linear, time invariant systems, we can also characterize the multipath phenomenon by the channel transfer function
428:
The signal due to indirect paths interferes with the required signal in amplitude as well as phase which is called multipath fading.
218:
487:
190:
3358:
2113:
171:
56:
17:
1733:
425:– geometric length and refraction (differing optical speed)), and thus arriving at the detector out of phase with each other.
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197:
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3348:
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506:
348:
336:
204:
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The obtained channel transfer characteristic has a typical appearance of a sequence of peaks and valleys (also called
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255:
237:
135:
70:
106:
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2349:
1765:
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is the number of received impulses (equivalent to the number of electromagnetic paths, and possibly very large),
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are usually more intense and complex. Where OFDM training is unsatisfactory, bridge taps may be removed.
1168:
Very often, just one parameter is used to denote the severity of multipath conditions: it is called the
3254:
3176:
3115:
2822:
2292:
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2006:
1916:
683:, the light takes 3 μs to cross a 1 km span). Thus, the received signal will be expressed by
62:
31:
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2832:
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630:
96:
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560:
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Where the magnitudes of the signals arriving by the various paths have a distribution known as the
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100:
92:
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3209:
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3004:
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2505:
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164:
1201:, and it is defined as the time delay existing between the first and the last received impulses
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2500:
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2165:
2079:
1921:
1715:
843:
293:
117:
536:
High-speed power line communication systems usually employ multi-carrier modulations (such as
30:
This article is about the electromagnetic propagation phenomenon. For usage in computing, see
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2852:
2817:
2737:
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2089:
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478:) multipath can cause errors and affect the quality of communications. The errors are due to
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2381:
870:
397:
A diagram of the ideal situation for TV signals moving through space: The signal leaves the
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8:
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2431:
2416:
2001:
1872:
1577:
422:
415:
289:
269:
1750:
810:{\displaystyle y(t)=h(t)=\sum _{n=0}^{N-1}{\rho _{n}e^{j\phi _{n}}\delta (t-\tau _{n})}}
3199:
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3087:
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401:(TX) and travels through one path to the receiver (the TV set, which is labeled RX)
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The mathematical model of the multipath can be presented using the method of the
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2847:
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2510:
2485:
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also use orthogonal frequency-division multiplexing to communicate with their
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2438:
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1966:
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948:(i.e., magnitude and phase) of the generic received pulse. As a consequence,
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597:
568:
491:
344:
309:
555:
standard provides a way to create a high-speed (up to 1 gigabit per second)
3097:
2937:
2882:
2812:
2777:
2712:
2611:
2601:
2453:
2313:
1788:
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467:
processing, multipath causes ghost targets to appear, deceiving the radar
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1806:
680:
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despite multipath. In this case the reflections may be caused by mixed
522:
441:
387:
347:. Where two components dominate, the behavior is best modeled with the
297:
497:
369:
Coherent waves that travel along two different paths will arrive with
3287:
2752:
2567:
2334:
2181:
2040:
574:
486:
are often used to correct the ISI. Alternatively, techniques such as
393:
459:
Radar multipath echoes from an actual target cause ghosts to appear.
153:
3282:
3272:
3189:
3014:
2837:
1931:
1884:
1842:
405:
414:
The condition necessary is that the components of the wave remain
3277:
3262:
2480:
1971:
1926:
1880:
541:
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3267:
2589:
2195:
2011:
1985:
1980:
1939:
1890:
1876:
1658:
448:
313:
1270:
Mathematical model of the multipath channel transfer function.
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3229:
2537:
2016:
1911:
1803:
578:
549:
464:
3234:
552:
537:
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1780:
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Multipath interference is a phenomenon in the physics of
1645:, a design that can reject extraneous reflection signals
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1210:
1180:
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1070:
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983:
954:
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873:
846:
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633:
601:
Mathematical model of the multipath impulse response.
343:
provides a more accurate model, and this is known as
335:. Where one component (often, but not necessarily, a
386:" in analog television broadcasts and of fading of
178:. Unsourced material may be challenged and removed.
