4G技术速成指南：LTE标准详解与实战应用

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《4G移动宽带通信技术详解》是一本专为快速掌握Long-Term Evolution (LTE) 技术读者编写的实用指南。作者是一位深度参与LTE标准制定的专家，书中深入浅出地阐述了LTE的新技术和它们对系统性能提升的关键作用。本书的核心内容涵盖了广泛的4G技术主题： 1. **网络架构与协议**：介绍LTE网络的基本组成，包括核心网、无线接入网以及它们之间的接口，帮助读者理解整个通信系统的运行机制。 2. **OFDM下行链路访问**：阐述了正交频分复用（OFDM）技术在4G中的重要性，这是一种高效的数据传输方式，提高了频谱利用率和抗多径衰落的能力。 3. **低功率发射（LPAT）SC-FDMA上行链路访问**：详细解释了单载波频率分复用（SC-FDMA）在用户设备（UE）上传输数据时如何降低功率消耗，同时保持信号质量。 4. **传输多样性与MIMO空间多工**：讲解了如何通过传输多样性技术提高信号的可靠性，以及MIMO（多输入多输出）在提高数据速率和信道容量方面的应用。 5. **频道结构与带宽**：阐述了LTE支持的不同带宽配置，如1.4MHz、3MHz、5MHz等，以及如何根据应用场景选择合适的带宽。 6. **小区搜索、参考信号与随机接入**：介绍了UE如何找到并连接到正确的小区，以及随机接入过程在初始连接时的作用。 7. **涡轮编码与无竞争交织器**：讨论了纠错编码在4G中的重要性，以及如何通过无竞争交织器优化数据传输效率。 8. **调度、链路自适应、混合自动重传请求（HARQ）和功率控制**：详细解释了这些关键技术在数据传输中的动态调整策略，确保最优性能。 9. **上行和下行物理控制信令**：讲解了控制信息的传输机制，如控制信道的结构和功能，以保证通信的稳定性和效率。 10. **干扰抑制技术**：探讨了如何有效管理小区间干扰，以提高整体网络的容量和质量。 11. **单一频率网络（SFN）广播**：介绍一种通过多个基站同步传输同一频率信号的技术，以增强覆盖范围和频谱效率。 12. **MIMO空间信道模型**：深入解析多天线技术如何模拟实际无线环境，以优化信号处理和资源分配。 13. **评估方法与系统性能**：提供了衡量和优化LTE系统性能的实用工具和指标，包括吞吐量、延迟、误码率等关键参数。通过阅读这本书，读者不仅能够获得扎实的4G技术理论知识，还能深入了解标准制定背后的决策过程和实战应用策略，对于从事4G网络设计、优化或维护的专业人士具有很高的实用价值。

Preface

The Global system for mobile communications (GSM) is the dominant wireless cellular

standard with over 3.5 billion subscribers worldwide covering more than 85% of the global

mobile market. Furthermore, the number of worldwide subscribers using high-speed packet

access (HSPA) networks topped 70 million in 2008. HSPAis a 3G evolution of GSM supporting

high-speed data transmissions using WCDMAtechnology. Global uptake of HSPA technology

among consumers and businesses is accelerating, indicating continued traffic growth for high-

speed mobile networks worldwide. In order to meet the continued traffic growth demands,

an extensive effort has been underway in the 3G Partnership Project (3GPP) to develop a

new standard for the evolution of GSM/HSPA technology towards a packet-optimized system

referred to as Long-Term Evolution (LTE).

The goal of the LTE standard is to create specifications for a new radio-access technology

geared to higher data rates, low latency and greater spectral efficiency. The spectral efficiency

target for the LTE system is three to four times higher than the current HSPA system. These

aggressive spectral efficiency targets require pushing the technology envelope by employing

advanced air-interface techniques such as low-PAPR orthogonal uplink multiple access

based on SC-FDMA (single-carrier frequency division multiple access) MIMO multiple-input

multiple-output multi-antenna technologies, inter-cell interference mitigation techniques, low-

latency channel structure and single-frequency network (SFN) broadcast. The researchers

and engineers working on the standard come up with new innovative technology proposals

and ideas for system performance improvement. Due to the highly aggressive standard

development schedule, these researchers and engineers are generally unable to publish

their proposals in conferences or journals, etc. In the standards development phase, the

proposals go through extensive scrutiny with multiple sources evaluating and simulating

the proposed technologies from system performance improvement and implementation

complexity perspectives. Therefore, only the highest-quality proposals and ideas finally make

into the standard.

