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Orthogonal frequency-division multiplexing
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=== Adaptive transmission === The resilience to severe channel conditions can be further enhanced if information about the channel is sent over a return-channel. Based on this feedback information, adaptive [[modulation]], channel coding and power allocation may be applied across all subcarriers, or individually to each subcarrier. In the latter case, if a particular range of frequencies suffers from interference or attenuation, the carriers within that range can be disabled or made to run slower by applying more robust modulation or [[error coding]] to those subcarriers. The term '''{{visible anchor|discrete multitone modulation}}''' ('''DMT''') denotes OFDM-based communication systems that adapt the transmission to the channel conditions individually for each subcarrier, by means of so-called ''bit-loading''. Examples are [[ADSL]] and [[VDSL]]. The upstream and downstream speeds can be varied by allocating either more or fewer carriers for each purpose. Some forms of [[rate-adaptive DSL]] use this feature in real time, so that the bitrate is adapted to the co-channel interference and bandwidth is allocated to whichever subscriber needs it most.
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