TDMM Chapter 16 Flashcards
(159 cards)
1
Q
Absorption
A
The loss of energy in an electromagnetic signal as it passes through a medium
2
Q
AGC
A
Automatic Gain Control
3
Q
Amplitude
A
The size or magnitude of a waveform
4
Q
Access Point (AP)
A
Standalone hardware device that acts as a wireless communications hub
5
Q
BSS
A
Basic Service Set
A single wireless LAN and its associated clients
6
Q
DAS
A
Distributed Antenna System
7
Q
Diffraction
A
The bending of sound, radio or light waves around an object
8
Q
Dispersion
A
The loss incurred by an RF signal due to the natural broadening of the wave front
9
Q
ERRCS
A
Emergency Responder Radio Coverage Systems
10
Q
Extended Service Set (ESS)
A
A collection of access points tied together by a wired backbone
11
Q
Frequency
A
The number of cycles or events per unit of time
12
Q
Independent Basic Service Set (IBSS)
A
A group of stations within a wireless LAN that communicate without a central access point
13
Q
IR (Standard)
A
Infrared (Standard)
A communications system built on the IR light spectrum
14
Q
LoS
A
Line of Signt
15
Q
NIC
A
Network Interface Card
16
Q
OS
A
Operating System
17
Q
PTP
A
Point to Point
A direct connection established between two points
18
Q
Reflection
A
The abrupt change in direction of a wave at a dissimilar media, such that the wave returns into the original media
19
Q
Refraction
A
The abrupt change in direction of a wave at a dissimilar media, such that the wave enters the second medium
20
Q
QoS
A
Quality of Service
21
Q
Scattering
A
A change in direction/frequency of a wave when it encounters particles sized similar to the wavelength
22
Q
Wavelength
A
The distance between points of a phase of one complete cycle of wave
23
Q
WLAN
A
Wireless Local Access Network
24
Q
Name three technological considerations in wireless design
A
- Scalability of the network
- Compatibility of the overall network
- Implementation of a wireless network based around standards
25
Name three factors that define the reliability of a wireless network
- Accessibility
- Continuity
- Consistency of Service
26
Name four factors that affect the throughput of a wireless network
- Application requirements
- Number of users
- Future requirements
- Capabilities of the products used
27
What type of impact do radio communications towers have on the footprint of a facility?
They have a limited footprint
28
Name three reasons the roof top of a tall building may be an unsuitable location for a cellular system
- Difficult to get signal to street level
- Increased potential for interference
- Reduces frequency reuse capabilities
29
Name three methods for evaluating the environment in which a wireless network will be used
- Site survey
- Propagation analysis
- Modeling
30
What two considerations does a QoS program attempt to balance?
- End user expectations
- Wireless network performance
31
What term is used to describe the number of cycles or events per unit of time?
Frequency
32
What unit of measure is used to express the frequency of an electromagnetic signal?
Herts (Hz)
33
What does one hertz equal?
One cycle per second
34
What term is used to describe the distance between two points of a corresponding phase of one complete cycle of a wave?
Wavelength
35
What unit of measure is typically used for wavelengths in an electromagnetic system?
Meters
36
What term is used to describe the motion of waves through or along a medium?
Propagation
37
Define line of sight in terms of propagation
A propagation in which the radiation from the transmitter to the receiver is unobstructed
38
Name two types of LoS propagation
- Visual
- Radio Frequency (RFI)
39
What is visual LoS?
The visual observation of one point to another as seen by the observers eye
40
What is RF LoS?
The line of sight between the receiving and transmitting antennas
41
What are Fresnel zones?
A series of concentric ellipsoids surrounding the path
42
How is the first Fresnel Zone used?
As a nominal unit to measure certain distances in terms of their effects on frequency
43
What is the minimum clearance requirement for reliable wireless service?
(expressed in fresnel zones)
60 percent of F1 clearance
44
Name two categories of barriers and obstructions that impede electromagnetic waves
- Natural
- Man made
45
What is free space loss?
The signal attenuation that would result if all reflection, scattering, diffraction and absorption influences were removed
46
What term refers to the abrupt change i. direction of a wave at the interface between two dissimilar media such that the wave returns into the medium from which it originated?
Reflection
47
What term refers to the abrupt change i. direction of a wave at the interface between two dissimilar media such that the wave enters the second medium?
Refraction
48
What term describes the change in frequency/direction of the wave when it encounters small particles
Scattering
49
What term is used to describe the bending of light around an object?
Diffraction
50
What term is used to describe the loss of energy in an electromagnetic signal as it passes through a medium?
Absorption
51
What is a sky wave?
A sky wave is a wave that is usable due to reflection and refraction in the ionosphere
52
What is the ionosphere?
The portion of earths upper atmosphere where ions and electrons are present in quantities sufficient to affect the propagation of radio waves
53
Normally the ionosphere extends to ?
30 miles to 621 miles above the earth
54
What causes the distance to the radio horizon to exceed the optical horizon within the troposphere?
Within the troposphere bending of radio waves by refraction makes the distance to the radio horizon exceed the distance to the optical horizon
55
At what distance does tropospheric refraction typically affect received signals?
