CS 3413 Data Communications, Fall 2004 Assignment 2 Comments

This assignment had 10 questions, each worth 10 points.

The maximum score on this assignment is 100 points.

1. For problem 1, If there are 32 intensity values, it takes 5 bits to specify the intensity.
2. For problem 2, it is just a matter of using different numbers in Example 3.2.
3. For problem 3, note that 1 4-bit word requires 2⁴ levels, so to use the Nyquist formula, M = 16.
4. For Problem 4, and other problems in which a signal to noise ratio is to be found, you should give your answer in dB.
5. In problem 5, it is easy to misinterpret the question. The decibel is a measure of the ratio of two power values, not voltage values. It is somewhat misleading to refer to a 30dB voltage gain. A 30dB gain corresponds to a ratio of the square of two voltages.
6. In problem 6, remember that data rates are usually specified in terms of bits per second, not bytes per second. Also, the 1.4 in 1.4-Mbyte floppy is an approximation, so it does not make sense to keep 9 significant figures.
7. In problem 7, it is much easier to keep track of the numbers if you use scientific notation.
8. In problem 8, first calculate the output power signal using the 20dB value. The calculate the signal to noise ration in dB. Remember that the noise is given in microwatts, not milliwatts.
9. In problem 9, use Figure 4.3. Values will be approximate in reading the graph. Notice that the horizontal axis is a logarithmic scale so 300 KHz will be about half way between 100 kHZ and 1Mhz.
10. In problem 10, you are just asked to find the wavelength of a 30 Hz electromagnetic wave in water. The speed of light in water is about 3/4 of that in vacuum.