Mobile Penetration

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Networks Illustrated: Principles without Calculus

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Princeton University

Networks Illustrated: Principles without Calculus

40 notes

What makes WiFi faster at home than at a coffee shop? How does Google order its search results from the trillions of webpages on the Internet? Why does Verizon charge $15 for every GB of data we use? Is it really true that we are connected in six social steps or less? These are just a few of the many intriguing questions we can ask about the social and technical networks that form integral parts of our daily lives. This course is about exploring the answers, using a language that anyone can understand. We will focus on fundamental principles like “sharing is hard”, “crowds are wise”, and “network of networks” that have guided the design and sustainability of today’s networks, and summarize the theories behind everything from the social connections we make on platforms like Facebook to the technology upon which these websites run. Unlike other networking courses, the mathematics included here are no more complicated than adding and multiplying numbers. While mathematical details are necessary to fully specify the algorithms and systems we investigate, they are not required to understand the main ideas. We use illustrations, analogies, and anecdotes about networks as pedagogical tools in lieu of detailed equations. All the features of this course are available for free. It does not offer a certificate upon completion.

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Power Control in Cellular Networks

How is it possible that we can all communicate effectively without disrupting each other's calls, messages, or Internet usage? In this lesson, we will take a look at some of the methods that have been developed for letting us "share" the air over which our phones communicate.

Rencontrer les enseignants

Christopher Brinton
Lecturer
Electrical Engineering
Mung Chiang
Professor
Electrical Engineering

Hello. Thanks again for joining us in Network's

Illustrated principals without calculus. In this lecture, we're going to look at a

device that you hold in your hands probably every day, your cell phone.

Specifically, we're going to look at the types of decisions that it has to make in

order to decide what power that it should be transmitting at any given time.

As we will see, the principle that sharing is hard, is very applicable.

Have you ever stopped to think, how many cellphones are there, either in the

world, or in a region, like a country? So, suppose we had six people?

Would we have, on average, less cellphones than people?

So, we have maybe four cellphones for every six people, meaning that every

person has on average less than one cellphone.

Would we have the same number, meaning that every person's going to have on

average one cellphone? Or would we have more?

Like, eight cellphones for every six people, meaning that every person has on

average more than one cellphone. A decade or two ago there were many, many

more people than there were cellphones, but the number of cellphones has risen

very dramatically in that time. So, these numbers are becoming closer and

closer to one another. At the end of 2012, there were about 7

billion people in the world, and there were about 6 billion mobile

subscriptions. So, we're not actually looking at the

number of manufactured devices, or the number of cellphones that have ever been

made, but we're looking at those that are currently in use or currently subscribe

to a mobile plan. And so, if we looked at the number of

cellphones relative to the number of people, we would have six over seven.

Meaning that for every six phones there are on an average for seven people.

So, this is approaching one, meaning that in the world they're soon going to be on

an average one cellphone per person. So, you may have guessed that number

would have been around one, maybe even a little less than one.

But what you probably didn't know is it's drastically different depends upon which

country you are look at. So, in this graph over here, we're

showing the penetration rate which is this number that we showed down here of

taking the number of mobile subscriptions and dividing it by the number of people

in the population. And this is as of December 2012.

So, if you look at the countries on the right-hand side, over here, you see that

the penetration rates for these countries are less than 100%.

Or, it's just really just this decimal number in percentage form..

And what that means is that there are more peoples than cellphones, that might

make sense because some of these countries have very large populations or

a dense populations. But on the left hand side of this arrow,

these countries have ratios that are over 100%, for instance, United States has

recently gone up to 103%. And that keeps going up more and more

which means that there are actually more cellphones then there are people.

And if we come all the way over here to Russia that is at 160% which means that

there is between one in two cellphones per person and it's closer to the two.

So, there's closer to two cell phones per person than there is one cell phone per

person in Russia. And just to sort of write this out, the

penetration rate is equal to the number of mobile devices.

Or the number of mobile subscriptions, to be exact, divided by the number of people

in whatever region we're talking about. So, with all of the six billion

cellphones there are in the world, how is it possible that we could all transmit on

the same network medium? Meaning, the air, without interfering

with each others conversations? Certainly, you've been next to someone

before who's also been on their cell phone and has been talking to someone

that you're not talking too, but you can't hear their conversation and you

can't hear what's going on. So, how is it possible that we can all

transmit at the same times and not cause a new problems with one another?

Well, the modern cellular system, we can write the cellular word now ,is the

results of decades of technological innovations in which engineers have

experimented with different ways of allowing us to share this network medium.

Or really share the air in this case, because the network medium is cellular is

the air. And so, they came up with many different

methods of allowing us to do that as efficiently as possible which is why you

can't hear your friend's conversation at the same time as yours.

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