discuss the following terms.attenuation, delay distortion, noise and crosstalk.
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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