IFT 372 Wireless Communication - Helm - Quiz 1-7 + Midterm + Lecture Activities
The receiver on a digital line of sight microwave link has a noise figure of 4 dB; What is the No for this receiver in dBm?
-170 dBm
The receiver on a digital line of sight microwave link has a noise figure of 7 dB. What is the No for this receiver in dBM?
-197 dBm
Given the decimal equation: y = a / b. Find the value of y (in decimal), given that a=16dB and b=7dB.
10^(16/10) = 40 10^(7/10) = 5 y = 40/5 y = 8
This is a _________________ constellation diagram. *Description* 16 points plotted in a circle on x y axis. 4 points in each quadrant.
16-PSK
Given the decimal equation: y = a * b. Find the value of y (in decimal), given that a=16dB and b=7dB.
16dB + 7dB = 23dB => 10^2.3 = 199.5 Round to 200
Given a binary signal with a bit rate of 50 kHz, what is the bandwidth?
25 kHz
For a 45 Mbps LTE data stream with a symbol time of 66.67 us, how many subcarriers are created?
3000 subcarriers created
For a 45 Mbps LTE data stream with a symbol time of 66.67 us, how many subcarriers are created?
45*10^6 / 15*10^3 => 3000 subcarriers created
Given an AM frequency of 25 kHz, what is the required bandwidth?
50 kHz
Given the two amplifier gains in a chain: x=33dB and y=4dB, how much would the decimal gain value be for this amplifier chain?
5000
What is the wavelength (in meters) of a 500 kHz signal?
600m
A baseband signal has frequency components from dc to 3.8kHz. Determine the Nyquist theoretical minimum sampling rate.
7.6kHz
What is the Base 2 logarithmic value for the following equation? Log2(956)
9.9
For a resolution of 0.02V, determine the voltages and ranges for the following linear seven-bit sign magnitude PCM code 1001011
= 1001011 = -1 (2^0 + 2^1 + 2^3) * 0.02 Voltage = -1 (11) * 0.02 = -0.22 Range = (-0.21, -0.23)
What parameter of the intelligent signal causes frequency deviation of the carrier?
Amplitude of the modulating signal
Identify four propagation factors.
Anomalous; propagation; diffraction; attenuation; and environmental noise
Fades vary in __________
depth, duration, frequency
What is the effective Temperature (Te in °K) for a system with a 28 dB input SNR and a 24 dB ouptut SNR?
F = (1 + Te/290) NF = 4 dB F = 2.5 2.5 - 1 = Te/290 438°K = Te
A modulated carrier occupies a single frequency.
False
What are the two factors that affect wave propagation?
Frequency and distance
Which system uses digital transmission?
ISDN & LANs
What are the disadvantages of digital communication?
Needs more bandwidth & Is more complex
What is the effective Temperature (Te in °K) for a system with 27 dB input SNR and a 24 dB output SNR?
Noise Factor (F) = [10^(27/10)] / [10^(24/10)] => 2; F = (1+Te/290) 2 - 1 = Te/290) Te = 290 OR Effective Temp (Te) = (F - 1) * 290 = (2 - 1) * 290 = 1 * 290 = 290
What is the noise figure (NF) for a system with a 36 dB input SNR and a 26 dB output SNR? Convert your answer into noise factor (F)
Noise figure = SNR(in)dB - SNR(out)dB = 36dB - 26dB Noise factor (F) = 10^(10/10) = 10
What is the primary tool used to mitigate fading in a wireless system?
Over build the link which increases the margin
Which carrier recovery method has the fastest acquisition time of the three methods?
Remodulator
In a data transmission system, the ___________ is the physical path between the transmitter and receiver
Transmission path and channel
What are the three values used to calculate the effective isotropic radiated power (EIRP)?
Transmitter power, transmission line loss, antenna gain
CCITT recommends a bit error rate (BER) of 1 * 10^-6 for error free communication.
True
What logarithmic base is used in digital communications?
Two
Noise power is measured in _________.
Watts
Given the decimal equation: y = a + b. Find the value of y (in dB), given that a = 10 (decimal) and b = 13 dB (decibel)
a = 10 b = 13 dB b(dec) = 10 ^(b(dB)/20) = 10^(13/20) = 10^0.65 = 4.47 Since decimal equation y = a + b = 10 + 4.47 = 14.47 Convert to dB y(dB) = 20log(y) = 20log(14.47) = 23.2
What is the noise power for a system with 30°C noise temperature in a 250 kHz bandwidth?
-148.3 dBw
What is the noise power for a system with 〖20〗^0C noise temperature in a 250 KHz bandwidth
-150dBW
The receiver on a digital line of sight microwave link has a noise figure of 5 dB. What is the No for this receiver in dBm?
-169
The receiver on a digital line of sight microwave link has a noise figure of 5 dB. What is the No for this receiver in dBM?
-169 dBm
The receiver on a digital line of sight microwave link has a noise figure of 5dB. What is the No for this receiver in dBm?
-169dBm
The receiver on a digital line of sight microwave link has a noise figure of 4 dB. What is the No for this receiver in dBm?
-170 dBm
Given the decimal equation: y = a + b. Find the value of y (in dB), given that a = 20 (decimal) and b = 40 dB (decibel)?
40 dB
Why does the term "symbol" take on different meaning in an OFDM system?
?
The radio of the power radiated to the total input power is called ____________.
Antenna efficiency
An FM signal has a deviation of 15 kHz and a modulating frequency of 5 kHz. The carrier frequency is 1600 kHz. Using Carson's Rule, what is the required bandwidth for this system?
BSCR = 2 * (15kHz + 5kHz) = 40 kHz
Energy per bit (Eb) is a function of the received signal power (Pr) divided by _______
Bit rate
For an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted in QPSK (4PSK)
C = 2 * B log2(m) C = 2 * 500 kHz * log2(4) C = 1000 kHz * 2 = 2000 kHz = 2 MHz
For an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted in 8PSK?
C = 2B log2 (M) C = 2 * 500 kHz * log2 (8) C = 1000 kHz *3 C = 3000 kHz => 3 MHz
The process of extracting a phase-coherent signal reference carrier from a received signal is called
Carrier recovery
Fades vary in ____________
Depth, Duration, Frequency
Which MIMO antenna use improves system performance?
