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Lecture16 17 feb26 mar16 04

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Unformatted text preview: MAC Protocols In Sensor Networks Multiple Access Control (MAC) Protocols MAC allows multiple users to share a common channel. Conflict-free protocols ensure successful transmission. Channel can be allocated to users statically or dynamically. Only static conflict-free protocols are used in cellular mobile communications - Frequency Division Multiple Access (FDMA): provides a fraction of the frequency range to each user for all the time - Time Division Multiple Access (TDMA) : The entire frequency band is allocated to a single user for a fraction of time - Code Division Multiple Access (CDMA) : provides every user a portion of bandwidth for a fraction of time Contention based protocols must prescribe ways to resolve conflicts - Static Conflict Resolution: Carrier Sense Multiple Access (CSMA) - Dynamic Conflict Resolution: the Ethernet, which keeps track of various system parameters, ordering the users accordingly Frequency Division Multiple Access (FDMA) Channels are assigned to the user for the duration of a call. No other user can access the channel during that time. When call terminates, the same channel can be re-assigned to another user FDMA is used in nearly all first generation mobile communication systems, like AMPS (30 KHz channels) Number of channels required to support a user population depends on the average number of calls generated, average duration of a call and the required quality of service (e.g. percen...
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