4G LTE-Advanced：移动宽带的未来技术

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4G LTE Advanced for Mobile Broadband 是一项旨在提供高速、可靠且高效移动通信服务的技术，它是第四代（4G）移动通信系统的关键组成部分，特别是针对移动宽带应用而设计的。4G LTE (Long-Term Evolution) 或者称为 LTE-Advanced 是在原有3G技术基础上的显著提升，它采用了OFDM（正交频分多址）调制方式，以及MIMO（多输入多输出）技术，这使得数据传输速度大大提高，能够支持更高的网络容量和更低的延迟。在4G LTE网络中，无线接入点（Base Station）与移动设备（Smartphones, tablets, IoT设备等）之间的连接更为强大，能够实现峰值理论下载速度超过100Mbps，上传速度也大幅提升，这在当时对于视频流、高清电话会议、大数据传输和在线娱乐等实时应用来说具有里程碑意义。此外，4G LTE还引入了更先进的调度和流量管理机制，提高了网络效率，使得用户能够同时处理多个数据流，满足多任务并行的需求。 4G LTE-Advanced进一步增强了这些特性，通过引入更高级的多点协作、动态信道分配、载波聚合等技术，将最大下行速率推高至数百Mbps甚至1Gbps以上，从而为用户提供极致的上网体验。这种技术的进步对物联网（IoT）设备的连接也产生了重大影响，因为它们需要低功耗但又能保持快速数据交换的能力。为了确保这些先进技术的实施，4G LTE-Advanced的标准化工作由3GPP（Third Generation Partnership Project）负责，这是一个由全球电信运营商、设备制造商和研究机构组成的国际组织。他们的目标是制定统一的技术规范，确保所有设备都能无缝接入4G网络，并进行跨厂商的互操作性测试。 4G LTE-Advanced的发展不仅推动了移动互联网的普及，而且为5G的诞生奠定了基础。尽管随着5G的到来，4G LTE的地位逐渐被取代，但4G LTE Advanced在移动宽带领域的历史贡献和其在提高移动数据服务质量和用户体验方面的突破，使其成为现代通信史上的一个重要里程碑。同时，它也是衡量一个国家或地区移动通信技术水平和网络覆盖能力的重要指标之一。

31.2 Evolution of Mobile Systems Before LTE

for service delivery, charging etc., gave a very clear indication of the potential for applications over

packet data in mobile systems, in spite of the fairly low data rates supported at the time.

With the advent of 3G and the higher-bandwidth radio interface of UTRA (Universal Terrestrial

Radio Access) came possibilities for a range of new services that were only hinted at with 2G and

2.5G. The 3G radio access development is today handled in 3GPP. However, the initial steps for 3G

were taken in the early 1990s, long before 3GPP was formed.

What also set the stage for 3G was the internationalization of cellular standards. GSM was a pan-

European project, but it quickly attracted worldwide interest when the GSM standard was deployed in

a number of countries outside Europe. A global standard gains in economy of scale, since the market

for products becomes larger. This has driven a much tighter international cooperation around 3G cel-

lular technologies than for the earlier generations.

1.2.1 The First 3G Standardization

Work on a third-generation mobile communication started in ITU (International Telecommunication

Union) in the 1980s, ﬁrst under the label Future Public Land Mobile Telecommunications Systems

(FPLMTS), later changed to IMT-2000 [1]. The World Administrative Radio Congress WARC-92

identiﬁed 230 MHz of spectrum for IMT-2000 on a worldwide basis. Of these 230 MHz, 2  60 MHz

was identiﬁed as paired spectrum for FDD (Frequency-Division Duplex) and 35 MHz as unpaired

spectrum for TDD (Time-Division Duplex), both for terrestrial use. Some spectrum was also set aside

for satellite services. With that, the stage was set to specify IMT-2000.

In parallel with the widespread deployment and evolution of 2G mobile-communication systems

during the 1990s, substantial efforts were put into 3G research activities worldwide. In Europe, a

number of partially EU-funded projects resulted in a multiple access concept that included a Wideband

CDMA component that was input to ETSI in 1996. In Japan, the Association of Radio Industries and

Businesses (ARIB) was at the same time deﬁning a 3G wireless communication technology based

on Wideband CDMA and also in the USA a Wideband CDMA concept called WIMS was developed

within the T1.P1

committee. South Korea also started work on Wideband CDMA at this time.

