Outline Wireless Ad Hoc and Sensor Networks - Energy Management • Energy Management Issue in ad hoc networks • Main Reasons for Energy Management in ad hoc networks • Classification of Energy Management S h Schemes • Summary WS 2010/2011 Prof. Dr. Dieter Hogrefe Dr. Omar Alfandi Dr. Omar Alfandi 2 Energy Management Issue in Ad Hoc Networks Outline • In ad hoc networks the devices are battery powered • Energy Management Issue in ad hoc networks • So the computation and communication capacity of each device is constrained • Main Reasons for Energy Management in ad hoc networks • Devices that expend their whole energy can be recharged when they leave the network • Energy resources and computation workloads have • Classification of Energy Management diff different distributions within the network t di t ib ti ithi th t k S h Schemes • Therefore it is beneficial to redistribute spare energy • Summary resources to satisfy varying workloads in the network resources to satisfy varying workloads in the network 3 4
Main Reasons for Energy Management in Ad Hoc Main Reasons for Energy Management in Ad Hoc Networks (1/2) Networks (2/2) • Limited Energy Reserve: The improvement in battery • Constraints on the battery source: The batteries should technologies is very slow be small and not heavy; So low power is available at • Difficulties in replacing the batteries: E.g. in battlefields or each node emergency applications emergency applications • Selection of optimal transmission power: Higher • Lack of central coordination: In ad hoc networks as distributed transmission power results in higher energy consumption networks some nodes may work as relay nodes; when relay traffic is et o s so e odes ay o as e ay odes; e e ay t a c s and higher interference between nodes and higher interference between nodes heavy the power consumption is high 5 6 In General Outline • Energy management deals with the process of managing • Energy Management Issue in Ad Hoc energy resources by means of : Networks • Main Reasons for Energy Management in ad hoc networks – Controlling the battery discharge – Adjusting the transmission power Adj ti th t i i • Classification of Energy Management – Scheduling of power sources Schemes • Summary To increase the lifetime of the nodes of an ad hoc wireless network 7 8
Classification of Energy Management Schemes (1/2) Classification of Energy Management Schemes (2/2) Energy Management E M t • Battery management : Schemes – Concerned with problems that lie in the selection of battery technologies, finding the optimal capacity of the battery t h l i fi di th ti l it f th b tt Battery Transmission power System power management management management schemes schemes schemes • Transmission power management: • Transmission power management: Processor power Device dependent Data link layer: e.g. – Attempt to find an optimum power level for the nodes in the ad management schemes: e.g. schemes: e.g. Dynamic power Power saving modes battery scheduling adjustment hoc wireless network Device management schems: Data link layer: e.g. Network layer: Power e.g. Low power design of Lazy packet • System power management: aware routings hardware scheduling g – Deals mainly with minimizing the power required by hardware peripherals of a node (such as CPU, DRAM and LCD display) Network layer: e.g. Higher layers: Routing based on Congestion control, battery status b tt t t Transmission policies at TCP/IP 9 10 Classification of Energy Management Schemes 1. Battery Management Schemes E Energy Management M t • The lifetime of a node is determined by the capacity of its Schemes energy source and the energy required by the node. • There are some device dependent approaches that increase Th d i d d t h th t i Battery Transmission power System power management management management the battery lifetime by exploiting its internal characteristics. schemes schemes schemes • Key Fact: Batteries recover their charge when idle Key Fact: Batteries recover their charge when idle Processor power Device dependent Data link layer: e.g. ⇒ Use some batteries and leave others to idle/recover management schemes: e.g. schemes: e.g. Dynamic power Power saving modes battery scheduling adjustment A) Device depending schemes: Device management I. Battery scheduling techniques: schems: Data link layer: e.g. • In a battery package of L cells, a subset of batteries can be Network layer: Power e.g. Low power design of Lazy packet aware routings hardware scheduling g scheduled for transmitting a given packet leaving other cells scheduled for transmitting a given packet leaving other cells to recover their charge. There are some approaches to select Network layer: e.g. the subset of cells, e.g.: Higher layers: Routing based on Congestion control, battery status b tt t t Transmission policies at TCP/IP 11 12