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288:by two or more paths. Causes of multipath include
3428:
105:but its sources remain unclear because it lacks
1623:{\displaystyle B_{C}\approx {\frac {1}{T_{M}}}}
312:of the signal. Destructive interference causes
977:also represents the impulse response function
2350:
1766:
616:Suppose you want to transmit a single, ideal
418:throughout the whole extent of their travel.
548:that multipath propagation would cause. The
3365:Global telecommunications regulation bodies
1256:{\displaystyle T_{M}=\tau _{N-1}-\tau _{0}}
71:Learn how and when to remove these messages
3401:
2357:
2343:
1773:
1759:
1674:Orthogonal frequency-division multiplexing
1307:, which is defined as the continuous time
474:In digital radio communications (such as
256:Learn how and when to remove this message
238:Learn how and when to remove this message
136:Learn how and when to remove this message
1265:
596:
592:
496:
488:orthogonal frequency division modulation
454:
404:
392:
364:
937:{\displaystyle \rho _{n}e^{j\phi _{n}}}
14:
3429:
2364:
1158:{\displaystyle \phi _{n}=\phi _{n}(t)}
1106:{\displaystyle \rho _{n}=\rho _{n}(t)}
1054:{\displaystyle \tau _{n}=\tau _{n}(t)}
2338:
2151:
1754:
3411:
517:Multipath propagation is similar in
373:, hence interfering with each other.
176:adding citations to reliable sources
147:
77:
36:
1366:
1006:of the equivalent multipath model.
24:
2152:
1408:
1400:
507:Global Positioning System receiver
349:two-wave with diffuse power (TWDP)
25:
3453:
867:is the time delay of the generic
512:
52:This article has multiple issues.
3410:
3400:
3391:
3390:
3379:
3000:Free-space optical communication
2307:
1727: This article incorporates
1722:
152:
82:
41:
1740:General Services Administration
1689:Two-ray ground-reflection model
664:{\displaystyle x(t)=\delta (t)}
354:
163:needs additional citations for
60:or discuss these issues on the
2247:Error detection and correction
1423:
1417:
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27:Concept in radio communication
13:
1:
1704:
3386:Telecommunication portal
3167:Telecommunications equipment
559:using existing home wiring (
7:
3442:Radio frequency propagation
2903:Alexander Stepanovich Popov
2320:Comparison of radio systems
1636:
431:
280:phenomenon that results in
10:
3458:
2607:Telecommunications history
2293:International broadcasting
2262:FM extended band in Brazil
501:GPS error due to multipath
358:
32:Multipath (disambiguation)
29:
3374:
3316:
3253:
3215:Public Switched Telephone
3175:
3139:
3096:
3037:
3027:telecommunication circuit
2988:Fiber-optic communication
2971:
2733:Francis Blake (telephone)
2680:
2528:Optical telecommunication
2372:
2301:
2280:
2219:
2179:
2158:
2147:
2103:
2060:
2030:
1994:
1959:
1952:
1904:
1833:
1802:
1795:
860:{\displaystyle \tau _{n}}
567:). G.hn uses OFDM with a
3126:Orbital angular-momentum
2563:Satellite communications
2402:Communications satellite
1569:of every linear system.
1311:of the impulse response
546:intersymbol interference
519:power line communication
480:intersymbol interference
339:component) dominates, a
91:This article includes a
3005:Molecular communication
2828:Gardiner Greene Hubbard
2657:Undersea telegraph line
2392:Cable protection system
2272:Shortwave relay station
2171:Audio signal processing
284:reaching the receiving
187:"Multipath propagation"
120:more precise citations.
3147:Communication protocol
2933:Charles Sumner Tainter
2748:Walter Houser Brattain
2693:Edwin Howard Armstrong
2501:Information revolution
2166:Audio data compression
1735:Federal Standard 1037C
1729:public domain material
1716:Federal Standard 1037C
1624:
1556:
1487:
1334:
1301:
1271:
1257:
1195:
1159:
1107:
1055:
1000:
971:
938:
891:
890:{\displaystyle n^{th}}
861:
834:
811:
749:
665:
624:power at time 0, i.e.