When the standardization activities for 3G started in ETSI in 1996, there were WCDMA concepts

proposed both from a European research project (FRAMES) and from the ARIB standardization in

Japan. The Wideband CDMA proposals from Europe and Japan were merged and came out as part

of the winning concept in early 1998 in the European work on Universal Mobile Telecommunication

Services (UMTS), which was the European name for 3G. Standardization of WCDMA continued in

parallel in several standards groups until the end of 1998, when the Third Generation Partnership

Project (3GPP) was formed by standards-developing organizations from all regions of the world.

This solved the problem of trying to maintain parallel development of aligned speciﬁcations in mul-

tiple regions. The present organizational partners of 3GPP are ARIB (Japan), CCSA (China), ETSI

(Europe), ATIS (USA), TTA (South Korea), and TTC (Japan).

At this time, when the standardization bodies were ready to put the details into the 3GPP speci-

ﬁcations, work on 3G mobile systems had already been ongoing for some time in the international

arena within the ITU-R. That work was inﬂuenced by and also provided a broader international

framework for the standardization work in 3GPP.

The T1.P1 committee was part of T1, which presently has joined the ATIS standardization organization.

4 CHAPTER 1 Background of LTE

1.3 ITU ACTIVITIES

1.3.1 IMT-2000 and IMT-Advanced

ITU-R Working Party 5D (WP5D) has the responsibility for IMT systems, which is the umbrella

name for 3G (IMT-2000) and 4G (IMT-Advanced). WP5D does not write technical speciﬁcations for

IMT, but has kept the role of deﬁning IMT in cooperation with the regional standardization bodies

and to maintain a set of recommendations for IMT-2000 and IMT-Advanced.

The main IMT-2000 recommendation is ITU-R M.1457 [2], which identiﬁes the IMT-2000 radio

interface speciﬁcations (RSPC). The recommendation contains a “family” of radio interfaces, all

included on an equal basis. The family of six terrestrial radio interfaces is illustrated in Figure 1.1,

which also shows the Standards Developing Organizations (SDO) or Partnership Projects that pro-

duce the speciﬁcations. In addition, there are several IMT-2000 satellite radio interfaces deﬁned, not

illustrated in Figure 1.1.

For each radio interface, M.1457 contains an overview of the radio interface, followed by a list

of references to the detailed speciﬁcations. The actual speciﬁcations are maintained by the individual

SDOs and M.1457 provides references to the speciﬁcations maintained by each SDO.

With the continuing development of the IMT-2000 radio interfaces, including the evolution of

UTRA to Evolved UTRA, the ITU recommendations also need to be updated. ITU-R WP5D continu-

ously revises recommendation M.1457 and at the time of writing it is in its ninth version. Input to the

updates is provided by the SDOs and Partnership Projects writing the standards. In the latest revision

of ITU-R M.1457, LTE (or E-UTRA) is included in the family through the 3GPP family members for

UTRA FDD and TDD, as shown in the ﬁgure.

ITU-R Family of

IMT-2000 terrestrial Radio Interfaces

(ITU-R M.1457)

(UTRA TDD and

E-UTRA TDD)

IMT-2000

CDMA TDD

3GPP

IMT-2000

CDMA Multi-Carrier

(CDMA2000 and

UMB)

3GPP2

IMT-2000

CDMA Direct Spread

(UTRA FDD and

E-UTRA FDD)

3GPP

IMT-2000

OFDMA TDD WMAN

(WiMAX)

IEEE

IMT-2000

FDMA/TDMA

(DECT)

ETSI

IMT-2000

TDMA Single-Carrier

(UWC 136)

ATIS/TIA

FIGURE 1.1

The deﬁnition of IMT-2000 in ITU-R.

