[LINK] Ten ways your smartphone knows where you are

[stephen at melbpc.org.au]

Ten ways your smartphone knows where you are

www.arnnet.com.au/article/420838/ten_ways_your_smartphone_knows_where/
Stephen Lawson (IDG News Service) 06 April, 2012 22:47


. There are at least 10 different systems in use or being developed that 
a phone could use to identify its location. In most cases, several are 
used in combination, with one stepping in where another is less effective.

1. GPS

Global Positioning System was developed by the U.S. Department of Defense 
and was first included in cellphones in the late 1990s. It's still the 
best-known way to find your location outdoors. GPS uses a constellation 
of satellites that send location and timing data from space directly to 
your phone. If the phone can pick up signals from three satellites, it 
can show where you are on a flat map, and with four, it can also show 
your elevation. Other governments have developed their own systems 
similar to GPS, but rather than conflicting with it, they can actually 
make outdoor location easier. Russia's GLONASS is already live and 
China's Compass is in trials. Europe's Galileo and Japan's Quasi-Zenith 
Satellite System are also on the way. Phone chip makers are developing 
processors that can use multiple satellite constellations to get a 
location fix faster. 

2. Assisted GPS

GPS works well once your phone finds three or four satellites, but that 
may take a long time, or not happen at all if you're indoors or in 
an "urban canyon" of buildings that reflect satellite signals. Assisted 
GPS describes a collection of tools that help to solve that problem. One 
reason for the wait is that when it first finds the satellites, the phone 
needs to download information about where they will be for the next four 
hours. The phone needs that information to keep tracking the satellites. 
As soon as the information reaches the phone, full GPS service starts. 
Carriers can now send that data over a cellular or Wi-Fi network, which 
is a lot faster than a satellite link. This may cut GPS startup time from 
45 seconds to 15 seconds or less, though it's still unpredictable, said 
Guylain Roy-MacHabee, CEO of location technology company RX Networks.

3. Synthetic GPS

The form of assisted GPS described above still requires an available data 
network and the time to transmit the satellite information. Synthetic GPS 
uses computing power to forecast satellites' locations days or weeks in 
advance. This function began in data centers but increasingly can be 
carried out on phones themselves, according to Roy-MacHabee of RX, which 
specializes in this type of technology. With such a cache of satellite 
data on board, a phone often can identify its location in two seconds or 
less, he said.

4. Cell ID

However, all the technologies that speed up GPS still require the phone 
to find three satellites. Carriers already know how to locate phones 
without GPS, and they knew it before phones got the feature. Carriers 
figure out which cell a customer is using, and how far they are from the 
neighboring cells, with a technology called Cell ID. By knowing which 
sector of which base station a given phone is using, and using a database 
of base-station identification numbers and locations, the carriers can 
associate the phone's location with that of the cell tower. This system 
tends to be more precise in urban areas with many small cells than in 
rural areas, where cells may cover an area several kilometers in 
diameter. 

5. Wi-Fi

Wi-Fi can do much the same thing as Cell ID, but with greater precision 
because Wi-Fi access points cover a smaller area. There are actually two 
ways Wi-Fi can be used to determine location. The most common, called 
RSSI (received signal strength indication), takes the signals your phone 
detects from nearby access points and refers to a database of Wi-Fi 
networks. The database says where each uniquely identified access point 
is located. Using signal strength to determine distance, RSSI determines 
where you are (down to tens of meters) in relation to those known access 
points. The other form of Wi-Fi location, wireless fingerprinting, uses 
profiles of given places that are based on the pattern of Wi-Fi signals 
found there. This technique is best for places that you or other 
cellphone users visit frequently. The fingerprint may be created and 
stored the first time you go there, or a service provider may send 
someone out to stand in certain spots in a building and record a 
fingerprint for each one. Fingerprinting can identify your location to 
within just a few meters, said Charlie Abraham, vice president of 
engineering at Broadcom's GPS division, which makes chipsets that can use 
a variety of location mechanisms. 