Diversity
List four uses of MIMO
Diversity for better system performance, beam-forming, spatial diversity, increased data rates
Antenna arrays are used for:
Diversity, Parallel data streams, beamforming, directional beams to multiple simultaneous users
Is spreading in frequency in a dispersive channel.
Doppler
______ is spreading in frequency in a dispersive channel.
Doppler
___________ is spreading in frequency in a dispersive channel.
Doppler
In a dispersive medium, what are the two kinds of spread?
Doppler and multipath spread
What are the two type of antenna elements?
Driven and parasitic
What type element is directly connected to the transmission line?
Driven element
Given that the radiation resistance of an antenna is 300 ohm and the elemental resistance is 275 ohm, what is the efficiency of this antenna?
E = Rr / (Rr + Re) E = 300 / (300 + 275) E = 0.522 or 52.2%
Advantages of digital communication are
Easy multiplexing, Easy processing, Reliable
OFDM does not efficiently use the wireless spectrum.
False
P9e) and BER are often used interchangeably because they both have the exact same meaning.
False
Short-term fading is caused mainly by absorption of a transmitted wave by local obstacles such a houses, buildings and other human-built structures or by natural obstacles, such as forests.
False
Signal exist in either the time domain or the frequency domain, but not both.
False
Signal wavelength does not impact parabolic antenna gain.
False
Signals can exist in the time domain or the frequency domain, but not both.
False
The frequency of a signal does not influence the gain of a parabolic reflector.
False
Which of the following are strengths of OFDM?
Frequency selective fading does not adversely affect all subcarriers & effectively uses the wireless spectrum.
The common cause of fading is________
Multipath
Internal noise power can be calculated. What is the formula - Pn = ?
Pn = kTB
Given that Pr = 10^-11 W; T = 30°C; fb = 2Mbps; B = 500 kHZ; Te = 295°K. What is the received noise power (in dBW) at the input to the amplifier chain?
Pr = 1 * 10e-11; Pn = kTB = 1.38e-23 W/Hz-deg K * (273 + 30) deg K * 500e3 Hz = 2.09 * e-15 => -146.8 dBW Pr/Pn = Pr(dBW) - Pn (dBW) = -110 dBW - ( - 146.8 dBW ) => 36.8 dB
Given that Pr = 10^-10 W; T = 30°C; fb = 3 Mbps; B = 400 kHZ; Te = 285°K. What is the energy per bit (Eb), in dB, in the amplifier?
Pr = 1e-10 fb = 3e6 Eb = (Pr/fb) = (1e-10/3e6) = 3.3e-17 => 10log(5e-16) = -164.8 dBJ
What is necessary for digital communication?
Precision timing, Frame synchronization, Character synchronization
Consider an OFDM implementation that uses 15 kHz subcarriers and use an OFDM symbol of 2048 subcarriers. The nominal cyclic prefix accounts for a 7% guard time. The extended cyclic prefix can use up to 25%. 1600 subcarriers can be used for data transmission. The rest are needed for pilot and null subcarriers. The transmission bandwidth is 25 MHz using 8 QAM modulation. What is the data rate for the nominal CP?
R = 25MHz * (1600 / [2048 + 205])*5=88.8 Mbps
Which MIMO antenna use improves capacity?
Spacial division
Free space propagation path loss is [a] / octave or [b] / decade where an octave means doubling the distance and a decade means a period of ten.
a = 6dB; b = 20dB
The interval of frequencies outside which the spectrum is zero is called as ________
absolute bandwidth
__________ rate refers to the rate of change of a signal on the transmission medium after encoding and modulation.
baud
Energy per bit (Eb) is a function of the received signal power (Pr) divided by the _______
bit rate
Linear prediction coding (LPC) and code-excited linear prediction (CELP) are two main approaches used in______.
vocoders
Given the decimal equation: y=a*b. Find the value of y (in decimal), given that a = 13dB and b = 7 dB
y=100
Given the decimal equation: y=a+b. Find the value of y (in dB), given that a=15 and b=60 dB
y=60dB
What parameter of the intelligence signal causes or determines the instantaneous rate of carrier frequency?
The frequency of intelligence signal determines the rate of carrier frequency deviation.
The __________ of a pulse-coded modulated signal is determined by dividing the maximum positive (or negative) voltage by the number of positive (or negative) nonzero PCM codes
Resolution
Given that the radiation resistance for a short dipole antenna is 300 ohm and the length is 150mm, at what frequency would one expect this antenna to radiate?
Rr = 200 * (I/A)^2; Given Rr = 300ohm; I = 150mm; A = c/f 300 = 200 * ((150 * 10^-3)^2 / (3 * 10^8 / f)^2 f^2 = 300 * (3 * 10^8)^2) / (200 * (150 * 10^-3)^2) f^2 = 6 * 10^18 f = 2.5 GHz
What is the power level or RSL (in dBM) entering the first active stage of the receiver at 2100 MHz being fed by a 20 meter coax with a loss of 20dB/km given that the isotropic receive level is -128dBW and the receiving station has a 2 meter radius dish? (assume 55% antenna efficiency)
Rx mision line loss(dB)=(20dB/1000m)×20m=.4dB G=20log(4)+20log(2.1)+17.8 G=12dB+6.44dB+17.8 G=36.2dB RSLDW=-128dBW+36.2dB-.4dB RSLDW=-92.2dBW or -62.2dBm
Given an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted if the SNR is 14 dB.
SNR = 14 dB = 25 I = B log2 (1 + SNR) I = 500 kHz * log2(1 + 25) I = 500 kHz * log2(26) = 2350 kHz = 2.35 MHz
What is the noise figure (NF) for a system with a 36dB input SNR and a 26dB output SNR? Convert your answer into noise factor (F)
SNRin(dB)-SNRout(dB) = 36dB - 26dB = 10dB
What is the noise figure (NF) for a system with a 27 dB input SNR and a 24dB output SNR? Convert your answer into noise factor (F)
SNRin(dB)-SNRout(dB)=27dB-24dB=3dB
Affects unequally the different spectral components of a radio signal
Selective fading
___________ affects unequally the different spectral components of a radio signal.
Selective fading
For a resolution of .06V, determine the voltages and ranges for the following linear seven-bit sign magnitude PCM code.
