An Efficient Power Mode Scheduling Algorithm for ...

Sharad Kumar Verma / International Journal of Engineering Science and Technology (IJEST)

An Efficient Power Mode Scheduling Algorithm for Adhoc Networks Sharad Kumar Verma Lecturer, Dept. of MCA Meerut Institute of Engineering & Technology, Meerut (UP), India Mob: 09219310290 Abstract An ad hoc network is a set of mobile wireless nodes that cooperatively form a network among themselves without any fixed infrastructure. Ad hoc networks therefore refer to networks created for a particular purpose. They are often created on-the-fly and for one-time or temporary use. Often, ad hoc networks are comprised of a group of workstations or other wireless devices which communicate directly with each other to exchange information. Power consumption within ad hoc networks is becoming a core issue for these low-power mobile devices. In this paper we focuses on a novel approach for energy conservation within the routing protocol of the ad hoc network. A wireless network interface in sleep mode expends an order of magnitude less power than in idle mode, but no packets can be sent or received while in sleep mode. In this paper, we propose two algorithms, for scheduling transition from idle mode to sleep mode. The Simulation results of these strategies show a substantial reduction in power usage, with only a slight decrease in performance. Keywords: exchange information, Power consumption, low-power mobile devices, routing protocol, scheduling transition.

1.

Introduction

In ad hoc networks, energy performance is as important as general performance since it directly affects the network operation time in the wireless environment. The sources of power consumption are communication and computation, with communication often being the chief power consumer. An ad-hoc (or "spontaneous") network is a local area network or other small network, especially one with wireless or temporary plug-in connections, in which some of the network devices are part of the network only for the duration of a communications session or, in the case of mobile or portable devices, while in some close proximity to the rest of the network. Ad hoc is Latin meaning "for this purpose." Ad hoc networks therefore refer to networks created for a particular purpose. They are often created on-the-fly and for one-time or temporary use. Often, ad hoc networks are comprised of a group of workstations or other wireless devices which communicate directly with each other to exchange information. There has been considerable research on conserving power in these routing protocols, although most of this research has focused on controlling the transmission power of the sender’s network interface. Although significant in terms of reducing the power consumption in the wireless transmitter of a sender, it does little to conserve power among the other nodes receivers, forwarders, and nodes not involved in this communication. A network receiver interface has four different modes: a.

Transmit Mode: In this mode, the node is transmitting a packet. The power consumption in this mode is the highest amongst the four modes. b. Receive Mode: In this mode, the node is receiving a packet. The power consumption in this mode is slightly lesser than the Transmit Mode c. Idle Mode: A receiver in idle mode can either receive or transmit. It burns power because it has to listen to the wireless medium all the time to determine whether or not there is a packet transmission going on. This mode takes slightly lesser power than Receive Mode.

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Sharad Kumar Verma / International Journal of Engineering Science and Technology (IJEST)

d. Sleep Mode: Sleep mode has very low power consumption. The network interface cannot receive or transmit in this mode unless it is woken up into idle mode by an explicit instruction. It takes a finite time to transition from sleep mode to idle mode and vice versa.

Figure 1: Overview of mobile node system architecture

In the evaluation of any algorithm for energy conservation, an estimate of energy consumption is necessary. Modes Sleep Idle Receive Transmit

Energy Consumption 14mA 178mA 204mA 280mA

Table 1: IEEE 802.11 2 MBPS WAVELAN PC CARD CHARACTERISTICS

In particular, the more closely a simulation reflects specific hardware, the more accurate the estimate of energy consumed in the simulation experiments is. In the evaluation of any algorithm for energy conservation, an estimate of energy consumption is necessary. Feeney [1] shows the specification and actual measured current drawn by one popular wireless network interface card in the four possible modes. Receive and idle mode require similar power, and transmit mode requires slightly greater power. Sleep mode requires more than an order of magnitude less power than idle mode. These measurements show that the network interface expends similar energy, whether it is just listening or actually receiving data. Hence, intelligently switching to sleep mode whenever possible will generally create significant energy savings. We now present two probabilistic algorithms which will achieve this. 2.

