Mobile computing (Wireless) Medium Access Control (MAC)

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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UNIT-II
(Wireless) MediumAccess
Control
Dr R JegadeesanProf-CSE
JyothishmathiInstitute of Technology and
Science, karimnagar

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Contents
1.Motivation for SpecializedMAC
•Hidden and ExposedTerminals
•Far and NearTerminals
2.AccessMethods
•SDMA
•FDMA
•TDMA
•CDMA

3. 1. Motivation for SpecializedMAC
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MULTIPLEXING
•A fundamental mechanism in
communication system andnetworks
•Enables multiple users to share amedium
•For wireless communication, multiplexing
can be carried out in four dimensions:
space, time, frequency andcode

7. AccessMethods
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2. Space Division Multiple Access(SDMA)
•Channels are assigned on the basisof
―space‖ (but operate on samefrequency)
•The assignment makes sure that the
transmission do not interfere witheach
(with a guard band inbetween)

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3. FDMA: Frequency Division MultipleAccess
1.Frequency domain is subdivided into several non-
overlapping frequencybands
2.Each channel is assigned its own frequency band(with
guard spaces inbetween)

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3. TDMA : Time Division MediumAccess
•A channel is given the whole bandwidth for a
certain amount oftime
–All senders use the same frequency, but atdifferent
point oftime
•Synchronization can be done byusing
–Fixed Allocation Schemeor
–Dynamic AllocationScheme

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15. ReservationAlgorithms
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16. Packet Reservation Multiple Access(PRMA)
/ ImplicitReservation
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•In this each terminal on the network is ableto
monitor the status of the channel before
transmittinginformation
•Variations:
–1-persistentCSMA
–non-persistent CSMA-
–p-persistentCSMA
–CSMA/CA
–Elimination yield –non-preemptive multipleaccess
(EY-NMPA)
Carrier Sense Multiple Access Protocols(CSMA)

18. Multiple Access with Collision Avoidance(MACA)
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20. POLLING
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21. Inhibit Sense Multiple Access(ISMA)
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4. CDMA: Code Division MultipleAccess
◼separation of channels achieved by assigningeach
channel its owncode
◼guard spaces are realized by having distancein
code space (e.g. orthogonalcodes)
◼transmitter can transmit in the same frequency
band at the same time, but have to usedifferent
code
◼Provides good protection against interferenceand
tapping
◼but the receivers have relatively highcomplexity.

23. Spread Aloha Multiple Access(SAMA)
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24. Comparisons ofS/T/F/CDMA
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25. Thank you