Optimized Location Aware Applications on iOS Content
1. Abstract………………………………………………………………1 2. Introduction…………………………………….…………………….1 3. Design & Analysis…..……………………………………………….2 3.1. Positioning Technologies………………………………………2 3.1.1. Cellular Triangulation……………………………………2 3.1.2. Global Positioning System (GPS).……………………….3 3.1.3. Assisted GPS (A-GPS).…………………………………..4 3.1.4. Wireless Positioning System (WPS)……………………..4 3.2. Location Detection on iOS…………………………………......5 3.2.1. Standard Location Service……………………………….5 3.2.2. Significant Location Change Service…………………….6 3.2.3. Region Monitoring Service……………………………....6 3.3. Challenges on iOS……………………………………………...6 3.3.1. Inaccurate Location Updates……………………………..6 3.3.2. Invalid Location Updates………………………………...7 3.3.3. Battery Drain…………………………………………......7 3.3.4. Limitations of Application Background Mode…………..7 3.3.5. Challenges with Significant Location Change (SLC).…...8 3.3.6. Challenges with Region Monitoring……………………..8 3.3.7. Privacy and Security……………………………………..9 3.4. Optimized Geo-fencing solution on iOS……………………….9 3.5. Addressing Privacy and Security Concerns……………………11 4. Conclusion…………………………………………………...............12

Optimized Location Aware Applications on iOS 1

Sourabh Raheja

Abstract Location aware applications are intuitive and have much better user experience. However there are number of challenges associated with development of location aware applications for mobile devices. Some of them being battery drainage by accurate geo-fencing solution, privacy and security concerns by end users etc. This paper elaborates those challenges and tries to find optimal solutions for them. It is focused primarily for iOS platform; however, some of the challenges/solutions are generic and apply for all mobile platforms. Introduction With availability of location services in all upcoming smart phones, a number of location aware applications have hit the market. Groupon, Foursquare, Loopt, Roamz and many more are now popular names among users. Let us start with understanding usefulness of such applications. Location aware applications are intuitive and have much better user experience. Let us say you are travelling and would like to know services and facilities available around you. All you have to do is open an application on your phone and you will get to know about various eating outlets around you and much more. Location awareness has enabled a number of new use cases. Things you earlier could have never thought off. User's location can be used to create solutions for various verticals: • Navigation: Google Maps, TomTom aid users in turn-by-turn navigation. • Networking: Foursquare helps you in finding friends currently in your neighborhood. • Local information about facilities and services: Roamz shows you social content about places, events and activities around you. • Geo marketing: Groupon features deals on the best stuff to do, see, eat and buy in your favorite neighborhoods. • Lifestyle: Location based reminders are now part of iOS 5. • Games: TrezrHunt is based on real locations where you have to find your way to witch Armagal's treasure. The benefits are immense for end users as well as business owners. However, despite so many benefits, adoption rate of such applications is not catching up at the rate expected. According to a new report from Forrester Research, out of 37000 U.S. online adults, only about 5% of users use location aware applications once a month. There are number of challenges associated with development of location aware applications for mobile devices. This paper elaborates those challenges and tries to find optimal solution for them. It is focused primarily for iOS platform; however, some of the challenges are generic and apply for all mobile platforms.

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Optimized Location Aware Applications on iOS

Sourabh Raheja

Kindly note some of the excerpts of this paper are from my own blog published at: http://xebee.xebia.in/2011/12/28/how-to-conceptualize-a-location-awareapplication/ 3 3.1 Design & Analysis Positioning Technologies The term positioning technologies refer to the technology within the mobile device that lets you know where the device is at any point in time with varied degree of accuracy. These technologies are a combination of hardware (for example GPS) and software (for example location detection using cell tower signals) with each one of them having its own advantages as well as dis-advantages. This section will give you an overview of main positioning technologies commonly used today: Cellular Triangulation, Global Positioning System (GPS), Assisted GPS (A-GPS) and Wireless Positioning System (WPS). 3.1.1 Cellular Triangulation Cellular Triangulation uses the known speed of radio signals (constantly emitted by mobile phones) to calculate the distance from receivers. Geometrically, by recording the distance of an object from three distinct points, it is possible calculate the location of that object. It takes at least three and preferably four receivers (cell towers) to get a good location fix. In densely populated locations, accuracy of the fix is higher (up to 200 meters) as there will be more cell towers with their signal radii overlapping. Figure 1 illustrates how the overlap between three cell towers is used to determine the cell phone’s location.

