Brooks was here… So was Red
The power of location tagged information
Mohit Gupta, Prashanth Mohan, Lenin Ravindranath
Microsoft Research India
While visiting the Louvre museum, Brooks had several experiences he wanted to share. He took a
number of photographs and leaves some of them at that location for others who visit the place. A
couple of years later, Red visits the Louvre and chances upon the photographs left by Brooks. Red reads
Brooks’ experiences and finds out about a lesser known section of the castle. When leaving, Red leaves
some of his own pictures and anecdotes there. People who visit the Louvre are able to look at it at
different points in the past by browsing through blog posts, pictures and videos left by others. In
essence, people leave their memories which others can view and feel when they visit that location.
1. Overview
To enable the scenario described above, in this paper we present a novel approach for automatically
tagging information published by a user with location data. The ability to search on location tagged
information like news, blog posts, pictures, videos and ads is going to have a strong presence in the
future. Our scenarios show the compelling applications that can be built on top of location tagged
information.
The reach of current localization techniques such as GPS and war driving is not sufficient to support
large scale services. In this paper, we present a novel approach to use existing Wi-Fi and GSM
infrastructure around the world as location landmarks. For most of the applications we discuss the
absolute location of the user is not needed. Our approach is readily deployable because it works with
existing mobile devices and does not require modification of clients or infrastructure. These location
based services will give Microsoft unique competitive advantages in mobile platform space and online
advertising.
2. More Scenarios
 Red visits a restaurant in the mall and is able to see reviews and comments that other people left at
the restaurant. He finds that one of the dishes is loved by many people and he decides to try it.
 As Red walks through a busy city street, he searches for nearby coffee shops. He is instantly served
with ads for nearby coffee shops. He also receives a discount coupon from the nearby Starbucks
Café.
 Brooks is sitting at his house and wants to know about a tourist place. He locates the place in the
map and searches for blog posts, photos and videos people uploaded from the place.
 Red is waiting at the airport for his flight. He searches for people nearby, he can play a game with.
He discovers that Brooks is also searching for people to play with.
 Red visits a new city. He wants to talk to people who visited the same location in the past. He finds
that Brooks visited the place some time ago. He is able to query him and ask about good hotels and
places to see.
3. Introduction
Mobile devices and contextual information retrieval are now allowing us to travel with information.
But software is still stuck in the old paradigm that expects users to explicitly declare context and
location. A major step forward would be to organize, tag and link information to specific locations [7].
Such location based services can provide Microsoft with an advantage in the growing advertising
business. This year, online advertising is a $40 billion business. It will grow to $80 billion by 2010 and
will continue to increase in the years beyond [3]. One of the key reasons for success in this market is
that the ads are targeted – the ads delivered to the end-user are relevant to the website visited by the
user, or the search query typed by the user.
Location based advertising is currently facing problems of reach. The number of GPS or GSM
localization enabled mobile devices remains relatively small. Indeed, many players are already testing
the waters in this market. For example, Google has announced to offer ad-supported free Wi-Fi access
in San Francisco. MSN has introduced the “Locate Me” feature, which can determine the approximate
location of the user based on what Wi-Fi networks the user can hear. Google CEO Eric Schmidt recently
expressed the company's interest in location based ads as the future in mobile advertising [6]. Last
year Google launched a mobile version of AdSense and their own mobile OS. We can definitely expect
location aware ads from them in the near future. Microsoft is appropriately placed to become a leader
in this space.
Microsoft's strong presence as a mobile platform and its large user base in the online messaging space
can be leveraged to provide compelling situated experiences. The Live Messenger and Hotmail
together form a massive network of more than 12 billion relationships [5]. New context rich, location
aware services built on top of this existing social network will allow users to extend their interactions in
rich mediated-spaces.
We propose location based services that will allow Microsoft unique competitive advantages in the
messaging and mobile platforms space. One obvious advantage is that MSR has already filed a number
of relevant patent applications on these ideas; we believe that Microsoft has two inherent structural
advantages.
4. Technology
Existing implementations of location based services [8, 9] require additional functionality to track the
device’s location. This usually means additional hardware requirements like GPS or extensive war
driving to map GSM (using triangulation) and Wi-Fi signature to latitude and longitude. GPS is
extremely power hungry and does not work inside buildings such as malls.
Features like MSN’s “Locate Me” and Google’s location apps use war driving data and locates users
geographically using nearby Wi-Fi Access Points and GSM towers. For the scenarios and applications
we discuss we do not require the absolute location of a user and hence war driving is unnecessary.
The system described leverages GPS or war driving data when available to improve the overall
experience. However, in its absence we use the following approach for localization.