The book provides detailed coverage of the air-interface technologies and protocols that

withstood the scrutiny of the highly sophisticated technology evaluation process typically

used in the 3GPP physical layer working group. We describe why certain technology choices

were made in the standard development process and how each of the technology components

selected contributes to the overall system performance improvement. As such, the book serves

as a valuable reference for system designers and researchers not directly involved in the

standard development phase.

I am indebted to many colleagues at Samsung, in particular to Zhouyue (Jerry) Pi,

Jianzhong (Charlie) Zhang, Jiann-An Tsai, Juho Lee, Jin-Kyu Han and Joonyoung Cho. These

colleagues and other valued friends, too numerous to be mentioned, have deeply influenced my

1 Introduction

The cellular wireless communications industry witnessed tremendous growth in the past

decade with over four billion wireless subscribers worldwide. The first generation (1G)

analog cellular systems supported voice communication with limited roaming. The second

generation (2G) digital systems promised higher capacity and better voice quality than

did their analog counterparts. Moreover, roaming became more prevalent thanks to fewer

standards and common spectrum allocations across countries particularly in Europe. The two

widely deployed second-generation (2G) cellular systems are GSM (global system for mobile

communications) and CDMA (code division multiple access). As for the 1G analog systems,

2G systems were primarily designed to support voice communication. In later releases of

these standards, capabilities were introduced to support data transmission. However, the data

rates were generally lower than that supported by dial-up connections. The ITU-R initiative

on IMT-2000 (international mobile telecommunications 2000) paved the way for evolution to

3G. A set of requirements such as a peak data rate of 2 Mb/s and support for vehicular mobility

were published under IMT-2000 initiative. Both the GSM and CDMA camps formed their

own separate 3G partnership projects (3GPP and 3GPP2, respectively) to develop IMT-2000

compliant standards based on the CDMAtechnology. The 3G standard in 3GPP is referred to as

wideband CDMA (WCDMA) because it uses a larger 5 MHz bandwidth relative to 1.25 MHz

bandwidth used in 3GPP2’s cdma2000 system. The 3GPP2 also developed a 5 MHz version

supporting three 1.25 MHz subcarriers referred to as cdma2000-3x. In order to differentiate

from the 5 MHz cdma2000-3x standard, the 1.25 MHz system is referred to as cdma2000-1x

or simply 3G-1x.

The first release of the 3G standards did not fulfill its promise of high-speed data

transmissions as the data rates supported in practice were much lower than that claimed

in the standards. A serious effort was then made to enhance the 3G systems for efficient data

support. The 3GPP2 first introduced the HRPD (high rate packet data) [1] system that used

various advanced techniques optimized for data traffic such as channel sensitive scheduling,

fast link adaptation and hybrid ARQ, etc. The HRPD system required a separate 1.25 MHz

carrier and supported no voice service. This was the reason that HRPD was initially referred

to as cdma2000-1xEVDO (evolution data only) system. The 3GPP followed a similar path

and introduced HSPA (high speed packet access) [2] enhancement to the WCDMA system.

The HSPA standard reused many of the same data-optimized techniques as the HRPD system.

A difference relative to HRPD, however, is that both voice and data can be carried on the same

5 MHz carrier in HSPA. The voice and data traffic are code multiplexed in the downlink. In

parallel to HRPD, 3GPP2 also developed a joint voice data standard that was referred to as

cdma2000-1xEVDV (evolution data voice) [3]. Like HSPA, the cdma2000-1xEVDV system

supported both voice and data on the same carrier but it was never commercialized. In the

2 Introduction

later release of HRPD, VoIP (Voice over Internet Protocol) capabilities were introduced to

provide both voice and data service on the same carrier. The two 3G standards namely HSPA

and HRPD were finally able to fulfill the 3G promise and have been widely deployed in major

cellular markets to provide wireless data access.

1.1 Beyond 3G systems

While HSPA and HRPD systems were being developed and deployed, IEEE 802 LMSC

(LAN/MAN Standard Committee) introduced the IEEE 802.16e standard [4] for mobile

broadband wireless access. This standard was introduced as an enhancement to an earlier

IEEE 802.16 standard for fixed broadband wireless access. The 802.16e standard employed a

different access technology named OFDMA (orthogonal frequency division multiple access)

and claimed better data rates and spectral efficiency than that provided by HSPA and HRPD.

