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AM, FM, and Digital Modulated Systems Chap. 5
5–59 Assume that 4,800-bits random data are sent over a bandpass channel by BPSK signaling. Find
the transmission bandwidth B T such that the spectral envelope is down at least 35 dB outside this
band.
5–60 As indicated in Fig. 5–22a, a BPSK signal can be demodulated by using a coherent detector
wherein the carrier reference is provided by a Costas loop for the case of h = 1.0. Alternatively,
the carrier reference can be provided by a squaring loop that uses a × 2 frequency multiplier.
A block diagram for a squaring loop is shown in Fig. P5–60.
(a) Using the squaring loop, draw an overall block diagram for a BPSK receiver.
(b) By using mathematics to represent the waveforms, show how the squaring loop recovers the
carrier reference.
(c) Demonstrate that the squaring loop does or does not have a 180 phase ambiguity problem.
BPSK
signal
input
Frequency
multiplier
× 2
Phase-locked loop
Loop
filter
VCO
Frequency
divider
2
Carrier
reference output
Figure P5–60
5–61 A binary data signal is differentially encoded and modulates a PM transmitter to produce a
differentially encoded phase-shift-keyed signal (DPSK). The peak-to-peak phase deviation is
180 and f c is harmonically related to the bit rate R.
(a) Draw a block diagram for the transmitter, including the differential encoder.
(b) Show typical waveforms at various points on the block diagram if the input data sequence is
01011000101.
(c) Assume that the receiver consists of a superheterodyne circuit. The detector that is used is
shown in Fig. P5-61, where T = 1R. If the DPSK IF signal v 1 (t) has a peak value of A c volts,
determine the appropriate value for the threshold voltage setting V T .
From IF
v 1 (t)
v 3 (t)
Integrator
(n + 1) T
( ) dt
nT
Unipolar
Threshold device
binary
output
v
v 4 (t) Sample v 5 (t) 6
v 6 (t)
& hold
t=nT
V T v 5
One-bit
delay, T
v 2 (t)
Matched filter
Figure P5–61