Tower A Tower B

Tower C Location of cell phone

Figure 1: Cellular Triangulation

Accuracy of the location fix using cellular triangulation increases further where directional antennae are installed on the cell tower, allowing for detection of not 2

Optimized Location Aware Applications on iOS

Sourabh Raheja

just distance but direction of the cell phone signal. In rural areas, where density of transmitting antennae is less, the precision may fall dramatically (to several kilometers). 3.1.2 Global Positioning System (GPS) GPS was originally developed by US military in the 1970s. Later it was made available for commercial use for the public (still controlled by US Department of Defense). It is the most accurate positioning technology commercially available today for mobile developers (up to a precision of 4 meters). It is free to use for end users, the only cost being the GPS chip which is included in the price of the device. GPS determines the device position by calculating the differences in the times signals from different satellites take to reach the receiver. Satellites orbit the earth at programmed altitudes, and they act as a reference point in the sky. GPS receiver also takes into consideration velocity of the satellites moving in their respective orbits for distance calculation. If a GPS navigator is receiving insufficient satellite data, it will notify the user rather than provide incorrect position information. Along with GPS (rather US GPS), there are two more satellite based positioning system: o GLONASS The Russian Federation Global Navigation Satellite System (GLONASS) is run and maintained by Russia’s Ministry of Defense. It was introduced in late 1970s for military purposes only. Later on, in 2007 it was made available for public use. o Galileo Galileo is counterpart to US GPS and Russian GLONASS positioning system for Europe. It was initiated by European Union in coordination with European Space Agency (ESA) in mid 2000. This system is still in development stages and is not yet operational.

Although GPS is potentially the most accurate method for location detection, it has some drawbacks: o It heavily consumes cell phone battery while in use. o It requires some warm-up after a cold start to get an initial fix on visible satellites. o It does not work in most of the indoor or covered environments. o It suffers from “canyon effects” in cities where satellite visibility is intermittent. o It also suffers from multipath deflections where the satellite signal bounces off from tall, glass-covered buildings, leading to position drift. 3

Optimized Location Aware Applications on iOS

Sourabh Raheja

3.1.3 Assisted GPS A-GPS is an enhanced positioning system which assist the embedded GPS chip in securing either a faster or more precise location fix in challenging conditions such as a weak satellite signal. In the standard GPS, the initial Time To First Fix (TTFF), often called as cold start, can take anywhere from 30 seconds to a couple of minutes. Using A-GPS, the TTFF is much faster. Very often cellular network towers have GPS receivers (or a base station nearby) and those receivers constantly pull down ephemeris date from the satellite. This data is then passed on to the cell phone when requested. This allows a comparison of fragmentary GPS data received by the handset with data from the network assistance server, thereby leading to more precise and faster calculation of the position. However there are some challenges with A-GPS. Implementation of A-GPS can vary by operator and by manufacturer, requiring extended analysis and testing. Also, A-GPS works by transferring location data over the mobile operator network and thus will incur a data transfer charge. 3.1.4 Wireless Positioning System (WPS) Wi-Fi positioning system was first developed for commercial use by Skyhook Wireless in 2005. It uses 802.11 radio signals emitted from wireless routers to determine the precise location of any Wi-Fi enabled device. The technology does not depend on whether Wi-Fi routers are encrypted and password protected or not. It does not require access to the wire-less network but only to the ID of the wireless transmission. This ID is then cross-referenced to a global database and used for determining the location of the device. Skyhook Wireless claims to cover over 90% of cities in North America and Europe and with a precision of 20 to 40 meters. A key advantage of WPS is that they work indoors where traditionally GPS has not been available. Another advantage is time to obtain a fix is low, providing fast positioning for use within mobile applications. However, there are some drawbacks also: • An active Wi-Fi scan on a mobile device may lead to rapid battery drainage though lesser than standard GPS. • The system requires service providers to constantly update their Wi-Fi hotspots databases. • Since Wi-Fi hotspots changes relatively frequently, some inaccuracy in location fix is possible.

