Chapter 2 - Medium Access Control

Chapter 2 - Medium Access Control - Medium Access Control...

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Lawrence Wong 1 Medium Access Control Protocols Chapter 2
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Protocol Layers Lawrence Wong 2 OSI Reference Model Application Presentation Session Transport Network Data Link Physical Medium Typical Wireless Network Reference Model Upper Layer Protocols TCP IP Layer Logical Link Control Medium Access Control Physical Medium Scope of most standards
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Medium Access Control (MAC) Basic MAC Protocols Conflict-free Static Allocation TDMA FDMA CDMA Dynamic Allocation Polling (Centralized Control) Contention-Based Static Resolution ALOHA CSMA Dynamic Resolution CSMA/CA Lawrence Wong 3
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Lawrence Wong 4 FDMA FDMA involves partitioning the available spectrum into smaller frequency bands, and each band or channel is used to support a user. Since individual bands are disjoint, there is no interference among users. Major disadvantage is that each user has fixed allocation of channel bandwidth regardless of whether it has information to transmit Used in 1 st generation mobile cellular network (AMPS, ETACS, etc.) in 800-900 MHz band Time Frequency Power Station 1 Station 2 Station 3 Station N R/N R Frequency
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Lawrence Wong 5 TDMA TDMA involves organizing communications resource into time slots and slots into frames. Each user is allocated a repetitive time slot to use. Guard bands ensure proper separation between slots Major disadvantage is that each user must have fixed allocation of channel time regardless of whether it has information to transmit A variation is called narrowband TDMA , where the allocated frequency spectrum is partitioned into bands, and each band implements a TDMA structure. 2 nd generation mobile cellular systems, i.e. GSM, uses this approach. Time Frequency Power S i S j S k S l S m Time
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