Chapter 4

Question 1

a material that allows electrical current to flow through it

Answer 1

Conductor

Question 2

passive conductor used to transmit electromagnetic waves through space

Answer 2

Antenna

Question 3

Simplest antenna is a bare metal wire called
Found on older automobiles and cellular phones
The length of the antenna should be at least one-quarter of the wavelength of the electromagnetic wave that is sending or receiving

Answer 3

whip antenna

Question 4

a system used to create and transmit RF signals
Labeled by the FCC
Specifically designed to send out electromagnetic waves (intentional)
Also designed to radiate out, or send, a signal (radiator)

Answer 4

Intentional Radiator

Question 5

source of RF waves that have the same magnitude or properties in all directions
No preference in the direction of radiation

Answer 5

Isotropic radiator

Question 6

amount of power that a theoretical isotropic radiator can generate
Includes any antenna amplification (gain)

Answer 6

Equivalent Isotropically Radiated Power (EIRP

Question 7

passive gain of power that is funneled from an antenna compared to that of an isotropic radiator sent in all directions
Focusing the signal in a specific direction is known as a passive gain (no additional power is added)

Answer 7

Decibels isotropic (dBi)

Question 8

most basic type of antenna

Answer 8

Dipole

Question 9

compares the antenna gain against that of a dipole antenna

Answer 9

Decibels dipole (dBd)

Question 10

most common type of antenna for a WLAN

Radiates its signal out horizontally in all directions equally

Answer 10

Omnidirectional antennas

Question 11

orientation of radio waves as they leave an antenna
Antennas must be polarized alike to be efficient
Antennas in a horizontal position will not communicate well with an antenna in a vertical position

Answer 11

Polarization

Question 12

Ability of an access point to examine multiple copies of a received transmission and then select the best signal
Selecting the best signal is known as switching

Answer 12

Antenna diversity

Question 13

the AP can transmit on the antenna that most recently received the strongest incoming signal

Answer 13

Transmit Diversity

Question 14

focuses energy in one direction

Primarily used for short and medium range remote wireless bridge networks

Answer 14

Semidirectional antennas

Question 15

divides the coverage area into different sectors and gives each sector its own antenna

Answer 15

Sectorized antenna

Question 16

multiple antennas that can be customized to send an optimal signal
Each antenna does not have to have the same power

Answer 16

Antenna array

Question 17

sends a narrowly focused signal beam long distances
Generally reflective devices that are shaped like a concave disk
Used for outdoor long-distance point-to-point wireless links, such as connecting buildings that are up to 25 miles apart
Not used for indoor WLANs

Answer 17

Highly-Directional Antennas

Question 18

used to illustrate an antenna’s radiation pattern

Answer 18

Antenna radiation chart

Question 19

represents the horizontal coverage

Answer 19

Azimuth chart

Question 20

used to show the vertical coverage

Answer 20

Elevation chart

Question 21

a measurement of a transmission’s width

Answer 21

Beamwidth

Question 22

theoretical straight line between a transmitter and the receiver
An object that is close to the path of the RF transmission can impact the signal

Answer 22

RF line of sight

Question 23

elliptical area immediately surrounding the visual line of sight for RF transmissions
Steps for mitigating obstructions in the Fresnel zone include:
Raising the antenna mounting point on the existing structure
Increasing the height of an existing power
Building a new structure that is tall enough to mount the antenna
Locating a different mounting point on another building or tower for the antenna
Cutting down trees

Answer 23

Fresnel zone

Question 24

A wireless device with multiple receive (Rx) antennas can improve transmissions by either:
Selecting the stronger incoming signal
Combining the individual signals at the receiver
system that uses one radio chain for each antenna
that each antenna can simultaneously transmit and receive signals
IEEE made MIMO the heart of 802.11n
Estimated the MIMO alone contributes 40% to the increase in speed
802.11n standard is sometimes called HT (MIMO) for High Throughput Multiple-Input Multiple-Output

Answer 24

Multiple Input Multiple Output (MIMO)

Question 25

a MIMO technique of sending the same transmission out from different antennas that will take different paths
Can increase reliability of an RF signal
Each transmission will take different paths (called spatial paths)
It is unlikely all paths will degrade the signal in the same way

Answer 25

Spatial diversity

Question 26

sends a normal version of the signal along with a shifted version of the same signal

Answer 26

Cyclic Shift Diversity (CSD)

Question 27

Instead of sending the same data out through multiple antennas, first splits up the data and sends it out over multiple antennas

Answer 27

spatial multiplexing

Question 28

The algorithm a MIMO AP uses when it receives multiple copies of a signal from a non-MIMO device
The AP will receive multiple copies of the multipath signal on each of its Rx antennas
MRC multiplies each received signal by a weight factor that is proportional to the signal amplitude

Answer 28

Maximal ratio combining (MRC):

Question 29

An option for reducing outside signal interference by using complex antenna systems to allow for different directions and bandwidths

Answer 29

Transmit Beam Forming (TxBF):

Question 30

a TxBF technique in which the receiver makes a series of computations and sends them to the transmitter, which then uses them to configure how to make the best transmissions

Answer 30

Explicit feedback

Question 31

information that is computed by the receiver and sent back to the transmitter for use in antenna configuration

Answer 31

Implicit feedback