6. Inertial sensors

If you go into a place where no wireless system works, inertial sensors 
can keep track of your location based on other inputs. Most smartphones 
now come with three inertial sensors: a compass (or magnetometer) to 
determine direction, an accelerometer to report how fast your phone is 
moving in that direction, and a gyroscope to sense turning motions. 
Together, these sensors can determine your location with no outside 
inputs, but only for a limited time. They'll work for minutes, but not 
tens of minutes, Broadcom's Abraham said. The classic use case is driving 
into a tunnel: If the phone knows your location from the usual sources 
before you enter, it can then determine where you've gone from the speed 
and direction you're moving. More commonly, these tools are used in 
conjunction with other location systems, sometimes compensating for them 
in areas where they are weak, Abraham said.

7. Barometer

Outdoor navigation on a sidewalk or street typically happens on one 
level, either going straight or making right or left turns. But indoors, 
it makes a difference what floor of the building you're on. GPS could 
read this, except that it's usually hard to get good GPS coverage indoors 
or even in urban areas, where the satellite signals bounce off tall 
buildings. One way to determine elevation is a barometer, which uses the 
principle that air gets thinner the farther up you go. Some smartphones 
already have chips that can detect barometric pressure, but this 
technique isn't usually suited for use by itself, RX's Roy-MacHabee said. 
To use it, the phone needs to pull down local weather data for a baseline 
figure on barometric pressure, and conditions inside a building such as 
heating or air-conditioning flows can affect the sensor's accuracy, he 
said. A barometer works best with mobile devices that have been carefully 
calibrated for a specific building, so it might work in your own office 
but not in a public library, Roy-MacHabee said. Barometers are best used 
in combination with other tools, including GPS, Wi-Fi and short-range 
systems that register that you've gone past a particular spot.

8. Ultrasonic

Sometimes just detecting whether someone has entered a certain area says 
something about what they're doing. This can be done with short-range 
wireless systems, such as RFID (radio-frequency identification) with a 
badge. NFC (near-field communication) is starting to appear in phones and 
could be used for checkpoints, but manufacturers' main intention for NFC 
is payments. However, shopper loyalty company Shopkick is already using a 
short-range system to verify that consumers have walked into a store. 
Instead of using a radio, Shopkick broadcasts ultrasonic tones just 
inside the doors of a shop. If the customer has the Shopkick app running 
when they walk through the door, the phone will pick up the tone through 
its microphone and the app will tell Shopkick that they've entered. The 
shopper can earn points, redeemable for gift cards and other rewards, 
just for walking into the store, and those show up immediately. Shopkick 
developed the ultrasonic system partly because the tones can't penetrate 
walls or windows, which would let people collect points just for walking 
by, CTO Aaron Emigh said. They travel about 150 feet (46 meters) inside 
the store. Every location of every store has a unique set of tones, which 
are at too high a frequency for humans to hear. Dogs can hear them, but 
tests showed they don't mind, Emigh said.

9. Bluetooth beacons

Very precise location can be achieved in a specific area, such as inside 
a retail store, using beacons that send out signals via Bluetooth. The 
beacons, smaller than a cellphone, are placed every few meters and can 
communicate with any mobile device equipped with Bluetooth 4.0, the 
newest version of the standard. Using a technique similar to Wi-Fi 
fingerprinting, the venue owner can use signals from this dense network 
of transmitters to identify locations within the space, Broadcom's 
Abraham said. Nokia, which is participating in a live in-store trial of 
Bluetooth beacons, says the system can determine location to within 10 
centimeters. With location sensing that specific, a store could tell when 
you were close to a specific product on a shelf and offer a promotion, 
according to Nokia.

10. Terrestrial transmitters

Australian startup Locata is trying to overcome GPS' limitations by 
bringing it down to Earth. The company makes location transmitters that 
use the same principle as GPS but are mounted on buildings and cell 
towers. Because they are stationary and provide a much stronger signal to 
receivers than satellites do from space, Locata's radios can pinpoint a 
user's location almost instantly to as close as 2 inches, according to 
Locata CEO Nunzio Gambale. Locata networks are also more reliable than 
GPS, he said. The company's receivers currently cost about $2,500 and are 
drawing interest from transportation, defense and public safety 
customers, but within a few years the technology could be an inexpensive 
add-on to phones, according to Gambale. Then, service providers will be 
its biggest customers, he said. Another company in this field, NextNav, 
is building a network using licensed spectrum that it says can cover 93 
percent of the U.S. population. NextNav's transmitters will be deployed 
in a ring around each city and take advantage of the long range of its 
900MHz spectrum, said Chris Gates, vice president of strategy and 
development.
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Cheers,
Stephen

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