Quiz
wireless midterm
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Fragen in diesem Quiz (74)
1memorize formulas
- ARichtig
- BFalsch
2Symbol rate is the number of ____ per second
- Asignal elements
- Bbit symbols
- CMWs
3Symbol duration/period is (T = 1 / R)
R = symbol rate- ARichtig
- BFalsch
4Bit rate is the number of ___ per second
- Abits
- Bsymbols
- Ckbs
5Bit duration/period is (T = 1 / R)
R = bit rate- ARichtig
- BFalsch
6Binary PSK
- A2 symbol states
1 bit per symbol
bit rate = symbol rate - B4 symbol states
2 bit per symbol
bit rate = symbol rate - C3 symbol states
2 bit per symbol
bit rate = symbol rate
- A2 symbol states
7Quadrature PSK
- A4 symbol states
2 bit per symbol
bit rate = 2 x symbol rate - B2 symbol states
1 bit per symbol
bit rate = 2 x symbol rate - C3 symbol states
1 bit per symbol
bit rate = 4 x symbol rate
- A4 symbol states
8M-PSK
- AM = 2, 4, 8, ....
r bits per symbol, r = log^2(M)
bit rate = r x symbol rate - BM = 2, 4, 8, ....
r bits per symbol, r = log^10(M)
bit rate = 2 x symbol rate - CM = 1, 2, 3, ....
r bits per symbol, r = log^4(M)
bit rate = r x symbol rate
- AM = 2, 4, 8, ....
9Phase shift keying (PSK)
Phase of the carrier is changed according to the data bits
- Amplitude and phase does not change
- ARichtig
- BFalsch
10Binary phase shift keying (BPSK)
- uses phase to offset the signal as high and low
- 360 degrees of phase to work with, 180 degree is max between 2 offsets
- high slopes (straight jump) is undesirable as they generate high frequency energy that interferes with other RF signals
- design the system so that 180 degree phase only occurs when signal is near 0 crossing- ARichtig
- BFalsch
11Quadrature amplitude modulation (QAM)
- combination of ASK + PSK
- amplitude and phase is modulated
- 4-QAM, 8-QAM, 16-QAM, ...
- bit rate = log^2(M x symbol rate)- ARichtig
- BFalsch
12QPSK has the 4 phases as follows in 4 diagonal direction:
10, 00, 01, 11
I and Q data channels
- ARichtig
- BFalsch
134-QAM to 64-QAM...
Too large of a #-QAM means symbols get too compact and data corruption more common
More power means you can pack QAM more compactly, but power is limited by regulation- ARichtig
- BFalsch
14#-QAM represents how many constellations the signal can carry
ie.
x | x
______
x | x- A4-QAM has 4 constellations (10, 00, 01, 11)
16-QAM has 16 constellations (4 per quadrant) ...
32-QAM has 32 constellations (8 per quadrant) ... - B4-QAM has 2 constellations (10, 01)
16-QAM has 8 constellations (2 per quadrant) ...
32-QAM has 16 constellations (4 per quadrant) ... - C4-QAM has 16 constellations (4 per quadrant) ...
16-QAM has 32 constellations (8 per quadrant) ...
32-QAM has 64 constellations (16 per quadrant) ...
- A4-QAM has 4 constellations (10, 00, 01, 11)
15ADVANTAGE OF MULTILEVEL SIGNALING
- Asaves on bandwidth
- BInformation is transmitted at the bit rate
- Cbandwidth is proportional to the symbol rate
- Dcan carry more phases per signal
- Eallows multiplexing of signals to save on data
16Bandwidth efficiency - A system which sends a lot of data in a small bandwidth is said to have good Bandwidth
Efficiency
Typical Values (assuming optimum pulse shaping):
BPSK: [blank_start]1[blank_end] bits/sec/Hz
QPSK: [blank_start]2[blank_end] bits/sec/Hz
8-ary PSK: [blank_start]3[blank_end] bits/sec/Hz
16 QAM: [blank_start]4[blank_end] bits/sec/Hz
2-ary FSK: 0.5 bits/sec/Hz
8-ary FSK: 3/8 bits/sec/Hz
GMSK: 1.354 bits/sec/Hz- A1
- B2
- C4
- D3
17Using an example, explain the relationship between symbol rate and bit rate
bit rate is the amount of data elements sent per second and symbol rate is the amount of symbol elements sent per second. For example 4-QAM transmits at 4 symbols per second and each symbol carries 2 bits so the bit rate would be 8 bits per second.- ARichtig
- BFalsch
18For the same symbol rate, QPSK have the double the bit rate than that of BPSK
system. Explain why.