01011101=>45 -45×.06=-2.7V .06/2=.03 2.7±.03=-2.67V to-2.73V (voltage range)
A baseline signal has frequency components from 7.5 kHz to 20 kHz. Determine the Nyquist ........
1/(2*[20-7.5])=.04 => 40kHz
For a 12 Mbps LTE data stream with a symbol time of 66.67 us, how many subcarriers are created?
1/66.67 = hz (12*10^6)/(15*10^3) 800
For a resolution of 0.02 V, determine the voltage and ranged for the following linear seven-bit sign magnitude PCM code. 1001011
1001011 => 11 * .02 = 0.22 +- .01 => 0.21V to 0.23V
For a 12-bit linear sign-magnitude PCM code with a resolution of 0.02 V, determine the voltage range that would be converted to the PCM code 110000000000
1024 * .02 => 20.47V to 20.49V
A baseband signal has frequency components from dc to 6.2kHz. Determine the Nyquist theoretical minimum sampling rate.
12.4kHz
Given the decimal equation: y = a / b. Find the value of y (in decimal), given that a=13dB and b=7dB.
13dB - 7dB = 6dB => 10^.6 = 3.98 Round to 4
Given a three stage amplifier system with stage 1 having a gain of 16 dB and a NF=3.5 dB, Stage 2 gain of 19 dB and a NF = 4.8 dB, Stage 3 having a gain of 20 dB and a NF = 6.2 dB, calculate the system noise figure.
16 dB => 40; 3.5 dB => 2.24; 19 dB => 80; 4.8 dB => 3.02; 20 dB => 100; 6.2 dB => 4.17 F = 2.24 + ((3.02-1)/40) + ((4.17-1)/(40*80)) = 2.29 => 3.6 dB
An FM signal has a deviation of 75 kHz and a modulating frequency of 15 kHz. The carrier frequency is 1600 MHz. Using Carson's Rule, what is the required bandwidth for this system?
180 kHz
If the received power at 1 km is 2 dBm, determine the received power at 4 km.
2 dBm - 12 dB = -10 dBm => .10mW
Given the two amplifier gains in a chain: x=20dB and y=13dB, how much would the decimal gain value be for this amplifier chain?
2000
Given x=23dB and y=7dB, how much is xdB + ydB?
23dB + 7dB = 30dB
Given the two amplifier gains in a chain: x=23dB and y=7dB, how much would the decimal gain value be for this amplifier chain?
23dB + 7dB = 30dB => 10^(30/10) = 1000
Given a binary signal with a bit rate of 50kHz, what is the bandwidth?
25 KHz
Determine the resolution and quantization error for a nine-bit linear sign magnitude PCM code for a maximum decoded voltage of 5.10 V
255= 5.10/Vres => Vres=5.10/255 = .02; Qe = .02/2 = .01
A certain transmission channel has a bandwidth of 2 MHz, neglecting the effects of noise, what is the channel capacity for 32 level encoding?
2MHz is 2000kHz C = 2B * Logbase2(32) = 2 * 2000kHz * 5 = 20000 kHz or 20MHz
If the received power at 1 km is 3 dBm, determine the received power at 18 km.
3 dBm - 18 dB = -15 dBm => .032 mW
The attenuation level in bounded power spectral density is
35 & 50
An FM signal has a deviation of 15 kHz and a modulating frequency of 5 kHz. The carrier frequency is 1600 kHz. Using Carson's Rue, what is the required bandwidth for this system?
40kHz
An FM signal has a deviation of 15 kHz and a modulating frequency of 5 kHz. The carrier frequency is 1600kHz. Using Carson's Rule, what is the required bandwidth for this system?
40kHz
Given the decimal equation: y = a + b. Find the value of y (in dB), given that a=15 and b=69dB.
60dB
Determine the minimum number of magnitude bits plus an additional sign bit required in a PCM code for a dynamic range of 60dB.
60dB = 20log(2^N-1) = 10(60/20) = 2^N - 1 => 1001 = 2^N => log(1001)/log(2) = 10 = N => 10 Magnitude bits required - 11 bits required when sign bit added
Determine the minimum number of magnitude bits plus an additional sign bit required in a PCM code for a dynamic range of 70dB.
70dB = 20log(2^N-1) = 10(70/20) = 2^N - 1 => 3163 = 2^N => log(3163)/log(2) = 11.6 = N => 12 Magnitude bits required - 13 bits required when sign bit added
Given the decimal equation: y = a/b. Find the value of y (in decimal), given that a = 16 dB and b = 7 dB.
8
This is a _______________ constellation diagram. *Description* 8 points on an x y axis in the shape of an X. 2 points in each quadrant.
8-QAM
Explain the difference between an OFDM "symbol" and a QAM "symbol"
A QAM symbol represents multiple bits in a digital system; i.e., 4 bits can be represented by 16 levels. An OFDM symbol is much more complex. An 802.11a OFDM carrier signal (burst type) is the sum of one or more OFDM symbols each comprised of 52 orthogonal subcarriers, with baseband data on each subcarrier being independently modulated using quadrature amplitude modulation (available formats: BPSK, QPSK, 16-QAM, or 64-QAM). So an OFDM symbol is really a multiple of QAM symbols.
What is the definition of a decibel?
A decibel is a mathematical representation of a power level on a logarithmic scale. a = 10lob(b), where a is the decibel value and b is the decimal value.
What is a logarithm?
A logarithm is an exponent based mathematical representation of a numerical value.
Signal-to-noise ratio is a dimensionless value with _________ power as the numerator and _______ power as the denominator.
Signal & noise
________refers to changes in signal strength between a transmitter and receiver as the distance between the two changes b y a larger distance, well in excess of a wavelength.
Slow Fading
The OFDM ______ process converts the parallel input to frequency domain output in the receiver.
ANSWER IS NOT IFFT
Which type of coding and error detection techniques are used to request transmission from the receiver to the transmitter in the presence of a transmission error?
ARQ
How do you convert dBW to dBm?
