NM-1.04 Flashcards
Explain what 802.11 is?
Family of evolving specifications for wireless local area networks develoepd and maintained by a group of IEEE.
What are the limitations of IEEE.802
- QoS
Throughput is lower
- Coexistence
- Multiple standards
-Overlapping frequency bands
- Security; Easy to eavesdrop
What are the goals of 802.11?
- Global Operation
- Coordination of international spectrum regulisation
What is the difference between Infrared and Radio
Infrared:
1. Short-range point-to-point data transfer
- Can use diffused reflected light, but generally requires LOS for good data rates
- Tx: LED or lasers
- Rx: photodiodes
Radio:
1. Most wireless networks use radio frequencies
Describe the difference between Infastructure-based and Adhov
Infrastructure-based
- Access point is responsible for forwarding messages, limited control and management functions
Access points acts as a bridge to other wirelines and wireless networks
- Applications: office-wide WLANs, hotspots
Ad-hoc
1. All devices directly connect to each other.
How many subcarriers does OFDM have?
52
Explain why the typical maximum layer 3 data rate is lower
Due to different things such as shadowing and free space path loss
Explain DSSS
Spread the signal that it’s noise like. 3G uses this and there’s issues when there’s a hundred users.
Explain the pros and cons of IEEE 802.11a
Adv:
- Fast max speed
- Supports multiple users
Disadv:
1. Highest cost
2. Shortest range signal -> inside the body; 5GHz
3. Easily obstructed
Explain the pros and cons of IEEE 802.11b
Explain the pros and cons of IEEE 802.11g
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
Explain IEEE 802.11n
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
Explain IEEE 802.11ad
- Data throughput -> 7Gbps
- Large bandwidth
- Reduced interference
Range -> few metres
Explain IEE 802.11ax
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
For which of the following scenarios an ad-hox architecture is at least indicated?
- Disaster aftermath
- Airport hotspot
- Vehicular networks
Airport hotspot -> you can wire cables to make this architecture but can’t do this for other 1 or 2
In a machine type…
- Four
- One
- Doesn’t matter
- One
What can the rank tell us about MIMO?
The higher the rank, better to go for MIMO spatial multiplexing
Lower the rank, better to go for spatial diversity
Explain the difference between 802.11a, 802.11b, 802.11g
802.11a; short range signal and fastest
802.11b
802.11g; longest range, data rates higher than 802.11b, not easily obstructed
In case we want to improve the spectral efficiency of a communication link, what should we do?
- Increase the bandwidth, transmit at a higher data rate.
- Increase the number of antennas
- Channel coding scheme with high redundancy