Energy Efficient Network Protocols for Wireless Networks

1. Energy Efficient Network Protocols for Wireless Networks Kiran Muthabatulla

2. Introduction • Wireless Networking exploding in Mobile and personal communications • Cell Phones, Personal Computing Systems, Wireless LAN's As a result… • Energy Efficiency is an important design consideration due to limited battery life of Mobile terminals.

3. Introduction • Network Interface : significant consumer of power. • Power consumption : On an Average system CPU-21%, 36% LCD. 18% Wireless Interface 18% Hard Disk, Power consumption. Hence.. • Low Power design of the Entire Network Stack is needed to enhance energy efficiency.

4. Infrastructure Network

5. Base Stations in BSS Mode • Coordinate Access to one or more transmission channels for mobiles within the coverage cell. • Wireless Access to and from the wired host occurs in the last hop between base stations and mobile hosts that share the bandwidth of the wireless channel.

6. Ad hoc Network

7. Ad-Hoc • Multi Hop wireless Networks, in which a set of mobiles cooperatively maintain network connectivity. • On-demand network, dynamic unpredictable, random, multi hop topologies which has no infrastructure support. • Mobiles must periodically update topology information for routing.

8. Protocol Stack

9. Responsibilities Data Link • Data Link: reliable and secure Logical Layer over unreliable Wireless Link. • Security : Encryption and Decryption • Network layer packet conversion into frames • Packet re-transmissions. • MAC: Allocates the time-frequency or code space modulations among mobiles sharing wireless channels in a region.

10. Low Power at PHY Layer • Increase Battery capacity • Slow progress. Developments in Battery technology is very slow • Decrease amount of energy consumed at the Wireless terminal. • Hardware means: • Variable Clock Speed CPU’s, flash memory, disk spin down.

11. Sources of Power Consumption • Communication related. • Transceiver at the source, intermediate and destination nodes. • Transmitter is used for sending control, route request and response, as well as data packets originating at the sender. • Receiver is used to receive data and control packets destined for the node. • Computation related: Usage of CPU, Main Memory, disk, data compression techniques.

12. Mobile Radio : Power Modes Proxim Range LAN2 2.4 GHz Transmit: 1.5 W in transmit Receive: 0.75 W in receive Standby: 0.01W in Standby

13. General Guidelines: • Collisions must be eliminated as they result in re-transmissions. • Re-transmissions lead to unnecessary power consumption and to possibly unbounded delays. • Broadcast environment, receiver remains on at all times. • Node Receives the packets and forwards only if it is meant to the receiving node. • Channel status monitoring.

14. Scheduling • Broadcast scheduling that contains the data transmission starting times for each mobile. • This enables the mobiles to switch to a standby mode until the receive start time. • Turn off the transceiver whenever the node determines that it will not be receiving data for a period of time.

15. Scheduling.. • Mobile Radio Switching between TX and RX. • A protocol that allocates permissions on a slot by slot basis suffers substantial over head. • Mobile should be allocated contiguous slots for TX or Rx to reduce turnaround. • Mobiles may request multiple transmission slots with a single reservation packet.

16. Scheduling.. • Mobiles transmit data transmission requests to the BS. The BS computes the system transmission schedule and broadcasts each mobiles transmission schedule. • Mobiles Wake up when its their schedule time. • Considerations : • Battery power at stations • QOS • Avoid TX when channel conditions are poor.

17. General Guidelines • Load Balancing of the Battery Power: • Avoid routing through nodes with lower battery power. • May want not to update routing information but may suffer performance. • Taking advantage of Broadcast Multicast packets.

18. MAC Sub Layer • IEEE 802.11 Standard. • CSMA/CA • Back off timers/Slots • Positive ACK’s • RTS/CTS. • PSP, NULL Data Frame. • Base Stations Store the Packets • Beacon updates

19. EC-MAC • Based on Reservation and Scheduling • Transmission organized by the BS into Frames, and each slot equals the basic unit of Wireless data transmission. • At the Start of Each Frame, The BS transmits the FSM which contains sync info and the uplink transmission order for the subsequent information and the uplink information order for the subsequent reservation phase.

