(2.59)
This improvement can also be seen in the BER curves in Fig. 2.90, where the receiver is assumed
to have used ideal coherent detection.
Eb
No
> S
N
# 1
k
Eb
No
S
N
# 1
k
# WTs
S
N
# 1
k
# W
Rs
Eb
No
S
N
# WTs
log2(M)
Eb
No
S
N
# W
Rb
MODULATION THEORY 103
SER
SNR [dB]
M = 2
M = 4
M = 16
Direction of Increasing M
FIGURE 2.89 M-ary FSK symbol error rate performance.
Coherent Detection of Orthogonal M-ary FSK
1.0E??“5
1.0E??“4
1.0E??“3
1.0E??“2
1.0E??“1
1.0E+0
0 1 2 3 4 5 6 7 8 9 10 11 12
Eb/No (dB)
Probability of Bit Error (Pb)
BFSK
4-FSK
8-FSK
16-FSK
64-FSK
FIGURE 2.90 Alternative representation of M-ary FSK Bit Error Rate performance.
2.2.10 M-ary Phase Shift Keying (PSK)
Let us consider the example of 16-PSK, the transmit signal is generated as shown in Fig. 2.91. The
input bit stream is grouped into sections of k bits, thus making 2k possible modulation levels. The
input bit rate is Rb bps and is converted to a symbol rate of Rs sps. In this case, Rs 1/4 Rb, hence
occupying less transmission BW.
104 CHAPTER TWO
LPF
+
X
X
cos(wct)
??“sin(wct)
I(t)
Q(t)
Quadrature Modulator
LPF
Group
4 Bits
into a
Symbol
Lookup
Table
(LUT)
m(t)
PA
Bits
Symbol
Index
Symbols
FIGURE 2.
Pages:
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178