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Selective fading or frequency selective fading is a radio propagation anomaly caused by partial cancellation of a radio signal by itself — the signal arrives at the receiver by two different paths, and at least one of the paths is changing (lengthening or shortening).
Frequency diversity: The signal is transmitted using several frequency channels or spread over a wide spectrum that is affected by frequency-selective fading. Later examples include: Later examples include:
Coherence bandwidth is a statistical measurement of the range of frequencies over which the channel can be considered "flat", [1]: 7 or in other words the approximate maximum bandwidth or frequency interval over which two frequencies of a signal are likely to experience comparable or correlated amplitude fading.
However, their performance differs greatly when comparing frequency-selective and frequency-flat fading channels. Whereas frequency-selective fading produces echoes that are highly disruptive for any of the M time-shifts used to encode PPM data, it selectively disrupts only some of the M possible frequency-shifts used to encode data for M-FSK.
The OFDM diversity gain and resistance to frequency-selective fading may partly be lost if very few sub-carriers are assigned to each user, and if the same carrier is used in every OFDM symbol. Adaptive sub-carrier assignment based on fast feedback information about the channel, or sub-carrier frequency hopping, is therefore desirable.
Selective Mutism: SJS Stevens–Johnson syndrome: SMA Spinal muscular atrophy: SMD Sensory modulation disorder SMEI Severe myoclonic epilepsy of infancy: SMS Smith–Magenis syndrome: SOD Septo-optic dysplasia: SPD Sensory processing disorder: SPS Stiff person syndrome: SSPE Subacute sclerosing panencephalitis: STEMI ST-elevation myocardial ...
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Frequency 5.1% (hypothesized [ 1 ] ) Cognitive disengagement syndrome ( CDS ) is a syndrome characterized by developmentally inappropriate , impairing, and persistent levels of decoupled attentional processing from the ongoing external context and resultant hypoactivity .