At distances beyond the radio horizon
56
What is a direct wave?
An RF wave that travels directly from the transmitting antenna to the receiving antenna
57
How can the LoS distance be extended in terrestrial communications?
By increasing the height of the transmitting antenna or receiving antenna
58
What is a ground wave?
A wave that travels along the surface
59
What is the maximum range of a surface path when high powered transmitters and efficient antennas are used?
310 miles
60
What is the relationship between the range of a surface path and frequency?
The surface path range decreases as frequency increases
61
What is isotropic gain?
The ratio of actual signal strength at the antenna relative to an ideal isotropic radiator
62
What is fading?
The variation of the amplitude of part of a signal
63
Name the two types of fading
- Multipath fading
- Delay spread
64
What is modulation
The process of altering the carrier signal
65
Name four types of modulation
- Amplitude modulation
- Frequency modulation
- Phase modulation
- Pulse modulation
66
What is amplitude modulation
superimposing a signal on a carrier wave
67
What is frequency modulation?
Superimposing a signal on an RF carrier wave
68
What is phase modulation?
The method of superimposing a signal on a carrier wave
69
What is pulse modulation?
The method of superimposing a series of pulses carrying the signal on a carrier wave
70
Which modulation technique uses two different phase angles that are usually out of phase by 180 degrees?
Binary Phase Shift Keying (BPSK)
71
Which modulation technique uses four different phase angles that are usually out of phase by 90 degrees?
Quadrature phase shift keying (QPSK)
72
What is complementary code keying (CCK)?
The basis for high rate physical layer extension to deliver data rates of 11 mb/s
73
Describe how the QAM modulation technique works
Two carriers at the same frequency are independantly amplitude modulated and combined for transmission
74
Describe how the OFDM modulation technique works
A large number of closely spaced orthogonal sub carriers are combined into parallel streams
75
How does the OFDMA modulation technique achieve a more efficient use of airtime?
By scheduling the transmissions from the clients so they do not clash with each other
76
What are harmonics
The multiples of an alternating currents fundamental frequency
77
What is the first harmonic?
The fundamental frequency
78
What is the second harmonic?
Twice the functional frequency
79
What is harmonic distortion?
The presence of unwanted harmonic frequencies
80
Name four types of harmonic filters
- high pass filter
- low pass filter
- band pass filter
- band stop filter
81
What term describes an increase in an RF signals power?
Gain
82
Name two sources of gain
- External power sources
- Passive sources
83
What term describes a decrease in signal strength?
Loss
84
Name the two main sources of loss in a wireless system
- Impedance of cables and connectors
- Absorption, reflection, refraction, scattering or destruction during propagation
85
What unit provides an absolute measurement of power?
Watt
86
What unit provides a measurement of the relative gain or loss of power?
Decibel
87
What rule is commonly used to calculate isotrpic gain for antennas?
The 6dB rule
88
Name eight types of information that should be gathered before the wireless network is required?
- Bandwidth requirement
- Number of uses
- Growth and expandability
- Existing data network
- User environment
- EM and RF noise
- Building Construction
- Climate
89
Name the two primary types of wireless networks
- Licensed
- Unlicensed
90
What is the frequency range for PTP licensed wireless networks?
6 GHz to 40 GHz
91
What frequencies are used primarily for public safety applications?
6 GHz to 11 GHz
92
What frequencies are primarily used in the private sector for PTP applications?
18 GHz and above
93
What frequencies are the most prevalent for wireless deployments for the unlicensed spectrum?
2.4GHz and 5 GHz
94
What frequency range is used by amateur radio operators?
2.4 GHz and below
95
How does licensing provide a higher level of interference protection that what is found in unlicensed systems?
By limiting the use of any frequency to a single user in any one area
96
What is path loss?
The loss of the RF signal power from its originating point to the ultimate end point
97
Name five factors that contribute to path loss
- Frequency of RF signal
- Transmission power
- Distance between the transmit and receive antenna
- Obstructions
- Terrain
98
Name five factors used to select the proper antenna for an application
- Required gain
- Allowable wind load
- Frequency
- Aesthetics
- Zoning
99
What is the purpose of a radome cover for a parabolic antenna?
To keep ice and snow off
100
How does a radome cover affect an RF signal?
It causes some loss
101
What is the common path loss when using radome covers?
0.5 dB isotropic
102
Name two problems associated with oversizing antennas
- Interference
- Damage to radio equipment
103
Name the two basic measurements used in analyzing radio waves and other wave forms
- Frequency
- Amplitude
104
Name the three categories of wireless tranceivers
- Half duplex
- Frequency division duplex
- Time division duplex
105
What type of transceiver is incapable of transmitting and receiving signals at the same time?
Half Duplex
106
How does a frequency division duplex transceiver operate?
Transmits and receives simultaneously
107
How does a time division duplex transceiver operate?
Transmits and receives at RF alternately in sequential time slots
108
Define Antenna
A means for coupling RF energy from a transmission onto a transmission medium
109
What will happen if the wrong connector is used in an antenna system?
