This set of Electronic Devices & Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Spread Spectrum”.

(Q.1-Q.3) A pseudo-noise (PN) sequence is generated using a feedback shift register of length m = 4. The chip rate is 107 chips per second.

1. The chip duration is
a) 1µs
b) 0.1 µs
c) 0.1 ms
d) 1 ms

2. The period of PN sequence is
a) 1.5 µs
b) 15 µs
c) 6.67 ns
d) 0.67 ns

3. The PN sequence length is
a) 10
b) 12
c) 15
d) 18

4. A fast FH/MFSK system has the following parameters.
Number of bits per MFSK symbol = 4
Number of pops per MFSK symbol = 4
The processing gain of the system is
a) 0 dB
b) 7 dB
c) 9 dB
d) 12 dB

5. A slow FH/MFSK system has the following parameters.
Number of bits per MFSK symbol = 4
Number of MFSK symbol per hop = 5
The processing gain of the system is
a) 13.4 dB
b) 37.8 dB
c) 6 dB
d) 26 dB

(Q.6-Q.7) A rate 1/2 convolution code with dfrec = 10 is used to encode a data sequence occurring at a rate of 1 kbps. The modulation is binary PSK. The DS spread spectrum sequence has a chip rate of 10 MHz.

6. The processing gain is
a) 14 dB
b) 37 dB
c) 58 dB
d) 104 dB

7. The coding gain is
a) 7 dB
b) 12 dB
c) 14 dB
d) 24 dB

(Q.8-Q.9) An FH binary orthogonal FSK system employs an m 15 stage liner feedback shift register that generates an ML sequence. Each state of the shift register selects one of L non over lapping frequency bands in the hopping pattern. The bit rate is 100 bits/s. The demodulator employ non coherent detection.[/expand]

8. If the hop rate is one per bit, the hopping bandwidth
for this channel is
a) 6.5534 MHz
b) 9.4369 MHz
c) 2.6943 MHz
d) None of the mentioned

9. In a fast FH spread spectrum system, the information is transmitted via FSK with non coherent detection. Suppose there are N = 3 hops/bit with hard decision decoding of the signal in each hop. The channel is AWGN with power spectral density 0.5No and an SNR 20 ~13 dB (total SNR over the three hops). The probability of error for this system is
a) 0.013
b) 0.0013
c) 0.049
d) 0.0049

10. Suppose the hop rate is increased to 2 hops/bit and the receiver uses square law combining the signal over two hops. The hopping bandwidth for this channel is
a) 3.2767 MHz
b) 13.1068 MHz
c) 26.2136 MHz
d) 1.6384 MHz