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Modulating Radio Frequency Carriers to Carry Digital Data

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Digital radio transmission requires the use of a carrier wave which is modulated by the digital data.
a. What are the three possible ways in which a radio frequency carrier can be modulated to carry
digital data?
b. Write down the equation for the occupied bandwidth of a digital band pass (radio) link that
has ideal RRC filters with alpha = 0.4 and a symbol rate Rs sps.
c. A digital radio link uses BPSK modulation and has a bit rate of 38.4 kbps. If the transmitter
and receiver have ideal RRC filters with alpha = 0.4, what is the bandwidth occupied by the RF
signal?
d. What is the RF bandwidth required by the radio link specified in part (c) above?

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Solution Preview

a. What are the three possible ways in which a radio frequency carrier can be modulated to carry digital data?

There are 3 components of a radio frequency carrier wave that can be modulated (shaped) to convey information:

(1) The amplitude of the carrier can be shaped or modulated by the information signal to convey the information. This is know as Amplitude Modulation (AM). There exists many types of AM depending on whether the modulating signal is analogue or digital in nature and the bandwidth used

(2) The frequency of the carrier can be shaped or modified by the modulating signal to convey ...

Solution Summary

The expert examines modulating radio frequency carriers to carry digital data.

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See Also This Related BrainMass Solution

TDMA cellular system, Power efficiency and spectral efficiency for a modulation scheme, Propagation index, Multipath, Fast fading, Direct sequence spread spectrum, Outgoing traffic intensity

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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