Approach
The density of Wi-Fi Access Points (APs) has increased rapidly [2]. Within the last five years, there has
been remarkable growth in the number of Wi-Fi hotspots and in the usage of Wi-Fi enabled devices –
recent research has shown that this trend is likely to continue [1].
Every Access Point has a 6-byte unique ID called the BSSID. A Wi-Fi client can scan for Access Points
around and get their BSSIDs. Access points once deployed are usually immobile and hence their BSSIDs
can be used as the landmark for that location. It should be noted here that clients can scan for Access
Points around even when they are completely disconnected.
Fig. 1 Architecture
If Wi-Fi Access Points are not available, we rely on GSM towers to function as landmarks. The wide
scale deployment of GSM towers around the world has enabled users to be connected all the time. We
use the GSM tower ID as a landmark in the same way we use APs. Using GSM tower as landmark info
even in the presence of Wi-Fi enables us to build smarter location services as explained in the
Applications section. In the scenario shown in Figure 1, AP1 and GSM1 form the landmarks.
When a user publishes data to a central server, we automatically tag the information with relevant
landmarks. Once location tagged information is published to the server, other users who visit the same
location can retrieve it by reporting the current location’s landmarks.
The approach is readily deployable as we do not rely on absolute location. Neither war driving nor
modification to clients, APs or GSM towers is necessary. We only make the assumption that the client
device (PDA or laptop) has a Wi-Fi card or a SIM card and can connect to the Internet.
We could also adopt this mechanism to passively perform much richer war driving of location
information. Users with GPS enabled devices could opt in to provide specific location information to
map Wi-Fi signatures and GSM signatures to exact location (latitude, longitude).
This technique of publishing and retrieving information from the server with location information
enables us to build several applications as discussed in the Applications Section.
Battery Power
Wi-Fi cards are power hungry and hence people often switch them off and prefer GPRS or EDGE
connections. When the current location’s Wi-Fi signature is required we turn on Wi-Fi, scan for Access
Points around and turn off Wi-Fi. Since the Wi-Fi card is used only to scan on demand, our approach is
not power hungry.
Offline Mode
It is not mandatory that a client needs to be connected to the Internet to publish information from a
location. The location’s Wi-Fi and GSM signatures can be obtained even if the client is not connected
and hence can the information can be tagged. The client can upload it later when he regains Internet
connectivity.
5. Applications
Post-Its in the air
Our application enables users to annotate physical locations with media. Users can post text, images
and videos on their blog. Behind the scene the post is tagged with the GSM and Wi-Fi signatures at that
location. This will enable users to tag locations with their memories and experiences. Other people
passing through the same location can serendipitously chance upon the located media, and leave
further comments and anecdotes.
Some scenarios describing such interactions are - People can post reviews about a restaurant after
they eat and others visiting the restaurant later can read and these reviews to choose a popular dish.
Users might like to leave photos they took at a beach for others to comment on. Users can leave
directions at a hotel to a nearby lagoon that is not shown on maps.
The application allows users to leave behind traces of their experiences and memories in-situ. At any
place, users can navigate and comment on media submitted by other users. They can continue to track
posts tagged to that location and also follow posts by a particular user.
Location Sensitive Search
Over time, a knowledge base of information tagged with location will be formed. The Internet search
of tomorrow can be in touch with the physical world. People can search for information filtered by the
contents’ physical location as against the location in which the content is stored. "M.G. Road" for
instance appears in most of the major cities of India; however, the disambiguation would be easy when
the location on the map is specified with search queries.
Location Sensitive Advertisements
Online advertising is the one of the fastest growing markets with a net worth of over 40 billion USD [3].
Microsoft realizes this fact and has invested large amounts of money in the advertising potential of
networks such as FaceBook and MySpace. The high hit to view ratio of context sensitive ads can be
improved phenomenally by taking the location of the user into account. Location sensitive ads are the
new wave in the online advertising industry.
We look at a scenario wherein, advertisers would bid for ads to be broadcast to users who see a
particular Wi-Fi Access Point or GSM Tower. Location sensitiveness can be combined with existing
search engine marketing techniques like bidding on keywords, etc to provide more targeted
advertisements to the user.
We make use of relative distance between Access Points (APs) to provide a richer experience. For
instance, if a user is browsing for information on a product, we could link him to nearby stores selling
similar products. Technical details of how we infer nearness using only Wi-Fi APs and GSM Towers
without war driving data is explained in Appendix A.
Discount and offer coupons from participating businesses can also be delivered to a client. A user with
the client application walking near a coffee shop receives a virtual coupon from the shop. The user can
then walk down to the coffee shop and present the coupon. Delivering location sensitive
advertisements with coupons greatly adds to the users’ experience.