602:
502:
460:
411:
402:
374:
318:multipath interference
294:ionospheric reflection
18:Multipath interference
3437:Broadcast engineering
3121:Polarization-division
2853:Narinder Singh Kapany
2818:Erna Schneider Hoover
2738:Jagadish Chandra Bose
2718:Alexander Graham Bell
2449:online video platform
2267:Multipath propagation
2090:MPEG-1 Audio Layer II
1960:Frequency allocations
1835:Frequency allocations
1625:
1557:
1461:
1335:
1302:
1269:
1258:
1196:
1194:{\displaystyle T_{M}}
1160:
1108:
1056:
1001:
972:
939:
892:
862:
835:
812:
723:
666:
600:
593:Mathematical modeling
500:
458:
408:
396:
368:
329:Rayleigh distribution
2963:Vladimir K. Zworykin
2923:Almon Brown Strowger
2893:Charles Grafton Page
2548:Prepaid mobile phone
2476:Electrical telegraph
2220:Technical (emission)
1587:
1346:
1333:{\displaystyle h(t)}
1315:
1300:{\displaystyle H(f)}
1282:
1208:
1178:
1120:
1068:
1016:
999:{\displaystyle h(t)}
981:
970:{\displaystyle y(t)}
952:
901:
871:
844:
824:
690:
631:
322:multipath distortion
172:improve this article
2913:Johann Philipp Reis
2672:Wireless revolution
2634:The Telephone Cases
2491:Hydraulic telegraph
1580:is thus defined as
1578:coherence bandwidth
1412:
563:, phone lines, and
544:OFDM) to avoid the
447:, multipath causes
423:optical path length
341:Rician distribution
331:, this is known as
290:atmospheric ducting
270:radio communication
3111:Frequency-division
3088:Telephone exchange
2958:Charles Wheatstone
2888:Jun-ichi Nishizawa
2863:Innocenzo Manzetti
2798:Reginald Fessenden
2533:Optical telegraphy
2366:Telecommunications
1643:Choke ring antenna
1620:
1552:
1392:
1330:
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1272:
1253:
1191:
1155:
1103:
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996:
967:
934:
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807:
661:
609:used for studying
603:
557:local area network
527:impedance mismatch
525:. In either case,
503:
461:
412:
403:
375:
93:list of references
3424:
3423:
3162:Store and forward
3157:Data transmission
3071:Network switching
3022:Transmission line
2868:Guglielmo Marconi
2833:Internet pioneers
2698:Mohamed M. Atalla
2667:Whistled language
2332:
2331:
2328:
2327:
2252:FM broadcast band
2159:Technical (audio)
2056:
2055:
1948:
1947:
1649:Diversity schemes
1618:
1309:Fourier transform
946:complex amplitude
833:{\displaystyle N}
585:, but those from
531:signal reflection
521:and in telephone
361:Wave interference
266:
265:
258:
248:
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222:
146:
145:
138:
75:
16:(Redirected from
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3414:
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3404:
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3394:
3393:
3384:
3383:
3382:
3255:Notable networks
3245:Wireless network
3185:Cellular network
3177:Types of network
3152:Computer network
3039:Network topology
2953:Thomas A. Watson
2808:Oliver Heaviside
2793:Philo Farnsworth
2768:Daniel Davis Jr.
