NM-1.04 Flashcards

1
Q

Explain what 802.11 is?

A

Family of evolving specifications for wireless local area networks develoepd and maintained by a group of IEEE.

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2
Q

What are the limitations of IEEE.802

A
  1. QoS

Throughput is lower

  1. Coexistence
  • Multiple standards
    -Overlapping frequency bands
  1. Security; Easy to eavesdrop
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3
Q

What are the goals of 802.11?

A
  1. Global Operation
    - Coordination of international spectrum regulisation
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3
Q

What is the difference between Infrared and Radio

A

Infrared:
1. Short-range point-to-point data transfer

  1. Can use diffused reflected light, but generally requires LOS for good data rates
  2. Tx: LED or lasers
  3. Rx: photodiodes

Radio:
1. Most wireless networks use radio frequencies

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4
Q

Describe the difference between Infastructure-based and Adhov

A

Infrastructure-based

  1. Access point is responsible for forwarding messages, limited control and management functions

Access points acts as a bridge to other wirelines and wireless networks

  1. Applications: office-wide WLANs, hotspots

Ad-hoc
1. All devices directly connect to each other.

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5
Q

How many subcarriers does OFDM have?

A

52

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6
Q

Explain why the typical maximum layer 3 data rate is lower

A

Due to different things such as shadowing and free space path loss

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7
Q

Explain DSSS

A

Spread the signal that it’s noise like. 3G uses this and there’s issues when there’s a hundred users.

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8
Q

Explain the pros and cons of IEEE 802.11a

A

Adv:

  1. Fast max speed
  2. Supports multiple users

Disadv:
1. Highest cost
2. Shortest range signal -> inside the body; 5GHz
3. Easily obstructed

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9
Q

Explain the pros and cons of IEEE 802.11b

A
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10
Q

Explain the pros and cons of IEEE 802.11g

A

2.4 GHz

Adv:
1. Longest range
2. Supports multiple users
3. Not easily obstructed

Disadv:
1. More costly than 802.11b
2. Other appliances may interfere in same frequency band

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11
Q

Explain IEEE 802.11n

A

Higher data rate through MIMO

Operating frequency: 2.4GHz/5GHz

Spacing of antennas; wavelength/2 = c/2f
Which is why ‘mm’ is good; Can pack in more antennas

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12
Q

Explain IEEE 802.11ad

A
  1. Data throughput -> 7Gbps
  2. Large bandwidth
  3. Reduced interference

Range -> few metres

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13
Q

Explain IEE 802.11ax

A

High-density public environments -> trains, stadiums

Beneficial for IoT

Designed for cellular data off-loading

Theoretical BW -> 14Gbps

Uses MU-MIMO w/ OFDMA -> don’t mix this up with duplexing

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14
Q

For which of the following scenarios an ad-hox architecture is at least indicated?

  1. Disaster aftermath
  2. Airport hotspot
  3. Vehicular networks
A

Airport hotspot -> you can wire cables to make this architecture but can’t do this for other 1 or 2

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15
Q

In a machine type…

  1. Four
  2. One
  3. Doesn’t matter
A
  1. One
16
Q

What can the rank tell us about MIMO?

A

The higher the rank, better to go for MIMO spatial multiplexing

Lower the rank, better to go for spatial diversity

17
Q

Explain the difference between 802.11a, 802.11b, 802.11g

A

802.11a; short range signal and fastest

802.11b
802.11g; longest range, data rates higher than 802.11b, not easily obstructed

18
Q

In case we want to improve the spectral efficiency of a communication link, what should we do?

A
  1. Increase the bandwidth, transmit at a higher data rate.
  2. Increase the number of antennas
  3. Channel coding scheme with high redundancy
19
Q
A