Wireless Communications Engineering

Lecture 12: 3G Systems

Prof. Mingbo Xiao

Dec. 23, 2004

Limits of 2G Cellular Systems 2G systems are highly successful, but … Capacity of the system saturated Transmit speed is too slow (9.6 Kbps or

14.4 Kbps) to support multimedia services

Symmetric transmission so not suitable for Internet traffic

Main service is voice, but voice service is becoming less profitable

Voice versus Data over Cellular

Internet Access from GSM

Enhanced Data for GSM Evolution (EDGE)

Common factor for GSM and IS-136; uses their existing spectrum bands

Support both packet- and circuit-switched services

Eight-phase-shift (8 PSK) modulation Every time slot can support up to 48

Kbps The highest speed is up to 384 Kbps 40 times of GSM and 3 times of GPRS

Packet-Switched Data in GPRS

Packet and circuit-switch in GPRS

Protocol Architecture

Protocol Architecture (cont.) Physical layer:

RFL (Physical RF Layer) – modulation, demodulation

PLL (Physical Link Layer) – error control, congestion detect

Data link layer: MAC (Medium Access Control) – slotted

ALOHA RLC (Radio Link Control) – error correction LLC (Logical Link Control) – always connected

Protocol Architecture (cont.) GPRS supports interworking of MSs with

X.25-, IP-based networks by encapsulation and decapsulation

Between SGSN and MS, further encapsulation is performed by SNDCP (SubNetwork-Dependent Convergence Protocols) including: multiplexing, compression,

segmentation The MAC is derived from a slotted

reservation ALOHA protocol, and operate between MS and BTS

More services Web browsing VoD Video phone call Mobile computation

Improved quality Higher rates: 2.048 Mbps for low speed users, 384 Kbps for

modest speed users and 144 Kbps for high speed users More reliable and larger capacity

Compatible with 2G systems More flexible

Support both circuit-switching and packet-switching Work in hierarchical mode with pico-/micro-/macro-cells Support asymmetric services …

Goals of 3G Systems

Interest to 3G Applications Western Eastern USA

Europe Europe

Emails 4.5 4.7 4.3 City maps/directions 4.3 4.2 4.2 Latest news 4.0 4.4 4.0 Authorize/enable payment 3.4 3.8 3.0 Banking/trading online 3.5 3.4 3.2 Downloading music 3.1 3.4 3.2 Shopping/reservation 3.0 3.1 2.9 Animated images 2.4 2.7 2.6 Chat rooms, forums 2.3 2.9 2.2 Interactive games 2.0 2.2 2.4 Games for money 1.8 1.8 1.8

(Means based upon a six-point interest scale, where 6 indicates high interest and 1 indicates low interest.)

Upgrade Paths to 3GIS-136PDC

GSMIS-95

IS-95B HSCSD

GPRS

EDGE

W-CDMAEDGE

TD-SCDMA

cdma200-1xRTT

cdma2000-1xEV,DV,DO

cdma200-3xRTT

2G

2.5G

3G

WCDMA

Network

Network Elements BTS Base Transceiving Station BSC Base Station Controller MSC Mobile Switching Center GMSC Gateway MSC RNC Radio Network Controller MS Mobile Station HLR Home Location Register VLR Visitor Location Register EIR Equipment Identity Register AUC Authentication Center OMC Operation and Maintenance Center SGSN Serving GPRS Support Node GGSN Gateway GPRS Support Node GR GPRS register

Interface Iu: Interface between the RNC and the Core

Network (MSC or SGSN).      - Iucs: Iu circuit switched (voice from/to MSC)      - Iups: Iu packet switched (data from/to SGSN)

