en picks up this noisy version of what was sent. It has the task of figuring out what the modulator sent from this noisy signal. It does this by breaking its job up into two tasks: a receiver front end, which maps the received signal r(t) into r, and a decision device, which, looking intensely at r, selects which signal was most likely to have been sent. Finally, we discussed how to go about telling someone how a modulator-demodu- lator pair performs. We decided on the measure called probability of error, or P(e), and I explained how you could calculate it. And SO here we are, at another crossroads, another end. But, as you'll learn when you turn your attention to Chapter 6-every ending is just a new beginning. See you there. Getting It from Here to There: Modulators and Demodulators Problems 1. Discuss the benefits and drawbacks of Manchester coding in terms of (1) DC component; (2) self-clocking; (3) bandwidth usage; (4) inversion insensitivity; and (5) noise immunity. 2. If you want a baseband modulation scheme that is (1) insensitive to amplitude inversions on the transmission line, and (2) insensitive to the 60-Hz spike (consider this a DC spike) in the EM spectrum caused by devices driven by AC current, what would be a good choice for the baseband modulator? 3. A 16-level quantizer has output levels -7,-6,...,6,7,8. It is followed by a symbol to bit mapper that maps -7 to 0000, -6 to 0001, and SO on. The output of the bit mapper feeds an 8-PSK modulator. (a) Assume that the output of the sampler (that feeds the quantizer) is 6.32 (amplitude of first sample), 4.16 (amplitude of second sample), and 1.12 (amplitude of third sample). Draw the output of the modulator. (b) If the sampling rate is 10,000 Hz, what is the symbol rate out of the modulator? 4. Given that the input bits are 000110101001, provide the output of a BPSK, QPSK, 8-PSK and 16-PSK modulator. 5. Given the four signals in Figure Q5.1, find an orthonormal basis for these signals. so(t) s((t) Figure Q5.1 Four signals s2(t) s3(t) Chapter Five 6. On