Sheet 1
Q1) differential coding is a technique used to
provide unambiguous signal reception when using some types
of modulation. It makes data to be transmitted to depend not
only on the current signal state, Is used to provide polarity
reversal protection , but also on the previous one.
Q2)When the continuous analog signal is sampled at a
frequency F, the resulting discrete signal has more frequency
components than did the analog signal. The Sampling
Theorem states that a signal can be exactly reproduced if it is
sampled at a frequency F, where F is greater than twice the
maximum frequency in the signal.
Q3) FM and PM cannot be distinguished at a constant
modulating frequency. However with change in modulating
frequency fm, the modulation index of FM will change and
that of the PM won’t.
Q4) Analog signals representing digital data would typically
have sudden changes in the signal values; this essentially
means that the frequency spectrum of the underlying signal is
wide. PCM is better at encoding such signals since it attempts
to approximate the actual signal value and can handle large
variations in short time (high frequency components). On the
other hand, Delta Modulation encodes the difference to
within some level of precision, and would have high
overload/underload effects when signal values have large
sudden variations.
Q5) In telecommunications, asynchronous communication
is transmission of data, generally without the use of an
external clock signal, where data can
be transmitted intermittently rather than in a steady stream.
Any timing required to recover data from the communication
symbols is encoded within the symbols. In Asynchronous.
Q6) Interference is avoided under frequency division
multiplexing by the use of guard bands, which are unused
portions of the frequency spectrum between subchannels.
Q7) Interference is avoided under frequency division
multiplexing by the use of guard bands, which are unused
portions of the frequency spectrum between subchannels.
Q8) A statistical Time Devision Multiplexing is more efficient
than a synchronous TDM because it allocates time slots
dynamically on demands and doesm't dedicate channel
capacity to inactive low speed lines.
Q9) In synchronous TDM, every device which is present in this
has given the same time slot to transmit data. It does not
consider whether the device contains data or not. The devices
place their data on the link when their time slots arrive, if
somehow any device does not contain data its time-slot
remains empty. There are various kinds of time slots that are
organized into frames and each frame consist of one or more
time slots dedicated to each sending device.
Q10) (SNR)db=6.02n+1.76, where n is the number of bits used
for quantization. In this case, (SNR)db=60.2+1.76 =61.96 dB
Q11) a. (SNR)db = 6.02 n + 1.76 = 30 dB
n = (30 – 1.76)/6.02 = 4.69
Rounded off, n = 5 bits
This yields 25 = 32 quantization levels
b. R = 7000 samples/s × 5 bits/sample = 35 Kbps
Q14)
Q15)
A)Total overhead; 2 x 10,000 = 20,000 bits.
Time overhead; 20,000/2400 = 8.3333 seconds.
B)10,000 characters/1000 per frame=10 frames required to
transmit file.
Overhead in bits is 10 x 48 = 480 bits.
Time overhead is 480/2400 =0.2 seconds.
Q16) synchronous TDM: 100 x 9600 bps = 960,000 bps
statistical TDM: 100 x 9600 bps x 0.5/0.8 = 600,000 bps
Q17) Assuming 4 k
Hz per voice signal, the required bandwidth for FDM is 24 × 4
= 96 kHz.
With PCM, each voice signal requires a data rate of 64 kbps,
for a total data rate of
24 × 64 = 1.536 Mbps. At 1 bps/Hz, this requires a bandwidth
of 1.536 Mhz
Q18) A synchronous time division multiplexer interleaves bits
from each signal and takes turns transmitting bits from each
of the signals in a round