Evolution of Mobile Communications: from 1G to 4G

1. Introduction

From the early analog mobile generation (1G) to the last implemented third generation (3G) the

paradigm has changed. The new mobile generations do not pretend to improve the voice communication

experience but try to give the user access to a new global communication reality. The aim is to reach

communication ubiquity (every time, everywhere) and to provide users with a new set of services.

The growth of the number of mobile subscribers over the last years led to a saturation of voice-oriented

wireless telephony. From a number of 214 million subscribers in 1997 to 1.162 millions in 2002 [1], it is

predicted that by 2010 there will be 1700 million subscribers worldwide [2] (see Figure 1). It is now time to

explore new demands and to find new ways to extend the mobile concept. The first steps have already been

taken by the 2.5G, which gave users access to a data network (e.g. Internet access, MMS - Multimedia

Message Service). However, users and applications demanded more communication power. As a response

to this demand a new generation with new standards has been developed - 3G. In spite of the big initial

euphoria that evolved this technology, only one 3G network exists in commercial use today. This network

has been deployed in Japan in 2001 using international standard IMT-2000, with great success.

2. The first mobile generations (1G to 2.5G)

The first operational cellular communication system was deployed in the Norway in 1981 and was

followed by similar systems in the US and UK. These first generation systems provided voice

transmissions by using frequencies around 900 MHz and analogue modulation.

The second generation (2G) of the wireless mobile network was based on low-band digital data

signaling. The most popular 2G wireless technology is known as Global Systems for Mobile

Communications (GSM). The first GSM systems used a 25MHz frequency spectrum in the 900MHz band.

FDMA (Frequency Division Multiple Access), which is a standard that lets multiple users access a group of

radio frequency bands and eliminates interference of message traffic, is used to split the available 25MHz

of bandwidth into 124 carrier frequencies of 200 kHz each. Each frequency is then divided using a TDMA

(Time Division Multiple Access) scheme into eight timeslots and allows eight simultaneous calls on the

same frequency. This protocol allows large numbers of users to access one radio frequency by allocating

time slots to multiple voice or data calls. TDMA breaks down data transmission, such as a phone

conversation, into fragments and transmits each fragment in a short burst, assigning each fragment a time

slot. With a cell phone, the caller does not detect this fragmentation.

Today, GSM systems operate in the 900MHz and 1.8 GHz bands throughout the world with the

exception of the Americas where they operate in the 1.9 GHz band. Within Europe, the GSM technology

made possible the seamless roaming across all countries.

While GSM technology was developed in Europe, CDMA (Code Division Multiple Access) technology

was developed in North America. CDMA uses spread spectrum technology to break up speech into small,

3. Third mobile generation networks (3G)

All 2G wireless systems are voice-centric. GSM includes short message service (SMS), enabling text

messages of up to 160 characters to be sent, received and viewed on the handset. Most 2G systems also

support some data over their voice paths, but at painfully slow speeds usually 9.6 Kb/s or 14.4 Kb/s. So in

the world of 2G, voice remains king while data is already dominant in wireline communications. And, fixed

or wireless, all are affected by the rapid growth of the Internet.

Planning for 3G started in the 1980s. Initial plans focused on multimedia applications such as

videoconferencing for mobile phones. When it became clear that the real killer application was the Internet,

3G thinking had to evolve. As personal wireless handsets become more common than fixed telephones, it is

clear that personal wireless Internet access will follow and users will want broadband Internet access

wherever they go.

Today's 3G specifications call for 144 Kb/s while the user is on the move in an automobile or train, 384

Kb/s for pedestrians, and ups to 2 Mb/s for stationary users. That is a big step up from 2G bandwidth using

8 to 13 Kb/s per channel to transport speech signals.

The second key issue for 3G wireless is that users will want to roam worldwide and stay connected.

Today, GSM leads in global roaming. Because of the pervasiveness of GSM, users can get comprehensive

coverage in Europe, parts of Asia and some U.S. coverage. A key goal of 3G is to make this roaming

capacity universal.

A third issue for 3G systems is capacity. As wireless usage continues to expand, existing systems are

reaching limits. Cells can be made smaller, permitting frequency reuse, but only to a point. The next step is

new technology and new bandwidth.

