Two challenges

• Wireless
  • wireless link
• Mobility
  • change of the point attachment to the network

Technology

• Cellular
• Wireless LAN/PAN (local/personal area network)
• GPS
• Satellite Based GPS
• Home networking
  • home router
• Ad hoc networks
  • mobile network with laptop
• Sensor network
  • IoT sensors
• Bluetooth
• IoT
• VLC (visual light communications)
• ...

Wireless Network Types

• Wireless LAN: Local
  • IEEE 802.11 a/b/g/n/ac...etc.
• Wireless PAN: Personal; home or vehicle
  • IEEE 802.15 bluetooth
• Wireless BAN: Body; wearable devices
  • IEEE 802.15.6 belongs to bluetooth
• Wireless MAN: Metropolitan
  • IEEE 802.16; using WiMAX, 3G, 4G

Architecture

• Network infrastructure; Backbone; Core network
• Base station; Access point
  • provide channels
  • to communicate with another base station, it needs switching
  • relay: deal with packets between hosts
• Wireless link
  • used to connect mobile to the base station
  • also used as backbone link
  • multiple access protocols for link access
• Wireless hosts
  • stationary or mobile

Wireless Communication Link

• Higher data rate -> shorter distance
• WiFi: only 10-30m

Characteristics

• Attenuation; signal strength decreases as it propagates through matter (path loss)
• Interference; frequencies shared by other devices; hard to decode
• Multipath propagation; radio signal reflects off objects or ground; receive signal in different path; arriving at destination at slightly different times

Infrastructure vs Ad-Hoc

• Infrastructure mode
  • we have base station.
  • handoff: MS move to another base station
• Ad hoc mode
  • no base stations.
  • nodes can only transmit to others in their coverage
  • nodes organize themselves into a network.

Taxonomy

• Infrastructure
  • single hop: host <-> base station
  • multiple hop: host -> base station -> infra -> base station -> host

Multiplexing

FDMA; Frequency Division Multiple Access

• frequency -> smaller channels
• 1 user per channel
• Bandwidth structure

TDMA; Time Division Multiple Access

• users can use the whole frequency
• 1 user per time division
• Frame structure

CDMA; Code Division Multiple Access

• all users using same frequency and time slot
• but using different code

OFDM; Orthogonal Frequency Division Multiplexing

• conventional
  • gap; guard band
• orthogonal
  • no gap
  • using less bandwidth

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Cellular Network Infrastructure

Cell

• hexagons

MS, BS, BSC, MSC and PSTN

• MS; mobile station
• BS; base station
• BSC; base station controller
• MSC; mobile switching center
• PSTN; public switching telephone network

Control and Traffic Channels

• Control channel: request signal, smaller data
• Traffic channel: bigger data

Call Setup

• BS & MS

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WiFi; Wireless Fidelity

• packet-based (<-> circuit based)

WiMAX; IEEE 802.16

• Lost to LTE

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Satellite Systems

• cover very large area

GPS; Global Positioning Systems

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