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Answer to Question #52548 in Other Programming & Computer Science for biruk

Question #52548
discuss the following terms.attenuation, delay distortion, noise and crosstalk.
Expert's answer
Answer:
ATTENUATIONIS THE LOSS OF POWER A SIGNAL SUFFERS AS IT TRAVELS FROM THE TRANSMITTING
DEVICE TO THE RECEIVING DEVICE. SOME POWER IS ABSORBED BY THE MEDIUM OR IS LOST
BEFORE IT REACHES THE RECEIVER. AS THE MEDIUM ABSORBS POWER, THE SIGNAL BECOMES
WEAKER, AND THE RECEIVING EQUIPMENT HAS LESS AND LESS CHANCE OF CORRECTLY
INTERPRETING THE DATA.THIS POWER LOSS IS A FUNCTION OF THE TRANSMISSION METHOD
AND CIRCUIT MEDIUM. ATTENUATION INCREASES AS FREQUENCY INCREASES OR AS THE
DIAMETER OF THE WIREDECREASES.
·       Signalstrength decreases with distance
·        Depends on the transmission medium
·       Receivedsignal strength:
– must behigh enough, allowing the signal to be detected
– must besufficiently higher than noise, such that the signal to be received accurately
(Solution: repeaters, amplifiers)
– higher the transmission frequency, higher theattenuation is (mainly concerns the analog signals)
 
DATAMAY ARRIVE AT DIFFERENT TIMES, DEPENDING ON WHAT FREQUENCY IS USED.
THENDELAY DISTORTION REFERS TO THE DISTORTION OF THE SIGNAL THAT OCCURS BECAUSE
DIFFERENT FREQUENCIES TRAVEL AT SLIGHTLY DIFFERENT SPEEDS THROUGH THE MEDIA.
IFDATA ARE TRANSMITTED AT TWO DIFFERENT FREQUENCIES, THEN THE BITS TRANSMITTED AT
ONE FREQUENCY MAY TRAVEL SLIGHTLY FASTER THAN THE BITS TRANSMITTED AT THE
SECOND FREQUENCY.
·       Specific to guided media (wires)
·       Signal propagation speed depends on the frequency
·       Frequency selectivity arises: various frequencycomponents of the signal will arrive at receiver with different delays
·       A kind of Inter Symbol Interference (ISI) occurs
·       Particularly annoying for digital data
 
Crosstalk is aneffect that occurs between neighbor pairs of wires. The electrical current
flowing through one wire will create an electromagnetic field which is captured
by the neighbor wire. Physically, this is very similar to the radio
transmissions: one wire acts as a transmitting antenna, whereas the other one
will be the receiving antenna. Near End Crosstalk (NEXT) is measured at one end
only of a cable, by transmitting a signal into one pair and measuring the
resulting signal power on an adjacent pair at the same end. Far End Crosstalk
(FEXT) is measured at both ends of a cable, by transmitting a signal into one
pair at one end and measuring the resulting signal power on an adjacent pair at
the other end.
 
Noise: Definition: “unwanted signals that are insertedsomewhere between transmission
and reception”
·       Four categories:
– Thermal noise
– Intermodulation noise
– Crosstalk
– Impulse noise
 
The thermal noise ispresent in all electronic circuits and transmission media. Generally, it is
mathematically described as a “white noise”. i.e. a noise whose power is
uniformly distributed over the whole frequency bandwidth. This is the most
common type of noise considered when modeling systems, and there is a huge
amount of literature (information theory, coding, data transmission) built on the
hypothesis that the noise that affects the signal is a white noise.

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