Friends near and who were here
Current social networking sites, model their contents as a tree of friends and their friends. Many of
these sites also provide us options to updates of their friends. We introduce a mechanism to provide
additional context to the social networking field in order to make it more useful. Users of our products
regularly upload their GSM and Wi-Fi signatures to the central server (to subscribe to location sensitive
material of that region).
A by-product of knowing the current location of users is that, users will be able to know if any of his
friends are currently nearby. Microsoft has multiple revenue generating possibilities in this space.
Users can also fine friends who were in the same region at some point in the past. He will be able to
contact them for additional information about the place. Users will also be allowed to contact the
authors of Post-Its left at that place. This can be restricted using incentive based schemes to reduce
spam issues. Also it will be made possible to optionally disable random people from contacting the
Post-It authors.
In order to overcome privacy issues, it will be possible to turn off regular updating of user's location.
Game Pairing
Mobile gaming is expected to be a $10 billion market by 2009 [4]. A major portion of this growth is
going to be in location-based games. Using our technology users can search for others around them
interested in playing games. These games can be played over peer-to-peer connections, or over the
internet. This can be extended to other scenarios where a user is looking for assistance with a
particular application.
Our location services can also identify users that are reading the same web page or book. Mobile
devices are fast becoming the preferred platform for reading books. The reading experience can be
enriched by finding other users in the vicinity, interested in the same topics, web pages or books.
6. Conclusion
Location sensitive content distribution is an upcoming field and Microsoft can become an early player
in the market. Our technology is readily deployable. As compared against existing solutions which
attempt to provide location sensitive information, we place no specific demands on the client or
infrastructure. Removing the requirement of GPS receivers also enables us to attract lower end smart
phones. We can leverage Microsoft's existing technologies to easily build our solution. The LiveID
platform provides an effective means to perform authentication. Post-Its in the air will add rich context
to Virtual Earth and Live Search for location specific search. MSN Messenger and Internet Explorer are
foundations on which the technology can be deployed. Services such as finding nearby friends will add
great value to the large user base of these technologies. Given Microsoft's existing technological
prowess, we have a painless path to dive into the field of location sensitive services.
7. References
[1] Worldwide PDA and SmartPhone Forecast. http://www.etforecasts.com/products/ES SP-PDA.htm.
[2] http://www.cs.cmu.edu/afs/cs/project/cmcl/archive/2005/mobicomchaotic.pdf
[3] Steve Ballmer’s mail on “Proposed Yahoo Acquisition”
[4] http://banners.noticiasdot.com/termometro/boletines/docs/consultoras/idate/2003/idate_1343.pdf
[5] http://www.microsoft.com/presspass/features/2006/jun06/06-19windowslivemessenger.mspx
[6] http://www.readwriteweb.com/archives/location_based_mobile_ads.php
[7] http://www.techconsumer.com/2007/07/16/the-next-big-thing-why-web-20-isnt-enough/
[8] http://research.microsoft.com/~jws/pubfiles/ubicomp2005-placeits.pdf
[9] http://www.csie.ndhu.edu.tw/~showyang/PerCom2003f/Papers/a-survey-cntxt-aware-mob-compresearch-2000.pdf
Appendix
A - Inferring nearness using only Wi-Fi APs and GSM Towers
GSM Cell base stations typically have a range of few hundred meters to few kilometers. We have found
that in developing countries like India, there is a very dense deployment of GSM cell towers making
localization using base stations very effective. Wi-Fi on the other hand provides fine grained
localization ranging up to 250 meters.
Figure 2 - Relative range of GSM vs. Wi-Fi
We need not know the absolute location (in terms of latitude and longitude) of Wi-Fi APs in order to
infer their nearness. Given that the GSM cell tower range is much more than the range of a Wi-Fi
Access Point, we can safely assume that the coverage of a single GSM tower would include multiple
Wi-Fi APs within itself (Refer to Figure 2). Due to existing limitations in Windows Mobile, we can
programmatically only infer the currently associated GSM tower. Also, the same operator could have
multiple cell towers with over lapping ranges. Given that users would be periodically uploading their
GSM and Wi-Fi signatures to the central database, over time a 2 level tree (Refer to Figure 3) would be
associating Wi-Fi APs with GSM cell towers.
Figure 3 – Wi-Fi and GSM landmarks association tree
Now when a user reports to the server a Wi-Fi, GSM signature, we can obtain from the tree, other GSM
towers in the range of the Wi-Fi AP, and the other Wi-Fi APs associated with this set of GSM towers.
We can thus infer that these Wi-Fi APs would be physically near.