Chapter 17: Wireless Signals and Modulation Flashcards

1
Q

The frequency range from around 3 kHz to 300 GHz.

A

Radio frequency (RF)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

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

A

Microwave

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

A contiguous range of frequencies.

A

Band

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Specific frequencies that bands are divided into.

A

Channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How wide is each channel in the 2.4 GHz band?

A

5 MHz (.005 GHz)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

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

A

Spectral Mask

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The range of frequencies used by a single channel or

a single RF signal.

A

Bandwidth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

T/F

Channel width should be less than signal bandwidth.

A

False.

Signal bandwidth should be less than the channel
width.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

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

A

Phase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Phase is measured in:

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

A

C. Degrees

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

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

A

Wavelength

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What happens to wavelength as frequency increases?

A

Wavelength decreases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

The strength of a wireless signal.

A

Amplitude

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Amplitude is measured in:

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

A

B. Watts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

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

A

dB

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

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

A

Law of zero.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

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

A

Isotropic antenna.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Effective isotropic radiated power (EIRP)

A

The power level that is radiated from the antenna.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the formula needed to calculate EIRP?

A

(transmitter power level + antenna gain) - cable length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

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

A

Link budget

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

A

True

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?

A

802.11

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.

A

802.11

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?

A

MIMO

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?

A

Radio

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.

A

True

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

A

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