BPSK signals send the signal using phase shifting limited to 360 degrees with maximum of 180 degrees between shifts. Each phase represents the bits as 1 or 0. QPSK sends 2 channels I and Q. Each channel represents a single bit as 1 or 0 depending on their phase. Because QPSK uses 2 channels of I and Q, it can send double the bit rate of BPSK.- ARichtig
- BFalsch
19What is the purpose of the channel coding in communication systems?
Used to protect the digital information from noise and interference and reduce the number of bit errors.- ARichtig
- BFalsch
20Carrier signal
- Carrier signal carries information signal
- split into two components
- In-phase and Quadrature
- ARichtig
- BFalsch
21Modulation technique
modulator encodes a sequence of bits onto the carrier signal by adjusting the parameters that describe it, e.g. phase or amplitude.- ARichtig
- BFalsch
22Modulation process
1. [blank_start]Bit to Symbol mapping[blank_end]
2. [blank_start]IF modulation (digital)[blank_end]
3. [blank_start]Digital to analog conversion[blank_end]
4. [blank_start]RF modulation (analog)[blank_end]
5. Transmit the real part of the signal through antenna- ABit to Symbol mapping
- BIF modulation (digital)
- CDigital to analog conversion
- DRF modulation (analog)
23De-modulation process:
1. Receive RF signal (with noise) through antenna
2. [blank_start]RF demodulation (analog)[blank_end]
3. Low pass filter (get only relevant IF signals)
4. [blank_start]Analog to digital conversion[blank_end]
5. [blank_start]IF demodulation (digital)[blank_end]
6. [blank_start]Channel estimation[blank_end]
7. Synchronization
8. [blank_start]Symbol detection[blank_end]
9. [blank_start]Symbol to bit mapping[blank_end]- ARF demodulation (analog)
- BAnalog to digital conversion
- CIF demodulation (digital)
- DChannel estimation
- ESymbol detection
- FSymbol to bit mapping
24Bandwidth of modulated signal
bandwidth is proportional to symbol rate
Bandwidth = symbol rate = 1 / symbol duration
For example, for a 1 Msps system, bandwidth of the modulated signal will be 1 MHz- ARichtig
- BFalsch
25What is the meaning of multiple access?