Battery Management Schemes Battery Management Schemes 1. Joint technique: The same amount of current is drawn equally II. Battery-Aware MAC Protocol: from all the cells which are connected in parallel. – to provide uniform discharge of the batteries of the nodes that 2. 2. Round robin technique: The current is drawn from the batteries in Round robin technique: The current is drawn from the batteries in contend for the common channel contend for the common channel turn by switching from one to the next one. – Lower back off interval for nodes with higher charge Random technique : any one of the cells is chosen at random with 3. C) Network Layer Battery Management a uniform probability. a uniform probability – Goal: Increase the lifetime of the network I. Shaping algorithm: B) Data link Layer Battery Management • introducing delay slots in the battery discharge process g y y g p I. Lazy Packet Scheduling: • If battery charge becomes below threshold, stop next transmission allowing battery to recover through idling – Reduce the power ⇒ Increase the transmission time (lower bit rate) • The remaining requests arriving at the system are queued up at a The remaining requests arriving at the system are queued up at a – But this may not suit practical wireless environment packets – But this may not suit practical wireless environment packets buffer ⇒ a transmission schedule is designed taking into account the delay • As soon as the battery recovers its charge and enters state higher constraints of the packets than the threshold it starts servicing the queued-up requests than the threshold, it starts servicing the queued-up requests 13 14 Classification of Energy Management Schemes 2. Transmission Power Management Schemes Energy Management E M t A) Link layer solutions: Schemes I. Power Save in IEEE 802.11 Ad Hoc Mode Battery Transmission power System power – Time is divided into beacon intervals management management management schemes schemes schemes – Each beacon interval begins with an ATIM (ad hoc traffic indication message) window indication message) window Processor power Device dependent Data link layer: e.g. management schemes: e.g. schemes: e.g. Dynamic power Power saving modes battery scheduling adjustment Device management schems: Data link layer: e.g. Network layer: Power e.g. Low power design of Lazy packet aware routings hardware scheduling g Network layer: e.g. Higher layers: Routing based on Congestion control, battery status b tt t t Transmission policies at TCP/IP 15 16
Transmission Power Management Schemes Transmission Power Management Schemes • If host A has a packet to transmit to B, A must send an ATIM • E.g. A has some data packets to send to B; C is idle Request to B during an ATIM Window • O On receipt of ATIM Request from A, B will send an ATIM Ack, i t f ATIM R t f A B ill d ATIM A k and stay up during the rest of the beacon interval • • If a host does not receive an ATIM Request during an ATIM If a host does not receive an ATIM Request during an ATIM window, and has no pending packets to transmit, it may sleep during rest of the beacon interval • Size of ATIM window and beacon interval affects performance: – If ATIM window is too large, energy saving is reduced and If ATIM i d i t l i i d d d may not have enough time to transmit buffered data – If ATIM window is too small not enough time to send ATIM If ATIM window is too small, not enough time to send ATIM request 17 18 Transmission Power Management Schemes Transmission Power Management Schemes II. Power Control in IEEE 802.11 Ad Hoc Mode • But difference in transmit power can lead to increased • A power control MAC protocol allows nodes to vary transmit power collisions level on a per packet basis level on a per-packet basis • In following example suppose nodes A and B use lower • When C transmits to D at a high power level, B cannot receive A’s power level than nodes C and D transmission due to interference from C • When A is transmitting to B, C and D may not sense the transmission • When C and D transmit to each other using higher Wh C d D t it t h th i hi h power, their transmission may collide with the on-going • If C reduces transmit power, it can still communicate to D If C reduces transmit power, it can still communicate to D transmission from A to B transmission from A to B – Reduces energy consumption at node C – Allows B to receive A’s transmission (spatial reuse) 19 20
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