Add 30 dB to dBW to obtain dBm value
What parameter of the intelligent signal causes or determines the instantaneous rate of carrier frequency?
Amplitude of the modulating signal
An FM signal has a deviation of 75 kHz and a modulating frequency of 15 kHz. The carrier frequency is 1600 MHz. Using Carson's rule, what is the required bandwidth for this system?
BSCR = 2 * (75kHz + 15kHz) = 180kHz
____________ rate refers to the rate of change of a digital signal.
Bit
For an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted in 8PSK?
C=2*500kHz*log2(8) C=1000kHz*3 = 3000kHz or 3MHz
What is the Nyquist equation that identifies the maximum allowable data rate with multilevel digital signaling?
C=2B log2(M)
Linear prediction coding (LPC) and _________ are two main approaches used in vocoders.
CELP
Linear prediction coding (LPC) and _____________ are two main approaches used in vocoders.
CELP
Which of the following are feed mechanism used in a parabolic antenna is the most complex?
Cassegrain feed
Which of the following are feed mechanisms used in a parabolic antenna?
Center feed & cassegrain feed
Which of the following are feed mechanisms used in a parabolic antenna?
Center feed and yagi feed
Which network blocks calls when traffic heavy?
Circuit-switched
_____________ is the angular separation between the two half-power points on the major lobe of an antenna radiation pattern.
Correct answer: Antenna Beamwidth
_________ ___________ is a quadrature process that uses two parallel tracing loops (I & Q) simultaneously to derive and recover carrier information.
Costas loop
_________ ____________ is a quadrature process that uses two parallel tracking loops (I & Q) simultaneously to derive and recover carrier information.
Costas loop
Determine the resolution and quantization error for a nine-bit linear sign magnitude PCM code for a maximum decoded voltage of 2.55 V
DR = 2.55/(2^8 - 1) DR = 2.55/(255) Vres = 0.01v Qe = 0.01/2 = 0.005
Determine the resolution and quantization error for a nine-bit linear sign magnitude PCM code for a maximum decoded voltage of 2.55V.
DR = 2^N - 1 = 2^8 - 1 =255 255 = 2.55/Vres => Vres = 2.55/255 = .01; Qe=.01/2=.005
Determine the minimum number of magnitude bits plus an additional sign bit required in a PCM code for a dynamic range of 65 dB
DR(db) = 20 log(Vmax/Vmin) = 20 log(2^n - 1) = 6.02n 6.02n = 65 n = 10.797 n - 11 bits 11 bits + 1 sign bit = 12 bits
Determine the minimum number of bits required in a PCM code with a sign bit for a dynamic range of 80 dB. What is the coding efficiency?
DR(db) = 20 log(Vmax/Vmin) 20 log(2^n - 1) 6.02n = 80dB n = 13.3 14 bits + 1 sign bit = 15 bits (round it up and add one extra bit)
________________ is a relationship of radiated power in a direction referenced to a spherical radiator.
Directivity
Parasitic elements that are shorter than its associated driven elements are called ____________.
Directors
Given that Pr=10^(-12) W;T=30C; fb=2mbps; B=500kHz; Te=295K. what is the energy per bit noise density (Eb/N0) ratio (in dB) in the amplifier.
Eb=(Pr/fb)=10log(5^(e-17))=183dB NF=10log(1+(295/290))=3.05dB=N0=-204dBW+3.05dB=-200.95dBW Eb/No =-183dBj-(-200.95dBW)=17.95dB
________ is the product of antenna gain and the transmitted power minus transmission line loss.
Effective isotropic radiated power
Why does the OFDM system implement an IFFT function on the transmit side and FFT on the receive side?
Ensure carriers do not interfere with each other
Why does the OFDM system implement and IFFT function on the transmit side and FFT on the receiver side?
Ensure carriers do not interfere with each other
Why does the OFDM system implement and IFFT function on the transmit side and FFT on the receiver side?
Ensure carriers don't interfere
OFDMA uses a combination of _________ by following users to use a subset of the subcarriers at different times.
FDMA and TDMA
Which type of coding and error detection techniques are used to detect and correct the presence of a transmission error?
FEC
The OFDM process uses ________ to compute the frequency domain output in the receiver.
FFT
16-QAM means there are 5 bits represented by each symbol
False
16-QAM means there are 5 bits represented by each symbol.
False
A packet switched network does not use switching nodes.
False
Attenuation is a decrease in atmospheric index of refraction with increasing altitude...
False
Audio signals are in the time-domain, but radio signals are in the frequency domain.
False
CCITT recommends a bit error rate (BER) of 1 * 10^-4 for error free communication.
False
CCITT recommends a bit error rate (BER) of 1 * 10^-5 for error free communication.
False
Circuit switching is the most efficient switching architecture.
False
Eb/No is directly proportional to bit error rate.
False
Energy is radiated into space when a direct current is passed through a wire.
False
In a circuit-switched network, each packet is treated independently, without reference to previous packets.
False
Mathematically, modulation involves addition of the carrier to the information signal.
False
Modulation is a linear process.
False
Multipath results in waves arriving at the destination at different frequencies and appears as noise interference.
False
Multipath results in waves arriving at the destination at different times, however, it has no effect on the reconstructed output.
False
Multipath results in waves arriving at the destination at different times; however, it has no effect on the reconstructed output.
False
Nyquist states that in order to reconstruct a band-limited signal from periodic samples, the sampling rate must be at least three times the frequency of the highest frequency component.
False
Radiation fields close to an antenna are the same as those at a distance.
False
Receive Signal Level (RSL) is the RF power impinging on the receive antenna.
False
Received Signal Level (RSL) is the RF power impinging on the receive antenna.
False
SNR is not a factor to consider when calculating the upper bound on achievable data rate.
False
The directional pattern of an antenna varies when the antenna is used to receive electromagnetic energy than when the antenna is used to transmit electromagnetic energy.
False
The path loss exponent does not change even if the environment changes.
False
The power entering the first active stage of the receiver is called the isotropic receive level (IRL)
False
The upper bound on achievable data rate is the maximum data rate between the max data rate using the SNR bound and the max data rate.
False
There can be more than one power value in a decibel (dB) equation.
