Digital Communication Refresher
Digital Communication Refresher
Digital Communication Refresher
PPM
1. Slope overload is a phenomenon that is c. PAM
generally observable on what bandwidth d. PFM
reduction technique? 8. ITU G.711 recommends the use of µ-law
a. DPCM and A-law with a sampling rate of ___
b. ADPCM and 8 binary digits per sample
c. DM a. 4 kHz
d. ADM b. 8 kHz
2. A compression characteristic of µ = 0 on c. 16 kHz
µ-law indicates d. 32 kHz
a. Uniform quantization 9. In keying techniques, this is also known
b. Medium compression as information density
c. Non-linear amplification a. Bandwidth efficiency
d. Non-uniform quantization b. Eb/No
3. Approximately how much decibel c. Dynamic range
improvement can one expect for a linear d. SNR
PCM system utilizing a 7-bit PCM code 10. In information theory, the ultimate data
assignment? compression is bounded by the system’s
a. 6 __
b. 24 a. Encoding technique
c. 30 b. Channel capacity
d. 42 c. Information measure
4. In checksum, the check digit is usually d. Entropy
the 11. A baud of 10000 is the same as
a. First digit a. 10 kbps
b. Second digit b. 10 KHz
c. Middle digit c. 10000 symbols/sec
d. Last digit d. 10000 cycles/bit
5. What encoding technique is used by the 12. Numerical indication of how a PCM code
IEEE standard? is efficiently utilized
a. NRZ-L a. Quantization
b. AMI b. Entropy
c. Manchester c. Coding efficiency
d. Differential Manchester d. Source efficiency
6. An input voltage of -7.275 V was 13. Message = 11100110, G(X) = X^4 + X^3 +
measured on a PCM system whose 1, find the CRC
resolution is 0.025V. This will be digitally a. 110
compressed into 8-bits as b. 0110
a. 01101010 c. 0011
b. 00010010 d. 1100
c. 01010110 14. This type of encoding uses two levels to
d. 01010010 represent a symbol
7. Simplest form of pulse modulation a. unipolar
a. PCM b. polar
c. bipolar 21. A supergroup has a bandwidth of
d. multipolar a. 60 kHz
15. Which of the following has the least b. 240 kHz
problem on the presence of dc c. 2.52 MHz (mastergroup)
components? d. 69.984 MHz
a. NRZ-L
b. AMI
c. NRZ-I
d. Unipolar
16. In this encoding, a symbol is represented
by 1.58 bits
a. NRZ-L
b. NRZ-I
c. Manchester 22. A T-1 line is used to implement a DS-1
d. Pseudoternary service with a data rate of
17. Which of the following codes is an a. 64 kbps
example of differential encoding? b. 1.544 Mbps
a. NRZ-L c. 2.048 Mbps
b. NRZ-I d. 6.312 Mbps
c. Manchester 23. How many voice channels are supported
d. AMI in an E-1 line?
18. The scrambling techniques, HDB3 and a. 24
B8ZS, were based on the rules of b. 30
a. NRZ-L c. 60
b. NRZ-I d. 300
c. Differential Manchester 24. Statistical TDM is also known as
d. AMI a. asynchronous TDM
19. This method of error detection has the b. synchronous TDM
least likelihood of achieving error c. isochronous TDM
detection d. multilayer TDM
a. the use of parity 25. TCM technique was primarily proposed
b. checksum by __.
c. CRC a. Ungerboeck
d. Hamming code b. Cutler
20. Five channels, each with a 100-kHz c. Reeves
bandwidth, are to be multiplexed d. Chiariglione
together. What is the minimum 26. Bandwidth efficiency for 64 QAM with a
bandwidth of the link if there is a need rate of 10 Mbps
for a guard band of 10kHz between the a. 1 bits/cycle
channels to prevent interference? b. 2 bits/cycle
a. 500 kHz c. 6 bits/cycle
b. 510 kHz d. 8 bits/cycle
c. 520 kHz 27. Determine the minimum bandwidth
d. 540 kHz required to achieve a Eb / No of 14 dB for
an 8-PSK system operating at 20 Mbps 30. A binary source sends a 1 with a
with a C/N of 11 dB. probability of 30%. Determine the
a. 40 MHz entropy of this source
b. 45 MHz a. 0.881 bit/symbol
c. 50.25 MHz b. 0.921 bit/symbol
d. 60 MHz c. 1 bit/symbol
d. 1.5 bits/symbol
31. Maximum rate at which information can
be transmitted through a channel
a. Bit rate
b. Baud rate
c. Coding
d. Channel capacity
*pareho ata soln ng 27&28 32. Information capacity is proportional to
_____.
28. Determine the minimum bandwidth for a a. bandwidth
32-QAM modulator with an input bit rate b. noise
of 20 Mbps c. power
a. 4 MHz d. flux
b. 5 MHz 33. Channel capacity of a 6-MHz channel
c. 15 MHz with a S/N ratio of 25 dB
d. 20 MHz a. 50 Mbps
b. 55 Mbps
c. 60 Mbps
d. 80 Mbps
𝑆𝑁𝑅(𝑑𝐵)
𝑆𝑁𝑅𝑤𝑎𝑡𝑡𝑠 = 10 10 ; C=(BW)x𝑙𝑜𝑔2 (1 + 𝑆𝑁𝑅)