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Optimized Location Aware Applications on iOS 3.2

Sourabh Raheja

Location Detection on iOS iOS is the operating system developed by Apple Inc. for iPhone, iPad and iPod touch devices. Native iOS application development is done in Objective-C programming language using Cocoa application framework. Within Cocoa framework, there exists Core Location framework that allows you to capture current location of the device and use that information in your application. The framework uses the information obtained from built-in cellular, Wi-Fi or GPS hardware to triangulate a location fix for the device. Based on how you configure the service, it also provides periodic updates as it receives new or improved data. There are three different services you can use to capture / monitor user’s current location: • Standard Location Service • Significant Location Change Service • Region Monitoring Service

3.2.1 Standard Location Service Standard Location Service is used to get user’s current location. It is available on all devices and in all versions of iOS. You can configure the desired accuracy of the location data and the distance that must be traveled before reporting a new location. Based on configuration, it will determine which radios to enable and then proceed to report location events to your application. Various possible configurations for desiredAccuracy are: kCLLocationAccuracyBestForNavigation Use the highest possible accuracy and combine it with additional sensor data. This level of accuracy is intended for use in navigation applications that require precise position information at all times. Use the highest-level of accuracy. Accurate to within ten meters of the desired target. Accurate to within one hundred meters. Accurate to the nearest kilometer. Accurate to the nearest three kilometers.

kCLLocationAccuracyBest kCLLocationAccuracyNearestTenMeters kCLLocationAccuracyHundredMeters kCLLocationAccuracyKilometer kCLLocationAccuracyThreeKilometers

The receiver does its best to achieve the requested accuracy; however, it does not guarantee the actual accuracy. Kindly note Core Location will automatically use whatever facilities the device 5

Optimized Location Aware Applications on iOS does have; all you have to do is ask for the device’s location with desiredAccuracy and distanceFilter.

Sourabh Raheja

3.2.2 Significant Location Change (SLC) service In iOS 4.0 and later, you can use Significant Change Location service to receive location updates. This service offers a significant power savings and provides accuracy that is good enough for most applications. It uses device’s cellular radio to determine the user’s location and report changes in that location, allowing the system to manage power usage much more aggressively than it could otherwise. This service is also capable of waking up an application that is currently suspended or not running in order to deliver new location data. 3.2.3 Region Monitoring Service In iOS 4.0 and later, applications can use Region Monitoring Service to be notified when the user crosses geographic boundaries. You can use this capability to generate alerts when the user gets close to a specific location. Regions associated with your application are tracked at all times, including when your application is not running. If a region boundary is crossed while an application is not running, that application is launched into the background to handle the event. Similarly, if the application is suspended when the event occurs, it is woken up and given a short amount of time to handle the event. 3.3 Challenges on iOS iOS has provided developers with various high level methods for capturing and monitoring user’s location. These services allow developers to focus more on innovative features of their application rather then worrying about detail integrities of the API’s. However, there are still some challenges and limitations of these services. We will now understand what these challenges are.

3.3.1 Inaccurate Location Updates Core Location framework attempts to achieve an accuracy that is as close as possible to the stated desiredAccuracy. However, there is no guarantee that the desired accuracy will be achieved, or that it can be maintained in cases where Core Location has been asked to continuously seek new locations over time. As a matter of fact, some of initial updates are not that accurate and are refined in subsequent location updates. Your design should take into account this variable precision and should provide users with a clear understanding of the reliability of the location data. In iOS, you can know accuracy of a location update using the property horizontalAccuracy. For example Maps application handles the inherent imprecision by drawing a circle with a radius that corresponds roughly to the accuracy of the location update. With each subsequent refinement, the circle animates and shrinks to show 6

Optimized Location Aware Applications on iOS

Sourabh Raheja

the new radius value. In a way, radius represents the margin of error in determining user’s location. 3.3.2 Invalid Location Updates Core Location framework caches the last known location of the device. It can take several seconds to determine the first location fix. Most of the times, this cached location is the first reported location update. This helps to improve user experience by supplying an application with a relevant starting point for the update request. It is important to validate timestamp property of the location update. In general, one should ignore location updates that are more than 15 seconds old, however, this threshold can be lower as per the need of your application.
- (BOOL)isValidLocationUpdate: (CLLocation *)newLocation { BOOL isValid = NO; NSDate *locationTimestamp = newLocation.timestamp; NSTimeInterval interval = [locationTimestamp timeIntervalSinceNow]; if (abs(interval) < 15.0) { isValid = YES; } return isValid; }

3.3.3 Battery Drain Receiving and transmitting data using radios of iOS require more power than any other operation on the device. Core Location framework relies on these radios to determine user’s current location. Request for higher accuracy requires Core Location framework to power up additional hardware (embedded GPS chip), which thereby, consumes more power. So one should never request higher accuracy than what is really needed for the application. For example, for turn-by-turn navigation higher accuracy is required along with frequent updates. However, for local weather updates, lower accuracy mode will also be able to achieve the desired results. 3.3.4 Limitations of Application Background Mode In iOS, only specific application types are allowed to run in the background: • Apps that play audible content to the user while in background • Apps that keep users informed of their location at all times • Apps that support Voice over Internet Protocol • Newsstand apps that need to download and process new content • Apps that receive regular updates from external accessories 7