Iub: Interface between the RNC and the Node B. Iur: Interface between two RNCs. Gn: Interface between SGSN and GGSN Gi: Interface between GGSN and external packet

data network

WCDMA Protocol Architecture

Network LayerNetwork Layer

Data Link LayerData Link Layer

Physical LayerPhysical Layer

Layer 3Layer 3RRC

Medium Access Control

Layer 2Layer 2

Layer 1Layer 1

Transport Channels

Logical Channels

MAC

RLCRadio Link Control

Physical Channels

Radio Resource Control

WCDMA Channels

Logical Channel Broadcast Control Channel (BCCH), Downlink

(DL), carries system and cell specific information Paging Control Channel (PCCH), DL Dedicated Control Channel (DCCH), UL/DL Common Control Channel (CCCH), UL/DL Dedicated Traffic Channel (DTCH) for point-to-

point data transmission in the uplink and downlink, UL/DL

Common Traffic Channel (CTCH), Unidirectional (one to many)

Transport Channels Dedicated Transport Channel (DCH), UL/DL, mapped to

DCCH and DTCH Broadcast Channel (BCH), DL, mapped to BCCH Forward Access Channel (FACH) for massages from the

base station to the mobile in one cell, DL, mapped to BCCH, CCCH, CTCH, DCCH and DTCH

Paging Channel (PCH) for messages to the mobiles in the paging area, DL, mapped to PCCH

Random Access Channel (RACH), UL, mapped to CCCH, DCCH and DTCH

Uplink Common Packet Channel (CPCH), UL, mapped to DCCH and DTCH

Downlink Shared Channel (DSCH), DL, mapped to DCCH and DTCH

Physical Channels Dedicated Transport Channel (DCH), UL/DL, mapped to

DCCH and DTCH Broadcast Channel (BCH), DL, mapped to BCCH Forward Access Channel (FACH) for massages from the

base station to the mobile in one cell, DL, mapped to BCCH, CCCH, CTCH, DCCH and DTCH

Paging Channel (PCH) for messages to the mobiles in the paging area, DL, mapped to PCCH

Random Access Channel (RACH), UL, mapped to CCCH, DCCH and DTCH

Uplink Common Packet Channel (CPCH), UL, mapped to DCCH and DTCH

Downlink Shared Channel (DSCH), DL, mapped to DCCH and DTCH

Channel Multiplexing

IQ/code multiplexing with complex spreading circuit

WCDMA

Parameters

cdma2000 Overview Introduction cdma2000 Architecture Physical Layer

Forward Links Reverse Links

Data Link Layer Link Access Control sublayer Media Access Control sublayer

Data Service in cdma2000 Packet data service High-speed circuit data service

Conclusions References

Introduction Backward compatibility to TIA/EIA-95-B

Supports TIA/EIA-95-B signaling and services Spreading bandwidths compatible with IS-95-B

deployments Supports cdma2000 to IS-95/IS-95-B hard handoff Minimal changes to IS-41 and IS-634 Protects operator investment in existing cdmaOne

networks Provides simple and cost-effective migration to 3G services

Overlay upgrade to TIA/EIA-95-B Supports backward compatible common channels Forward Link orthogonality maintained between cdma2000

mobiles and IS-95-A/B mobiles

Introduction (cont.) Support of IMT-2000 data rates

Vehicular – 144 kbps (supported by 1X systems) Pedestrian – 384 kbps (supported by 3X systems) Indoor – 2 Mbps

Advanced Medium Access Control (MAC) Support different quality of service for a wide range

of advanced services concurrently Simultaneous voice/data support for multi-service QoS support for multimedia applications

Significantly improved mobile stand-by time Spot beam and smart antenna coverage

cdma2000 Architecture

Physical Layer The Radio Configurations (RCs) specify the

data rates, channel encoding, and modulation parameters supported on the traffic channel

For Spreading Rates (SRs) 1 and 3, there are 6 RCs for the reverse link and 9 RCs for the forward link

RCs 1 and 2 are specified to provide backward compatibility with TIA/EIA-95-B

There are 6 reverse and 11 forward physical channels in cdma2000

Forward Links Features Supports chip rates of N x 1.2288 Mcps,

N=1,3,6,9,12 N = 1

similar to IS-95B, but QPSK modulation and fast closed-loop power control are used

N > 1 Multicarrier Direct spread

Multicarrier and Direct Spread

f1 f2 f3

1.25 1.25 1.25 1.25

MulticarrierN = 3

0 1 2 3 4 5 MHz

MHz

1.2288 Mcps

1 2 3 4 5 MHz

3.6864 McpsDirect Spread

N = 3

Key Characteristics of Forward Links Channels are orthogonal and use variable-

length Walsh codes. QPSK modulation is used before spreading to

increase the number of usable Walsh codes. Forward Error Correction (FEC) is used

Convolutional codes (k=9) are used for voice and data.

