Solutions to Practice Problems
Practice Problem 22.1
You have an FSK transmitter using a carrier of 500 kHz sending 10 kbps and a frequency deviation of 100 kHz. How much
bandwidth do you need for your transmission?
BW = 2 (Δf + Rb) = 2 ( (100 x 103) + (10 x 103) ) = 2 (110 x 103) = 220 kHz
Practice Problem 22.2
Sketch an OOK signal that represents the bit stream below.
Practice Problem 22.3
90˚
Using the signal constellation shown, answer the following questions.
a)
What type of modulation does this represent?
16 symbols, all with same amplitude but different
phases, so this is 16-PSK.
180˚
0˚
b) How many symbols are represented (M)?
M = 16
270˚
c)
How many bits per symbol are used (N)?
N = log2M = log216 = 4
d) If the Baud Rate is 10,000 symbols/second, what is the bit rate (Rb)?
Rb = Rs x N = 10,000 symbols/sec x 4 bits/symbol = 40 kbps.
e)
Would 16-QAM be more or less susceptible to noise than this type of modulation?
If correctly designed, 16 QAM should in general be less susceptible to noise because the symbols would be
spread further apart. This makes it less likely for the receiver to make an error.
Practice Problem 22.4
Label the modulation schemes.
OOK (carrier is either on or off)
FSK (2 different frequencies shown)
BPSK (2 symbols with same amplitude and frequency, but different
phases)
QPSK (4 symbols with same amplitude and frequency, but different
phases)