Wireless (RF basics)

Question 1

What is Frequency

Answer 1

The number of cycles that passes a point in a second, measured in Hz.

Question 2

What is the frequency range for RF communication.

Answer 2

3kHz - 300GHz

Question 3

What are the RF band’s used for wireless communication

Answer 3

2.4GHz
5GHz
6GHz

Question 4

What is a channel

Answer 4

When the RF band is divided up into specific frequencies.

Question 5

What is channel-width / channel separation

Answer 5

The distance in Hz between the channels.

Question 6

What is signal bandwidth

Answer 6

The amount of frequency required to transmit the signal.

Question 7

What is Phase

Answer 7

It is the shift in time relative to the start of a cycle. measured in degrees.

Question 8

What is wavelength

Answer 8

The measurement of the length of the wave.

Question 9

What is the relationship between frequency and wavelength

Answer 9

Higher frequency lower wavelength , lower frequency higher wavelength.

Question 10

What is amplitude

Answer 10

Is the measurement of the strength of the wave, measured from peak to trough. in watts (W).

Question 11

What unit of measurement is power compared in

Answer 11

dB

Question 12

What are the 3 laws for comparing the power in dB

Answer 12

Law of zero
Law of 3’s
Law of 10’s

Question 13

What is the effective isotropic radiated power (EIRP)

Answer 13

Is an actual power measurement of the transmitter, this accounts for the transmit power - cable loss + antenna gain.

Question 14

What is FSPL

Answer 14

Free Space Path Loss, is the measurement of loss in free space (vacuum) it is a function of frequency and distance only!

Question 15

What is RSSI

Answer 15

Received Signal Strength Indicator (RSSI), is a measurement of received signal power levels. In the standard it is measured from 0 to 255 however is often mapped to dBm values.

Question 16

What is sensitivity level

Answer 16

The threshold that divides intelligible signals from un-intelligible signals.

As long as received power > sensitivity level: data should be understood.

Question 17

What is ‘noise’

Answer 17

All other signals received on the same frequency.

Question 18

What is the ‘Nosie floor’

Answer 18

The average signal power strength of the noise.

Question 19

What is a carrier signal

Answer 19

The basic RF signal that is used to carry data on a waveform.

Question 20

What is the purpose of modulation

Answer 20

To alter the carrier signal modulation alters either frequency, amplitude or phase to indicate data been carried.

Question 21

Lower data rates require less bandwidth for modulation.

True or False

Answer 21

False - the higher the data rate the more bandwidth is required for modulation.

Question 22

What is spread spectrum

Answer 22

When data is sent across a number of frequencies there are 2 types.

Question 23

What is direct sequence spread spectrum

Answer 23

Used in the 2.4GHz band where a small number of fixed width channels to support complex modulation.

Question 24

What is Orthogonal Frequency Division Multiplexing (OFDM)

Answer 24

used in 2.4, 5 & 6 GHz bands.

OFDM allows multiple clients to transmit simultaneously to the AP.

Question 25

Which Wi-Fi standard is is not supported on the 5GHz band

Answer 25

802.11b (Wifi 1) 802.11g (Wifi 3)

Question 26

Which Wi-Fi standard is not supported on the 2.4GHz band

Answer 26

802.11a (Wi-Fi 2)

Question 27

wireless signals can only transmit once at a time when the air is clear. True or False

Answer 27

False - 802.11ax (Wi-Fi 6) uses OFDM to simultaneously transmit data to multiple clients.

Question 28

What is a single-in-single-out radio

Answer 28

a device that has 1 transmitter and 1 receiver

Question 29

What is a multi-in-multi-out radio

Answer 29

multiple transmitters and multiple receivers on the same device. denoted Tx x Rx MIMO

Question 30

What is a radio chain

Answer 30

one set of radio's (transmitter and receiver)

Question 31

What is spatial multiplexing

Answer 31

When data is distributed across 2 or more radio chains

Question 32

What is a spatial stream

Answer 32

When data is sent in independent stream

Question 33

What is Transmit beam-forming (TF)

Answer 33

Is where a transmitting device with multiple radio chains can prefer one receiver over the other.

Question 34

What Wi-Fi standards are supported by TF

Answer 34

802.11n 802.11ac 802.11ax

Question 35

What is Maximal-ratio combining

Answer 35

When a receiver has lower quality copies of the same signal and combines the copies for the best signal.

Question 36

What is dynamic rate shifting (DRS)

Answer 36

IS a technology used when closer to a transmitting source the higher data rates will be achieved using more complex modulation. As the receiver moves further away the data rates decrease and the modulation technology is less complex.