Comparison of Different Modulation Techniques and Error Detection Process

1. Convert the binary data “011010” into analog waveforms using following
modulation techniques:
a. Two level Amplitude Shift Keying
b. Two level Frequency Shift Keying
c. Two level Phase Shift Keying
d. Differential Phase shift keying
e. Four level Amplitude Shift Keying
f. Four level Phase Shift Keying
g. Eight level Amplitude Shift Keying
ANS:
a. Two level Amplitude Shift Keying
 Amplitude Shift Keying is the simplest type of digital
CW modulation.
 The ASK modulator is nothing but a multiplier followed by band
pass filter.
 This multiplier multiply the NRZ digital signal and the sinusoidal
carrier to produce the ASK signal as its output.
 Two level ASK means Binary ASK. Due to the multiplication the
ASK output will present only a binary 1 is to be transmitted.
 ASK output corresponding to binary 0 is zero.

b. Two level Frequency Shift Keying
 In FSK frequency of the carrier signal varies according to the
digital input signal but there is no change in the amplitude and
phase of the carrier.
 Two level FSK called as Binary FSK. The output of a FSK
modulated wave is high in frequency for a binary 1 input and is
low in frequency for a binary 0 input.
c. Two level Phase Shift Keying
 Binary PSK is the most efficient of the three modulation methods,
i.e ASK, FSK, PSK. Therefore it is used for high bit rate.
 In BPSK phase of the sinusoidal carrier changes according to
the data bit to be transmitted.
 In BPSK carrier phase is changed between 0 degree and 180
degree by the bipolar digital signal.
d. Differential Phase shift keying

 DPSK combines two basic operations
1) The differential encoding and
2) Phase shift keying
 DPSK will eliminate the ambiguity about whether the received
data was inverted or not.
 DPSK does not require the synchronous carrier at the demodulator
at the detection.
e. Four level Amplitude Shift Keying
 In four level Amplitude Shift Keying amplitude of carrier signal
changes in four levels according to the input digital signal which
is divide in 2 bit symbols.
 Here binary input is 011010 ,so divide this in 2 bit symbol like this
01 10 10
 For 00, 01, 10, 11 inputs 4 different amplitude carrier signal will
get at the output.

f. Four level Phase Shift Keying
 In Four level PSK carrier changes in 4 phases
(0,90,180,270 degrees) according to the 2 bit(symbol) input
digital signal.
 For 00, 01, 10, 11 input signal phases are 0, 90, 180, 270 degree
respectively.
g. Eight level Amplitude Shift Keying
 In eight level ASK amplitude of carrier signal changes in eight
level according to the binary input signal which is 3bit symbol.
 Here binary input is 011010 ,so divide it into 3 bit symbol like this
011 010
 For 000 , 001, 010, 011, 100, 101, 110, 111 these eight binary
input signal 8 different amplitude assigned.