Multiple Access is the use of multiplexing techniques to provide communication service to multiple users over a single channel. It allows for many users at one time by sharing a finite amount of spectrum.- ARichtig
- BFalsch
26Random access methods
Random Access methods are often employed for the control channels
Also, used for data-oriented network (packet switched):
- bursts of data
- each packet contains signal info related to address of destination and source
ie. Slotted ALOHA, CSMA/CA- ARichtig
- BFalsch
27Code division multiple access (CDMA)
- AFDMA/TDMA techniques avoid interference by making all signals orthogonal to one
another - BFDMA/TDMA techniques avoid interference by making all signals perpendicular to one
another - CFDMA/TDMA techniques avoid interference by making all symbols perpendicular to one
another - DFDMA/TDMA techniques avoid interference by making all symbols orthogonal to one
another
- AFDMA/TDMA techniques avoid interference by making all signals orthogonal to one
28Code Division Multiple Access (CDMA) systems employing Direct Sequence Spread Spectrum (DSSS):
- ASignals all transmit at the same time
- BSignals all transmit on the same frequency
- CReceiver uses code or signature sequence to isolate desired signal
- DSignals use spectrum efficiency to reduce bandwidth
- ECDMA uses techniques to increase interference with other signals
29ALOHA
- A terminal transmits a packet when the packet arrives from the upper layer
- Each packet has an error detection code
Pros:
- simple
- does not require synchronization between terminals
cons:
- low throughput in heavy load conditions- ARichtig
- BFalsch
30SLOTTED ALOHA
- synchronized version of ALOHA
- Transmission time is divided into time slot
- When a terminal generates packet of data, the packet is buffered and transmitted at the beginning of the next time slot
- maximum throughput is doubled from pure ALOHA- ARichtig
- BFalsch
31Channel coding is often used in digital communication systems to protect the digital information from noise and interference and reduce the number of bit errors
- ARichtig
- BFalsch
32Duplexing modes:
- AFrequency Division Duplex (FDD) - back and forth from cell tower and cellphone
- BTime Division Duplex (TDD) - cell tower to cellphone
- CHalf duplex FDD - cellphone to cell tower to another cellphone
33Wireless transmission usual impairments
- Apath loss
- BAttenuation and attenuation distortion
- Cnoise
- DAtmospheric absorption
- EMultipath
- FRefraction
- Gbuildings
- Hdistance
- Iearth curvature
34Large Scale propagation Model
- Loss due to signal spreading from the source
PL (pathloss) = Pt / Pr
Pt = transmit power
Pr = receive power- ARichtig
- BFalsch
35Friis Free Space equation:
Pr = transmit power
Gt = gain of Tx antenna
Gr = gain of Rx antenna
λ = wavelength
L = system loss not related to propagation
- ARichtig
- BFalsch
36FREE SPACE PATH LOSS
wavelength and distance
??B = −20 log (?) + 20 log (?) + 21.98 dB
frequency and distance
??B = 20 log (f) + 20 log (?) - 147.56 dB- ARichtig
- BFalsch
37received power in free space
d0 = chosen to be smaller than any distance used in practical wireless communication systems
Pr(d0) = estimated from measurement data
- ARichtig
- BFalsch
38The path loss at a Tx-Rx separation of distance d can be expressed as..
if the distance increases by a factor of 10, the path loss increases by 20 dB
- ARichtig
- BFalsch
39path loss exponent
n is the path loss index that depends on the environment
Free Space = 2
Urban = 2.7~3.5
Shadowed Urban = 3~5
In building LOS = 1.6~1.8
Obstructed in building = 4~6
Obstructed in factories = 2~3- ARichtig
- BFalsch
40Shadowing
- equations do not consider the fact that the surrounding environmental clutter may be vastly different at two different locations having the same Tx-Rx separation
- As a result the measured signals vary widely from the average value predicted by equation 4
This is known as the shadowing effect since the variation is caused by obstacles between the Tx and Rx- ARichtig
- BFalsch
41small scale propagation model
describes the...
- Rapid fluctuations of amplitude or phase and/or
- Multipath delays
of a radio signal over...
