ECET 380 Midterm Chicago

Question 1.

Question :

 (TCO  1) Multipath occurs in a radio channel creating small-scale fading due to the following factor:

  Rapid changes in signal strength

  Random frequency modulation

  Time dispersion

  All of the above

  None of the above

Question 2.

Question :

(TCO  1)  Wavelength is ________________ proportional to frequency.

  directly

  inversely

  not

  equally

 3.

Question :

(TCO 1)  A vehicle is traveling at 25 m/s directly toward the transmitter while receiving a mobile signal at 1900 MHz.  What is the received frequency?

  1900.00158 MHz

  1900 MHz

  1899.99842 MHz

  1900.000158 MHz

  None of the above

 4.

Question :

(TCO 1)  The coherence bandwidth of a communication channel is estimated to be 2 kHz. Small scale propagation measurements are made in real time from a vehicle moving at 70 m/s. Assuming that samples are taken at intervals of 1/4 the Coherence time to ensure correlation of consecutive samples, how many samples are taken over a 20 m travel distance?

  1600

  800

  3200

  2400

  None of the above

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 6.

Question :

(TCO 1) A spread spectrum system using sliding correlation has the following properties:  Chip Rate = 32 Mbps; Slide factor 10^-4; 24 shift registers in the sequence generator.  What is the time between maximum correlations (ΔT)?

  68.3 µs

  57.6 µs

  25.4 µs

  46.5 µs

  None of the above

 7.

Question :

(TCO 1)  In small scale fading based on Doppler spread, fast fading has the characteristics of:

  Low Doppler spread

  Coherence time less than symbol period

  Channel variations slower than baseband signal variations

  Both b and c

  None of the above

Question 8.

Question :

(TCO 2)  _________________ diversity can be created without using additional bandwidth.

  Frequency

  Time

  Spatial

  all of the above

  None of the above

Question 9.

Question :

(TCO 2)  A certain transmission channel has a bandwidth of 2 MHz. What is the channel capacity if the SNR is 37 dB?

  12.3 Mbps

  18.6 Mbps

  24.58 Mbps

  36.3 Mbps

  None of the above

Question 10.

Question :

(TCO 2)  Multiple input, multiple output (MIMO) diversity gains can be obtained with the following:

  multiple receive antennas

  multiple transmit antennas

  both a and b

  neither a nor b

Question 11.

Question :

(TCO 3) What is the bandwidth of a raised cosine filter pulse with a symbol time of 64 µs and a roll-off factor of 0.25?

  19.5 kHz

  80 MHz

  26.4 kHz

  19.5 MHz

  None of the above

Question 12.

Question :

(TCO 3)  Linear predictive coders (LPC) belong to the ____________ domain class of vocoders.

  frequency

  spatial

  hybrid

  time

  None of the above

Question 13.

Question :

(TCO 3)  A frequency hopping spread spectrum system has a spread spectrum bandwidth of 2.1 MHz and each hop bandwidth is 7 kHz.  How many frequency hop slots are there in this system?

  21

  15

  250

  300

  None of the above

Question 14.

Question :

(TCO 3)  What is the processing gain (in dB) of a spread spectrum system that has system bandwidth of 400 MHz and an information bandwidth of 200 KHz?

  33 dB

  27 dB

  -33 dB

  -27 dB

  None of the above

Question 15.

Question :

(TCO 3)  PN sequences in a spread spectrum communication system ______________ repeat after the period of the sequence is generated.

  never

  occasionally

  always

  annually

Question 16.

Question :

(TCO 3)  A correlation function equals _______________ if the two codes have nothing in common.

  one

  64

  zero

  None of the above

Question 17.

Question :

(TCO 3)  Frequency division duplexing (FDD) provides __________ distinct bands of frequencies for every user.

  One

  Three

  Five

  Seven

  None of the above

Question 18.

Question :

(TCO 3) A TDMA system has a 25 MHz bandwidth with single channels of 250 kHz bandwidth each, with each frequency channel containing eight TDMA conversation channels.  If each user is assigned one transmit and one receive slot within each frequency channel, calculate the number of users this system can support.  Assume there is no separate guard band.

  100

  800

  400

  200

  None of the above

Question 19.

Question :

(TCO 3)  A system has eight trailing bits, eight guard bits, 32 synchronizing bits, and three traffic bursts of 64 bits of data per time slot.  What is the frame efficiency if there are eight time slots per bit frame?

  20%

  40%

  60%

  80%

  None of the above

Question 20.

Question :

(TCO 4)  In a cellular system, channels are reused within _________________.

  same cell

  same cluster

  coverage area

  Never

Question 21.

Question :

(TCO 4)  One of the differences between 2G Mobile Radio Networks and 2.5G Mobile Radio Networks is:

  Internet browsing is not supported in 2G systems

  Different transmit frequencies are used

  Different multiple access technologies are used

  All of the above

  None of the above

Question 22.

Question :

(TCO 4)  CDMA systems increase a user’s data throughput by _____________________

  assigning more frequencies

  increasing spatial separation between users

  increasing the length of a PN code

  allowing the use of multiple Walsh codes

  None of the above