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Wireless Sensor Networks COE 499

Medium Access ControlTarek Sheltami

KFUPMCCSECOE

www.ccse.kfupm.edu.sa/~tarek

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Outline Traditional MAC protocols Asynchronous sleep techniques Sleep-scheduled techniques Contention free protocols

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Traditional MAC protocols

1. ALOHA protocol2. CSMA

Hidden terminal problem Exposed terminal problem

04/21/23(a) hidden node (b) exposed node

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Traditional MAC protocols

1. ALOHA protocol2. CSMA

Hidden terminal problem Exposed terminal problem

04/21/23(a) hidden node (b) exposed node

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Traditional MAC protocols..

3. MACA RTS CTS

4. IEEE 802.11 (CSMA/CA)5. IEEE 802.15.4 MAC (LR-WPAN)

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Energy efficiency in MAC protocols

1. Power management in IEEE 802.11RTS

2. Power aware medium-access with signalling (PAMAS)

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Asynchronous sleep techniques

1. Secondary wake-up radio One low power Tx/Rx always on and main Tx/Rx always off

2. Low power listening/preamble sampling

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Asynchronous sleep techniques..

3. Transmitter/receiver-initiated cycle receptions (TICER/RICER)

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Asynchronous sleep techniques..

4. Reconfigurable MAC protocol (B-MAC)

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Sleep-scheduled techniques1. Sensor MAC (S-MAC)

All node wake up and go to sleep simultaneously

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Sleep-scheduled techniques..2. Timeout MAC (T-MAC)

Very similar to S-MAC, however, The length of each cycle is kept constant, but the end of the active period is determined dynamically by the use of a timeout mechanism

3. Data-gathering MAC (D-MAC)

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Sleep-scheduled techniques..4. Delay-efficient sleep scheduling (DESS)

each node picks a unique slot out of k slots to use as a reception slot and publishes this to its neighbors

5. Asynchronous sleep schedules

A (7,3,1) design for slotted asynchronous wake-up (P2+P+1, P+1, 1)

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Contention-free protocols1. Stationary MAC and Startup (SMACS)

Each node need only maintain local synchronization During the starting phase, each node decides on a

common communication slot with a neighboring node through handshaking on a common control channel

Each link also utilizes a unique randomly chosen frequency or CDMA frequency hopping code

It is assumed that there are sufficiently many frequencies/codes (no contention)

The slot is then used periodically, once each cycle, for communication between the two nodes.

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Contention-free protocols2. BFS/DFS-based scheduling

BFS, each node gets contiguous time slots DFS, each node does not have contiguous slots, but the

slots from each sensor source to the sink are contiguous, ensuring that intermediate node buffers are not filled up during data-gathering.

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Contention-free protocols..3. Reservation-based synchronized MAC (ReSync)

Each node choose a unique time slot of k and publishes this to its neighbors

4. Traffic-adaptive medium access (TRAMA) A distributed TDMA technique that allows for flexible and

dynamic scheduling of time slots Time epochs are divided into a set of short signaling slots,

followed by a set of longer transmission slots1. Neighbor protocol (NP)2. Schedule exchange protocol (SEP)3. Adaptive election algorithm (AEA)