Energy Management Issue in Ad Hoc Networks Outline In ad hoc - - PowerPoint PPT Presentation

Wireless Ad Hoc and Sensor Networks

• Energy Management

WS 2010/2011

• Prof. Dr. Dieter Hogrefe
• Dr. Omar Alfandi
• Dr. Omar Alfandi

Outline

• Energy Management Issue in ad hoc

networks

• Main Reasons for Energy Management

in ad hoc networks

• Classification of Energy Management

S h Schemes

• Summary

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Energy Management Issue in Ad Hoc Networks

• In ad hoc networks the devices are battery powered
• So the computation and communication capacity of each

device is constrained

• Devices that expend their whole energy can be

recharged when they leave the network

• Energy resources and computation workloads have

diff t di t ib ti ithi th t k different distributions within the network

• Therefore it is beneficial to redistribute spare energy

resources to satisfy varying workloads in the network resources to satisfy varying workloads in the network

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Outline

• Energy Management Issue in ad hoc

networks

• Main Reasons for Energy Management

in ad hoc networks

• Classification of Energy Management

S h Schemes

• Summary

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Main Reasons for Energy Management in Ad Hoc Networks (1/2)

• Limited Energy Reserve: The improvement in battery

technologies is very slow

• Difficulties in replacing the batteries: E.g. in battlefields or

emergency applications emergency applications

• Lack of central coordination: In ad hoc networks as distributed

networks some nodes may work as relay nodes; when relay traffic is et o s so e

• des

ay

• as e ay
• des;

e e ay t a c s heavy the power consumption is high

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Main Reasons for Energy Management in Ad Hoc Networks (2/2)

• Constraints on the battery source: The batteries should

be small and not heavy; So low power is available at each node

• Selection of optimal transmission power: Higher

transmission power results in higher energy consumption and higher interference between nodes and higher interference between nodes

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In General

• Energy management deals with the process of managing

energy resources by means of :

– Controlling the battery discharge Adj ti th t i i – Adjusting the transmission power – Scheduling of power sources

To increase the lifetime of the nodes of an ad hoc wireless network

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Outline

• Energy Management Issue in Ad Hoc

Networks

• Main Reasons for Energy Management

in ad hoc networks

• Classification of Energy Management

Schemes

• Summary

8

Classification of Energy Management Schemes (1/2)

E M t Energy Management Schemes

Battery management schemes Transmission power management schemes System power management schemes Device dependent schemes: e.g. battery scheduling Data link layer: e.g. Dynamic power adjustment Processor power management schemes: e.g. Power saving modes Data link layer: e.g. Lazy packet scheduling Network layer: Power aware routings Device management schems: e.g. Low power design of hardware g Network layer: e.g. Routing based on b tt t t Higher layers: Congestion control, 9 battery status Transmission policies at TCP/IP

Classification of Energy Management Schemes (2/2)

• Battery management :

– Concerned with problems that lie in the selection of battery t h l i fi di th ti l it f th b tt technologies, finding the optimal capacity of the battery

• Transmission power management:
• Transmission power management:

– Attempt to find an optimum power level for the nodes in the ad hoc wireless network

• System power management:

– Deals mainly with minimizing the power required by hardware peripherals of a node (such as CPU, DRAM and LCD display)

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Classification of Energy Management Schemes

E M t Energy Management Schemes

Battery management schemes Transmission power management schemes System power management schemes Device dependent schemes: e.g. battery scheduling Data link layer: e.g. Dynamic power adjustment Processor power management schemes: e.g. Power saving modes Data link layer: e.g. Lazy packet scheduling Network layer: Power aware routings Device management schems: e.g. Low power design of hardware g Network layer: e.g. Routing based on b tt t t Higher layers: Congestion control, 11 battery status Transmission policies at TCP/IP

• 1. Battery Management Schemes
• The lifetime of a node is determined by the capacity of its

energy source and the energy required by the node. Th d i d d t h th t i

• There are some device dependent approaches that increase

the battery lifetime by exploiting its internal characteristics.

• Key Fact: Batteries recover their charge when idle

Key Fact: Batteries recover their charge when idle ⇒ Use some batteries and leave others to idle/recover A) Device depending schemes:

• I. Battery scheduling techniques:
• In a battery package of L cells, a subset of batteries can be

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 the subset of cells, e.g.:

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Battery Management Schemes

1. Joint technique: The same amount of current is drawn equally from all the cells which are connected in parallel. 2. Round robin technique: The current is drawn from the batteries in 2. Round robin technique: The current is drawn from the batteries in turn by switching from one to the next one. 3. Random technique: any one of the cells is chosen at random with a uniform probability a uniform probability.