- Short travel distance and/or
- short period of time- ARichtig
- BFalsch
42MULTIPATH PROPAGATION
Presence of objects in the propagation environment result in multiple copies of the transmitted signal at the receiver
One other complicating factor is the relative motion of the objects with respect to the mobile station- ARichtig
- BFalsch
43Fade margin
A Margin or additional signal power in path loss calculation, taken to provide a certain fraction of the locations at the edge of the coverage with required signal strength- ARichtig
- BFalsch
44Attenuation
Strength of signal falls off with distance over transmission medium- ARichtig
- BFalsch
45[blank_start]Thermal noise[blank_end]: Noise arising from the movement of electron in the devices
[blank_start]Intermodulation noise[blank_end]: Occurs if signals with different frequencies share the same medium
[blank_start]Crosstalk[blank_end]: Unwanted coupling between signal paths
[blank_start]Impulse noise[blank_end]: Irregular pulses or noise spikes- AThermal noise
- BIntermodulation noise
- CCrosstalk
- DImpulse noise
46[blank_start]Thermal noise[blank_end]: Noise arising from the movement of electron in the devices
[blank_start]Intermodulation noise[blank_end]: Occurs if signals with different frequencies share the same medium
[blank_start]Crosstalk[blank_end]: Unwanted coupling between signal paths
[blank_start]Impulse noise[blank_end]: Irregular pulses or noise spikes- AThermal noise
- BIntermodulation noise
- CCrosstalk
- DImpulse noise
47Thermal noise
- Due to agitation of electrons
- Present in all electronic devices and transmission media
- cannot be eliminated
Additive White Gaussian Noise (AWGN)
- Additive because it is added to any noise that effects the signal
- White refers to uniform power across the frequency band for signal
- Gaussian because it has a normal distribution- ARichtig
- BFalsch
48basic cellular network architecture
- Acore network (CN)
- Bradio access network (RAN)
- Cradio interface
- Duser device
49coverage area is divided into smaller area each of which is serviced by its own base station
Each of these smaller area is called a cell
Cells are grouped into clusters
Each cluster utilizes the entire spectrum
Clusters are required to make sure that adjacent cells do not use the same channels- ARichtig
- BFalsch
50Number of cells in a cluster increases = capacity increases
cons:
- more base stations needed
- co-channel interferers are closer
- higher number of hand-offs: higher signal load
Another option for capacity improvement would be smaller cluster size i.e. smaller frequency reuse factor (N)- ARichtig
- BFalsch
51Co-channel interference
- Same channel used in some other cells
- Co-channel interference can not be overcome by increasing the transmitter power
- cells must be physically separated by a minimum distance to provide sufficient isolation
Adjacent channel interference
- Neighboring channel used in the same cell or in neighboring cells
- ARichtig
- BFalsch
52cell sizes
[blank_start]macro cell[blank_end], radius 1-30km, typically used
[blank_start]micro cell[blank_end] - radius 200-2000m, high density
[blank_start]pico cell[blank_end] - radius 4-200m, high density
[blank_start]femto cell[blank_end] - used by a user in a household- Amacro cell
- Bmicro cell
- Cpico cell
- Dfemto cell
- Elarge cell
- Fwide area cell
53high level architecture of LTE
- AHSS
- BMME
- Cserving gateway
- DUE
- EPDN gateway
- FPCRF
54[blank_start]Core network[blank_end]
- carries traffic from one RAN to other RAN
- hosts controlling servers
[blank_start]radio access network (RAN)[blank_end]
- provides radio access to user
- connects user to core network
[blank_start]UE (user equipment)[blank_end]
- provides user interface- ACore network
- Bradio access network (RAN)
- CUE (user equipment)
55UTRAN architecture
- ARNC
- Bother RNC
- Ccore network
56Radio network controller (RNC) of UTRAN network
passes user voice information data between nodeB and Core network
controls mobile radio communications by signaling invisible messages- ARichtig
- BFalsch
57Handover
When a mobile moves from one part of the network to another, it has to stop communicating with one cell and start communicating with the next cell along.
Hard handover: Break before make
Soft handover: Make before break- ARichtig
- BFalsch
58eNB (enhanced NodeB)
The base station that is communicating with a mobile is known as its serving eNB
In LTE handover between eNBs are hard handover
- Sends radio transmissions to all mobiles on the downlink and receives transmissions from them on the
uplink
- Controls the low-level operation of all mobiles, by sending them signaling messages such as
handover commands
- Combines the functions of NodeB and RNC of UMTS
image is Enhanced UTRAN architecture
- ARichtig
- BFalsch
59What is 'Femto Cell'?
