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# Cellular System

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I need the answers to the questions so that my study group can have the correct information in preparation for a group assignment. This is just for reference and will not be submitted for a grade to any school.

Answer the following questions. Explain your answer and show your work in a logical manner. Use any needed formula -- show the formula, the substitutions made, and explain why.

1. A TDMA cellular system uses a 200 KHz bandwidth carrier, which carries 8 channels. What defines or determines each channel, and how much bandwidth does each channel occupy and why?

2. Define what is meant by power efficiency and spectral efficiency for a modulation scheme? What is the measure used for each?

3. Order the following modulation types in terms of spectral efficiency (best to worse) and explain why (be specific, show a number and how you got it): 64-QAM, QPSK, 8-PSK, and BPSK. Assume that the r=0, perfect filtering.

4. Propagation in a wireless channel is sometimes modeled using the propagation index n. Explain how the propagation index n varies and why. If there are two channels, where n=2 for the first one and n=3 for the second one (as for both the same power is transmitted and the same modulation/coding is used), in which channel will the signal be detectable further away and why?

5. Describe why multipath occurs in wireless. Describe fast fading, and some technique to counter it.

6. Describe how direct sequence spread spectrum (DSSS) suppresses interference from other transmissions in the same frequency band.

7. A telephone switching board can handle 120 phones. Assuming the following, determine the outgoing traffic intensity and the number of channels:
* On average 5 calls/hour per phone
* 60% of all calls made are external
* Average call duration time is 4 minutes
* QoS = 0.9%

Please refer to the attachment for multiple choice questions.

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