213:-like networks, the problem is commonly solved by dynamic output power adjustment of the transmitters. That is, the closer transmitters use less power so that the SNR for all transmitters at the receiver is roughly the same. This sometimes can have a noticeable impact on battery life, which can be dramatically different depending on distance from the base station. In high-noise situations, however, closer transmitters may boost their output power, which forces distant transmitters to boost their output to maintain a good SNR. Other transmitters react to the rising noise floor by increasing their output. This process continues, and eventually distant transmitters lose their ability to maintain a usable SNR and drop from the network. This process is called
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solution (for that distance) is for both you and your friend to speak louder. Of course, this increases the overall noise level in the bar, and every other patron has to talk louder too (this is equivalent to power control runaway). Eventually, everyone has to shout to make themselves heard by a person standing right beside them, and it is impossible to communicate with anyone more than half a meter away. In general, however, a human is very capable of filtering out loud sounds; similar techniques can be deployed in signal processing where suitable criteria for distinguishing between signals can be established (see
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To place this problem in more common terms, imagine you are talking to someone 6 meters away. If the two of you are in a quiet, empty room then a conversation is quite easy to hold at normal voice levels. In a loud, crowded bar, it would be impossible to hear the same voice level, and the only
182:(SNR) for the further transmitter is much lower. This makes the farther transmitter more difficult, if not impossible, to understand. In short, the near–far problem is one of detecting or filtering out a weaker signal amongst stronger signals.
217:. This principle may be used to explain why an area with low signal is perfectly usable when the cell isn't heavily loaded, but when load is higher, service quality degrades significantly, sometimes to the point of unusability.
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Consider a receiver and two transmitters, one close to the receiver, the other far away. If both transmitters transmit simultaneously and at equal powers, then due to the
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Taking this analogy back to wireless communications, the far transmitter would have to drastically increase transmission power which simply may not be possible.
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Dynamic output power control – Nearby transmitters decrease their output power so that all signals arrive at the receiver with similar signal strengths.
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techniques, the near–far problem is exploited to disrupt ("
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220:Other possible solutions to the near–far problem:
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106:Learn how and when to remove this message
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351:Code-division multiple access (CDMA)
272:Handbuch der Spread-Spectrum Technik
44:adding citations to reliable sources
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396:Frequency-hopping spread spectrum
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390:Direct-sequence spread spectrum
241:Direct-sequence spread spectrum
31:needs additional citations for
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641:Code division multiple access
128:adjacent-channel interference
584:Low probability of intercept
553:PN (pseudorandom noise) code
408:Time-hopping spread spectrum
270:Goiser, Alois M. J. (1998).
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192:adaptive signal processing
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333:in digital communications
280:10.1007/978-3-7091-6818-9
610:Statistical multiplexing
132:co-channel interference
568:Power spectral density
600:Digital communication
462:Major implementations
402:Chirp spread spectrum
251:Signal-to-noise ratio
215:power control runaway
180:signal-to-noise ratio
209:systems and similar
40:improve this article
246:Hidden node problem
158:") communications.
124:hearability problem
168:inverse square law
55:"Near–far problem"
636:Signal processing
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188:signal processing
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96:January 2021
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38:Please help
33:verification
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361:Hedy Lamarr
630:Categories
605:Modulation
257:References
150:. In some
136:distortion
66:newspapers
490:Bluetooth
201:Solutions
162:Analogies
615:Waveform
596:See also
532:Qualcomm
523:CDMA2000
506:Cellular
438:TD-SCDMA
235:See also
537:Verizon
485:GLONASS
480:Galileo
453:MC-CDMA
448:FH-CDMA
443:DS-CDMA
433:TD-CDMA
420:schemes
382:methods
371:More...
357:History
80:scholar
513:Mobile
471:(NASA)
428:W-CDMA
410:(THSS)
398:(FHSS)
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178:, the
172:signal
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517:IS-95
511:EV-DO
418:CDMA
404:(CSS)
176:noise
87:JSTOR
73:books
558:Chip
528:Also
499:DECT
284:ISBN
207:CDMA
148:CDMA
118:The
59:news
475:GPS
276:doi
205:In
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122:or
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