False
Thermal noise is not present in all transmission media including all communication equipment and passive devices
False
Thermal noise is not present in all transmission media including all communication equipment and passive devices.
False
Two different factors affecting path loss are frequency and wavelength
False
Two different factors that influence path loss are distance and amplitude.
False
When current flows in an antenna, there is no energy loss because the energy is dissipated into electromagnetic energy.
False
________ refers to changes in signal strength between a transmitter and receiver as the distance between the two changes by a small distance of about one-half a wavelength.
Fast fading
Two multiplexing techniques used in telecommunications are ________ and ________.
Frequency division multiplexing (FDM) Time division multiplexing (TDM)
Carson's rule is an approximation for _________ signal bandwidth
Frequency modulation (FM)
Given an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted if the SNR is 14 dB.
I = B log2 (1 + SNR); SNR = 14dB => 25 I = 500 kHz * log2 (1 + 25) I = 500 kHz * log2 (26) I = 2350kHz or 2.35MHz
Given an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted if the SNR is 26 dB.
I = B log2(1+SNR); SNR = 26 => dB => 400 I = 500 kHz * log2(1 + 400) I = 500 kHz * log2(401) I = 4324 kHz or 4.324 MHz
Given an RF bandwidth of 500 kHz, determine the maximum information rate (in bps) that can be transmitted if the SNR is 26dB.
I=B log2(1+SNR); SNR=26 db400 I=500kHz*log2(1+400) I=500kHz*log2(401) = 4324 kHz or 4.324 MHz
__________ noise is noncontiguous consisting of irregular pulses or noise spikes of short duration and of relatively high amplitude.
Impulse
______________ noise is noncontiguous consisting of irregular pulses or noise spikes of short duration and of relatively high amplitude.
Impulse
_______noise is noncontinuous consisting of irregular pulse or noise spike of short duration and of relatively high amplitude.
Impulse
____________ noise produces signals at a frequency that is the sum or difference of the two original frequency or multiples of those frequencies.
Intermodulation
Name two places where noise originates.
Internal within equipment and external in the channel. Channel and comm equipment.
Error rate is ______ proportional to Eb/No.
Inversely
Given that a repeater is 45 km from a transmitter sending data at a frequency of 3100 MHz, what is the path loss between the transmitter and repeater?
L(dB) = 92.4 + 20log10(F(GHZ)) + 20log10(D(km)) = 92.4 + 20log10(3.1) + 20log(45) dB = 135.33
Given that a repeater is 15 km from a transmitter sending data at a frequency of 1900 MHz, what is the path loss between the transmitter and repeater?
LdB = 92.4 + 20log10(F GHz) + 20log10(Dkm) LdB = 92.4 dB + 20log(1.9) + 20log(15) LdB = 121.5 dB
What is the dB related free space path loss formula given frequency in GHz and distance in km?
LdB = 92.4 + 20log10(FGHz) = 20log10(Dkm)
Given that the repeater is 15 km from a transmitter sending data at a frequency of 1900 MHz .....
Ldb = 92.4 + 20 log(FGHz) + 20 log(Dkm) = 92.4 + 20 log(1.9) + 20 log(15) = 121.5 dBw
Digital communication is _______ to environmental changes?
Less sensitive
___________ results in waves arriving at the destination at different times and appears as noise interference.
Multipath
What is the noise power density (No) of the system (in dBm) including the amplifier given Te=500°K? (Hint use No dB formula)
No = 10log(kTF) = -204dBW/Hz + NFdB => NF = 10log(1 + Te/290) = 4.4 dB = -199.6 dBW + 30dB = -169.6 dBm
What is the noise power density (No) of the system (in dBm) including the amplifier given Te=450°K? (Hint: Use No dB formula)
No=10log(kTF)=-204dBW/Hz+NFdb=10log(1+Te/290)=4.1dB =-199.9dBw = -169.9dBm
Which source of delay is due to checking for bit errors and identifying the output link?
Nodal
Which of the following are sources of packet delay?
Nodal processing, queueing, transmission delay, propagation delay
What is the effective Temperature (Te in °K) for a system with a 29 dB input SNR and a 23 dB output SNR?
Noise Factor (F) = 10^2.9 / 10^2.3 => 4 Effective Temp (Te) = (F - 1) * 290 = (4 - 1) * 290 = 3 * 290 = 870 OR F = (1 + Te/290) 4 = (1 + Te/290) 4 - 1 = Te/290 870°K = Te
What is the definition of noise?
Noise is defined as any unwanted interference that completes with the signal of interest and diminishes the signal of interest's ability to successfully communicate the information.
A typical parabolic antenna gain has n____________ antenna efficiency. Given answers: 80%, 90%, 75%, 60%, None of the above
None of the above
Given an AM frequency of 20 kHz, what is the required bandwidth? Given: 20 kHz, 30 kHz, 50 kHz, 10 kHz, None of the above
None of the above
Given an AM frequency of 20 kHz, what is the required bandwidth? Options: 20kHz, 30kHz, 50kHz, 10kHz, none of these
None of the above
Given an AM frequency of 20kHz, what is the required bandwidth? Given: 20kHz, 30kHz, 50kHz, 10 kHz, None of the above
None of the above
Given an AM frequency of 30 kHz, what is the required bandwidth? Given: 30 kHz, 40 kHz, 50 kHz, 15 kHz, None of the above
None of the above
Given an AM frequency of 30kHz, what is the required bandwidth? Given: 30kHz, 40kHz, 50kHz, 15 kHz, None of the above
None of the above
The energy per bit (Eb) is equal to the ____________ divided by the bit rate. Noise power, noise spectral density, effective isotropic radiated power, isotropic receive level, none of the above.
None of the above
The energy per bit (Eb) is equal to the _________________ divided by the bit rate. Given: Noise power, noise spectral density, effective isotropic radiated power, isotropic receive level, none of the above
None of the above
What is(are) the reason(s) for using SC-FDMA?
None of the above
The net gain or (loss) of a transmission system is a radio between the _________ __________ and ____________ ____________ where the ___________ is the numerator and the ___________ ____________ is the denominator.
