attachment_learning service express(10)--lte air interface

8/11/2019 Attachment_Learning Service Express(10)--LTE Air Interface

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1 The Air Interface


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1.1 Evolution of Cellular Networks

Cellular mobile networks have been evolving for many years. The initialnetworks are referred to as First Generation!. These have now been replacedwith Second Generation!and Third Generation!networks. It is only now

that 4G orFourth Generation

!systems are being deployed.

Figure 1-1Evolution of Cellular Networks

1.1.1 First Generation Mobile Systems

The 1G (First Generation) mobile systems were not digital, i.e. they utilizedanalogue modulation techniques. The main systems included:

l AMPS (Advanced Mobile Telephone System) - This first appeared in1976 in the United States. It was mainly implemented in the Americas,Russia and Asia. Various issues including weak security features madethe system prone to hacking and handset cloning.

l TACS (Total Access Communications System) - This was the European

version of AMPS with slight modifications, as well as operating indifferent frequency bands. It was mainly used in the United Kingdom, aswell as parts of Asia.

l

ETACS (Extended Total Access Communication System) - This providedan improved version of TACS. It enabled a greater number of channelsand therefore facilitated more users.

These analogue systems were all proprietary based FM (Frequency

Modulation) systems and therefore they all lacked security, any meaningfuldata service and international roaming capability.

1.1.2 Second Generation Mobile Systems

2G (Second Generation) systems utilize digital multiple access technology,such as TDMA (Time Division Multiple Access) and CDMA (Code Division

Multiple Access). Figure 1-2 illustrates some of the different 2G mobilesystems, these include:

l GSM (Global System for Mobile communications) - this is the mostsuccessful of all 2G technologies. It was initially developed by ETSI(European Telecommunications Standards Institute) for Europe and

designed to operate in the 900MHz and 1800MHz frequency bands. Itnow has world-wide support and is available for deployment on manyother frequency bands, such as 850MHz and 1900MHz. A mobile

described as tri-band or quad-band indicates support for multiplefrequency bands on the same device. GSM is TDMA, such that itemploys 8 timeslots on a 200kHz radio carrier.

l cdmaOne - this is a CDMA (Code Division Multiple Access) system

based on IS-95 (Interim Standard 95). It uses a spread spectrum


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technique and utilizes a mixture of codes and timing to identify cells andchannels. The system bandwidth is 1.25MHz.

l D-AMPS (Digital - Advanced Mobile Phone System) - this is based on

IS-136 (Interim Standard 136) and is effectively an enhancement toAMPS which provides a TDMA access technique. It has been primarilyused on the North American continent, as well as in New Zealand andparts of Asia-Pacific.

Figure 1-2Second Generation Mobile Systems

2G (Second

Generation)

GSM

cdmaOne

(IS-95)

D-AMPS

(IS-136)

Other

In addition to being digital, as well as improving capacity and security, these2G digital systems also offer enhanced services such as SMS (Short Message

Service) and circuit switched data.

2.5G Systems

Most 2G systems are being evolved. For example, GSM was extended with

GPRS (General Packet Radio System) to support efficient packet data services,

as well as increasing the data rates.

As this feature does not meet 3G requirements, GRPS is often referred to as2.5G. A comparison between 2G and 2.5G systems is illustrated in Table 1-1.

2.75G Systems

GSM/GPRS systems also added EDGE (Enhanced Data Rates for Global

Evolution). This nearly quadruples the throughput of GPRS. The theoretical

data rate of 473.6kbit/s enables service providers to efficiently offermultimedia services. Like GPRS, since it does not comply with all thefeatures of a 3G system, EDGE is usually categorized as 2.75G.


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organization formed to promote conformity and interoperability betweenvendors.

Figure 1-3Third Generation Mobile Systems

1.1.4 Fourth Generation Mobile Systems

4G (Fourth Generation) cellular wireless systems need to meet the

requirements set by the ITU (International Telecommunication Union) as partof IMT Advanced (International Mobile Telecommunications Advanced).These features are illustrated in Table 1-2 and enable IMT Advanced to

address evolving user needs.

Table 1-2IMT Advanced Features

Key IMT Advanced Features

A high degree of commonality of functionality worldwide while retaining

the flexibility to support a wide range of services and applications in a costefficient manner.

Compatibility of services within IMT and with fixed networks.

Capability of interworking with other radio access systems.

High quality mobile services.

User equipment suitable for worldwide use.User-friendly applications, services and equipment.

Worldwide roaming capability.

Enhanced peak data rates to support advanced services and applications(100Mbit/s for high and 1Gbit/s for low mobility were identified as targets).

The main three 4G systems include:

l LTE Advanced - LTE (Long Term Evolution) is part of 3GPP, however it

does not meet all IMT Advanced features, as such it is sometimes

referred to as 3.99G. In contrast, LTE Advanced is part of a later 3GPP

Release and has been designed specifically to meet 4G requirements.


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l WiMAX 802.16m - The IEEE and the WiMAX Forum have identified802.16m as their offering for a 4G system.

l UMB (Ultra Mobile Broadband) - This is identified as EV-DO Rev C. It

is part of 3GPP2 however most vendors and service providers havedecided to promote LTE instead.

Figure 1-4Forth Generation Mobile System

LTE

Advanced

UMB

(EV-DO Rev C)

WiMAX

802.16m

4G (Fourth

Generation)

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