Optimized Location Aware Applications on iOS

Sourabh Raheja

Apps that implement these services must declare the services they support and use system frameworks to implement the relevant aspects of those services. Declaring the services lets the system know which services you use, but in some cases it is the system frameworks that actually prevent your application from being suspended. So if your application is in background and you are not using any of the specified location service, iOS will suspend your application. Generally most of the periodic location aware solutions are either displacement based or time based. What that means is application will get the next location update from the device after x meters of displacement or after t seconds of time interval. One can play with these parameters and make them dynamic on each subsequent update to optimize battery usage In iOS it is not possible to have time-interval based location aware application. One has to continuously use location services to remain active in background; else iOS will suspend the application. And location services only allow you to configure distanceFilter. You cannot specify time interval after which you will like to get location update. And for sure, using location services continuously in background will drain battery. 3.3.5 Challenges with Significant Location Change (SLC) Significant Location Change service, without consuming much battery, provides periodic location updates using cellular tower and Wi-Fi hotspots. However, accuracy and frequency of location updates varies from place to place depending on the density of cellular towers and Wi-Fi hotspots. On an average, accuracy of significant location change update is around 500m and average frequency of such updates is every 2 Km. Kindly note this can go up to very large values depending on cellular tower density and availability of Wi-Fi hotspots. So, we cannot use SLC purely for monitoring regions of small radii. 3.3.6 Challenges with Region Monitoring Like SLC, Region Monitoring is also completely dependent on cellular tower and availability of Wi-Fi hotspots. So, frequency of location updates and accuracy using Region Monitoring is also low. This service is ideal for monitoring regions with radii greater than 1.5 KM. However, for regions with radii lesser than that, this service is very erratic and cannot be purely relied upon.

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Optimized Location Aware Applications on iOS

Sourabh Raheja

Also, Core Location framework limits the number of regions that may be simultaneously monitored by a single application. Regions are a shared system resource and the total number of regions available system wide is limited. 3.3.7 Privacy and Security Location aware application raises a major concern for the users about their Security and Privacy. Users are not comfortable with idea that some one is watching them or someone is trying to look inside their head to understand their shopping behavior. Some of the countries have stringent laws surrounding public privacy such that several layers of authorization on the operator’s network protect a mobile subscriber’s location. 3.4 Optimized Geo-fencing Solution on iOS As per Wikipedia: “A Geo-fence is a virtual parameter for a real world geographic area. When the location aware device of a user enters or exits a geo-fence, the device receives a generated notification”. Problem iOS Region Monitoring Service has good accuracy for geo-fencing nonoverlapping regions of radius greater than 2 km. However, for monitoring regions with radius lesser than that, let us say for regions with radius 50 meters, we need to have a custom solution that generates notifications even when the application is in background. The simplest solution for the problem is to register for location updates with Core Location framework with desired accuracy as kCLLocationAccuracyBest and distanceFilter as 10 meters. However, this drains out battery at a very fast rate. On an average, with this solution the battery of your iPhone does not lasts more than 2 hours. Optimized Solution For a solution that drains lesser battery and which is accurate as well, we will use three location managers: • SLC Location Manager • Low Accuracy Location Manager • High Accuracy Location Manager Configuration • SLC Location Manager is used to register for significant location change events. distanceFilter for the same is set to kCLDistanceFilterNone, which means there is no distance filter and every location update should be notified to the application. • For Low Accuracy Location Manager desiredAccuracy is set to kCLLocationAccuracyHundredMeters and distanceFilter is set to 50m. This 9

Optimized Location Aware Applications on iOS

Sourabh Raheja

•

means registering to Low Accuracy Location Manager will give us location updates after every 50m with an accuracy of 100m. For High Accuracy Location Manager desiredAccuracy is set to kCLLocationAccuracyBest and distanceFilter is set to kCLDistanceFilterNone. This means registering to High Accuracy Location Manager will give us location updates with the best possible accuracy.