Output power & Input power
Determine the total radiated power from an elemental antenna 118.5 mm long if the uniform rms current is 260 mA and the frequency is 1900 MHz.
P = 789 * [l/λ]^2 (i^2) = RMS P = 789/2 * [l/λ]^2 (i^2) = Peak P = 789 * [l/λ]^2 (i^2) λ = (3*10^8 / f) = 0.158m = 789* [ (118.5* (10) ^(-3))/(0.158) ]^2 * (300* ) (10^-3 )^2 = 16 dBW
Determine the noise power (in dBm) at 27° C in a 500 kHz bandwidth.
PN = 10 log (1.38*10^-23*(27+273)*500kHz) = -146.8 dBw => -116.8 dBm
______________ elements receive energy through mutual inductance.
Parasitic
Determine the noise power (in dBm) at 27° C in a 20 MHz bandwidth system.
Pn=kTB; k=1.38*(10^-23)W°K-Hz; T(°K)=27°C+273=300°K; B=20*10^6Hz =10log(1.38*(10^-23)*300*20*10^6) =10log(8.28*(10^-14)) =-130.82 dBW =-130.82 dBW +30 dB =-100.8 dBm
What is the direction of the electric field called?
Polarization
__________ means the direction of the electric field.
Polarization
______________ means the direction of the electric field.
Polarization
OFDMA uses a combination of ______ by allowing users to use a subset of the subcarriers at different times.
Possible answer: FDMA & TDMA
What is the most commonly used digital modulation scheme?
Pulse-code Modulation
Which source of delay depends on the congestion level of the router?
Queuing
Consider an OFDM implementation that uses 15 kHz subcarriers and use an OFDM symbol of 2048 subcarriers. The nominal cyclic prefix accounts for a 10% guard time. The extended cyclic prefix can use up to 25%. 1600 subcarriers can be used to for data transmission. The rest are needed for pilot and null subcarriers. The Transmission bandwidth is 25 MHz using 32 QAM modulation. What is the data rate for the extended CP?
R = 25 MHz * (1600 / [2048 + 512]) * 5 = 78.1 Mbps
What is the receive signal level (in dBm) of a system that has an EIRP of 57 dBW, a path loss of 130 dB, a receive antenna gain of 24 dB and receive transmission line loss of 0.6 dB?
RSL = RSL(dBW) = IRL(dBW) + Rx Antenna Gain (dB) - Rx Transmission Line Loss (dB) IRL(dBw) = EIRP(dBW) - Path Loss(dB) Given: EIRP = 57 dBW Path Loss = 130 dB Rx Antenna = 24 dB IRL = 57 dBW - 130 dB = -73 dBW RSL = -73 dBW + 24 - 0.6 = -49.6 dBW = -19.6 dBm
What is the receive signal level (in dBm) of a system that has an EIRP of 54 dBW, a pass loss of 130 dB, a receive antenna gain of 20 dB and a receive transmission line loss of .4 dB?
RSL=RSL_dBW+R_x Antenna Gain(dB)-Rx Tranmission line Loss (dB) IRL(dBW)=EIRP(dBW)-path loss (dB) Given:EIRP=54dBW;path loss=130dB;Rx Antenna=20dB; Rx trans line=.4dB IRL=54dBW-130dB=-76dBW RSL=-76dBW+20-0.4 =56.4dBW or-26.4dBM
Given that radiation resistance for a short dipole antenna is 75Ω and the length is 150mm at what frequency would one expect this antenna to radiate?
R_r=200×(I/A) 75=200×((150*10^(-3))/A)^2 f^2=(75*(3*10^8 )^2 )^ /(200*(150*10^(-3))^2 )^ =√(1.5*10^18 ) f=1.22GHz
The energy per bit (Eb) is equal to the __________ divided by the bit rate.
Received signal power (Pr)
What is (are) the reasons for using SC-FDMA?
Reduce the PAPR Problem
Synchronization available in digital communication are
Symbol synchronization, Frame synchronization, Carrier synchronization
For a 45 Mbps LTE data stream with a symbol time of 66.67 us, how many subcarriers are created?
T = 1/66.67 = 15 kHz = 45 * 10^6 / 15 * 10^3 = 3000 us
OFDM signals have a higher peak-to-average power ratio because of the following
The peak value of the signal is substantially larger than the average value.
What is carrier recovery?
The process of extracting a phase-coherent reference carrier from a receiver signal.
A baseband signal has frequency components from dc to 15 kHz. Determine the Nyquist theoretical minimum sampling rate.
The signal frequency components are as follows: 0 - 7.5 Hz In this, 0 is the dc frequency. The Nyquist theoretical sampling rate is given as follows: fs > 2fm Where, fs represents the rate of sampling and, fm represents the component of maximum frequency. Therefore, fs for the given component is as follows: fs > 2 * 15 kHz fs > 30 kHz
______ noise is due to thermal agitation
Thermal
A communication network is a collection of switching nodes.
True
A communications network is a collection of switching nodes.
True
A modulated carrier with a digital information signal typically occupies multiple frequencies
True
A switching node is an intermediate device that moves data.
True
All radio signals exist in both the time and frequency domains simultaneously.
True
Analog signals can be transmitted digitally
True
Anomalous Propagation is a decrease in atmospheric index of refraction with increasing altitude.
True
At a given frequency, the gain of a parabolic antenna is a function of its effective area.
True
Attenuation occurs when the strength of a signal falls off with distance over the transmission medium.
True
Both analog and digital radio systems use analog carriers to transport the information through the transmission medium.
True
CCITT recommends a bit error rate (BER) of 1*10^-6 for error free communication.
True
Dynamic Range is the ratio of the largest possible magnitude to the smallest possible magnitude.
True
Energy is radiated into space when an alternating current is passed through a wire.
True
Error rates on a wireless link can be high, resulting in a large number of retransmissions.
True
In a packet-switched network, two stations with different data rates can exchange information.
True
Information capacity represents the number of independent symbols that can be carried through a system in a given unit of time.
True
It takes 22dB to launch a wave just 1 wavelength distance from an antenna.
True
Long-term fading is the average or envelope of the fading signal.
True
M-ary PSK and QAM are digital modulation techniques used to increase data rate and limit overall bandwidth.
