w 8-2

Week 8 Discussion 2

COLLAPSE

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Data Transmission.  Please respond to the following:

• Compare the four items related to channel capacity: data rate, bandwidth, noise, and error rate. Determine the most important and justify its significance over the remaining items.
• Describe real-world examples of attenuation and white noise. Examine the effect on the information-carrying capacity of the link and present a way to avoid these types of interruptions.

Compare the four items related to channel capacity: data rate, bandwidth, noise, and error rate. Determine the most important and justify its significance over the remaining items.

Data rate, bandwidth, noise and error rate are the four items related to channel capacity, and they can influence each other. Data rate is the rate to descript data communication, it is in bits per second (bps). Bandwidth is a kind of constrain for transmitted signal. It always occur by constrain of transmitter and the nature of medium. It is expressed in Hertz. Noise is an unwanted electromagnetic energy when signal transmits between transmitter and receiver. Error rate means the errors about transmit a 1 but the reception of a 0, or the opposite situation.

We can know that all other things being equal, doubling the bandwidth doubles the data rate. Thus bandwidth can influence the data rate. And the higher the data rate, the more unwanted noise we will get. If the data is increased, the bits become “shorter,” and the noise will affect more bits. So, at a given noise level, the higher the data rate will occur higher error rate. We have an equation to express their relations like

 C is the capacity of the channel in bits per second and B express bandwidth. SNR, or S/N is the signal-to-noise ratio, it means the ratio of the power which contained in the noise during transmission. We can find these content in our text book from page 452 to 453. And from the above description, I think bandwidth is the most important item because it can influence all the three other items.

Describe real-world examples of attenuation and white noise. Examine the effect on the information-carrying capacity of the link and present a way to avoid these types of interruptions.

Attenuation is a phenomenon that when signal transmits in a medium, the energy of the signal will become thermal energy or absorbed by medium, and the strength of the signal will be weaker. Attenuation is a nature, and cannot be eliminated. Real-world example of attenuation is the light transmits in optical fiber, the light signal will be weaker and weaker during transmitting. The way to avoid attenuation is to add amplifiers in the transmitting channel cables.

White noise, or thermal noise, it causes by the electron thermal vibration in conductor. White noise exists in all the devices and transmitting mediums, and it only effected by temperature. It is also cannot be eliminated, too. To reduce the white noise, we can choose the medium with lower resistance.

Reference:

http://www.computerhope.com/jargon/e/errorate.htm

https://mars.nasa.gov/msl/mission/communicationwithearth/data/