51.3 ITU Activities

In addition to maintaining the IMT-2000 speciﬁcations, a main activity in ITU-R WP5D is the

work on systems beyond IMT-2000, now called IMT-Advanced. The term IMT-Advanced is used for

systems that include new radio interfaces supporting the new capabilities of systems beyond IMT-

2000, as demonstrated with the “van diagram” in Figure 1.2. The step into IMT-Advanced capabili-

ties is seen by ITU-R as the step into 4G, the next generation of mobile technologies after 3G.

The process for deﬁning IMT-Advanced was set by ITU-R WP5D [3] and was quite similar to the

process used in developing the IMT-2000 recommendations. ITU-R ﬁrst concluded studies for IMT-

Advanced of services and technologies, market forecasts, principles for standardization, estimation of

spectrum needs, and identiﬁcation of candidate frequency bands [4]. Evaluation criteria were agreed,

where proposed technologies were to be evaluated according to a set of minimum technical require-

ments. All ITU members and other organizations were then invited to the process through a circular

letter [5] in March 2008. After submission of six candidate technologies in 2009, an evaluation was

performed in cooperation with external bodies such as standards-developing organizations, industry

forums, and national groups.

An evolution of LTE as developed by 3GPP was submitted as one candidate to the ITU-R evalu-

ation. While actually being a new release (release 10) of the LTE system and thus an integral part

of the continuing LTE development, the candidate was named LTE-Advanced for the purpose of

ITU submission. 3GPP also set up its own set of technical requirements for LTE-Advanced, with the

ITU-R requirements as a basis. The speciﬁcs of LTE-Advanced will be described in more detail as

part of the description of LTE later in this book. The performance evaluation of LTE-Advanced for

the ITU-R submission is described further in Chapter 18.

The target of the process was always harmonization of the candidates through consensus build-

ing. ITU-R determined in October 2010 that two technologies will be included in the ﬁrst release of

IMT-Advanced, those two being LTE release 10 (“LTE-Advanced”) and WirelessMAN-Advanced [6]

based on the IEEE 802.16m speciﬁcation. The two can be viewed as the “family” of IMT-Advanced

1 Mbit/s 1000 Mbit/s100 Mbit/s10 Mbit/s

Peak data rate

Low

High

3G evolution

Enhanced

IMT-2000

New mobile

access

New nomadic/local

area wireless access

Mobility

IMT-Advanced =

New capabilities

of systems beyond

IMT-2000

FIGURE 1.2

Illustration of capabilities of IMT-2000 and IMT-Advanced, based on

the framework described in ITU -R Recommendation M.1645 [4].

6 CHAPTER 1 Background of LTE

technologies as shown in Figure 1.3. The main IMT-Advanced recommendation, identifying the IMT-

Advanced radio interface speciﬁcations, is presently named ITU-R.[IMT.RSPEC] [7] and will be

completed during 2011. As for the corresponding IMT-2000 speciﬁcation, it will contain an overview

of each radio interface, followed by a list of references to the detailed speciﬁcations.

1.3.2 Spectrum for IMT Systems

Another major activity within ITU-R concerning IMT-Advanced has been to identify globally avail-

able spectrum, suitable for IMT systems. The spectrum work has involved sharing studies between

IMT and other technologies in those bands. Adequate spectrum availability and globally harmonized

spectrum are identiﬁed as essential for IMT-Advanced.

Spectrum for 3G was ﬁrst identiﬁed at the World Administrative Radio Congress WARC-92,

where 230 MHz was identiﬁed as intended for use by national administrations that want to implement

IMT-2000. The so-called IMT-2000 “core band” at 2 GHz is in this frequency range and was the ﬁrst

band where 3G systems were deployed.

Additional spectrum was identiﬁed for IMT-2000 at later World Radio communication confer-

ences. WRC-2000 identiﬁed the existing 2G bands at 800/900 MHz and 1800/1900 MHz plus an

additional 190 MHz of spectrum at 2.6 GHz, all for IMT-2000. As additional spectrum for IMT-2000,

WRC’07 identiﬁed a band at 450 MHz, the so-called “digital dividend” at 698–806 MHz, plus an

additional 300 MHz of spectrum at higher frequencies. The applicability of these new bands varies on

a regional and national basis.