Algorithm for Sleep-Mode Scheduling

All the nodes in ad-hoc network do not always participate in receiving, sending, and forwarding of data packets. Rather, many nodes do not need to be in the topology to maintain connectivity. If these nodes can be identified, then they can be put into sleep mode, rather than them staying in idle mode. The following are the Options of sleep mode. 2.1 Normal Sleep: (Power management menu - Sleep mode – unit of measure is minutes) When normal Sleep is activated, the main terminal goes dormant, and the modem’s power is left ON. Once activated, this provides good battery life. When the terminal ‘wakes up’, the modem is already connected to the network.

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Sharad Kumar Verma / International Journal of Engineering Science and Technology (IJEST)

2.2 Deep Sleep: (Power management menu – Comm Device) When deep Sleep is activated, the main terminal goes dormant, and the modem’s power is completely OFF. Once activated, this provides the longest battery life. The disadvantage is that when the terminal ‘wakes up’, the modem must reinitialize and connect to the cellular carrier (just like when you turn your cellular phone ON). The result is the first transaction will take slightly longer. Sleep mode uses an order of magnitude less energy than idle mode, so this would be very useful in terms of saving energy. The nodes that are probable candidates for putting into sleep mode are those that have not originated, forwarded, or received data for a certain fixed interval. These nodes are then sent to the sleep mode. However, these nodes are present in the network and can work as forwarders if the need arises. Being in sleep mode prevents a node from being able to receive any packets. So, there is a need to use some technique to periodically wake these nodes to idle mode. Algorithm is as follows. Step1: Sort the nodes with respect to remaining energy levels; for each node i in the ascending order do Step2: if redundancyCheck(i) then node(i).state = SLEEP; Step 3: Otherwise node(i).state = ACTIVE; Step 4: Stop 2.3 Clock Synchronization: IEEE 802.11 PS mode assumes a completely connected network, and hence a beacon frame transmission can synchronize all the nodes. In ad-hoc network though, this simple clock synchronization is not possible because of communication delays and mobility. Clock Synchronization among all nodes in a sensor network is a problem that has been tackled in recent years. GPS can be used to provide exact time synchronization between the nodes. In the absence of GPS, clock synchronization can be ensured by some protocol. 2.4 Neighbour Discovery: A wireless node is aware of the existence of neighbours only if there is an ongoing transmission while the node is awake. As PS mode reduces the period of being awake, it diminishes its chances of having accurate neighbour information as well as the chance of itself being discovered by other nodes. In Section IV-B.3, we describe why very accurate prediction of the number of neighbours is not necessary. Our two algorithms are based on this, and extend it to include multi-hop ad hoc networks. We assume clock synchronization between the nodes through some mechanism. 3.

Proposed Algorithms:

3.1

The Adaptive Sleep Algorithm

In the Adaptive Sleep Algorithm, a node periodically switches between idle and sleeps modes. An interval called Sleep Interval (SI) is a period of times from the last the receipt of any Route Request by a node. After SI time interval, the periodic sleep cycle starts. The periodic sleep cycle repeats at a period called the Sleep Period (SP). A mobile device moving at low speed can afford to increase the sleep period without missing critical information. Speed based adaptation uses the above observation to adapt the sleep period to the current nodal speed observed. The algorithm is as follows. Step1: Calculate current speedi, Tsleepi Step2: for each data packet in Queue Step3: if MP predicts current position is good or deadline reaches ordelay + Tsleepi > deadline Step 4: send packet Step 5: Otherwise delay = delay + Tsleepi Step 6: SLEEP(Tsleepi ) Step 7: Stop

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Sharad Kumar Verma / International Journal of Engineering Science and Technology (IJEST)

Hence, the SP needs to be small enough so that, although a node may have missed the initial ROUTE REQUEST, it wakes up in time to receive the subsequent re-broadcasts. In densely populated ad hoc networks, many nodes can be interchangeably used for routing purposes. In a dense network, any node might sleep for a longer duration, as the relative utility (for forwarding purposes) of all nodes decrease. Estimate Neighbour Count: There are a number of published approaches for estimating the neighbour count of a node in a wireless network. Estimate of Duty Cycle: The idea is to keep the total idle time for all nodes in a neighborhood constant. So, the duty cycle is kept proportional to the recent estimate of neighbour count. There is no need for accurate count of the number of neighbours, since the algorithm provides a natural feedback mechanism. If the neighbour count is underestimated by a node, that node stays awake for a longer time, during which it hears from more neighbours, and subsequently reduces its duty cycle. 3.2