2743:Charles Bourseul
2703:John Logie Baird
2412:Data compression
2407:Computer network
2359:
2352:
2345:
2336:
2335:
2314:Radio portal
2312:
2311:
2310:
2288:History of radio
2232:AM expanded band
2149:
2148:
2032:Commercial radio
1957:
1956:
1800:
1799:
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1768:
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1742:. Archived from
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607:impulse response
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107:inline citations
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2873:Robert Metcalfe
2728:Tim Berners-Lee
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2496:Information Age
2368:
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2333:
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2257:FM broadcasting
2227:AM broadcasting
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1995:Digital systems
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1694:Ultra wide-band
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691:
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632:
629:
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622:electromagnetic
595:
515:
434:
363:
357:
333:Rayleigh fading
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97:related reading
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35:
28:
23:
22:
15:
12:
11:
5:
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3106:Space-division
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2960:
2955:
2950:
2945:
2943:Camille Tissot
2940:
2935:
2930:
2925:
2920:
2918:Claude Shannon
2915:
2910:
2908:Tivadar Puskás
2905:
2900:
2895:
2890:
2885:
2880:
2878:Antonio Meucci
2875:
2870:
2865:
2860:
2855:
2850:
2848:Charles K. Kao
2845:
2840:
2835:
2830:
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2823:Harold Hopkins
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2800:
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2662:Videotelephony
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2558:Radiotelephone
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2153:Related topics
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2110:
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2100:
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2014:
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1746:on 2022-01-22.
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944:represent the
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677:speed of light
672:
671:
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657:
654:
651:
648:
645:
642:
639:
636:
611:linear systems
594:
591:
565:coaxial cables
514:
513:In wired media
511:
492:rake receivers
433:
430:
359:Main article:
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310:phase shifting
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101:external links
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3132:
3131:Code-division
3129:
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3119:
3117:
3116:Time-division
3114:
3112:
3109:
3107:
3104:
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3044:
3042:and switching
3040:
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3023:
3020:
3016:
3013:
3012:
3011:
3008:
3006:
3003:
3001:
2998:
2994:
2993:optical fiber
2991:
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2989:
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2984:
2983:Coaxial cable
2981:
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2899:
2898:Radia Perlman
2896:
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2799:
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2789:
2788:Lee de Forest
2786:
2784:
2783:Thomas Edison
2781:
2779:
2776:
2774:
2773:Donald Davies
2771:
2769:
2766:
2764:
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2758:Claude Chappe
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2603:
2602:Smoke signals
2600:
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2580:Semiconductor
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2440:
2439:Digital media
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2242:Digital radio
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1786:digital audio
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1700:
1699:Rake receiver
1697:
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1687:
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1680:
1679:Rician fading
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1567:eigenfunction
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569:cyclic prefix
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494:may be used.
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345:Rician fading
