Đề thi MOB MOB

Đề thi MOB MOB

UNIVERSITÉ NATIONALE DE HO CHI MINH VILLE

PÔLE UNIVERSITAIRE FRANÇAIS HO CHI MINH VILLE

TEST Subject : MOB (TD)

Duration: 90 minutes;

Note: Remember to mark your answers on the answer sheet and NOT on the test booklet. Exam code

132

Name:

Student’s code:

Question 1: How many frequencies does a full-duplex QAM-64 modem use?

Question 2: An analog cellular system has 20 MHz of band-width and uses two channels simplex of

25 kHz to provide a transfer service of full-duplex What is the number of full-duplex channels

available by cell for a reuse factor K = 4?

Question 3: A modem constellation diagram similar to figure How

many bps can a modem with these parameters achieve at 1200

baud?

Question 4: Ten signals, each requiring 4000Hz, are multiplexed on to a single channel using FDM

How much minimum bandwidth is required for the multiplexed channel? Assume that the guard bands are 400Hz wide.

Question 5: The spectrum of a channel is between 2.4 GHz and 2.401 GHz and SNRdB = 4 dB For this channel the bit rate is?

Question 6: Suppose a transmitter produces 50W of power The transmitter’s power is applied to a

unity gain antenna with a 900MHz carrier frequency The close-in distance is d0 = 100m The value

Pr (d0) may be predicted from equation

L d

G G P

2

) 4 ( π

λ

= , where Gt, Gr are antenna gain at transmitter,

receiver, and L ≥ 1 is the system loss factor If Pr is in unit of dBm, the received power is given by

Pr(d) = 10log10[Pr(d0)/0.001] + 20log10(d0/d), where d ≥ d0 What is the received power at a free space distance of 10km?

Question 7: A channel has a bit rate of 5 kbps and a propagation delay of 20 msec For what range of

frame sizes does stop-and-wait give an efficiency of at least 50%?

Question 8: Need to share with each subnet have 510 hosts maximum in a class B address, should

use the Subnet Mask?

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Question 9: Suppose that 1 MHz is dedicated to the control channels and that only a control channel

is necessary by cluster; determine a reasonable distribution of the voice traffic channels for each cell,

for the 9 reuse factors given previously.

A 8 cells with 53 voice channels and 4 cells with 54 voice channels

B 8 cells with 71 voice channels and 1 cell with 72 voice channels

C 4 cells with 91 voice channels and 3 cells with 92 voice channels

D A, B and C are wrong

Question 10: The signal can be written















−

− +

+

=

10 ) 4 / 2

cos(

00 )

4 / 3 2

cos(

01 )

4 / 3 2

cos(

11 ) 4 / 2

cos(

) (

for t

f A

for t

f A

for t

f A

for t

f A

t s

c c c c

π π

π π

π π

π π

.

What is the modulation type?

Question 11: A typical

Bluetooth data frame

describe in figure

Which field determines

the active devices?

Question 12: If the diameter of receiving antennas parabolas is 30 cm, what is the frequency

concerned?

Question 13: The signal can be written







=

0 0

1 )

2 cos(

) (

binary for

binary for t f A

t

.

What is the modulation type?

Question 14: The output power at transmitter is 1W, power received is 100mW The gain is?

Question 15: A telephone line has a bandwidth of 4kHz The signal-to-noise ratio is 3162 For this

channel the capacity is?

Question 16: Suppose a frequency reuse pattern similar to figure

The radius of a cell is 800m What is the minimum distance

between centers of cells that use the same band of frequencies?

Question 17: What is the baud rate of the standard 10-Mbps Ethernet?

Question 18: The power of a signal is 100 mW and the power of the noise is 1W; what are the values

of SNRdB?

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A +100 dB B +10 dB C 0.1 D − 10 dB

Question 19: Assume that the TV picture is to be transmitted over a channel with 4.5MHz bandwidth

and a 35dB signal-to-noise ratio Find the capacity of the channel?

