Data/Digital Communications

With four bits of encoding, how many distinct symbols can be represented?

• 8

• 16

• 32

• 64

Also referred to as the symbol rate.

• Any of these

• Bit rate

• Information capacity

• Baud rate

For a given bandwidth, what is the highest theoretical bit rate with binary encoding?

• Half the bandwidth

• Twice the bandwidth

• M times the bandwidth

What is the theoretical information capacity that may be propagated at a 10kHz bandwidth and if

the SNR is 30dB?

• 100 kbps

• 99 kbps

• 50 kbps

• 49 kbps

Answer explanation

SOLUTION: I = 10k x log2 (1+10^3) = 99.7kbps (use 99kbps)

What is the theoretical information capacity that may be propagated at a 10kHz bandwidth if the

system uses 64 levels of encoding?

• 120 kbps

• 60 kbps

• 90 kbps

• 240 kbps

Answer explanation

SOLUTION: I = 2(10k) x log2(64) = 120kpbs

A telephone line has a bandwidth of 3.2 kHz and a signal-to-noise ratio of 45 dB. A signal is

transmitted down this line using a four-level code. Calculate the maximum theoretical data rate.

• 12.8 kbps

• 42.52 kbps

• 47.84 kbps

• 6.4 kbps

Answer explanation

SOLUTION: I = 3200log2(1+10^4.5)=47.84kbps; Also I=2*3200*log2(4) = 12.8kbps.

Therefore max I = 12.8kbps

What is the minimum bandwidth to secure 4Mbps transmission speed using 8-bit modulation at

27dB SNR?

• 500 kHz

• 450 kHz

• 250 kHz

• 550 kHz

Answer explanation

SOLUTION: Using Shannon’s Limit: 4Mbps = B log2(1 + 10^2.7); B = 446kHz

Using Shannon-Hartley: 4Mbps = 2B*8; B = 250kHz

Therefore: Min B = 450kHz

What is the minimum SNR required in a communications system with 100kHz bandwidth using

64QAM?

• 18 dB

• 24 dB

• 30 dB

• 36 dB

Answer explanation

SOLUTION: For 64QAM (M=64, N=6) at 100kHz, then the bit rate = 6*100k = 600kbps

Using Shannon’s Limit: 600k = 100k *log2(1 + SNR);

SNR(dB) = 10 log (63) = 18dB

Which type of pulse modulation involves varying the amplitude of the carrier signal to represent

binary data?

• Amplitude Modulation (AM)

• Amplitude-Shift Keying (ASK)

• Pulse Amplitude Modulation (PAM)

• Frequency-Shift Keying (FSK)

Which digital modulation technique is most resistant to noise and interference?

• Amplitude-Shift Keying (ASK)

• Frequency-Shift Keying (FSK)

• Phase-Shift Keying (PSK)

• Pulse Width Modulation (PWM)