B) Data link Layer Battery Management

I. Lazy Packet Scheduling: – Reduce the power ⇒ Increase the transmission time (lower bit rate) – But this may not suit practical wireless environment packets – But this may not suit practical wireless environment packets ⇒ a transmission schedule is designed taking into account the delay constraints of the packets

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Battery Management Schemes

• II. Battery-Aware MAC Protocol:

– to provide uniform discharge of the batteries of the nodes that contend for the common channel contend for the common channel – Lower back off interval for nodes with higher charge

C) Network Layer Battery Management

– Goal: Increase the lifetime of the network

• I. Shaping algorithm:
• introducing delay slots in the battery discharge process

g y y g p

• If battery charge becomes below threshold, stop next transmission

allowing battery to recover through idling

• The remaining requests arriving at the system are queued up at a

The remaining requests arriving at the system are queued up at a buffer

• As soon as the battery recovers its charge and enters state higher

than the threshold it starts servicing the queued-up requests than the threshold, it starts servicing the queued-up requests

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Classification of Energy Management Schemes

E M t Energy Management Schemes

Battery management schemes Transmission power management schemes System power management schemes Device dependent schemes: e.g. battery scheduling Data link layer: e.g. Dynamic power adjustment Processor power management schemes: e.g. Power saving modes Data link layer: e.g. Lazy packet scheduling Network layer: Power aware routings Device management schems: e.g. Low power design of hardware g Network layer: e.g. Routing based on b tt t t Higher layers: Congestion control, 15 battery status Transmission policies at TCP/IP

• 2. Transmission Power Management Schemes

A) Link layer solutions:

• I. Power Save in IEEE 802.11 Ad Hoc Mode

– Time is divided into beacon intervals – Each beacon interval begins with an ATIM (ad hoc traffic indication message) window indication message) window

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Transmission Power Management Schemes

• If host A has a packet to transmit to B, A must send an ATIM

Request to B during an ATIM Window O i t f ATIM R t f A B ill d ATIM A k

• On receipt of ATIM Request from A, B will send an ATIM Ack,

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 i d i t l i i d d d – If ATIM window is too large, energy saving is reduced and may not have enough time to transmit buffered data – If ATIM window is too small not enough time to send ATIM

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If ATIM window is too small, not enough time to send ATIM request

Transmission Power Management Schemes

• E.g. A has some data packets to send to B; C is idle

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Transmission Power Management Schemes

II. Power Control in IEEE 802.11 Ad Hoc Mode

• A power control MAC protocol allows nodes to vary transmit power

level on a per packet basis level on a per-packet basis

• When C transmits to D at a high power level, B cannot receive A’s

transmission due to interference from C

• If C reduces transmit power, it can still communicate to D

If C reduces transmit power, it can still communicate to D – Reduces energy consumption at node C – Allows B to receive A’s transmission (spatial reuse)

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Transmission Power Management Schemes

• But difference in transmit power can lead to increased

collisions

• In following example suppose nodes A and B use lower

power level than nodes C and D

• When A is transmitting to B, C and D may not sense the

transmission Wh C d D t it t h th i hi h

• When C and D transmit to each other using higher

power, their transmission may collide with the on-going transmission from A to B transmission from A to B

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Transmission Power Management Schemes

• As a solution to this problem, RTS-CTS are transmitted

at the highest possible power level but DATA and ACK t th i i l l t i t at the minimum power level necessary to communicate

• In figure nodes A and B send RTS and CTS respectively

with highest power level such that node C receives the with highest power level such that node C receives the CTS and defers its transmission

• By using a lower power level for DATA and ACK
• By using a lower power level for DATA and ACK

packets, nodes can save energy

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Transmission Power Management Schemes

• In the previous scheme, RTS-CTS handshake is used to

decide the transmission power for subsequent DATA d ACK hi h b hi d i t diff t and ACK which can be achieved in two different ways

1 Suppose node A wants to send a packet to node B Node

• 1. Suppose node A wants to send a packet to node B. Node

A transmit RTS at power level pmax (maximum possible). When B receives the RTS from A with signal level pr, B

r,

calculates the minimum necessary transmission power level, pdesired. For the DATA packet based on received power level p transmitted power level p and noise power level, pr, transmitted power level, pmax, and noise level at the receiver B. Node B specifies pdesired in its CTS to node A. After receiving CTS, node A sends DATA

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using power level pdesired.

Transmission Power Management Schemes

2.

When a destination node receives an RTS, it responds by sending a CTS (at power level pmax). When source node receives CTS it calculates p based on node receives CTS, it calculates pdesired based on received power level, pr, and transmitted power level (pmax) as

a

Pdesired = (pmax / pr) x Rxthresh x c where Rxthresh is minimum necessary received signal

thresh

y g strength and c is a constant

• III. Centralized Topology Control:

The power of each node is reduced until it has single connectivity, i.e. there is one path between each pair of nodes bi ti it

• r bi-connectivity

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Transmission Power Management Schemes B) Network layer solutions:

I. Common Power Control:

Given reachability of each node as a function of power find the – Given reachability of each node as a function of power, find the min power level that provides network connectivity – If the common power level is selected too high, this may lead to interference (fig. a); if too low, the reachability of nodes may become weak (fig. b) ⇒ choosing an optimum value is a difficult task ⇒ choosing an optimum value is a difficult task.