Birthday Sleep Algorithm

The Birthday Sleep Algorithm is proposed in this paper for scheduling transition to sleep mode for saving energy without losing much in terms of performance. The inspiration behind this protocol is the birthday paradox, which is the probability that at least two people in a room have their birthday on the same day. We use a similar idea for convergence between a receiver and a transmitter. Suppose that over a period of n fixed length slot periods, two wireless nodes independently and randomly select m of these slots. In each of these m slots chosen by a node, the node remains in idle mode listening for packets. In the remaining n-m slots, it goes to sleep mode, thereby saving energy. The energy saved is approximately (n - m) =n x 100 percent of the original energy consumed by the wireless network interface. n = 10 m=6 n slots (T time) n slots (T time) IM

IM

IM

SIM sent out SIMs received

IM

IM

SM

IM

IM

IM

IM

IM

IM

IM

SIM sent out SIMs received Time

IM -- Idle Mode -- Sleep Mode Figure 2: The Birthday Algorithm Strategy

For two nodes, A & B: The probability of B choosing k slots all different than those chosen by A is C (n - m, k) / C (n, k) ……. (1) The probability of B choosing at least 1 slot the same as those chosen by A, within k slots is 1 – C (n – m, k) = C (n, k) .......... (2) Let pi = mi / n denote the probability of staying awake for nodei, where mi i is the number of slots nodei is awake and n is the total number of slots. If a node is a sender or receiver of data or if it is an active forwarder of data, then the node always remains awake. Hence, pi = 1 for i є S, D, F Where S is the set of all active source nodes, ∏ is the set of all active destination nodes, and F is the set of all active forwarder nodes at the current time. For all other nodes, pi depends on the policy.

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Sharad Kumar Verma / International Journal of Engineering Science and Technology (IJEST)

All nodes are awake for the first slot out of n slots. Depending on pi, each node randomly chooses mi out of the n slots to be idle. Each node builds a Sleep Indication Map (SIM) containing n bits, with the rth bit set to 1 or 0 depending on whether the node will be idle or asleep in the rth slot of that T period. A node uses the knowledge gained from the SIM packets from its neighbours to build a Sleep Indication Table (SIT). A node uses its SIT to schedule packets to any neighbour. 3.2.1

Simulation Results

In our simulation experiments we first wanted to see how effective our scheme is in putting the nodes into sleep mode, i.e. what percent of nodes can be put into sleep mode without harming the network’s expected functionality which is covering a region to sense and monitor.

Figure 3: Percentage distance saving with different wakeup strategies.

Figure 4: Number of wakeups with different wakeup algorithms.

3.2.2

Conclusion

Effective and energy-efficient sampling of node movement enables motion-predicted communication, which can save significant energy of wireless transmission. In this paper we proposed a scheme for prolonging the lifetime of dense sensor networks that selects a set of active nodes to be used for sensing and communication activities. The scheme maintains the total sensing coverage achieved by the initially deployed sensor nodes. It reconfigures the network periodically and distributes the energy consumption load more evenly to the sensor nodes. In this paper, we have presented an adaptive scheduler for determining an effective sampling schedule given dynamic system conditions. We evaluated our scheme via simulations and we observed a significant lifetime and coverage increase. References [1]

[2] [3] [4] [5]

L. Feeney and M. Nilsson. Investigating the Energy Consumption of a Wireless Network Interface in an Ad Hoc Networking Environment. In Proceedings of INFOCOM 2001, volume 3, pages 1548–1557, Anchorage, Alaska, Apr. 2001. S. PalChaudhuri. Power Mode Scheduling for Ad Hoc Network Routing. Masters Thesis, Computer Science, Rice University, May 2002. David Mills. Internet Time Synchronization: the Network Time Protocol. IEEE Transactions on Communications, 39(10):1482– 1493, October 1991. Jeffrey Monks, Vaduvur Bharghavan, and Wen-Mei Hwu. A Power Controlled Multiple Access Protocol for Wireless Packet Networks. In Proceedings of INFOCOM 2001, volume 1, pages 219–228, Anchorage, Alaska, April 2001. Santashil PalChaudhuri and David B. Johnson. Power Mode Scheduling for Ad Hoc Networks. In Proceedings of the 10th IEEE International Conference on Network Protocols (ICNP’02), Paris, France, November 2002.

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[6]

D. B. Johnson, D. A. Maltz and J. Broch, “DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks,” Ad Hoc Networks, edited by C. E. Perkins, Chap. 5, pp. 194-172, Addison-Wesley, 2001

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