International Mobile Telecommunications-2000 (IMT-2000) is the official International

Telecommunication Union name for 3G and is an initiative intended to provide wireless access to global

telecommunication infrastructure through both satellite and terrestrial systems, serving fixed and mobile

phone users via both public and private telephone networks. GSM proponents put forward the universal

mobile telecommunications system (UMTS), an evolution of GSM, as the road to IMT-2000. Alternate

schemes have come from the U.S., Japan and Korea. Each scheme typically involves multiple radio

transmission techniques in order to handle evolution from 2G. Agreeing on frequency bands for IMT-2000

has been more difficult and the consensus included five different radio standards and three widely different

frequency bands. They are now all part of IMT-2000. To roam anywhere in this "unified" 3G system, users

will likely need a quintuple-mode phone able to operate in an 800/900 MHz band, a 1.7 to 1.9 GHz band

and a 2.5 to 2.69 GHz band.

Third-generation wireless also requires new infrastructure. There are two mobility infrastructures in

wide use. GSM has the mobile access protocol, GSM-MAP. The North American infrastructure uses the

IS-41 mobility protocol. These protocol sets define the messages passed between home location registers

and visitor location registers when locating a subscriber and the messages needed to deal with hand-offs as

a subscriber moves from cell to cell. 3G proponents have agreed on an evolution path so that existing

operators, running on either a GSM-MAP or an IS-41 infrastructure, can interoperate. But the rest of the

landline infrastructure to support IMT-2000 will be in flux in the near future. The IMT-2000 family is

illustrated in figure 3.

4. Future mobile generation networks (4G)

The objective of the 3G was to develop a new protocol and new technologies to further enhance the

mobile experience. In contrast, the new 4G framework to be established will try to accomplish new levels

of user experience and multi-service capacity by also integrating all the mobile technologies that exist (e.g.

GSM - Global System for Mobile Communications, GPRS - General Packet Radio Service, IMT-2000 -

International Mobile Communications, Wi-Fi - Wireless Fidelity, Bluetooth).

In spite of different approaches, each resulting from different visions of the future platform currently

under investigation, the main objectives of 4G networks can be stated in the following properties:

4.1. Migrating to 4G

The fact that 4G mobile networks intend to integrate almost every wireless standard already in use,

enabling its simultaneous use and interconnection poses many questions not yet answered. The research

areas that present key challenges to migrate current systems to 4G are many but can be summarized in the

following: Mobile Station, System and Service. [7]

To be able to use 4G mobile networks a new type of mobile terminals must be conceived. The terminals

to be adopted must adapt seamless to multiple wireless networks, each with different protocols and

technologies. Auto reconfiguration will also be needed so that terminals can adapt to the different services

available. This adaptation may imply that it must download automatically configuration software from

networks in range. Moreover terminals must be able to choose from all the available wireless networks the

one to use with a specific service. To do this it must be aware of specifications of all the networks in terms

of bandwidth, QoS supported, costs and respect to user preferences.

Terminal mobility will be a key factor to the success of 4G networks. Terminals must be able to provide

wireless services anytime, everywhere. This implies that roaming between different networks must be

automatic and transparent to the user. There are two major issues in terminal mobility, location

management and handoff management [7]. Location management deals with tracking user mobility, and

handling information about original, current and (if possible) future cells. Moreover it must deal with

authentication issues and QoS assurances. Handoff management primary objective is to maintain the

communications while the terminal crosses wireless network boundaries. In addition, 4G networks, in

opposition to the other mobile generations, must deal with vertical and horizontal handoffs, i.e., a 4G

mobile client may move between different types of wireless networks (e.g. GSM and Wi-Fi) and between

cells of the same wireless network (e.g. moving between adjacent GSM cells). Furthermore, many of the

services available in this new mobile generation like videoconference have restrict time constraints and

QoS needs that must not be perceptible affected by handoffs. To avoid these problems new algorithms must

be researched and a prevision of user mobility will be necessary, so as to avoid broadcasting at the same

time to all adjacent antennas what would waste unnecessary resources. Another major problem relates to

security, since 4G pretends to join many different types of mobile technologies. As each standard has its

own security scheme, the key to 4G systems is to be highly flexible.

Services also pose many questions as 4G users may have different operators to different services and,

even if they have the same operator, they can access data using different network technologies. Actual

billing using flat rates, time or cost per bit fares, may not be suitable to the new range of services. At the

same time it is necessary that the bill is well understood by operator and client. A broker system would be

advisable to facilitate the interaction between the user and the different service providers.

Another challenge is to know, at each time, where the user is and how he can be contacted. This is very

important to mobility management. A user must be able to be reached wherever he is, no matter the kind of

terminal that is being used. This can be achieved in various ways one of the most popular being the use of a

mobile-agent infrastructure. In this framework, each user has a unique identifier served by personal mobile

agents that make the link from users to Internet.