Question 20: The output power of the transmitter is 100 mW and its antenna gain is 2 dBi,

performing in the 2.4 GHz The card sensitivity is -85 dBm for 11 Mbit/s If you suppose both antennas are in direct line of sight and if you don’t consider additional losses What will be the maximum propagation range?

Question 21: Four transmitter having key A: ( − 1 − 1 − 1 +1 +1 − 1 +1 +1), B: ( − 1 − 1 +1 − 1 +1 +1 +1

− 1), C: ( − 1 +1 − 1 +1 +1 − 1 − 1 − 1) and D: ( − 1 +1 − 1 − 1 − 1 − 1 +1 − 1) The received chip sequence is ( − 2 − 2 0 − 2 0 − 2 +4 0) What happened?

A A, B send bit 1 and C, D send bit 0 B A, B, C and D send bit 1

Question 22: The transmitter is performing in the 2.4 GHz What the height shall you place the

antennas above the ground?

Question 23: What is the minimum Eb/N0 required to achieve a channel of low-pass type has a band-width of 1 MHz and a SNR = 3162?

Question 24: The channel of low-pass type has a band-width of 4.5 MHz and a SNR = 3162 What is

the maximum spectral efficacy that one can theoretically reach on such a channel?

A ≈ 38.4Baud/s B ≈ 862bit/s/Hz C ≈ 52321850bit/s D ≈ 11.63bit/s/Hz

Question 25: The digital video having the following characteristics: matrix of 480×640 pixels where

each pixel corresponds to an intensity which can take 32 different values The required speed is of 25 images per second What is the modulation rate of the video source?

A ≈ 7680000b/s B ≈ 38.4Mb/s C ≈ 7680000Baud/s D ≈ 38.4Baud/s

Question 26: The relationship between bit rate and modulation rate?

N

S

) C R =

T S

1

D D = R × n

Question 27: In the cellular network, Q = D/R called co-channel reuse ratio Suppose i = 3 and j = 1

What is the Q?

Question 28: For the network address 172.16.0.0/16 How many subnets this network can be split

up?

Question 29: The telephone line is now to have a loss of 20dB The input signal power is measured

as 0.5W, and the output noise level is measured as 4.5 µ W Calculate the output SNR in dB?

Question 30: Suppose a transmitter produces 50W of power If the transmitter’s power is applied to a

unity gain antenna with a 900MHz carrier frequency, what is the received power in dBm at a free

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space distance of 100m? The value Pr(d0) may be predicted from equation

L d

G G P

2

) 4 ( π

λ

= , where Gt,

Gr are antenna gain at transmitter, receiver, and L ≥ 1 is the system loss factor.

Question 31: One class A address borrowed 21 bits to divide subnet, the Subnet Mask is?

Question 32: The radius of a cell in cellular network is 1600m What is the distance between centers

of adjacent cells?

Question 33: Consider a noiseless channel with a bandwidth of 3000 Hz transmitting a signal with 16

signal levels The maximum bit rate can be?

Question 34: A group of N stations share a Slotted ALOHA channel of 1 Mb/s Each station emits in

average a frame of 12000 bits/second By taking again the results obtained for Smax (maximum

efficiency) determine the maximum value of N that one can have?

Question 35: One takes the antenna gains into account; microwaves transmitter has an output power

of 0.1W at 2 GHz The EIRP of the transmitted signal is 10W What is the wavelength of receiving antennas parabolas?

Question 36: The network’s Subnet Mask is 255.255.255.224, determine its broadcast address if that

a computer which has the address 192.168.1.1?

Question 37: Consider building a CSMA/CD network running at 1 Gbps over a 1–km cable with no

repeaters The signal speed in the cable is 200000 km/sec What is the minimum frame size?

Question 38: What is EIRP of a dipole antenna fed with a power of 100 mW?

Question 39: We need to send 56 kbps over a noiseless channel with a bandwidth of 4 kHz How

many signal levels do we need?

Question 40: Which modulation does a constellation diagram

correspond to?

- The end

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