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337:line of sight
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189: –
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183:Find sources:
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161:This article
159:
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129:
126:November 2009
119:
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109:
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98:
94:
89:
80:
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74:
72:
65:
64:
59:
58:
53:
48:
39:
38:
33:
19:
3098:Multiplexing
2973:Transmission
2938:Nikola Tesla
2928:Henry Sutton
2883:Samuel Morse
2813:Robert Hooke
2778:Amos Dolbear
2713:John Bardeen
2632:
2612:Telautograph
2516:Mobile phone
2471:Edholm's law
2454:social media
2387:Broadcasting
2305:
2266:
1789:broadcasting
1744:the original
1734:
1720:
1632:
1573:
1571:
1564:
1277:
1273:
1169:
1167:
1008:
819:
673:
615:
604:
573:
535:
516:
504:
473:
462:
445:transmission
435:
427:
420:
413:
376:
355:Interference
326:
321:
317:
306:interference
273:
267:
252:
234:
228:October 2021
225:
215:
208:
201:
194:
182:
170:Please help
165:verification
162:
132:
123:
112:Please help
104:
68:
61:
55:
54:Please help
51:
3298:NPL network
3010:Radio waves
2948:Alfred Vail
2858:Hedy Lamarr
2843:Dawon Kahng
2803:Elisha Gray
2763:Yogen Dalal
2688:Nasir Ahmed
2622:Teleprinter
2486:Heliographs
2237:Cable radio
2180:Technical (
1940:DVB-T2 Lite
1796:Terrestrial
1711:MIL-STD-188
1684:Signal flow
1669:Olivia MFSK
618:Dirac pulse
587:bridge taps
583:wire gauges
561:power lines
523:local loops
399:transmitter
388:radio waves
371:phase shift
278:propagation
118:introducing
3431:Categories
3344:Antarctica
3303:Toasternet
3225:Television
2708:Paul Baran
2640:Television
2624:(teletype)
2617:Telegraphy
2595:transistor
2573:Phryctoria
2543:Photophone
2521:Smartphone
2511:Mass media
2119:DirectBand
2105:Subcarrier
1807:modulation
1705:References
681:free space
575:DSL modems
484:Equalizers
442:television
436:In analog
302:reflection
298:refraction
198:newspapers
57:improve it
3328:Americas
3317:Locations
3288:Internet2
3049:Bandwidth
2753:Vint Cerf
2650:streaming
2628:Telephone
2568:Semaphore
2459:streaming
2182:AM stereo
2041:Sirius XM
2034:providers
1953:Satellite
1601:≈
1541:τ
1534:π
1525:−
1509:ϕ
1491:ρ
1481:−
1463:∑
1441:π
1432:−
1409:∞
1401:∞
1398:−
1394:∫
1245:τ
1241:−
1233:−
1226:τ
1138:ϕ
1125:ϕ
1086:ρ
1073:ρ
1034:τ
1021:τ
924:ϕ
906:ρ
849:τ
795:τ
791:−
782:δ
771:ϕ
753:ρ
743:−
725:∑
650:δ
438:facsimile
274:multipath
63:talk page
3396:Category
3283:Internet
3273:CYCLADES
3190:Ethernet
3140:Concepts
3064:terminal
3015:wireless
2838:Bob Kahn
2681:Pioneers
2506:Internet
2397:Cable TV
2281:Cultural
2211:Magnavox
2184:formats)
2134:SCA/SCMO
2129:RDS/RBDS
1932:HD Radio
1922:DRM/DRM+
1917:DAB/DAB+
1637:See also
469:receiver
432:Examples
416:coherent
384:ghosting
3416:Commons
3406:Outline
3359:Oceania
3278:FidoNet
3263:ARPANET
3076:circuit
2645:digital
2374:History
2107:signals
2075:AMR-WB+
1927:FMeXtra
1574:notches
542:wavelet
529:causes
482:(ISI).
286:antenna
276:is the
212:scholar
114:improve
3354:Europe
3324:Africa
3308:Usenet
3268:BITNET
3205:Mobile
3081:packet
2590:MOSFET
2585:device
2382:Beacon
2201:Harris
2196:C-QUAM
2085:HE-AAC
2062:Codecs
2046:Canada
2012:DVB-SH
1986:S band
1981:L band
1967:C band
1891:L band
1782:Analog
1659:Fading
820:where
449:jitter
410:plane.
314:fading
300:, and
214:
207:
200:
193:
185:
3337:South
3332:North
3293:JANET
3230:Telex
3220:Radio
3059:Nodes
3054:Links
2975:media
2553:Radio
2538:Pager
2466:Drums
2432:video
2427:image
2417:audio
2191:Belar
2017:S-DMB
2007:DAB-S
1912:CAM-D
1825:COFDM
1804:Radio
1731:from
579:DSLAM
550:ITU-T
505:In a
465:radar
379:waves
219:JSTOR
205:books
99:, or
3349:Asia
3235:UUCP
3195:ISDN
2139:DARC
2114:AMSS
2095:DRA+
1976:band
1885:high
1784:and
553:G.hn
538:OFDM
490:and
440:and
308:and
296:and
191:news
3240:WAN
3210:NGN
3200:LAN
2481:Fax
2422:DCT
2124:PAD
2080:HDC
2070:AAC
2022:SDR
2002:ADR
1936:CDR
1895:UHF
1881:mid
1877:low
1873:VHF
620:of
540:or
533:.
476:GSM
463:In
320:or
268:In
174:by
3433::
1883:/
1879:/
1867:HF
1863:SW
1857:MF
1853:MW
1847:LF
1843:LW
1820:FM
1815:AM
1738:.
1174:,
613:.
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292:,
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1147:(
1142:n
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1129:n
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1098:t
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991:t
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216:·
209:·
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168:.
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20:)
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