# Data Communications

Pages: 4 (1027 words) Published: June 25, 2013
Short Questions:

Differentiate between guided media and unguided media.
Differentiate between an analog and a digital electromagnetic signal. What are three important characteristics of a periodic signal. What is the relationship between the wavelength and frequency of a sine wave. Define fundamental frequency.

What is the relationship between a signal's spectrum and its bandwidth. What is attenuation?
Define channel capacity.
What key factors affect channel capacity?

Problems:

Figure 1 shows the frequency domain function for a single square pulse. The signal pulse could represent a digital 1 in a communications system. Note that an infinite number of higher frequencies of decreasing magnitudes is needed to represent the single pulse. What implication does that have for a real digital transmission system?

Suppose that a digitised TV picture is to be transmitted from a source that uses a matrix of 480 x 500 picture elements (pixels), where each pixel can take on one of 32 intensity values. Assume that 30 pictures are sent per second. (This digital source is is roughly equivalent to broadcast TV standards that have been adopted.) Find the source rate R (bps) Assume that the TV picture is to be transmitted over a channel with 4.5Mhz bandwidth and a 35dB signal-to -noise ratio. Find the capacity of the channel (bps). Discuss how the parameters given in part (a.) could be modified to allow transmission of colour TV signals without increasing the required value for R. What is the channel capacity for a teleprinter channel with a 300Hz bandwidth and a signal-to-noise ratio of 3dB, where the noise is white thermal noise? A digital signalling system is required to operate at 9600bps. If a signal element encodes a 4-bit word, what is the minimum required bandwidth of the channel? Repeat part (a.) for the case of 8-bit words.

Given the narrow (usable) audio bandwidth of a telephone transmission facility, a nominal SNR of 56dB (400,000), and a certain...

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