Terminology For the solution we will introduce following new terms: • Actual Radius: It is actual radius of the region to be monitored, for our analysis let us say 50 meters. • Outer Radius: It implies that if a user in outer radius of a region, he is approaching towards the region. The value of outer radius depends on the average distance between two subsequent SLC updates. The concept of outer radius has been added so that we are able to capture location updates in the areas missed by pure SLC based events. After some heuristics based on experiments, we will assume this value to be 1.5 KM. • Considered Radius: This implies radius that should be used to determine whether a user is in that region or not. For high accuracy location updates, this is equal to the actual radius. For low accuracy location updates, this is equal to sum of actual radius and accuracy of the update event. Figure 2 shows what does Actual and Outer Radius imply. It also shows three regions where user can be: A, B and C at any given point of time:

C B A
Actual Radius Outer Radius

Figure 2: User Location

When user is in location A, it means he is inside the monitored region. When he is in location B, it implies user is in the periphery of monitored region. And when user is in location C, it means he is far away from the monitored region. 10

Optimized Location Aware Applications on iOS

Sourabh Raheja

Algorithm 1. We will register for SLC updates. 2. On each subsequent SLC update as well as on first launch and whenever application comes in foreground, we will use High Accuracy Location Manager to capture accurate location. We will persist this location update along with its timestamp. 3. Using the accurate location update and considered radius being equal to actual radius, we will determine where user currently is: a. Location A: If user is found in Location A, we will notify our application that user is in so and so monitored region. At this moment, we will stop location updates from High Accuracy Location Manager and will register for periodic location updates from Low Accuracy Location Manager. b. Location B: If the user is found in Location B, we will stop location updates from High Accuracy Location Manager and register for periodic location updates from Low Accuracy Location Manager. c. Location C: If the user is found in Location C, we will stop location updates from High Accuracy Location Manager and will wait for next SLC. 4. On subsequent update from Low Accuracy Location Manager, we will use considered radius as sum of actual radius and the accuracy of location update event. a. Location A: If the user is found to be in Location A, we will stop location updates from Low Accuracy Location Manager and capture a high accuracy location update. We will then validate his location as done in Step 3. b. Location B: If the user is found to be in Location B, we will continue with periodic location updates from Low Accuracy Location Manager. c. Location C: If the user is found in Location C, we will stop location updates from Low Accuracy Location Manager and will wait for next SLC update. So, this way we have reduced number of high accuracy location updates by a large extent. We can further reduce it in step 4.a by using value of last known accurate location update and its timestamp. In step 4.a we will not request for another high accuracy location update if region found is same as one in last accurate location update given that its timestamp is not older than 5 minutes. 3.5 Addressing Privacy and Security Concerns An application should be conceptualized and built in such a way that it does not hinder with user's privacy and is readily accepted among them. Some of the basic concepts that one should incorporate while creating a location aware application are:
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Awareness First and foremost, a user should be well informed about the purpose of the 11

Optimized Location Aware Applications on iOS

Sourabh Raheja

application. How his location will be used to achieve the desired results? He should be made aware of optional and configurable features in the application. Most of the smart phones do show a permission dialog as soon as application tries to use location for the first time. Sometimes it is not immediately apparent to the user why the application will use his location. If, at that moment user disallows use of his location, your application will never get the location access, unless he explicitly allows it from phone's settings, which is less probable. So, one should always add appropriate information in the application description available on app store. iOS lately has introduced a customizable "Purpose Property" that is shown in the permission dialog required for authorization. One should make full use of such features to make user understand the context and benefits.
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Opt-in Tracking User should be able to turn off location tracking as and when he wants. He should be able to define criteria when his location should be tracked. For example, he may like to do location aware networking during a trade fair, not when he is celebrating his marriage anniversary. Another example can be location aware services should be turned off at night when he is sleeping. User should also be able to configure accuracy level to achieve the desired results, thereby preserving his privacy to an extent and reap benefits as well. Opt-in Usage User should be able to configure how his location should be used. For example, in geo marketing applications, user should be able to choose the brands from whom he should receive offers or on his social network, he should be able to filter his location updates among his friends. Some of the latest applications are mining location information to predict users' future locations. Such features should be optional and configurable. Secure One should understand that location data is very sensitive and personal. So if possible, the application should never store it. However, if not, application should either use one of the anonymization techniques or encrypt it before storing user's location specific data. Applications can also obfuscate location by degrading the quality of information about an individual's location in order to protect his privacy.

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Conclusion Using the optimized solution for Geo-fencing of regions with 50m radii, battery of your iPhone does lasts for more than 10 hours. The accuracy of this solution is around 90%. So, we have improved battery usage from 2 hours to 10 hours with a decent accuracy. We can further improve accuracy by using larger outer radius, however, it will consume more battery. 12

Optimized Location Aware Applications on iOS

Sourabh Raheja

While conceptualizing your application, it is easy to fall into short term benefits trap by overlooking concerns related to Privacy and Security. However, adhering to the fundamental concepts mentioned in section 3.5 will ensure more acceptability among users in the longer run.

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