Will cause degredation
110
Name five considerations for implementing an outdoor PTP solution
- Distance
- Terrain
- Climate
- Physical obstructions
- Cabling attenuation
111
What is a jinpole?
A rigging tool that is used to hoist sections up a tower
112
What is the benefit of using jumpers to connect the RF media to the antenna and the equipment?
Allows system to be serviced without damaging other parts
113
What is the weakest part of an antenna system?
The antenna connector
114
What is the purpose of a voltage injector?
To power electronic equipment located away from a convenient power source
115
Name two major types of voltage injectors
- Coaxial
- PoE
116
How far above the roof should RF media be supported?
At least 1.5 in
117
What is a distributed antenna system?
A system that transmits signals where outdoor network signals cant penetrate
118
Name seven components of a DAS
- Transmitter
- Receiver
- Amplifier
- Converter
- Cabling
- Connector
- Antenna
119
Name five types of cable that are commonly recognized for DAS cabling distribution
- SM Fiber
- MM Fiber
- Hybrid fiber
- Twisted pair
- Coaxial cable
120
What category of twisted pair is recommended for DAS cabling distribution?
Category 6A
121
Excluding the base station hardware, what is the most expensive part of a DAS?
The antenna network
122
Name four types of Antennas used in a DAS?
- Omnidirectional
- Directional
- Radiating cable
- Combination of all three
123
What type of antenna broadcasts equally in all directions of one cross section of its toroidal radiation pattern?
Omnidirectional
124
What type of antenna concentrates the radiated signal in one direction more than in another?
Directional
125
Why is a radiating coaxial cabling useful in combined systems?
It has a wide bandwidth, from 70 MHz to 2.4 GHz
126
True or False
A radiating cable should be placed in a metal conduit for protection?
False
127
Name five common types of active DAS equipment
- Transceiver
- Bidirectional amplifiers
- Unidirectional amplifiers
- Repeaters
- Power supply units
128
What is a transceiver?
A device that uses many of its components to transmit and receive RF signals
129
What function is typically performed by the power supply unit?
Converts AC to DC
130
What is the primary headend device?
Master Control Unit (MCU)
131
Name three suitable locations for an Master Control Unit (MCU)
- Main Equipment Room
- Telecom Room
- Penthouse near roof
132
Where is DAS backend equipment typically located?
In the TR
133
Name the three primary means used by active DAS to transport radio signals
- Analog modulation
- Down conversion
- Digital sampling of RF signals
134
What is an advantage of analog modulation?
The ability to modulate a large portion of the radio spectrum over one optical path
135
What is a major problem associated with analog systems?
The direct dependency of the modulation and recovery of the RF signal to the optical transport
136
What is the primary medium used for DAS analog systems?
Singlemode optical fiber
137
How do DAS analog systems compensate for the dependency on optical losses?
By using automatic gain control (AGC) as a feedback loop
138
How is passive distribution equipment in a DAS defined?
As equipment that does not require external power input
139
What is a directional coupler?
A device that splits power from one input connector to two or more output connectors
140
What piece of passive DAS equipment combines dc power with the ac RF signals on a coaxial cable and taps it off at the other end?
Bias Tee
141
What piece of passive DAS equipment is used to combine two wireless bands to a single antenna feed or distribution cable?
Hybrid coupler
142
Which piece of passive DAS equipment accepts an input signal and delivers multiple output signals with specific phase and amplitude characteristics?
Power Splitter
143
Name three characteristics of output signals in power splitters
- Equal amplitude
- Zero degree phase relationship between any two output signals
- High isolation between each output signal
144
Name two common topologies that serve a DAS within a building structure
- Star topology
- Tapped trunk topology
145
Name three factors that may affect the selection of a cabling topology for a DAS
- DAS equipment
- Cabling medium used in a new installation
- Legacy cabling system
146
What cabling mediums may be used in the installation of a star topology?
- Twisted pair
- Coaxial
- Fiber
- Combination
147
What types of cabling may be used to install a tapped trunk topology?
- Coaxial
- Fiber
148
What component is used to tap into the coaxial cable of a tapped trunk topology?
Splitter or vampire tap
149
Name two potential problems associated with using a DAS to support mobile communications in buildings
- Availability of RF signals
- Ability to support required capacity
150
Name the three phases associated with DAS design
- Pre Installation
- Installation
- Acceptance
151
What is the purpose of conducting RF measurements during an on site survey of the radio environment?
To identify existing signals and their frequency strength
152
Name two factors that determine the overall usability and capability of an installed DAS
- Selection
- Location
153
What is the link budget (operating margin)
The sum of ICT gains and losses in an ITS
154
What is a personal Area Network (PAN)
The interconnection of information technology devices within a personal operating space
155
What is the typical radius of a PAN?
10 m (33 ft)
156
Name three key factors for a PAN
- Lower power consumption
- Low cost
- Superior ease of use
157
True or False
IS is unaffected by RF
True
158
What is the intended purpose of a public WLAN or hotspot?
To provide convenient access to internet based information
159
Name three categories of WLAN services based on access restrictions
- Unrestricted access
- Established account acces
- Temporary account access
