Wireless (RF basics) Flashcards
What is Frequency
The number of cycles that passes a point in a second, measured in Hz.
What is the frequency range for RF communication.
3kHz - 300GHz
What are the RF band’s used for wireless communication
2.4GHz
5GHz
6GHz
What is a channel
When the RF band is divided up into specific frequencies.
What is channel-width / channel separation
The distance in Hz between the channels.
What is signal bandwidth
The amount of frequency required to transmit the signal.
What is Phase
It is the shift in time relative to the start of a cycle. measured in degrees.
What is wavelength
The measurement of the length of the wave.
What is the relationship between frequency and wavelength
Higher frequency lower wavelength , lower frequency higher wavelength.
What is amplitude
Is the measurement of the strength of the wave, measured from peak to trough. in watts (W).
What unit of measurement is power compared in
dB
What are the 3 laws for comparing the power in dB
Law of zero
Law of 3’s
Law of 10’s
What is the effective isotropic radiated power (EIRP)
Is an actual power measurement of the transmitter, this accounts for the transmit power - cable loss + antenna gain.
What is FSPL
Free Space Path Loss, is the measurement of loss in free space (vacuum) it is a function of frequency and distance only!
What is RSSI
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.
What is sensitivity level
The threshold that divides intelligible signals from un-intelligible signals.
As long as received power > sensitivity level: data should be understood.
What is ‘noise’
All other signals received on the same frequency.
What is the ‘Nosie floor’
The average signal power strength of the noise.
What is a carrier signal
The basic RF signal that is used to carry data on a waveform.
What is the purpose of modulation
To alter the carrier signal modulation alters either frequency, amplitude or phase to indicate data been carried.
Lower data rates require less bandwidth for modulation.
True or False
False - the higher the data rate the more bandwidth is required for modulation.
What is spread spectrum
When data is sent across a number of frequencies there are 2 types.
What is direct sequence spread spectrum
Used in the 2.4GHz band where a small number of fixed width channels to support complex modulation.
What is Orthogonal Frequency Division Multiplexing (OFDM)
used in 2.4, 5 & 6 GHz bands.
OFDM allows multiple clients to transmit simultaneously to the AP.
Which Wi-Fi standard is is not supported on the 5GHz band
802.11b (Wifi 1)
802.11g (Wifi 3)
Which Wi-Fi standard is not supported on the 2.4GHz band
802.11a (Wi-Fi 2)
wireless signals can only transmit once at a time when the air is clear.
True or False
False - 802.11ax (Wi-Fi 6) uses OFDM to simultaneously transmit data to multiple clients.
What is a single-in-single-out radio
a device that has 1 transmitter and 1 receiver
What is a multi-in-multi-out radio
multiple transmitters and multiple receivers on the same device.
denoted Tx x Rx MIMO
What is a radio chain
one set of radio’s (transmitter and receiver)
What is spatial multiplexing
When data is distributed across 2 or more radio chains
What is a spatial stream
When data is sent in independent stream
What is Transmit beam-forming (TF)
Is where a transmitting device with multiple radio chains can prefer one receiver over the other.
What Wi-Fi standards are supported by TF
802.11n
802.11ac
802.11ax
What is Maximal-ratio combining
When a receiver has lower quality copies of the same signal and combines the copies for the best signal.
What is dynamic rate shifting (DRS)
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.
