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CCNP Encor 350-401 > Chapter 17: Wireless Signals and Modulation > Flashcards

Chapter 17: Wireless Signals and Modulation Flashcards

1
Q

The frequency range from around 3 kHz to 300 GHz.

A

Radio frequency (RF)

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2
Q

What category of frequency ranges do the 2.4 and 5 GHz bands used for WLANs fall into?

A

Microwave

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3
Q

T/F

The 5 GHz WLAN band contains 4 contiguous bands 5.150 and 5.825.

A

False

There is a gap between 5.350 and 5.470

  1. 150 to 5.250 GHz
  2. 250 to 5.350 GHz
  3. 470 to 5.725 GHz
  4. 725 to 5.825 GHz
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4
Q

A contiguous range of frequencies.

A

Band

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5
Q

Specific frequencies that bands are divided into.

A

Channels

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6
Q

How wide is each channel in the 2.4 GHz band?

A

5 MHz (.005 GHz)

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7
Q

What do wireless devices use to ignore parts of a signal that falls outside the bandwidth boundaries?

A

Spectral Mask

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8
Q

The range of frequencies used by a single channel or

a single RF signal.

A

Bandwidth

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9
Q

T/F

Channel width should be less than signal bandwidth.

A

False.

Signal bandwidth should be less than the channel
width.

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10
Q

A measure of shift in time relative to the start of a cycle.

A

Phase

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11
Q

Phase is measured in:

A. MHz
B. Ohms
C. Degrees
D. kHz

A

C. Degrees

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12
Q

A measure of the physical distance that a wave travels over one cycle.

A

Wavelength

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13
Q

T/F

Radio waves travel at exactly the speed of light through air.

A

False

Radio waves travel at exactly the speed of light through a vacuum.

Radio waves travel at slightly less than the speed of light through air.

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14
Q

What happens to wavelength as frequency increases?

A

Wavelength decreases

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15
Q

The strength of a wireless signal.

A

Amplitude

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16
Q

Amplitude is measured in:

A. Amps
B. Watts
C. Joules
D. Voltage

A

B. Watts

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17
Q

A function that uses logarithms to compare one absolute measurement to another.

A

dB

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18
Q

A value of 0 dB means the two absolute power levels are equal.

A

Law of zero.

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19
Q

A value of 3 dB means that the power value of

interest is double the reference value; a value of −3 dB means the power value of interest is half the reference.

A

Law of 3s.

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20
Q

A value of 10 dB means that the power value of interest is 10 times the reference value; a value of −10 dB means the power value of interest is 1/10 of the reference. When P2 is 10 times P1, the ratio is always 10. Therefore,

A

Law of 10s.

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21
Q

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

A

Isotropic antenna.

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22
Q

Effective isotropic radiated power (EIRP)

A

The power level that is radiated from the antenna.

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23
Q

What is the formula needed to calculate EIRP?

A

(transmitter power level + antenna gain) - cable length

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24
Q

Cumulative sum of gains and losses measured in dB over the complete RF signal path

A

Link budget

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25
Q

Signal loss as a RF signal travels through the air.

A

Free space path loss

26
Q

Why does a RF signal degrade when it travels though the air?

A

The wave expands as it travels.

27
Q

T/F

Free space path loss occurs quickly near the transmitter but more slowly further away.

28
Q

An internal 1-byte relative value ranging from 0 to 255, where 0 is the weakest and 255 is the strongest, as seen by receiver.

A

Received signal strength indicator (RSSI)

29
Q

What IEEE standard defines the RSSI?

30
Q

A threshold that divides intelligible, useful signals from unintelligible ones.

A

Sensitivity level

31
Q

What is the noise floor?

A

The average signal strength of the noise.

32
Q

The difference between the signal and the noise.

A

Signal-to-noise ratio.

33
Q

What type of signal is used to transport other useful information?

A. Carrier signal
B. Transport signal
C. RF signal
D. Radio signal

A

A. Carrier signal

34
Q

Manipulating the carrier signal according to some other source.

A

Modulation

35
Q

What are these goals of?

Carry data at a predefined rate
Be reasonably immune to interference and noise
Be practical to transmit and receive

A

RF modulation schemes

36
Q

What attributes of a RF signal can a modulation scheme alter?

A

Frequency
Phase
Amplitude

37
Q

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

A

spread spectrum

38
Q

A wireless LAN method in which a transmitter uses a single fixed, wide channel to send data. Used in 2.4 GHz band.

A. Orthogonal Frequency Division Multiplexing (OFDM)
B. Direct sequence spread spectrum (DSSS)

A

B. Direct sequence spread spectrum (DSSS)

39
Q

A data transmission method that sends data bits in parallel over multiple frequencies within a single 20 MHz wide
channel. Used in both 2.4 and 5 GHz bands.

A. Orthogonal Frequency Division Multiplexing (OFDM)
B. Direct sequence spread spectrum (DSSS)

A

A. Orthogonal Frequency Division Multiplexing (OFDM)

40
Q

IEEE standard that defines multiple wireless mechanisms.

41
Q

T/F

802.11ac can be used on 2.4 GHz band and 5 GHz band.

A

False

802.11ac can only be used on 5 GHz band.

42
Q

What type of system is a device containing multiple antennas, multiple transmitters, and multiple receivers is known as?

43
Q

Distributing data across two or more radio chains.

A

Spatial multiplexing

44
Q

What does 802.11ax use to schedule and control access to the wireless medium?

A

OFDM Access

45
Q

What do a transmitter and a receiver combine to form?

46
Q

Benefit of spacial multiplexing.

A

Increased throughput

47
Q

What technology does 802.11n, ac, ax use to customize a transmitted signal to prefer one receiver over other?

A

Transmit beamforming

48
Q

Benefits of transmit beamforming.

A

Improve signal quality and SNR.

49
Q

Combining copies of a signal to produce one signal that represents the best version at any given time.

A

Maximal-Ratio combining

50
Q

2 ways to decrease free space path loss

A
  1. Increase transmitter’s output power.

2. Increase antenna’s gain.

51
Q

A mechanism used by an 802.11 device to change the modulation coding scheme (MCS) according to
dynamic RF signal conditions.

A

Dynamic Rate Shifting (DRS)

52
Q

T/F

Less complex modulation and coding results in greater range and lower data rates.

53
Q

The signal strength level in dBm that an AP receives from a wireless device.

A

Received signal strength (RSS)

54
Q

What 2 components form a radio?

A

Transmitter

Receiver

55
Q

What does a single-in, single-out (SISO) system consist of?

A

A single radio-chain

56
Q

An independent data stream that is distributed across multiple radio chains.

A

Spatial stream

57
Q

What does this represent?

3x3:2

A

3 Transmitters x 3 Receivers : 2 unique spatial streams

58
Q

T/F

The number of spatial streams supported by a device depends on the number of its radios.

A

False

The number of spatial streams supported by a device depends on the processing capacity and the transmitter feature of the device.

59
Q

What happens if 2 devices do not support the same number of spatial streams?

A

The devices inform each other of their capabilities and negotiate a connection.

60
Q

During transmit beamforming, what is altered as the signal is fed into each transmitting antenna?

A. Frequency
B. Amplitude
C. Signal strength
D. Phase

61
Q

T/F

802.11b and 802.11n both offer a method to customize the signal to prefer one receiver over others.

A

F

802.11n, 802.11ac, and 802.11ax

CCNP Encor 350-401 (10 decks)

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