The worldwide frequency arrangements for IMT-2000 are outlined in ITU-R recommendation

M.1036 [8], which is presently being updated with the arrangements for the most recent frequency

bands added at WRC’07. The recommendation outlines the regional variations in how the bands are

implemented and also identiﬁes which parts of the spectrum are paired and which are unpaired. For

the paired spectrum, the bands for uplink (mobile transmit) and downlink (base-station transmit) are

identiﬁed for Frequency-Division Duplex (FDD) operation. The unpaired bands can, for example, be

used for Time-Division Duplex (TDD) operation. Note that the band that is most globally deployed

for 3G is still 2 GHz.

IMT-Advanced terrestrial Radio Interfaces

(ITU-R M.[IMT.RSPEC])

WirelessMAN-Advanced

(WiMAX/

IEEE 802.16m)

IEEE

LTE-Advanced

(E-UTRA/

Release 10)

3GPP

FIGURE 1.3

Radio interface technologies for IMT-Advanced.

71.4 Drivers for LTE

1.4 DRIVERS FOR LTE

The evolution of 3G systems into 4G is driven by the creation and development of new services for

mobile devices, and is enabled by advancement of the technology available for mobile systems. There

has also been an evolution of the environment in which mobile systems are deployed and operated, in

terms of competition between mobile operators, challenges from other mobile technologies, and new

regulation of spectrum use and market aspects of mobile systems.

The rapid evolution of the technology used in telecommunication systems, consumer electron-

ics, and speciﬁcally mobile devices has been remarkable in the last 20 years. Moore’s law illustrates

this and indicates a continuing evolution of processor performance and increased memory size, often

combined with reduced size, power consumption, and cost for devices. High-resolution color displays

and megapixel camera sensors are also coming into all types of mobile devices. Combined with a

high-speed internet backbone often based on optical ﬁber networks, we see that a range of technology

enablers are in place to go hand-in-hand with advancement in mobile communications technology

such as LTE.

The rapid increase in use of the internet to provide all kinds of services since the 1990s started

at the same time as 2G and 3G mobile systems came into widespread use. The natural next step was

that those internet-based services also moved to the mobile devices, creating what is today know as

mobile broadband. Being able to support the same Internet Protocol (IP)-based services in a mobile

device that people use at home with a ﬁxed broadband connection is a major challenge and a prime

driver for the evolution of LTE. A few services were already supported by the evolved 2.5G systems,

but it is not until the systems are designed primarily for IP-based services that the real mobile IP rev-

olution can take off. An interesting aspect of the migration of broadband services to mobile devices is

that a mobile “ﬂavor” is also added. The mobile position and the mobility and roaming capabilities do

in fact create a whole new range of services tailored to the mobile environment.

Fixed telephony (POTS) and earlier generations of mobile technology were built for circuit

switched services, primarily voice. The ﬁrst data services over GSM were circuit switched, with

packet-based GPRS coming in as a later addition. This also inﬂuenced the ﬁrst development of 3G,

which was based on circuit switched data, with packet-switched services as an add-on. It was not

until the 3G evolution into HSPA and later LTE/LTE-Advanced that packet-switched services and IP

were made the primary design target. The old circuit-switched services remain, but will on LTE be

provided over IP, with Voice-over IP (VoIP) as an example.

IP is in itself service agnostic and thereby enables a range of services with different requirements.

The main service-related design parameters for a radio interface supporting a variety of services are:

Data rate. Many services with lower data rates such as voice services are important and still

occupy a large part of a mobile network’s overall capacity, but it is the higher data rate services

that drive the design of the radio interface. The ever increasing demand for higher data rates for

web browsing, streaming and ﬁle transfer pushes the peak data rates for mobile systems from

kbit/s for 2G, to Mbit/s for 3G and getting close to Gbit/s for 4G.

Delay. Interactive services such as real-time gaming, but also web browsing and interactive ﬁle

transfer, have requirements for very low delay, making it a primary design target. There are, how-

ever, many applications such as e-mail and television where the delay requirements are not as

strict. The delay for a packet sent from a server to a client and back is called latency.

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