Chap 18 - Wireless Terms

Question 1

Amplitude

Answer 1

Amplitude is the height from the top peak to the bottom peak of the signal’s waveform,

Question 2

Band

Answer 2

A contiguous range of frequencies.

Question 3

Bandwidth

Answer 3

The range of frequencies used by a single channel or a single RF signal.

Question 4

Carrier Signal

Answer 4

The basic, steady RF signal that is used to carry other useful information.

Question 5

Channel

Answer 5

An arbitrary index that points to a specific frequency within a band.

Question 6

dBd

Answer 6

dB-dipole, the gain of an antenna, measured in dB, as compared to a simple dipole antenna.

Question 7

dBi

Answer 7

dB-isotropic, the gain of an antenna, measured in dB, as compared to an isotropic reference antenna.

Question 8

dBm

Answer 8

dB-milliwatt, the power level of a signal measured in dB, as compared to a reference signal power of 1 milliwatt.

Question 9

dB

Answer 9

A logarithmic function that compares one absolute measurement to another.

Question 10

Demodulation

Answer 10

The receiver’s process of interpreting changes in the carrier signal to recover the original information being sent.

Question 11

dsss

Answer 11

Direct Sequence Spread Spectrum, a wireless LAN method in which a transmitter uses a single fixed, wide channel to send data.

Question 12

drs

Answer 12

Dynamic Rate Shifting - a mechanism used by an 802.11 device to change the modulation coding scheme (MCS) according to dynamic RF signal conditions.

Question 13

EIRP

Answer 13

Effective Isotropic Radiated Power - the resulting signal power level, measured in dBm, of the combination of a transmitter, cable, and an antenna, as measured at the antenna.

Question 14

Frequency

Answer 14

The number of times a signal makes one complete up and down cycle in 1 second.

Question 15

Hertz

Answer 15

A unit of frequency equaling one cycle per second.

Question 16

In Phase

Answer 16

The condition when the cycles of two identical signals are in sync with each other.

Question 17

Isotropic Antenna

Answer 17

An ideal, theoretical antenna that radiates RF equally in every direction.

Question 18

Link Budget

Answer 18

The cumulative sum of gains and losses measured in dB over the complete RF signal path; a transmitter’s power level must overcome the link budget so that the signal can reach a receiver effectively.

Question 19

MRC

Answer 19

Maximal-ratio Combining - an 802.11n technique that combines multiple copies of a signal, received over multiple antennas, to reconstruct the original signal.

Question 20

Modulation

Answer 20

The transmitter’s process of altering the carrier signal according to some other information source.

Question 21

Narrowband

Answer 21

RF signals that use a very narrow range of frequencies.

Question 22

Noise Floor

Answer 22

The average power level of noise measured in dB at a specific frequency.

Question 23

OFDM

Answer 23

Orthogonal Frequency Division Multiplexing - a data transmission method that sends data bits in parallel over multiple frequencies within a single 20 MHz wide channel. Each frequency represents a single subcarrier.

Question 24

Out of Phase

Answer 24

The condition when the cycles of one signal are shifted in time in relation to another signal.

Question 25

Phase

Answer 25

A measure of shift in time relative to the start of a cycle; ranges between 0 and 360 degrees.

Question 26

QAM

Answer 26

Quadrature Amplitude Modulation - modulation method that combines QPSK phase shifting with multiple amplitude levels to produce a greater number of unique changes to the carrier signal. The number preceding the QAM name designates how many carrier signal changes are possible.

Question 27

RF

Answer 27

Radio Frequency - the portion of the frequency spectrum between 3 kHz and 300 GHz.

Question 28

RSSI

Answer 28

Received Signal Strength Indicator - the relative measure of signal strength (0 to 255), as seen by the receiver.

Question 29

Sensitivity Level

Answer 29

The RSSI threshold (in dBm) that divides unintelligible RF signals from useful ones.

Question 30

SNR

Answer 30

Signal-to-Noise Ratio - a measure of received signal quality, calculated as the difference between the signal’s RSSI and the noise floor. A higher SNR is preferred.

Question 31

Spatial Multiplexing

Answer 31

Distributing streams of data across multiple radio chains with spatial diversity.

Question 32

Spatial Stream

Answer 32

An independent stream of data that is sent over a radio chain through free space. One spatial stream is separate from others due to the unique path it travels through space.

Question 33

Spread Spectrum

Answer 33

RF signals that spread the information being sent over a wide range of frequencies.

Question 34

TxBF

Answer 34

TXmit BeamForming - a method of transmitting a signal over multiple antennas, each having the signal phase carefully crafted, so that the multiple copies are all in phase at a targeted receiver.

Question 35

Wavelength

Answer 35

The physical distance that a wave travels over one complete cycle.