small, low-power cellular base station, typically designed for use in a home or small business- ARichtig
- BFalsch
60architecture of EPC
- Aother MME
- BMME
- CS-GW
- DHSS
- EP-GW
61Main components of EPC architecture
- AHome Subscriber Server (HSS)
- BPDN Gateway (P-GW)
- CServing Gateway (S-GW)
- DMobility Management Entity (MME)
- ESignal Gateway (S-GW)
- FPort Gateway (P-GW)
62PDN Gateway (P-GW)
EPC’s gateway to the Packet Data Networks (PDN)
Connects to one or more data networks and LTE servers
Access point name (APN) identifies each PDN- ARichtig
- BFalsch
63Serving gateway (S-GW)
acts as high level router
forwards data between base station and PDN gateway
each mobile is assigned to a single S-GW- ARichtig
- BFalsch
64Mobility management entity (MME)
controls high-level operation of mobile
sends signal messages to mobiles about security, other elements of network, management of data streams
one MME is responsible for mobiles in region
each mobile assigned to one MME- ARichtig
- BFalsch
65Home subscriber server (HSS)
continued from UMTS
central database
contains information on all subscribers- ARichtig
- BFalsch
66Network areas of EPC
[blank_start]MME pool area[blank_end] - overlapping, mobile does not change MME in area
[blank_start]S-GW service area[blank_end] - overlapping, mobile does not change S-GW in area
[blank_start]Tracking area[blank_end] - non-overlapping, used to track locations of mobiles on standby
- AMME pool area
- BS-GW service area
- CTracking area
67OFDM
modulation/multiplexing format that achieves:
- dividing the bandwidth into subcarriers
- combat intersymbol interference (ISI)
High Data Throughput - By transmitting hundreds or thousands of carriers simultaneously
High Spectral Efficiency - By spacing the carriers very closely
High Data Integrity - By transmitting at a relatively low symbol rate- ARichtig
- BFalsch
68spectral efficiency of OFDM
Spectral Efficiency: How much digital bandwidth (bps) is carried per analog bandwidth- ARichtig
- BFalsch
69OFDM advantages
- Aeasy and efficient in dealing with multi-path
- Bmakes efficient use of the spectrum by allowing overlap
- Celiminates ISI and ICI through use of a cyclic prefix
- Dcomputationally efficient by using FFT techniques
- Eexpands the channels into wideband parent channels
- Fcan recover from bit loss due to high bandwidth
70disadvantages of OFDM
- Ahighly sensitive to time and frequency synchronization errors
- BPAPR is calculated by 10log (N)
- Cas the number of subcarriers (N) increase the PAPR increases
- DPeak-to-Average Power Ratio (PAPR) reduces the power efficiency of RF amplifier
at the transmitter - Edoes not allow LTE systems to send signals under 12dB
71ORTHOGONAL FREQUENCY DIVISION MULTIPLE ACCESS (OFDMA)
Multi-user version of the OFDM technology
Subdivides a channel into smaller frequency allocations - called Resource Units (RUs)
Used in LTE downlink- ARichtig
- BFalsch
72Resource Unit (RU) is a unit in OFDMA terminology used to denote a group of bandwidth subcarriers used in both DownLink and UpLink transmissions
- ARichtig
- BFalsch
73International Mobile Equipment Identity (IMEI) - Unique [blank_start]identity for the mobile equipment[blank_end]
International Mobile Subscriber Identity (IMSI) - Unique [blank_start]identity for the UICC and the USIM[blank_end]
M Temporary Mobile Subscriber Identity (M-TMSI) - [blank_start]Identifies a mobile to its serving MME[blank_end]
Globally Unique Temporary Identity (GUTI)
- Aidentity for the mobile equipment
- Bidentity for the UICC and the USIM
- CIdentifies a mobile to its serving MME
74how UMTS evolved into LTE
- ARichtig
- BFalsch
Informationen
- Beschreibung
- Computer Science Quiz am wireless midterm, erstellt von Duncan Levings am 10/03/2021.
- Autor
- Duncan Levings
- Sprache
- English
- Aufrufe
- 5
- Schlagwörter
- Bewertung
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