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Mobile computing (Wireless) Medium Access Control (MAC)

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Jyothishmathi Institute of Technology and Science Karimnagar
Jyothishmathi Institute of Technology and Science Karimnagar

Motivation for a specialized MAC (Hidden and exposed terminals, Near and far terminals), SDMA, FDMA, TDMA, CDMA, Wireless LAN/(IEEE 802.11) Mobile Network Layer: IP and Mobile IP Network Layers, Packet Delivery and Handover Management, Location Management, Registration, Tunneling and Encapsulation, Route Optimization, DHCP

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1 UNIT-II (Wireless) Medium Access Control Dr R Jegadeesan Prof-CSE Jyothishmathi Institute of Technology and Science, karimnagar
2 Contents 1. Motivation for Specialized MAC • Hidden and Exposed Terminals • Far and Near Terminals 2. Access Methods • SDMA • FDMA • TDMA • CDMA
1. Motivation for Specialized MAC 3
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6 MULTIPLEXING • A fundamental mechanism in communication system and networks • Enables multiple users to share a medium • For wireless communication, multiplexing can be carried out in four dimensions: space, time, frequency and code
Access Methods 7
8 2. Space Division Multiple Access (SDMA) • Channels are assigned on the basis of ―space‖(but operate on same frequency) • The assignment makes sure that the transmission do not interfere with each (with a guard band in between)
9
10 3. FDMA: Frequency Division Multiple Access 1. Frequency domain is subdivided into several non- overlapping frequency bands 2. Each channel is assigned its own frequency band (with guard spaces in between)
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12 3. TDMA : Time Division Medium Access • A channel is given the whole bandwidth for a certain amount of time – All senders use the same frequency, but at different point of time • Synchronization can be done by using – Fixed Allocation Scheme or – Dynamic Allocation Scheme
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14
Reservation Algorithms 15
Packet Reservation Multiple Access (PRMA) / Implicit Reservation 16
17 • In this each terminal on the network is able to monitor the status of the channel before transmitting information • Variations: – 1-persistent CSMA – non-persistent CSMA - – p-persistent CSMA – CSMA/CA – Elimination yield – non-preemptive multiple access (EY-NMPA) Carrier Sense Multiple Access Protocols (CSMA)
Multiple Access with Collision Avoidance (MACA) 18
19
POLLING 20
Inhibit Sense Multiple Access (ISMA) 21
22 4. CDMA: Code Division Multiple Access ◼ separation of channels achieved by assigning each channel its own code ◼ guard spaces are realized by having distance in code space (e.g. orthogonal codes) ◼ transmitter can transmit in the same frequency band at the same time, but have to use different code ◼ Provides good protection against interference and tapping ◼ but the receivers have relatively high complexity.
Spread Aloha Multiple Access(SAMA) 23
Comparisons of S/T/F/CDMA 24
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Mobile computing (Wireless) Medium Access Control (MAC)

  • 1. 1 UNIT-II (Wireless) Medium Access Control Dr R Jegadeesan Prof-CSE Jyothishmathi Institute of Technology and Science, karimnagar
  • 2. 2 Contents 1. Motivation for Specialized MAC • Hidden and Exposed Terminals • Far and Near Terminals 2. Access Methods • SDMA • FDMA • TDMA • CDMA
  • 3. 1. Motivation for Specialized MAC 3
  • 4. 4
  • 5. 5
  • 6. 6 MULTIPLEXING • A fundamental mechanism in communication system and networks • Enables multiple users to share a medium • For wireless communication, multiplexing can be carried out in four dimensions: space, time, frequency and code
  • 8. 8 2. Space Division Multiple Access (SDMA) • Channels are assigned on the basis of ―space‖(but operate on same frequency) • The assignment makes sure that the transmission do not interfere with each (with a guard band in between)
  • 9. 9
  • 10. 10 3. FDMA: Frequency Division Multiple Access 1. Frequency domain is subdivided into several non- overlapping frequency bands 2. Each channel is assigned its own frequency band (with guard spaces in between)
  • 11. 11
  • 12. 12 3. TDMA : Time Division Medium Access • A channel is given the whole bandwidth for a certain amount of time – All senders use the same frequency, but at different point of time • Synchronization can be done by using – Fixed Allocation Scheme or – Dynamic Allocation Scheme
  • 13. 13
  • 14. 14
  • 16. Packet Reservation Multiple Access (PRMA) / Implicit Reservation 16
  • 17. 17 • In this each terminal on the network is able to monitor the status of the channel before transmitting information • Variations: – 1-persistent CSMA – non-persistent CSMA - – p-persistent CSMA – CSMA/CA – Elimination yield – non-preemptive multiple access (EY-NMPA) Carrier Sense Multiple Access Protocols (CSMA)
  • 18. Multiple Access with Collision Avoidance (MACA) 18
  • 19. 19
  • 21. Inhibit Sense Multiple Access (ISMA) 21
  • 22. 22 4. CDMA: Code Division Multiple Access ◼ separation of channels achieved by assigning each channel its own code ◼ guard spaces are realized by having distance in code space (e.g. orthogonal codes) ◼ transmitter can transmit in the same frequency band at the same time, but have to use different code ◼ Provides good protection against interference and tapping ◼ but the receivers have relatively high complexity.
  • 23. Spread Aloha Multiple Access(SAMA) 23