Deck 10: Wireless Digital Communications

Question 1

The three groups of wireless technologies are

A) wired wireless, mobile wireless, IR wireless
B) wired wireless, mobile wireless, wired IR
C) fixed wireless, mobile wireless, wired wireless
D) fixed wireless, mobile wireless, IR wireless

Answer 1

D

Question 2

A cyclic prefix in OFDM means

A) the very end of a symbol is copied to the beginning of the data stream thus leaving a gap
B) the very end of a symbol is copied to the beginning of the data stream thus leaving no gap
C) the very end of a symbol is copied to the beginning of the data stream thus leaving a defined gap
D) the very beginning of a symbol is copied thus leaving no gap

Answer 2

B

Question 3

The terms sin^2(A) can be written as

A) )5 [1 - cos 2A]
B) )5 [1 - cos A]
C) )5 [1 x cos 2A]
D) )5 [1 + cos 2A]

Answer 3

A

Question 4

A PN code of length 2^n - 1 is said to be of

A) repetitive
B) lengthy
C) maximal length
D) minimal length

Question 5

Determine the sequence length of a properly connected PN sequence generator containing 31 shift registers

A) 2,147,483,648
B) 2,147,483,647
C) 2,147,483,646
D) 2,147,483,649

Question 6

The signature sequence in DSSS is

A) the pseudo random digital sequence used to spread the signal
B) aids with the reception of weak signals
C) limits the data rate
D) eliminates the need for QPSK transmission

Question 7

The output data of a digital communication link is shown in the figure below. The modulation technique being used is:

A) 8QAM
B) 8PSK
C) BPSK
D) QPSK

Question 8

How is the high frequency component removed for the output of a QPSK phase detector with a value of 0.5A cos (0 + (phi)d) - (0.5A cos 2(omega)ct)?

A) band-stop filter
B) high-pass filter
C) low-pass filter
D) notch filter

Question 9

FSK is a form of:

A) FM
B) PM
C) AM
D) none of the above

Question 10

Determine the channel bandwidth required for a wideband FSK system

A) 5 to 10 kHz
B) 20 to 25 kHz
C) 5 to 15 kHz
D) not enough information to answer

Question 11

The output signal of a M-ary system is called a

A) star
B) array
C) constellation
D) none of the above

Question 12

This type of code has an output that appears to be noise-like

A) spread code
B) pseudo noise code
C) pseudo spectrum
D) pseudo code

Question 13

What is the purpose of a loop back when used in digital modulation systems?

A) the loop back is never compared with the original data
B) the loop back is compared with the original data to indicate system performance
C) the loop back is only compared with the original data to indicate a system noise figure
D) the loop back is compared with the original data to indicate system data rate

Question 14

Determine the sequence length of a properly connected PN sequence generator containing 5 shift registers

A) 69
B) 32
C) 31
D) 36

Question 15

A general rule is that the chip rate is what relative to the data modulation rate?

A) must be less that 12% of the modulation rate
B) approximately 5 to 7 times the modulation rate
C) is independent of the modulation rate
D) must be greater than 70.7% of the modulation rate

Question 16

DSSS uses a pseudorandom sequence of pulses shorter than the message bit. These are called

A) chips
B) parce bits
C) fractals
D) fractures

Question 17

Determine the spreading of a DSSS signal given the following parameters: Modulation bit rate: 56 kbps Chip rate: 280 kbps

A) spreading = 1.2
B) spreading = 0.2
C) spreading = 1.0
D) spreading = 5.0

Question 18

The term for the situation when two spread spectrum transmitters momentarily transmit at the same time is called

A) lost data
B) a data burst
C) a hit
D) design error

Question 19

Another name for OFDM is

A) DSSS
B) QPSK
C) multitone modulation
D) discrete modulation

Question 20

If two signals are sent over the same media without interference the two signals are said to be

A) symmetrical
B) orthogonal
C) vertical
D) parallel

Question 21

The term for an analog digital FM signal that shares the same bandwidth is

A) hybrid FM
B) PCM AM
C) spread spectrum FM
D) SSB FM

Question 22

The LM1871 and LM1872 integrated circuits

A) can handle more than one channel of digital data
B) use PWM as a pulse modulation technique
C) can be used to create a radio-telemetry system that operates at a frequency of approximately 49 MHz.
D) all of the above

Question 23

Which of the following is an advantage of transmitting in a digital format?

A) less sensitive to noise
B) lower distortion levels
C) less crosstalk
D) all of the above

Question 24

The digital data rate for FM digital is

A) 1.544 Mbps
B) 96 kbps
C) 96 kbps
D) 36 kbps

Question 25

The digital data rate for AM digital is

A) 36 kbps
B) 56 kbps
C) 1.544 Mbps
D) 56 kbps