True
Multipath results in waves arriving at the destination at different times and appears as noise interference.
True
Noise Figure is a figure of merit, indicating how much a component, stage, or series of stages degrades the signal-to-noise ratio of a system.
True
Nyquist states that in order to reconstruct a band-limited signal from periodic samples, the sampling rate must be at least twice the frequency of the highest frequency component.
True
Okumura and Hata created models derived from empirical measurements that can be used to calculate path loss in various types environments.
True
One main technical problems with OFDM is the intercarrier interference caused by subcarriers that are not in frequency synchronization.
True
Orthogonal Frequency Division Multiple Access (OFDMA) is an OFDM MAC mechanism where multiple uses share a channel by using different OFDM subcarriers.
True
Orthogonal frequency division multiplexing (OFDM) is a scheme that divides a broadband signal into multiple,
True
Packet switching is the most commonly used switching technique in the internet.
True
Quadrature Amplitude Modulation (QAM) is a form of digital modulation where the information is contained in both the amplitude and the phase of the transmitted carrier.
True
Received Signal Level (RSL) is the power level entering the first active stage of the receiver.
True
Reciprocity in an antenna is defined as the directional pattern of an antenna being the same when the antenna is used to receive electromagnetic energy as it is when the antenna is used to transmit electromagnetic energy.
True
SNR is one factor that must be considered when calculating the upper bound on achievable data rate.
True
Sampling alone at the Nyquist rate in not a digital technique.
True
Signal wavelength is inversely proportional to parabolic antenna gain.
True
Single-carrier FDMA (SC-FDMA) is a variant of OFDM that performs extra DFT operations at the transmitter and receiver.
True
Single-carrier FDMA (SC-FDMA) is a variant of OFDM that performs extra DFT operations at the transmitter and receiver...
True
The bit error rate (or bit error probability) for digital data in a digital amplifier chain is a function of Eb/No
True
The cyclic prefix addresses the problem of inter symbol inter symbol interference caused by multipath delay spread
True
The cyclic prefix addresses the problem of intersymbol interference caused by multipath delay spread
True
The directional patter of an antenna is the same when the antenna is used to receive electromagnetic energy as it is when the antenna is used to transmit electromagnetic energy.
True
The directional pattern of an antenna is the same when the antenna is used to receive electromagnetic energy as it is when the antenna is used to transmit electromagnetic energy.
True
The error from the quantum value to the true value is quantizing distortion.
True
The isotropic receive level (IRL) is can be calculated is dB by subtracting the path loss (in dB) from the EIRP (in dBW or dBm).
True
The thermal noise level of a receiver is a function of the receiver noise figure and its bandwidth.
True
The thermal noise lever of a receiver is a function of the receiver noise figure and its bandwidth?
True
Throughput is the rate at which bits are transferred between a sender and a receiver.
True
Two different factors affecting path loss are distance and frequency.
True
When current flows in an antenna, there is no energy loss.
True
When you add two decibel values, you are multiplying those values in decimal (I.e. 3 dB + 6 dB = 9 dB which is equivalent to 2 * 4 = 8 in decimal)
True
You cannot mix decimal and decibel values in an equation (i.e., you either have to work with decimal values or decibel values)
True
Both analog and digital signals use analog carrier signals.
Ture
Which of the following is (are) true about parasitic elements in an antenna?
Uses mutual induction
Given the two amplifier gains in a chain: x = 23 dB and y = 7 dB, how much would the decimal gain value be for this amplifier chain?
Voltage gain in dB A = B + P = 23 dB + 7 dB = 30 dB For decimal gain A(gain in dB)/20 A(dec) = 10 = 10 ^ (30/20) = 10 ^ 1.5 = 31.6
What is the wavelength (in meters) of a 750 kHz signal?
W = (3.0*10^8)/(750*10^6) => 0.4 m
A transmission channel has a bandwidth of 16 kHz. Neglecting the effects of noise, determine the channel capacity for a. 128-level encoding b. if the SNR is 40 dB , what is the maximum data rate? c. Which factor is limiting in this system?
a. 224 kHz b. 212.6 kHz c. SNR C = 2B * log2(128) = 2 * 16kHz * 7 = 224 kHz C = Blog2(1 + SNR) = 16 kHz * 8log2(100001) = 212.6 kHz
A VoIP network is converting the analog voice into digital data. The full range of converter is 3 volts and the rms quantization error (Qe) is 0.5 millivolt a. How many bits are required for the converter, including a sign bit? b. What is the dynamic range of the converter (in dB)?
a. 2^N - 1 = 3V/0.001 = 3000 2^N - 1 = 3000 2^N = 3001 N = log(3001)/log(2) N = 11.55 = 12 Magnitude bits + 1 sign bit = 13 bits b. 20log(2^12-1) = 72.2 dB
A VOIP network is converting the analog voice into digital data. The full range of the converter is 4 volts and the rms quantization error (Qe) is 1 millivolt. a. How many bits are required for the converter, including a sign bit? b. What is the dynamic range of the converter (in dB)?
a. 2^N - 1 = 4V/.002 = 2000 N = log(2001)/log(2) = 10.97 11 Magnitude bits +1 sign bit 12 bits total b. 20 log(2^11 - 1) = 66.2 dB
A digital communications system is being designed with the goal of transmitting 32 kbits/s over a channel having a bandwidth of 8 kHz. Determine (a) the number of encoding levels required and (b) the minimum signal to noise ratio required i n the channel.
a. 32 kbps = 2 * 8 kHz * log2(M) 32 kbps = 16 kHz * log2(M) log2(M) = 32 kbps/16 kHZ log2(M) = 2 = 2 * log(2) = 0.602 = 10^0.602 = 3.9994475 = 4 b. C = Blog2(1 + SNR) = (32 kbps/8kHz) = log2(1 + SNR) = 4 = log2(1 + SNR) = 2^4 = 1 + SNR = 16 - 1 = SNR = 11.8 dB
What are the (a) noise figure, (b) noise factor, and (c) effective temperature (Te) for a system with a 16 dB input SNR and a 12 dB output SNR?