Turbo codes (k=4) are used for high data rate on SCHs Supports nonorthogonal forward link

channelization These are used when running out of orthogonal space

(insufficient number of Walsh codes) Quasiorthogonal functions are generated by masking

existing Walsh functions

Key Characteristic of Forward Links (cont.)

Synchronous forward links Forward link transmit diversity Fast-forward power control (closed

loop) 800 times per second

Key Characteristics of Reverse Links

Continuous waveform Minimizes interference to biomedical devices Enables the interleaving to be performed over the

entire frame Orthogonal channels with different-length

Walsh sequences Higher data rate channels -> shorter Walsh

sequences Rate matching

Puncturing Symbol repetition Sequence repetition

Key Characteristics of Reverse Link (cont.) Independent data channels

Enables the system to be optimized for multiple simultaneous services

The channels are separately coded and interleaved and may have different transmit power level and FER set points.

Reverse power control Open loop Closed loop Outer loop

Key Characteristics of Reverse Link (cont.) Separate dedicated control channels

Allows for a flexible dedicated control channel structure that does not impact the other pilot and physical channel frame structures.

Forward error correction Convolutional codes (k=9) are used for

voice and data Parallel turbo codes (k=4) are used for high

data rates on supplemental channels Fast-reverse power control

800 times per second

Data Link Layer Subdivided into two sublayers

Link Access Control (LAC) sublayer Manages point-to-point communication channels

between peer upper layer entities Provides framework to support a wide range of

different end-to-end reliable link layer protocols Media Access Control (MAC) sublayer

MAC control state Best-effort delivery Multiplexing and QoS control

Data Link Layer: MAC Control States

Active stateSuspended

stateDormant

stateControl

hold state

Timeout Timeout Timeout

Traffic

Traffic

Traffic

Traffic, PC, andcontrol channelsassigned

PC and controlchannels assigned

Very fast trafficchannelreassignment

No dedicatedchannels

RLP and PPPstate maintained

"Virtual active set"Slotted submode

No dedicatedchannels

No BS, MSCresources

PPP statemaintained

Small data bursts

Data Services in cdma2000 (1) Packet data services

Support a large number of mobile stations using packet data services

Dedicated channels for packet service users are allocated on demand and released immediately after the end of the activity period

Short data bursts can be transmitted over a common traffic channel

Using Mobile IP to support wireless packet data networking capability

Data Services in cdma2000

Data Services in cdma2000 (2) High-speed circuit data service

Dedicated traffic and control channels are typically assigned to the MS for extended periods of time during the circuit service sessions

Some delay-sensitive services such as video applications require a dedicated channel for the duration of the call

什么是 TD － SCDMA Time Division-Synchronous Code Division

Multiple Access （时分双工的同步码分多址技术） 是 ITU 正式发布的第三代移动通信空间接口技术规范之一，

它得 到了 CWTS 及 3GPP 的全面支持 是中国电信百年来第一个完整的通信技术标准，是 UTRA

－ FDD 可替代的方案 是集 CDMA 、 TDMA 、 FDMA 技术优势于一体、系统

容量大、频谱利用 率高、抗干扰能力强的移动通信技术 它采用了智能天线、联合检测、接力切换、同步 CDMA 、

软件无线 电、低码片速率、多时隙、可变扩频系统、自适应功率调整

等技术

TD-SCDMA TD-SCDMA 的关键技术的关键技术

时分双工方式 智能天线：降低多径、多址干扰 联合检测：降低多址干扰 上行同步：减少码间串扰 接力切换：提高切换可靠性 软件无线电 低码片速率 ...

