A binary signal is mapped to one of two possible phase
changes. This mapping is fully described by a phase state
table. For example, let??™s consider the phase state table in
Table 2.1.
This table is translated to a signal constellation diagram
(see Fig. 2.20). This modulation scheme has the two phase
states located 180 degrees out of phase. This is the furthest possible distance that phase states can be
separated on this two-dimensional plane. BPSK is also commonly called ???antipodal signaling??? and
TABLE 2.1 BPSK Phase State Table
Data bit Phase change
0 0
1
achieves the best probability of error in an AWGN channel [23]. This scheme has a spectral efficiency
of 1 bps/Hz.
The transmitted signal is mathematically represented as
(2.10)
As the constellation shows BPSK is a real-valued signal. A block diagram of the BPSK modulator is
shown in Fig. 2.21. The time interval of the information signal m(t) is denoted as Tb, bit time. An LPF
was inserted to reduce the out-of-band emissions.
S(t) m(t) # cos (vct)
64 CHAPTER TWO
Q-Axis
I-Axis
Phase
States
???0??? ???1???
FIGURE 2.20 BPSK signal constellation diagram.
LPF
+
X
X
cos(wct)
??“sin(wct)
I(t)
Q(t)
S(t)
m(t)
Information Signal
Zero
Quadrature Modulator
Tb ??“1
+1
m(t)
t
FIGURE 2.
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