Although the IEEE 802.16 family of standards is officially called WirelessMAN in IEEE, it

has been dubbed WiMAX (worldwide interoperability for microwave access) by an industry

group named the WiMAX Forum. The mission of the WiMAX Forum is to promote and certify

the compatibility and interoperability of broadband wireless access products. The WiMAX

system supporting mobility as in IEEE 802.16e standard is referred to as Mobile WiMAX. In

addition to the radio technology advantage, Mobile WiMAX also employed a simpler network

architecture based on IP protocols.

The introduction of Mobile WiMAX led both 3GPP and 3GPP2 to develop their own

version of beyond 3G systems based on the OFDMA technology and network architecture

similar to that in Mobile WiMAX. The beyond 3G system in 3GPP is called evolved universal

terrestrial radio access (evolved UTRA) [5] and is also widely referred to as LTE (Long-Term

Evolution) while 3GPP2’s version is called UMB (ultra mobile broadband) [6] as depicted

in Figure 1.1. It should be noted that all three beyond 3G systems namely Mobile WiMAX,

GSM WCDMA/HSPA LTE LTE-advancedLTE-advanced

CDMA

Cdma2000/

HRPD

UMB

802.16e/

WiMAX

802.12.16m802.16m

2G 3G/IMT-2000 Beyond 3G and 4G/IMT-advanced

3GPP

3GPP2

IEEE

802

LMSC

Figure 1.1. Cellular systems evolution.

1.2 Long-Term Evolution (LTE) 3

Table 1.1. LTE system attributes.

Bandwidth 1.25–20 MHz

Duplexing FDD, TDD, half-duplex FDD

Mobility 350 km/h

Multiple access

Downlink OFDMA

Uplink SC-FDMA

MIMO

Downlink 2 × 2, 4 × 2, 4 × 4

Uplink 1 × 2, 1 × 4

Peak data rate in 20 MHz

Downlink 173 and 326 Mb/s for 2 × 2 and 4 × 4

MIMO, respectively

Uplink 86 Mb/s with 1×2 antenna configuration

Modulation QPSK, 16-QAM and 64-QAM

Channel coding Turbo code

Other techniques Channel sensitive scheduling, link

adaptation, power control, ICIC and

hybrid ARQ

LTE and UMB meet IMT-2000 requirements and hence they are also part of IMT-2000 family

of standards.

1.2 Long-Term Evolution (LTE)

The goal of LTE is to provide a high-data-rate, low-latency and packet-optimized radio-

access technology supporting flexible bandwidth deployments [7]. In parallel, new network

architecture is designed with the goal to support packet-switched traffic with seamless

mobility, quality of service and minimal latency [8].

The air-interface related attributes of the LTE system are summarized in Table 1.1. The

system supports flexible bandwidths thanks to OFDMA and SC-FDMA access schemes. In

addition to FDD (frequency division duplexing) and TDD (time division duplexing), half-

duplex FDD is allowed to support low cost UEs. Unlike FDD, in half-duplex FDD operation

a UE is not required to transmit and receive at the same time. This avoids the need for a costly

duplexer in the UE. The system is primarily optimized for low speeds up to 15 km/h. However,

the system specifications allow mobility support in excess of 350 km/h with some performance

degradation. The uplink access is based on single carrier frequency division multiple access

(SC-FDMA) that promises increased uplink coverage due to low peak-to-average power ratio

(PAPR) relative to OFDMA.

The system supports downlink peak data rates of 326 Mb/s with 4 × 4 MIMO (multiple

input multiple output) within 20 MHz bandwidth. Since uplink MIMO is not employed in

the first release of the LTE standard, the uplink peak data rates are limited to 86 Mb/s within

20 MHz bandwidth. In addition to peak data rate improvements, the LTE system provides two

to four times higher cell spectral efficiency relative to the Release 6 HSPA system. Similar

improvements are observed in cell-edge throughput while maintaining same-site locations

as deployed for HSPA. In terms of latency, the LTE radio-interface and network provides

capabilities for less than 10 ms latency for the transmission of a packet from the network to

the UE.

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