a. 4dB b. 2.51 c. 437.9°K F = (1 + Te/290) => 290(2.51 - 1) = 437.9°K
A digital communications system is being designed with the goal of transmitting 64 kbits/s over a channel having a bandwidth of 10kHz. Determine... a. The number of encoding levels required b. The minimum signal-to-noise ratio required in the channel.
a. 64 kbps = 2 * 10 khz * log2 (M) = (64 kbps/20 kHz) = log2 (M) = 9.18 levels => round up to 16 b. 6.4 = log2(1 + SNR) => 2^6.4 = 1 + SNR => 84.4 - 1 = SNR = 83.3 => 19.2 dB C = B log2(1 + SNR) => (64 kbps/10 kHz) = log2(1 + SNR) = 6.4 C = log2(1 + SNR) => 2^6.4 = 1 + SNR => 84.4 -1 = SNR => 19.2 dB
A transmission channel has a bandwidth of 8 kHz. Neglecting the effects of noise determine the channel for (a) 64- level encoding (b) If the SNR is 38 dB, what is... (c) Which factor is limiting in this system?
a. 96 kHz b. 101 kHz c. Levels C = 2B * log2 (128) = 2 * 16kHz * 7 = 224 kHz C = B log2 (1 + SNR) = 16 kHz 8 log2 (10001) = 212.6 kHz
Use the following information for this question. Pr = 10^-12 W; T=17°C; fb=2Mbps; B=1MHz; Te=296°K (Hint: Don't confuse dBW and dBm) a. What is the carrier-to-noise ratio (SNR) at the input to the amplifier? b. What is the energy per bit to noise density ratio (Eb/N0) for the receiver system (including the amplifier)?
a. C = -120 dBW; N = -144 dBW C/N = 24 dB b. Eb = -120 dBw - 63 dB = -183 dBJ; No = -204 + 3.05 dB = -200.95 Eb / No = -183 dBj -(-200.95) = -17.95 dB
Use the following information for this question. Pr = 10^-12W; T = 17°C; fb = 2 Mb ps; B = 1 MHz; Te = 296°K (Hint: Don't confuse dBW and dBm) a. What is the carrier-to-noise ratio (SNR) at the input to the amplifier? b. What is the energy per bit to noise density ratio (Eb/No) for the recei ver system (including the amplifier)
a. C = -120 dBW; N = -144 dBW; C/N = 24 dB b. Eb = -120 dBW - 63 dB => -183 dBJ No = -204 + 3.05 dB => -200.95 Eb/No = -183 dBJ - (-200.95) => 17.95 dB
Use the following information for this question. Pr = 10^-13 W; T=23°C; fb=1Mbps; B=1MHz; Te=296°K (Hint: Don't confuse dBW and dBm) a. What is the carrier-to-noise ratio (SNR) at the input to the amplifier? b. What is the energy per bit to noise density ratio (Eb/N0) for the receiver system (including the amplifier)?
a. C = -130 dBW; PN = -143.9 dBW C/N = -130 dBW - (-143.9) dBW = 13.9 b. Eb = -130 - 60 dB = -190 dBJ; No = -204 + 3.05 dB = -200.95 Eb / No = -190 - ( -200.95) = 10.95 dB
All modulated signals in a wireless system are transmitted via
analog transmission carrier
__________ is a decibel value referenced to watts and ______ is a decibel value referenced to milliwatts.
dBW & dBm
Given the two amplifier gains in a chain: x=20dB and y=13dB, how much would the decimal gain value be for this amplifier chain?
decimal gain = 2000
What is the ratio of the strongest possible signal that can be transmitted and the weakest discernible signal?
dynamic range
What is the noise power density (No) of the system (in dBm) including the amplifier given Te = 450 degrees K? (Hint: Use No dB formula)
k = 1.38 * 10^-23 Te = T = 450°C F = 1 + [Te / 290] N(x) = 10log(x) No = N(kTF) = N(kT) + N(F) = 10log((1.38 * 10^-23)(450)) + N(F) = 10log((1.38 * 10^-23)(450)) + 4.1 dB = -202.07 dBW/Hz + 4.07 dB = -199.9 dBW = -169.9 dBm
Determine the noise power (in dBm) at 23°C in a 500 kHz bandwidth.
k = 1.38 * 10^23 T = 27 + 273 = 300 B = 5e5 PN = 10log(kTB) = 10log(1.38 * 10^23 * 300 * 5e5) = -146.8 = -146.8 + 30 dB = -116.8 dBm
What are the three commonly identified probability density functions?
log normal, Rayleigh, Rician
What is the Base 2 logarithmic value for the following equation? log2 (3096)?
log2 (3096) = 11.6
What is the Base 2 logarithmic value for the following equation? log2 (3096)?
log2(956) = log10(956) / log10(2) log2 (956) = 9.9
How do you find a log2 value on a calculator that only has log10 functionality? (Hint: what is the formula?)
log2(a) = [log10(a) / log10(2)]
The resolution of a pulse-coded modulated signal is determined by dividing the ________________ by the number of positive (or negative) non-zero PCM codes.
maximum positive (or negative) voltage
The practice of assigning a binary sequence to each voltage sample is called _______
quantization
The _________ of a pulse-coded modulation signal is determined bu dividing the maximum positive (or negative) voltage by the number of positive (or negative) non-zero PCM codes.
resolution
A_______is commonly used in BPSK transmission to recover the carrier.
squaring loop
Two multiplexing techniques used in telecommunications are ________ and _________.
time division multiplexing (TDM); frequency division multiplexing (FDM)
Which source of delay is a function of the link bandwidth and the packet length?
transmission
What is the wavelength (in meters) of a 750 MHz signal?
wvl = c/f = (3 * 10^8 m/s)/(750 * 10^6) = 0.4 m/s
Given x=20dB and y=13dB, how much is x dB + y dB?
xdB+ydB=33dB
Given the decimal equation: y = a * b. Find the value of y (in decimal), given that a=13dB and b=7dB.
y = 13dB + 7dB = 20dB => 10^2 = 100 OR y = 10^1.3 * 10^.7 y = 20 * 5 y = 100
Given the decimal equation: y=a/b. Find the value of y (in decimal), given that a=16dB and b=7dB
y=8