(..)5421 3 6

智能天线 智能天线 ((Smart Antenna))

• Antenna array + BB digital data Processing• Providing a beamformed pattern for each user• Fast beamforming to follow the moving user

空分多址大大增加系统容量

智能天线 智能天线 ((Smart Antenna))

天线子系统 圆形天线阵 ：全向小区 扇形天线阵： 120o 小区 射频前端集成在天线系统内以

提高性能 实时校准技术 冗余设计，任何天线单元的失

效都不会明显影响系统性能 低成本

天线阵

天线罩

射频前端

电缆出口

使用智能天线 ... 定向发射、定向接收 正在通信的移动终端在

整个小区内处于受跟踪状态

不使用智能天线 ... 全向发射、全向接收 所有小区内的移动终端

均相互干扰，此干扰是CDMA 容量限制的主要原因

智能天线的优势 减少小区间小区间和小区内干扰小区内干扰 降低多径干扰多径干扰 等效发射功率提高 提高接收灵敏度 改进了小区覆盖（合成波

束）

增加了容量及小区覆盖半径

降低发射功率，基站成本降低

智能天线 智能天线 (S.A.)(S.A.) 的优势的优势

联合检测 联合检测 ((J.D.)J.D.)

联合检测作用 避免多址干扰 检测动态范围急剧增大 小区内干扰最小化

联合检测原理 特定的空中接口（帧结构）允许收信机对无线信道进行信道估计 根据估计的无线信道，对所有信号同时进行检测

• ＣＤＭＡ系统中多址干扰（ M.A.I. ）是主要干扰 ; 小区间的干扰在最恶劣 的情况下也不超过小区内部干扰的６０％。• 传统的ＣＤＭＡ系统信号分离方法把ＭＡＩ看作热噪声。• J.D. 充分利用ＭＡＩ中的先验信息

智能天线和联合检测的结合智能天线和联合检测的结合

智能天线的主要作用： 降低多址干扰，提高 CDMA 系统容量 提高接收灵敏度和发射 EIRP

智能天线所不能克服的问题 用户处于相同方向 多普勒效应 ( 高速移动 )

联合检测：利用训练序列作信道估值，同时处理多码道的干扰抵消。但存在 多码道时处理复杂。

在 TD-SCDMA 移动通信系统中，结合使用智能天线和联合检测，获得了理 想的效果

动态信道分配 动态信道分配 ((DCA)DCA)

在ＴＤＤ模式的ＣＤＭＡ系统中，信道的定义包括： 扩频码 – 码域 时隙 - 时域 载频 - 频域 波束 - 空域

动态信道分配是指：

在终端接入和链路持续期间，根据多小区之间的干扰情况和本小

区内的干扰情况，进行信道的分配和调整。

目的： 1) 增加系统容量　　　　 2) 减小干扰。

定义 上行链路各终端信号在基站解

调器完全同步 优点

CDMA 码道正交， 降低码道间干扰， 提高 CDMA 容量 简化硬件，降低成本

t基站解调器

码道 1

码道 2

码道 N

上行同步技术上行同步技术

低码片速率低码片速率

载波频带窄 ...在 1.6MHz带宽内可实现

2Mbps 的数据业务

低码片速率的优势

频谱利用率高频率使用灵活系统设备成本

低

MS 和 BS0 通信 BS0 通知邻近基站信息

基站类型、工作载频、定时偏差、忙闲等等

MS搜索基站 , 建立同步 BS或MS 发起切换请求 系统决定切换执行 MS 同时接收来自两个基站的

相同信号 完成切换 优点

节省系统资源，提高系统容量，降低设备成本

BS0

BS1

BS2

MS

接力切换

TD-SCDMA 的优势 易于使用非对称频段 , 无需具有特定双工间隔的成对频段

适应用户业务需求，灵活配置时隙，优化频谱效率

上行和下行使用同个载频，故无线传播是对称的 , 有利于智能天线技术的实现

无需笨重的射频双工器，小巧的基站，降低成本

时分双工 (TD-SCDMA):上行频带和下行频带相同

D U D D D D DD

频分双工 (FDD):上行频带和下行频带分离

D D D D D DD

U

U 上行 D 下行 未使用 资源 :

