CHAPTER 5 Medium Access Control ( MAC) PROTOCOLS CS5602: Principles and Techniques for Sensors and Information Perception
CHAPTER 5. Medium Access Control (MAC) PROTOCOLS CS5602: Principles and Techniques for Sensors and Information Perception 1
What is a MAc protocol? CS5602: Principles and Techniques for Sensors and Information Perception
What is a MAC protocol? CS5602: Principles and Techniques for Sensors and Information Perception 2
Objectives of MAC Protocols Collision Avoidance Energy Efficiency Scalability Latency Fairness Throughput Bandwidth Utilization CS5602: Principles and Techniques for Sensors and Information Perception
Objectives of MAC Protocols ▪ Collision Avoidance ▪ Energy Efficiency ▪ Scalability ▪ Latency ▪ Fairness ▪ Throughput ▪ Bandwidth Utilization CS5602: Principles and Techniques for Sensors and Information Perception 3
POWER CONSUMPTION RADIO 15 E SENSOR CPU TX RX 工DLE SLEEP CS5602: Principles and Techniques for Sensors and Information Perception
POWER CONSUMPTION CS5602: Principles and Techniques for Sensors and Information Perception 4 SENSOR 0 5 10 15 20 Power (mW) CPU TX RX IDLE SLEEP RADIO
Major Sources of Energy Waste 工 dle listening ★ Transmitter Common to all wireless networks ★R2 ceiver OBJECTIVE: Reduce energy consumption !! CS5602: Principles and Techniques for Sensors and Information Perception
Major Sources of Energy Waste CS5602: Principles and Techniques for Sensors and Information Perception 5 * Idle Listening * Transmitter * Receiver OBJECTIVE: Reduce energy consumption !! Common to all wireless networks
Challenges for MAc in WsNs 1. WSN Architecture High density of nodes Increased collision probability Signaling overhead should be minimized to prevent further collisions Sophisticated and simple collision avoidance protocols required CS5602: Principles and Techniques for Sensors and Information Perception
Challenges for MAC in WSNs ▪ 1. WSN Architecture ▪High density of nodes ▪Increased collision probability ▪Signaling overhead should be minimized to prevent further collisions ▪Sophisticated and simple collision avoidance protocols required CS5602: Principles and Techniques for Sensors and Information Perception 6
Challenges for MAc in WSNs 2. Limited Energy Resources Connectivity and the performance of the network is affected as nodes die Transmitting and receiving consumes almost same energy Frequent power up/down eats up energy Need very low power MAC protocols Minimize signaling overhead Avoid idle listening Prevent frequent radio state changes(activesleep CS5602: Principles and Techniques for Sensors and Information Perception
Challenges for MAC in WSNs ▪ 2. Limited Energy Resources ▪ Connectivity and the performance of the network is affected as nodes die ▪ Transmitting and receiving consumes almost same energy ▪ Frequent power up/down eats up energy ▪ Need very low power MAC protocols ▪ Minimize signaling overhead ▪ Avoid idle listening ▪ Prevent frequent radio state changes (activesleep) CS5602: Principles and Techniques for Sensors and Information Perception 7
Challenges for MAc in WsNs 3. Limited Processing and Memory Capabilities Complex algorithms cannot be implemented Conventional layered architecture may not be appropriate Centralized or local management is limited Simple scheduling algorithms required Cross-layer optimization required Self-configurable, distributed protocols required CS5602: Principles and Techniques for Sensors and Information Perception
Challenges for MAC in WSNs ▪ 3. Limited Processing and Memory Capabilities ▪Complex algorithms cannot be implemented ▪Conventional layered architecture may not be appropriate ▪Centralized or local management is limited ▪Simple scheduling algorithms required ▪Cross-layer optimization required ▪Self-configurable, distributed protocols required CS5602: Principles and Techniques for Sensors and Information Perception 8
Challenges for MAc in WSNs 4. Lim ited Packet size Unique node ID is not practical Limited header space Local ids should be used for inter-node communication MAC protocol overhead should be minimized 5 Cheap Encoder/Decoders Cheap node requirement prevents sophisticated encoders/decoders to be im plemented Simple FEC codes required for error control Channel state dependent MAc can be used to decrease error rate CS5602: Principles and Techniques for Sensors and Information Perception
Challenges for MAC in WSNs ▪ 4. Limited Packet Size ▪ Unique node ID is not practical ▪ Limited header space ▪ Local IDs should be used for inter-node communication ▪ MAC protocol overhead should be minimized ▪ 5. Cheap Encoder/Decoders ▪ Cheap node requirement prevents sophisticated encoders/decoders to be implemented ▪ Simple FEC codes required for error control ▪ Channel state dependent MAC can be used to decrease error rate CS5602: Principles and Techniques for Sensors and Information Perception 9
Challenges for MAc in WSNs a 6. Inaccurate Clock Crystals Cheap node requirement prevents expensive crystals to be implemented Synchronization problems a TDMA-based schemes are not practical 7. Event-based Networking Observed data depends on physical phenomenon Spatial and temporal correlation in the physical phenomenon should be exploited BOTTOMLINE: Existing MAC protocols cannot be used for WSNs!!! CS5602: Principles and Techniques for Sensors and Information Perception
Challenges for MAC in WSNs ▪ 6. Inaccurate Clock Crystals ▪ Cheap node requirement prevents expensive crystals to be implemented ▪ Synchronization problems ▪ TDMA-based schemes are not practical ▪ 7. Event-based Networking ▪ Observed data depends on physical phenomenon ▪ Spatial and temporal correlation in the physical phenomenon should be exploited CS5602: Principles and Techniques for Sensors and Information Perception 10 BOTTOMLINE: Existing MAC protocols cannot be used for WSNs!!!