Minimizing the Power Consumption of Location-Based Services on - PDF document

This article has been accepted for publication in IEEE Pervasive Computing but has not yet been fully edited. Some content may change prior to final publication. Minimizing the Power Consumption of Location-Based Services on Mobile Phones Mikkel Baun Kjærgaard ∗ ∗ Department of Computer Science University of Aarhus, Denmark mikkelbk@cs.au.dk This article provides an understanding of when it is Abstract —Location-based services have to pay careful attention to their power consumption in order not to important to minimize the power consumption of a LBS, drain the batteries of mobile phones. It is not a simple how different mobile phone features consume power, and task to build low-power location-based services that can how existing LBSs consume power. Following that, the run for hours, because such services make heavy use of article gives a survey of methods for the minimization many power-consuming features of mobile phones. In this of power consumption and discuss design considerations article we discuss the power consumption of location-based services and mobile phone features, survey methods for for LBS developers. how to minimize power consumption and summarize a number of design considerations for location-based service I. P OWER C ONSUMPTION AND L OCATION - BASED developers. S ERVICES A successful Location-Based Service (LBS) must not The importance of an LBS saving power depends on drain the battery of, e.g., a mobile phone. Battery ca- the usage pattern, battery recharge options, and how the pacity is a scarce resource in mobile phones, because service uses the phone’s features. With regards to the the capacity of batteries is not increasing at the same usage pattern, an important parameter is how long a pace as new power-demanding features are added to service will be running on the phone. The LBSs that mobile phones. If users experience that a specific LBS are most important to minimize the consumption of are drains or significantly shortens the battery’s lifetime, those that are long running for hours or days, however, they might stop using the service. It is, however, not a as will be presented later, the power saving methods simple task to build low-power-consuming LBSs because for such services are fortunately able to provide the such services make heavy use of many power-consuming largest savings. The importance of minimizing the power features of mobile phones, such as the screen to display consumption also depends on users’ recharge options, maps, the radio to receive and send data, or a built-in because a service may consume a lot of power if a GPS receiver for positioning. Therefore, an LBS has user is able to recharge the phone when finished using to take great care in how it uses a phone’s features the service. Due to such considerations, it might be to minimize the power consumption, especially if the situation dependent how important it is for a user that a service is to run continuously. In this article we dedicate service consumes minimal power. In regards to the phone our attention to LBSs on mobile phones, but some LBSs feature usage, the consumption impact depends on the also use other types of battery-powered devices such as power consumption of the individual features. Section II positionable tags, where minimal power consumption is both describes how to profile the power consumption of also an important issue. individual phone features and gives some values for a So far research on the technical challenges of LBSs typical mobile phone. has mainly focused on how to improve positioning A classification of the power consumption for different accuracy and coverage. Only a small amount of research types of LBSs are shown in Figure 1. The classified types has yet focussed on minimizing power consumption. are inspired by the service types introduced by Bellavista 1 Digital Object Indentifier 10.1109/MPRV.2010.47 1536-1268/$26.00 ) 2010 IEEE

This article has been accepted for publication in IEEE Pervasive Computing but has not yet been fully edited. Some content may change prior to final publication. where they are on maps or satellite imagery and pro- Hours / Days Location-based Social Networking vide navigation directions to a location. Location-based games are games that use location as an element in the Proactive Location-based Search game play, for example, the finding of physical caches Service Running Time Place and Activity Recognition using GPS positioning known as Geocaching or Live Pac Power Minimized Man with real persons running around as monsters to Services catch you. Sports trackers are services that can log where Sports Trackers Minutes and when you exercise for sharing and analysis. Again, Location-based Games the consumption of such services are medium to high Maps and Navigation but, because they run for minutes, their impact on the battery lifetime is higher. When services run for minutes it is an advantage that they have a low consumption but maybe not a must, e.g., if a user is able to recharge the Seconds phone when finished. However, one problem that users Reactive Location-Based Search might experience is that if they forget to turn a service Geotagging off, it might discharge the phone without them noticing this before it is too late. For this methods for minimizing Low (0.1w) Medium (0.5w) High (1w+) the power consumption can be used to lower the power x2 x10 x20+ consumption to prolong the battery life. Power Consumption Three services are shown that run for hours or days. Place and activity recognition are services that can Fig. 1. Service types groups by service running time and power con- register the whereabouts and activities of a user to, e.g., sumption with multiplicity factors for power consumption compared to a 0.05 watt stand-by consumption. construct a daily diary or calculate a CO 2 footprint from the user’s behavior. Proactive location-based search are services that can push information to the user of query et. al. [1]. The figure classifies service types with respect results, e.g., if a user registers a search for free city to their running time and power consumption. Running bikes, the user will be notified about free city bikes when times are classified into second-long, minute-long and in proximity of them. Location-based social networking hours / days-long, and power consumption into low-, are services that enable the user to link location to medium- and high-consuming services; a factor is given social networking, e.g., to be notified when in proximity indicating the impact on the battery lifetime compared of friends or events. Again, the consumption of such to a stand-by battery consumption of 0.05 watt. services is medium to high but, because the services run for hours or days, it is very important that they The figure shows two service types that only run for consume a minimal amount of power, as they would seconds. Geotagging are services that attach location otherwise have a major impact on how fast the battery information to other digital material, e.g., pictures, and will discharge, e.g., twenty times faster with a high con- reactive location-based search are services that, when sumption compared to stand-by consumption. Therefore, requested, search for information related to the user’s for long-running services, it is crucial to apply methods location, for instance, about the nearest subway stations. for minimizing the power consumption. The consumption of such services is medium to high due to that the screen, communication and positioning II. P OWER P ROFILING A M OBILE P HONE features are all used. Furthermore, the power consump- tion of such services is difficult to minimize by software To understand the power consumption of mobile means, because a short well-defined task has to be phones one could as a first step consult their specifica- carried out. However, the impact on the battery lifetime tions. However, these will often not give the full picture, is not significant, as these services are used for a short because values are missing (e.g. CPU) and dynamic amount of time and not frequently rerun. aspects are not considered. The dynamic aspects are due Three service types are given that run for minutes. to that features do not instantly power on or off, e.g., Maps and navigation are services that can show people a 3G radio needs several seconds to power on before 2 Digital Object Indentifier 10.1109/MPRV.2010.47 1536-1268/$26.00 ) 2010 IEEE