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Transmission Power Management Schemes

• II. Min Variance in Node Power Levels:

– The motivation is to ensure that all the nodes are given equal importance and no node is drained at a faster rate compared to other importance and no node is drained at a faster rate compared to other nodes in the network – For transmitting a packet, a node selects the next-hop node so that it has the least amount of traffic among all neighbours of the node has the least amount of traffic among all neighbours of the node

• III. Min Battery Cost Routing:

– Minimize sum of battery cost along a path ⇒ Does not ensure that lower charge nodes are not used

»

⇒ The lower path is used

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Transmission Power Management Schemes

IV.Conditional Min-Max Battery Cost Routing:

– Using only nodes that have battery charge over a threshold, Find the min total power path min total power path.

• V. Minimum Energy Disjoint Path Routing:

– The important need for having disjoint paths in ad hoc networks is b f th d f li bl k t t i i d because of the need for reliable packet transmission and energy efficiency. – Ad hoc networks are highly unreliable due to the mobility of nodes and h h b bili f li k f il i i hi h i h k hence the probability of link failure is quite high in such networks. – This problem can be overcome by means of link disjoint routing. – Also, since the ad hoc nodes have stringent battery constraints, node g y disjoint routing considerably increases the lifetime of the network by choosing different routes for transmitting packets at different points of time.

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Classification of Energy Management Schemes

E M t Energy Management Schemes

Battery management schemes Transmission power management schemes System power management schemes Device dependent schemes: e.g. battery scheduling Data link layer: e.g. Dynamic power adjustment Processor power management schemes: e.g. Power saving modes Data link layer: e.g. Lazy packet scheduling Network layer: Power aware routings Device management schems: e.g. Low power design of hardware g Network layer: e.g. Routing based on b tt t t Higher layers: Congestion control, 27 battery status Transmission policies at TCP/IP

• 3. System Power Management Schemes
• Efficient design of the hardware brings about significant reduction in

the power consumed.

• This can be effected by operating some of the peripheral devices in
• This can be effected by operating some of the peripheral devices in

power-saving mode by turning them off under idle conditions.

• System power consists of the power used by all hardware units of

the node. This power can be conserved significantly by applying the following schemes:

– Processor power management schemes – Device power management schemes

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System Power Management Schemes

A) Processor Power Management Schemes:

– Deals with techniques that try to reduce the power consumed by the processor, e.g. reducing the number of calculations performed. g g p

I. Power-Saving Modes:

– The nodes consume a substantial amount of power even when they are in an idle state since they keep listening to the channel awaiting in an idle state since they keep listening to the channel, awaiting request packets from the neighbours. – As a solution, the nodes are switched off during idle conditions and switched on only when there is an arrival of a request packet switched on only when there is an arrival of a request packet. – Since the arrival of request packets is not known a priori, it becomes difficult to calculate the time duration for which the node has to be switched off switched off. – One solution to this problem calculates the node's switch-off time based

• n the quality of service (QoS) requirements. Hard QoS requirements

k th d t ti t f th ti make the node stay active most of the time.

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System Power Management Schemes

• As soon as the node enters the idle state, it is switched off by the

remote activated switch RAS. The receiver of the RAS switch still listens to the channel. The remote neighbours send the wake-up signal and a

• sequence. The receiver, on receiving the wake-up signal, detects the

sequence (the waking-up signal). The logic circuit compares it with the standard sequence for the node. It switches on the node only if both the sequences match.

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System Power Management Schemes

II. Power-Aware Multi-Access Signaling (PAMAS):

• Power-Aware Multi-Access Signaling is another approach for

determining the time duration for which the node should be turned determining the time duration for which the node should be turned

• ff.

– Conditions under which the node enters the power-off mode:

• Condition 1: The node has no packets for transmission.
• Condition 2: A neighbour node is transmitting or receiving packets,

that is, the channel is busy. , y

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System Power Management Schemes B) Device Power Management Schemes:

• Some of the major consumers of power in ad hoc wireless networks

th h d d i t i th d D i are the hardware devices present in the nodes. Device power management schemes minimize the power consumption.

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System Power Management Schemes

I. Low-Power Design of Hardware: varying clock speed CPUs, disk spin down, and flash memory II CPU Power Consumption: by changing the clock frequency etc II. CPU Power Consumption: by changing the clock frequency, etc. III. Power-Aware CPU Scheduling: a small reduction in the value of the voltage produces a quadratic in the power consumed, so clock rate has to be also reduced. IV. Hard Disk Drive (HDD) Power Consumption: by bring down the speed of spinning on the disc drives speed of spinning on the disc drives

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Outline

• Energy Management Issue in Ad Hoc

Networks

• Main Reasons for Energy Management

in ad hoc networks

• Classification of Energy Management

Schemes S

• Summary

34

Summary

• Three major divisions in energy management
• Battery Management:

When idling increases the capacity of the battery

• Transmission Power Management:

Distance vs. Power tradeoff

• System Power Management:

Put system/components to sleep whenever possible y p p p

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