20. EC-MAC

21. PAMAS Protocol • Power Aware Multiple Access • For Ad hoc Networks. • Separate Channels for RTS/CTS and data packets. • Mobile sends RTS, Waits CTS, if received, the mobile sends over Data Channel. • Sets the Control Channel to busy.

22. PAMAS Protocol • Mobiles not receiving and sending packets turn off the wireless interface. • Data transmissions need not be overheard by all the neighbors of the transmitter. • Separate control channel determines when and how long to power off. • Mobile should power itself off • No packets to TX and neighbor begins to send packet not for it. • Has packets to send, but some other pair already started to communicate. • Probe protocol to see how long to sleep.

23. LLC : Error Control. • Automatic Repeat Request (ARQ) • A type of communications link where the receiver asks the transmitter to re-send a block of data when errors are detected • Forward Error Correction (FEC) • A method of error control where the receiving node automatically corrects as many channel errors as it can without referring to the sending node.

24. Disadvantages Both of them waste network bandwidth and consume power resources due to retransmissions of data packets Greater overhead necessary in error correction.

25. Adaptive Error Control With ARQ. • New Design Metric : Energy efficiency of a protocol which is defined as the ratio between total amount of data delivered and total amount of energy consumed. • If more data is transmitted for a given amount of energy consumption, the energy efficiency increases.

26. Guidelines • Avoid Persistence in Retransmitting Data. • Trade off number of re-transmission attempts for probability of successful transmission • Inhibit transmissions when channel conditions are poor.

27. Guidelines.. • Probing Protocol that slows data transmission when degraded channel conditions are encountered. • ARQ works normal until the Transmitter detects an error in either the data or control channel due to lack of an ACK. • At this time, the protocol enters a probing mode, in which the probing packet is transmitted every t-slots. • This mode is continued until ACKs start to show up. • Then protocol returns to normal mode.

28. Other Schemes proposed. • Adaptive Error control with ARQ/FEC combination • Adaptive Power control and coding scheme

29. Network Layer • Routing Packets • Mobiles cooperate to maintain Topology information • Use Multi hop packet routing • Usual Approaches : • Frequent topology results in improved routing • Infrequent topology results in decreased update messages. • Congestion Control

30. Network Layer • Typical Metrics: • Shortest Hop • Shortest Delay • Locality stability

32. Unicast Traffic : Metrics • Energy Consumed per packet : Min • Time to network Partition : Max • Critical Nodes drain their power at equal rates. • Variance in power levels across mobiles : Min • All nodes are at the same priority level • All mobiles are equal and no one mobile is penalized or privileged over the other. • Cost per packet : Min • Routes with depleted energy reserves don’t lie in many routes. • Maximum Mobile cost : Min • Minimize cost to move the packet through this node.

33. Broadcast Traffic • Single transmission, a mobile is able to broadcast a packet to all immediate neighbors. • Intermediate Nodes re-transmit the packet to all its immediate. • Turn off after receiving the packet if the neighbor already received the packet.

34. Broadcast Traffic • Traditional : Flooding • No Global topology information requiring little control overhead and completes the broadcast with minimum number of hops. • Solution: • Collect topology information. • Ensure that transmission reaches as many new nodes as possible. • Construct trees with lowest cost per outgoing degree.

35. Transport Layer • TCP degrades over Wireless Link • Large number of Re-transmissions • Frequently invoke congestion control measures. • Confusing Wireless Link Errors • Loss due to handoff as channel congestion. • Significantly reduces throughput and introduce unacceptable delays.

36. New Schemes • TO reduce Retransmissions • Split connection protocols • Hide the wireless link from the wired network by terminating the Tcp connection at the Base station. • Link Layer protocols • Hide link related Losses from the TCP source by using a combination of local retransmissions and FEC. • End to End Protocols. • Modified versions of TCP sensitive to Wireless environment

37. Split Connection

38. Link Layer Protocols

39. References • This presentation is a understanding based on the research paper. A survey of energy efficient network protocols for wireless networks. Wireless Networks, 7(4):343--358, July 2001. by C. E. Jones, K. M. Sivalingam, P. Agrawal, and J. C. Chen.