wireless ch.4 key terms

spatial multiplexing

A MIMO technique of sending independent streams of information at the same time over the same frequencies

spatial diversity

A MIMO technique of sending the same transmission out from different antennas that will take different paths.

MIMO diversity

A MIMO technique of sending the same transmission out on different paths from different antennas

explicit feedback

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.

Azimuth chart

A chart that represents the horizontal coverage area of an antenna.

elevation chart

A chart that represents the vertical coverage area of an antenna. Equivalent (also called Effective) Isotropically Radiated Power (EIRP) The amount of power that a theoretical isotropic radiator can generate.

antenna radiation chart

A chart used to illustrate an antenna's radiation pattern

amplifier

A device that amplifies or increases the amplitude of an RF signal.

RF attenuator

A device that decreases the RF signal and is used when the gain of an antenna did not match the power output of an AP.

RF signal splitter

A device that divides the power in the input signal to multiple outputs.

bidirectional amplifier

A device that increases the RF signal before it is injected into the device that contains or is directly connected to the antenna.

lightning arrestor

A device that limits the amplitude and disturbing interference voltages by channeling them to the ground.

conductor

A material that allows an electrical current to flow through it.

Voltage Standing Wave Ratio (VSWR)

A measure of how well an electrical load is impedance-matched to its source.

beamwidth

A measurement of a transmission's width.

decibels dipole (dBd)

A measurement that compares the antenna gain against that of a dipole antenna

ground rod

A metal rod inserted in the earth to ground an antenna

antennas

A passive conductor used to transmit electromagnetic waves through space.

radio chain

A radio with supporting infrastructure such as devices to amplify the signal or convert an analog signal into a digital signal.

link budget

A rough calculation of all known elements of a link to determine if a signal will have the proper strength when it reaches its destination.

isotropic radiator

A source of RF waves that have the exact same magnitude or properties in all directions.

Multiple-Input Multiple-Output (MIMO)

A system that uses one radio chain for each antenna so that each antenna can simultaneously transmit and receive signals

intentional radiator (IR)

A system used to create and transmit RF signals as defined by the Federal Communications Commission (FCC).

Cyclic Shift Diversity (CSD

A technique that sends a normal version of the signal along with a shifted version of the same signal

RF line of sight

A theoretical straight line between a transmitter and the receiver

single-input single-output (SISO)

A wireless communication system that uses one radio chain

Space Time Block Coding (STBC

An 802.11n option that sends a redundant copy of part or all of the transmited signal on an unused antenna.

variable-loss attenuator

An RF attenuator that allows the user to set the amount of loss.

fixed-loss attenuator

An RF attenuator that limits the RF power by a set amount.

dipole

An antenna consisting of a single stretched wire with connection in the middle.

sectorized antenna

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

semidirectional antenna

An antenna that focuses energy in one direction.

omnidirectional antenna

An antenna that radiates its signal out horizontally in all directions equally.

highly-directional antenna

An antenna that sends a narrowly focused signal beam long distances.

Fresnel zone

An elliptical area immediately surrounding the visual line of sight of an RF transmission.

transmit beam forming (TxBF)

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

visual line of sight

An unobstructed straight line between objects

high-gain antennas

Antennas that have longer ranges and higher signal quality than low-gain antennas yet must be aimed precisely in a particular direction

low-gain antennas

Antennas with a shorter range than high-gain antennas that do not have to be precisely aimed at the receiver.

HT (MIMO)

High Throughput Multiple-Input Multiple-Output for IEEE 802.11n WLANs that utilize a radio chain for each antenna.

implicit feedback

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

antenna array

Multiple antennas that can be customized to send an optimal signal

return loss

The VSWR as measured in dB.

antenna diversity

The ability of an access point to examine multiple copies of a received transmission and then select the best signal.

transmit diversity

The ability of an access point to transmit on the antenna that most recently received the strongest incoming signal.

plenum

The air-handling space above drop ceilings that is used to circulate and handle air in a building.

maximal ratio combining (MRC

The algorithm a MIMO AP uses when it receives multiple copies of a signal from a non-MIMO device

system operating margin (SOM

The difference between the received signal level and the signal level that is required by that radio to assure that the transmission can be decoded without errors.

fade margin

The difference between the received signal level and the signal level that is required by that radio to assure that the transmission can be decoded without errors.

active gain

The gain in which additional power was sent to the antenna from the power source.

passive gain

The gain in which no additional power is added

polarization

The orientation of radio waves as they leave an antenna

decibels isotropic (dBi)

The passive gain of power that is funneled from an antenna compared to that of an isotropic radiator sent in all directions.

switching

The process of choosing which antenna reception to accept.

sensitivity

The signal strength needed for a good reception

unidirectional amplifier

a device that increases the RF signal level before it is injected into the transmitting antenna.