DOGUS UNIVERSITY
FACULTY OF ENGINEERING
ELECTRONICS AND COMMUNICATIONS
ENGINEERING DEPARTMENT (ECED)
CEE 312
EXPERIMENT 5:
BINARY PHASE SHIFT KEYING (BPSK)
Objective:
This project is about the Generation of Phase Shift Keying – PSK.
Equipment:
LabVIEW 7.0
Pre Lab:
1- Draw the block diagram of a BPSK modulator.
2- One can use Q-PSK, 8-PSK, 16-PSK, 2m-PSK etc. Explain the trade-off
between bit rate and error probability.
General Information:
In PSK (Phase Shift Keying), the phase of a carrier is changed between two values
according to the binary signal level. The information about the bit stream is contained in
the phase changes of the transmitted signal. For instance to transmit the signals “0” and
”1”, PSK signals can be chosen as follows:
0(t) = Asin (ω0t + 0)
1(t) = Asin (ω1t + 1), 0<t≤Ts
Here, 1 and 2 are constant phase shifts. For Binary PSK (BPSK) the state of 1-0 =
180 simplifies the modulator design. Moreover, π radian between phases of PSK signals
will be most appropriate from error-performance point of view. For example, (0, 1)
phase values can be chosen as (0, π) or (π/2, 3π/2). Therefore, 0(t) and 1(t) waves can
be written as follows:
0(t) =
Acos(ω0t) 0<t≤Ts
0,
otherwise
1(t) = - 0(t) =
- Acos(ω0t) = Acos(ω0t - π),
0,
0<t≤Ts
otherwise
Page | 1
DOGUS UNIVERSITY
FACULTY OF ENGINEERING
ELECTRONICS AND COMMUNICATIONS
ENGINEERING DEPARTMENT (ECED)
BPSK is illustrated in Figure 1:
Carrier
wave (ω0)
(t)= s(t)sin(ω0t)
×
~
Ü
Bipolar bit stream T
+V
0
BPSK signal
centered on ω0
T = bit clock period
ω0 >> 2π/T
-V
Figure 1. Generation of BPSK
As seen from the Figure 1, a sinusoidal waveform is multiplied by the input bit stream.
Each time the bit stream changes sign (by crossing zero level), the phase of the PSK
signal also changes. The time domain illustration of a BPSK signal waveform is given in
Figure 2.
Figure 2. Binary Input Signal and BPSK Output
Demodulation of PSK signal:
The synchronous demodulator diagram is given in Figure 3. Translation back to baseband requires a local synchronized carrier. This can be either 1(t) or 0(t).
Page | 2
DOGUS UNIVERSITY
FACULTY OF ENGINEERING
BPSK
centered on ω0
ELECTRONICS AND COMMUNICATIONS
ENGINEERING DEPARTMENT (ECED)

Integrator
∫
t=T
Carrier ω0
ϕ1(t) or ϕ0(t)
Decision
Making
Circuit
l
Binary
Signal
Treshold = 0
Figure 3. Demodulation of BPSK signal
At the instants which are a multiple of the period T, decision for the bit value is given as
follows: if the output of integrator, that’s l, is positive (l>0) then the decision maker
produces ‘1’. If l is negative (l<0) then binary ‘0’ is produced.
Procedure:
a) Create two controls at Front Panel, “f_sine, f_pulses”
b) Also, as usual, create “flat sequences” and a “while loop” in it at the block diagram.
Wire constants to local variables at block diagram as you did in last experiments. Also,
insert “local variables” in “while loop” in read mode. Let the sine wave with frequency of
fsine = 50 Hz and the square wave with frequency of fpulses = 25 Hz, respectively.
c) You need to generate signals with frequencies fpulses, and fsine. Use “Simulate Signal”
function, following the path;
-Right click--Input—Simulate Signal
d) Wire fpulses, and fsine to frequency input of “Simulate Signal function”. Select “Square” as
signal type for pulses and “Sine” for sine wave. Set the “Amplitude” 0.5 and “Off-Set” 0.5
for pulse signals.
e) Using these signals design a BPSK modulator. You can benefit from Figure 1.
f) Letting fsine = 100 Hz and the square wave frequency of fpulses = 50 Hz, check and
observe the operation of the “vi” file you designed.
g) You should obtain the output graph, similar to in Figure 4.
Page | 3
DOGUS UNIVERSITY
FACULTY OF ENGINEERING
ELECTRONICS AND COMMUNICATIONS
ENGINEERING DEPARTMENT (ECED)
Figure 4 BPSK Modulated Signal
Lab Instructor’s Initials:
DATE)_______________(SUPERVISOR)____________(SIGNATURE)_____________
Post Lab:
1- BPSK is used to transmit information over an AWGN. A noise power spectral density
N0/2 is equal to 10-10 W/Hz. The transmitted signal energy Eb is equal to A2T/2, where T
is the bit interval and A is the signal amplitude. Determine the signal amplitude required
to achieve an error probability of 10-6 if the data rate is
a) Kx10 kbits/sec
b) Kx100 kbits/sec
c) K Mbits/sec.
d) Kx10 Mbits/sec
Here, the value K is your first non-zero digit in your school number, right to left. For
example if your school number is 200934020, take the value of K, “2”.
Page | 4