Class3-Shared_Medium_Access

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EE/CS 652: Wireless Sensor Networks EE/CS 652: Wireless Sensor Networks Fall 2007 Fall 2007 Bhaskar Krishnamachari Assistant Professor, EE-S, CS University of Southern California Autonomous Networks Research Group http://ceng.usc.edu/~bkrishna/ bkrishna@usc.edu Lecture 3: Shared Medium Access Lecture 3: Shared Medium Access
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Aloha, Slotted Aloha The most basic schemes for wireless MAC are Aloha, Slotted Aloha Easiest schemes to analyze. Weakness: no attempt to avoid collisions.
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Classical CSMA-CD (wired Ethernet) does not work due to (a) Hidden Terminal and (b) Exposed Terminal Problems CSMA in Wireless Networks CSMA in Wireless Networks C B A D C B A D (a) Channel free at sender, busy at receiver (b) Channel busy at sender, free at receiver
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MACA: A way of virtually sensing the channel at receiver. “request-to-send”/“clear-to-send” messages: If a node has packet to send, it first transmits a RTS packet. If available receiver responds with CTS. After sender receives CTS, it transmits data. Nodes that hear RTS wait long enough for transmitter to receive CTS. Nodes that hear CTS back off long enough to allow receiver to receive data. Collision Avoidance Collision Avoidance P. Karn, MACA: A new channel access method for Packet Radio, AARL Computer Networking Conference, 1990.
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IEEE 802.15.4
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IEEE 802.x.x IEEE 802.11 WLAN IEEE 802.16 Broadband Wireless Access Standards IEEE 802.15 IEEE 802.15.1: Bluetooth High data rate High power consumption small network IEEE 802.15.4 For Low power low rate Wireless Personal Network IEEE 802.11: an “overkill technology” Bluetooth: high data rate for multimedia applications, small size network, high power consumption
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802.15.4 Applications LR-WPAN Low Rate Wireless Personal Area Network
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802.15.4 Applications Low-Rate Low-Power Wireless Networks
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This note was uploaded on 12/21/2010 for the course EE 652 taught by Professor Bhaskarkrishnamachari during the Fall '07 term at USC.

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Class3-Shared_Medium_Access -...

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