The aim of 3G (third generation) is to deliver the capability of much higher data rates to mobile communications devices over a large geographical area. Data rates of up to 2megabits per second will be capable in some areas.
It is also the aim of 3G to unify the wireless devices the world over, so a user from the UK, can travel Europe, and the US, and use the same, highspeed data links, seamlessly as they travel the globe.
3G is a packet switched suite of protocols, a technology which was originally developed for the internet, it also uses techniques such as Code Division Multiple Access (originally developed by the military) to allow efficient, fast, and secure communications over the wireless medium. For a very in-depth technological explanation of 3G, go to the “How Does 3G work?” Section.
To the end user, 3G means fast World Wide Web browsing, file transfers, emailing, even video phoning and video conferencing from their mobile phone, PDA, or laptop. With coverage over all of Europe, the USA, China, Japan, and the rest of the world, with seamless integration between all of these countries and more.
Although 3G is relatively an infant, the technology is growing fast, with more and more wireless technology companies developing devices with 3G capabilities, such as Nokia, Siemens and Sony Ericsson. See the 3G phones section for an overview of the latest 3G handsets on the market.
On the horizon is 4G, a technology which will truly integrate the internet, and mobile telecommunications.
3G History
As you may guess, being called 3G, or third generation, there is, inevitably, a first and second generation.
1G refers to the original analogue mobile phones, which resembled a brick. They were large, and very heavy, due to the weight of the battery, they were also very expensive. However, they paved the way for something that was soon to become a revolution in the technological world, phones would soon start to be smaller, lighter, cheaper, and better. Operating time increased while battery weight dropped, this was due to advancements in battery technology, as well as circuit design which allowed for much lower power consumption.
2G saw the birth of the digital mobile phone, and a standard which is the greatest success story in the history of the mobile phone to date. The Global System for Mobile Communications (GSM) is a standard that unified Europe’s mobile phone technologies, it allows one phone to be used throughout Western Europe. Using TDMA (Time division multiple access – see the How does 3G work section for more info), the GSM standard allowed millions of users throughout Europe to travel freely and still be able to use there phone. Although Europe enjoyed a unified standard, in America, three standards still exist, from three different companies. Because of this mobile communications haven’t become nearly as popular in the States, as they have done in Europe.
2G worked well for voice communications, it provided data rates of up to 9.6Kbps, good enough for voice, but no where near enough for bandwidth demanding modern day media, such as Video and file transfers. Something which the world was screaming out for, and to provide this, 3G was developed.
Due to the nature of 3G, and its incredible complexity and expensive, the move from 2G to 3G wasn’t going to happen over night, so the 2.5G standard was developed.
The 2.5G standard had a major technically different feature compared to its predecessor, it used Packet Switching technology (see the how does 3G work section for more info) to transmit data. The General Packet Radio Service (GPRS) replaced GSM as the 2.5G standard. GPRS actually overlays a packet switched technology onto the original GSM circuit switched network.
Data rates of 2.5G can reach 50kbps, some may think this is a waste of time, and service provides should have gone straight to the goal and implemented 3G, however, the 2.5G standard is a much needed step, as it gives service providers experience of running packet switched networks, and charging on a data bases, rather than a time basis.
Other than GPRS, another standard called EDGE is another upgrade option from GSM, and is three times faster with a maximum transfer rate of 150Kbps as opposed to GPRS’s 50Kbps. EDGE also can be an upgrade from TDMA networks, so some American operators may go this route – see the How 3G works section for an in depth explanation of this.
Currently there is one 3G enabled network in the UK, known simply as '3'. It is expected that other UK operators will make begin to make the switch in the near future.
How does 3G work?
3G is a packet switched technology, much like the internet. There are some basic principles of Radio Transmission Technologies (RTT’s) you need to understand before you can understand how 3G works, these are:
Simplex and Duplex, TDD and FDD, Symmetric and Asymmetric transmission, and 3G geographical cells.
I will explain each of the following, and then move onto the methods underlying the technology of the 3G network.
Simplex and Duplex
In a simplex transmission, information can only flow one way at one time, this is because there is only one frequency being used to communicate on. The easiest way of explaining this is to use walkie-talkies as an example. With a set of walkie-talkies, only one person can talk to the other at any given time, for the other person to transmit, they must wait until the other person has stopped.
In a duplex transmission, two data transmissions can be sent at any one time, this is how mobile phones work, it allows both people to speak at the same time, without any delay. If more than two data transmissions can happen at any one time, this is called multiplex.
So, you may be wondering how two or more transmissions can happen at the same time, on the same frequency?
TDD and FDD
Up until the recent developments of mobile phones, FDD (frequency division duplex) was used, this is where several frequencies are used, one for the upstream (signals going from the phone to the base station), and one for the downstream (the opposite, from the base station to the phone). A “guard band” is also needed, which sits in between the frequencies to separate them and provide isolation.
Although FDD works, it is very wasteful, as it uses several frequencies in total, and not to there full potential. This is why TDD was developed.
TDD means Time Division Duplex, and as the name suggests, this uses time, rather than frequency to do the duplexing, hence saving valuable frequencies. It works by switching the signals very rapidly. First the upstream transmits, then the downstream transmits and this continues to cycle, this happens so quick, it seems like the upstream and downstream are permanently connected. This gives the same end product as FDD, but uses much less frequencies. As with FDD, this also requires some sort of guard, but as we are duplexing in the time domain, it uses a guard time, rather than a guard frequency.
Symmetric and Asymmetric Transmission
A symmetric transmission is where the upstream, and downstream are the same speed, or data rate. Things such as voice on mobile phones use symmetric transmission, as the data rate needed to transmits your voice is the same as receiving another persons.
For things like video broadcasts, internet surfing etc, a lot more downstream bandwidth is required, as you will mostly be receiving data. Typically the only things being sent upstream in that case is requests (for instance, you clicking on a link in your wap/internet browser), or packet acknowledgments (discussed more later). A typical example of an Asymmetric connection is ADSL broadband, the A, which coincidently enough stands for Asymmetric, usually has 256Kbps of upstream, and 512+kbps on the downstream bandwidth.
3G geographical cells
The 3G network has a hierarchal network of different sized cells. These are:
A Macro cell this is the biggest of the three areas, coverage is normally around the size of a city.
A Micro cell this cell has the coverage, of about the size of city centre.
A Pico cell The smallest coverage, perhaps a office complex, hotel, or airport. A Pico cell is often known as a “hot spot”.
The reason for the above division of regions is simple, shorter range communications are faster, and allow for a higher amount of users. This is why a Pico cell, or hot spot., is located to a small geographical area which is a very busy area, such as an airport.
TDD isn’t good in transmitting long distances, this is because of the delay. If you think, TDD uses time to duplex signals onto the same frequency. The further the mobile phone is away from the base station, the longer it takes a signal to travel, because it takes longer, there is more of a delay, so because of this the switching between time slots cannot happen so quick, so the useable bandwidth decreases.
The Future of 3G
There’s no doubt what is wanted for the future of 3G, and that’s convergence. Leading 3G figureheads around the world want a convergence of the phone networks, to unite the world as a whole with a wireless technology that is compatible across the globe.
There’s a good chance this will happen, as it has already begun to. And it possible won’t be far off that we see perhaps a sub-standard introduced that converges the different 3G standards into one global roaming capable standard.
On the horizon is 4G, which promises to bring true convergence of internet’s IP protocol technology to mobiles. By the time 4G is distributed, IPv6 will be well on its way, and the possibilities will be endless. Ever thought about texting your boiler to tell it to get the heating on just as you leave work?
Tidak ada komentar:
Posting Komentar