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Đề thi MOB MOB
UNIVERSITÉ NATIONALE DE HO CHI MINH VILLE PÔLE UNIVERSITAIRE FRANÇAIS HO CHI MINH VILLETEST Subject: MOB (TD)Duration: 90 minutes; Note: Remember to mark your answers on the answer sheet and NOT on the test booklet. Exam code 132Name: Student’s code: .Question 1: How many frequencies does a full-duplex QAM-64 modem use?A. 1 B. 12 C. 6 D. 2Question 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?A. 400 B. 200C. 100 D. A, B and C are wrongQuestion 3: A modem constellation diagram similar to figure. How many bps can a modem with these parameters achieve at 1200 baud?A. 4800bps B. 2400bpsC. 1200bps D. A, B and C are wrongQuestion 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.A. 40800Hz B. 40400HzC. 44000Hz D. A, B and C are wrongQuestion 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?A. ≈ 485427bps B. ≈ 2321928bpsC. ≈ 1812246bps D. A, B and C are wrongQuestion 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 equationLdGGPPrttr222)4(πλ=, 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?A. ≈ −24.5dBm B. ≈ −64.5dBmC. ≈ +64.5dBm D. A, B and C are wrongQuestion 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%?A. frame size < 100 bits B. 100 bits < frame size < 200 bitsC. frame size > 200 bits D. frame size < 200 bitsQuestion 8: Need to share with each subnet have 510 hosts maximum in a class B address, should use the Subnet Mask?A. 255. 255. 255.0 B. 255. 255. 255.192 C. 255. 255.252.0 D. 255.255.254.0 Page 1/4 - Exam code 132π/43π/45π/47π/4A11010010 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 channelsB. 8 cells with 71 voice channels and 1 cell with 72 voice channelsC. 4 cells with 91 voice channels and 3 cells with 92 voice channelsD. A, B and C are wrongQuestion 10: The signal can be written−−++=10)4/2cos(00)4/32cos(01)4/32cos(11)4/2cos()(fortfAfortfAfortfAfortfAtsccccππππππππ.What is the modulation type?A. QAM-4 B. PSK-4 C. PSK-2 D. QAM-2Question 11: A typical Bluetooth data frame describe in figure. Which field determines the active devices?A. Header B. Access code C. Address D. ChecksumQuestion 12: If the diameter of receiving antennas parabolas is 30 cm, what is the frequency concerned?A. 1GHz B. 1MHzC. 1kHz D. A, B and C are wrongQuestion 13: The signal can be written=001)2cos()(binaryforbinaryfortfAtscπ.What is the modulation type?A. ASK-2 B. ASK-4 C. PSK-2 D. QAM-2Question 14: The output power at transmitter is 1W, power received is 100mW. The gain is?A. −10 dB B. 100 C. 10 dB D. 1Question 15: A telephone line has a bandwidth of 4kHz. The signal-to-noise ratio is 3162. For this channel the capacity is?A. ≈ 46480 bps B. ≈ 40000 bpsC. ≈ 37944 bps D. A, B and C are wrongQuestion 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?A. ≈ 3666m B. ≈ 4850mC. ≈ 9699m D. A, B and C are wrongQuestion 17: What is the baud rate of the standard 10-Mbps Ethernet?A. 10 Mega baud B. 20 Mega baud C. 30 Mega baud D. 5 Mega baudQuestion 18: The power of a signal is 100 mW and the power of the noise is 1W; what are the values of SNRdB? Page 2/4 - Exam code 132 A. +100 dB B. +10 dB C. 0.1 D. −10 dBQuestion 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?A. ≈ 46.6Mb/s B. ≈ 23.3Mb/sC. ≈ 52.3Mb/s D. A, B and C are wrongQuestion 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?A. ≈ 14km B. ≈ 70kmC. ≈ 29km D. A, B and C are wrongQuestion 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 1C. A, B, C and D send bit 0 D. A, B and D send bit 1, C send bit 0Question 22: The transmitter is performing in the 2.4 GHz. What the height shall you place the antennas above the ground?A. ≈ 1m B. ≈ 20mC. ≈ 0.66m D. A, B and C are wrongQuestion 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?A. ≈ 11 B. ≈ 272C. ≈ 10.65 dB D. A, B and C are wrongQuestion 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/HzQuestion 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/sQuestion 26: The relationship between bit rate and modulation rate?A. R ≤ 2B B. C = B log2 (1 +NS) C. R = TS1D. D = R × nQuestion 27: In the cellular network, Q = D/R called co-channel reuse ratio. Suppose i = 3 and j = 1. What is the Q?A. ≈ 6 B. ≈ 6.24C. ≈ 4.58 D. A, B and C are wrongQuestion 28: For the network address 172.16.0.0/16. How many subnets this network can be split up?A. 16 B. 214C. 216D. A, B and C are wrongQuestion 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 4.5µW. Calculate the output SNR in dB?A. ≈ −30.5dB B. ≈ +30.5dBC. ≈ −89dB D. A, B and C are wrongQuestion 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 Page 3/4 - Exam code 132 space distance of 100m? The value Pr(d0) may be predicted from equationLdGGPPrttr222)4(πλ=, where Gt, Gr are antenna gain at transmitter, receiver, and L ≥ 1 is the system loss factor.A. ≈ +47dBm B. ≈ −24.5dBmC. ≈ +24.5dBm D. A, B and C are wrongQuestion 31: One class A address borrowed 21 bits to divide subnet, the Subnet Mask is?A. 255.255.255.248 B. 255.255.224.0 C. 255.255.192.0 D. 255.255.248.0Question 32: The radius of a cell in cellular network is 1600m. What is the distance between centers of adjacent cells?A. ≈ 2770m B. ≈ 1600mC. ≈ 3200m D. A, B and C are wrongQuestion 33: Consider a noiseless channel with a bandwidth of 3000 Hz transmitting a signal with 16 signal levels. The maximum bit rate can be?A. 48000 bps B. 3000 bps C. 12000 bps D. 6000 bpsQuestion 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?A. ≈ 300 B. ≈ 700C. ≈ 600 D. A, B and C are wrongQuestion 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?A. ≈ 1.2m B. ≈ 0.64mC. ≈ 0.32m D. A, B and C are wrongQuestion 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?A. 192.168.1.255 B. 192.168.1.15 C. 192.168.1.31 D. 192.168.1.96Question 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?A. 500 bits B. 5000 bits C. 1000 bits D. 10000 bitsQuestion 38: What is EIRP of a dipole antenna fed with a power of 100 mW?A. ≈ 100mW B. ≈ 0.1WC. ≈ 0.16W D. A, B and C are wrongQuestion 39: We need to send 56 kbps over a noiseless channel with a bandwidth of 4 kHz. How many signal levels do we need?A. 1 B. 64 C. 2 D. 128Question 40: Which modulation does a constellation diagram correspond to?A. QAM-4 B. PSK-4 C. PSK-2 D. QAM-2---------------------------------------------------------- The end ---------- Page 4/4 - Exam code 132π/43π/45π/47π/4A11010010 . HO CHI MINH VILLE PÔLE UNIVERSITAIRE FRANÇAIS HO CHI MINH VILLETEST Subject: MOB (TD)Duration: 90 minutes; Note: Remember to mark your answers on the answer. spectrum of a channel is between 2.4 GHz and 2.401 GHz and SNRdB = 4 dB. For this channel the bit rate is?A. ≈ 485427bps B. ≈ 2321928bpsC. ≈ 1812246bps D.