时分双工 时分双工 ((TDD)TDD)

在通用芯片上用软件实现专用芯片 的功能

软件无线电的优势可克服微电子技术的不足

系统增加功能通过软件升级来实现

减少用户设备费用支出快速适应新技术

软件无线电软件无线电

TD-SCDMA物理层 低码片速率 :1.28Mcps(WCDMA 的 1/3) ，带宽为1.6MHz 适合智能天线和同步 CDMA 的帧结构 所有码道可以同时工作 采用和 3GPP 相同的调制、信道编码、交织和复接技术 提供不对称上下行业务 功率调整和同步控制 :

控制频率 :0-200次/秒 功率控制步长 :1-3dB 同步控制精度 :1/8 码片宽度 开环和闭环控制

Radio frame10ms

System Frame Number

Sub-frame

5ms

TS5TS4TS0 TS2TS1

GP

TS3 TS6

DwPTS UpPTS

Data Midamble Data

675us

gL1

144chips

TD-SCDMA帧结构

每帧有两个上 / 下行转换点TS0为下行时隙TS1为上行时隙三个特殊时隙 GP, DwPTS, UpPTS其余时隙可根据根据用户需要进行灵活 UL/DL配置

TD-SCDMATD-SCDMA 系统独特的帧结构系统独特的帧结构

每时隙由 704 Chips组成，时长 675us； 业务和信令数据由两块组成，每个数据块分别由 352

Chips组成； 训练序列 (Midamble)由 144 Chips组成； 16 Chips为保护； 可以进行波束赋形；

Data352chips

Midamble144chips

GP16

Data352chips

675 s

时隙时隙 (TS)(TS) 结构结构

TD-SCDMATD-SCDMA 全向码道和赋形码道全向码道和赋形码道

两种赋形波束 得到小区覆盖的全向波束 针对用户终端的赋形波束

BCH/DwPTS必须使用全向波束，覆盖整个小区，在帧结构

中使用专门时隙 业务码道通常使用赋形波束，只覆盖个别用户

GDwPTS UpPTSBCH

TS5TS4TS0 TS2TS1 TS3 TS6

TD-SCDMA 系统应用特点

第三代移动通信的国际标准之一，中国自主知识产权

唯一事实上的 TDD 标准

具有最高的频谱利用率

最适合移动互联网的业务

能工作于各种环境，适应各种组网要求

成本低，对运营商和最终用户带来利益

TD-SCDMA 代表了未来技术的发展方向

TDD 双工方式的特点

频谱使用灵活性：不需要成对频谱 上下行链路使用相同载波频率，便于使用新技术 用时间来自适应上下行业务量，支持不对称数据业务， 适应无线互联网的需求，这是比FDD 方式最突出的优点 低成本 TD-SCDMA还有频谱利用率最高的优点

TD-SCDMA 系统具有最高的频谱利用率

定义：话音通信：频谱利用率 == 同时工作信道数 /MHz/ 小区数据： 频谱利用率 == 最大传输数据速率 /MHz/ 小区

GSM IS95 CDMA2000 WCDMA TD-SCDMA频率复用系数 7 1 1 1 1每载波频宽 (MHz) 0.4 2.5 2.5 10 1.6每载波同时工作信道数 8 20 30 60 24频谱利用率（话音） 2.8 8 12 6 15最大数据传输速率 － － 2.5Mbps 4Mbps 2Mbps频谱利用率（数据 , Mbps/MHz/cell ） 1.0 0.4 1.25

IMT-2000 技术发展方向Main tech discussed in ITU WP8F

(Ref. ITU Doc. 8F/TEMP/65-E, Oct. 2000, Geneva) Smart Antenna （智能天线）

Not only for TDD(as TD-SCDMA), but also for FDD, it may lead to change physical layer design in FDD

Software Defined Radio （软件定义无线电） Simplifying hardware Multi-mode UE for worldwide roaming

High speed down-link package data transmission Using the concept in TDD: Higher

modulation scheme (16QAM)----HDR in some time slots in FDD

结论：“ TD-SCDMA 代表 3G 技术发展方向”