Chapter 4 Wireless Widearea Networks(Part Three in textbook)

Outline 4.1 Satellite Communications

4.2 Cellular Wireless Networks

4.3 Cordless Systems and Wireless Local Loop

4.4 Mobile IP and Wireless Application Protocol

4.1 Satellite Communications

卫星通信的基本概念

什么叫卫星通信 什么叫静止卫星和静止卫星通信系统 卫星覆盖区 实现全球通信的条件 衡量卫星通信系统性能的主要技术指标 卫星通信的特点

卫星通信——利用人造地球卫星作为中继站转发无线电信号 , 在两个或多个地球站之间进行的通信。

什么叫静止卫星？ 一、卫星的种类 二、什么叫静止卫星？

卫星的种类—— 1

按卫星的结构划分无源卫星有源卫星

卫星内部是否含有有源器件

卫星的种类—— 2 按卫星的轨道划分

1 ）按卫星轨道的形状划分 圆形轨道卫星 椭圆形轨道卫星2 ）按卫星距地球表面的高度划分

低高度： H<5,000Km ; h< 4小时 中高度： 5,000Km< H <20,000Km; 4小时 < h < 12 小时高高度： H> 20,000Km ; h > 12 小时

注： H ：表示高度， h ：旋转一圈所需时间

圆形轨道卫星

椭圆形轨道卫星

卫星的种类—— 2 续

3 ）按卫星轨道平面与地球赤道平面的夹角

θ = 0° ，赤道轨道卫星 ； θ = 90° ，极轨道卫星;

0°< θ < 90°,倾斜轨道卫星

注： θ表示夹角

θ = 0° ，赤道轨道卫星

地球赤道 赤道轨道

卫星轨道平面与地球赤道平面的夹角示意图

卫星轨道平面与地球赤道平面的夹角示意图 θ =90° 极轨道卫星 ;

地球赤道

卫星轨道

0°< θ < 90°, 倾斜轨道卫星

地球赤道

倾斜轨道

卫星轨道平面与地球赤道平面的夹角示意图

卫星轨道平面与地球赤道平面的夹角示意图

0<θ<90° 倾斜轨道

θ=0 赤 道轨道

θ=90° 极轨道

卫星的种类—— 2 续

按卫星的轨道划分（续） 按相对于地面观察点的位置划分

运动轨道卫星 同步轨道卫星 静止轨道卫星

什么叫静止卫星？ 卫星在地球赤道上空，距地面

35,786 公里的圆形轨道上绕地球旋转，卫星轨道平面与地球赤道平面的夹角为 0° ，其绕地球旋转一周的时间和地球自转一周所需时间相同为 24 小时，并且其围绕地球旋转的方向和地球自转的方向相同，不论在地球的什么地方观察卫星，卫星始终是相对静止不动的我们把这种卫星称为静止卫星。

什么叫同步卫星？ 同步卫星：其公转与轨道中央星自转

的周期与方向均相同的卫星。

静止卫星是同步卫星的一个特例。

卫星覆盖区一、定义： 卫星在地球表面的投影

二、静止卫星覆盖区：

覆盖面积超过地球表面总面积的三分之一

B

AB 间 弧 长18100KM

35786KM

地球

静止卫星

A

实现全球通信的条件 在静止卫星轨道上等间距地放置三颗静止卫星 , 在卫星覆盖区的重叠部分建立转发站 ，则经过一次跳变，即通过一颗卫星或经过二次跳变和转发站便可实现二个地球站间的通信联络 ，并可基本实现全球通信

P3

P2

P1

GMDSS原理与操作

衡量卫星通信系统性能的主要技术指标

有效全向辐射功率（ EIRP） 用来衡量收发器发射分系统性能的 EIRP越大，则表明发射分系统的性能越好。

符号 : EIRP 单位： dBW 或 dBm； 1dBW = 30 dBm

C 船站 EIRP: 12 dBW < EIRP<16 dBW

衡量卫星通信系统性能的主要技术指标

增益噪声温度比（ G/T ） 增益噪声温度比又叫优值比 常用来衡量接收分系统性能的好坏 增益噪声温度比越大，则表明接收分系统的性能越好，接收微弱信号的能力越强。

符号 : G/T 单位是 db/°k

C 船站 G/T >= -23db/°k

卫星通信的特点 优点 :

覆盖面积大、通信距离远、灵活机动并可基本实现全球通信。

频带宽、通信容量大。 抗干扰能力强，通信质量高。 卫星通信系统是实时、全天候通信系统。 功效高。

缺点： 技术难度大，投资多，费用高。 卫星通信有较大的信号延迟和回声干扰。

返回

Satellite-Related Terms Earth Stations – antenna systems on or near earth Uplink – transmission from an earth station to a

satellite Downlink – transmission from a satellite to an

earth station Transponder – electronics in the satellite that

convert uplink signals to downlink signals

Ways to CategorizeCommunications Satellites Coverage area

Global, regional, national Service type

Fixed service satellite (FSS) Broadcast service satellite (BSS) Mobile service satellite (MSS)

General usage Commercial, military, amateur, experimental

Classification of Satellite Orbits Circular or elliptical orbit

Circular with center at earth’s center Elliptical with one foci at earth’s center

Orbit around earth in different planes Equatorial orbit above earth’s equator Polar orbit passes over both poles Other orbits referred to as inclined orbits

Altitude of satellites Geostationary orbit (GEO) Medium earth orbit (MEO) Low earth orbit (LEO)

寻星所需设备 卫星天线、高频头（馈源一体化）、卫

星接收机、电视机、指南针、量角器以及连接线若干。

馈源的主要功能是将天线收集的信号聚集送给高频头（ LNB ）。

寻星所需参数 对于固定式天线系统，需要根据天线所

在地的经纬度及所要接收卫星的经度计算出天线的方位角和仰角，并以此角度调整天线使其对准相应的卫星。 对于极化的卫星信号，还需调整高频头的极化角，圆极化信号则不必。

Geometry Terms Elevation angle - the angle from the

horizontal to the point on the center of the main beam of the antenna when the antenna is pointed directly at the satellite从接收点仰望卫星的视线与水平线构成的夹角就是仰角。

Minimum elevation angle Coverage angle - the measure of the portion

of the earth's surface visible to the satellite

Elevation angle

Minimum Elevation Angle Reasons affecting minimum elevation angle

of earth station’s antenna (>0o) Buildings, trees, and other terrestrial objects

block the line of sight Atmospheric attenuation is greater at low

elevation angles Electrical noise generated by the earth's heat

near its surface adversely affects reception

方位角 (azimuth) 从接收点到卫星的视线在接收点的水平

面上有一条正投影线，从接收点的正北方向开始，顺时针方向至这条正投影线的角度就是方位角。

GEO Orbit Advantages of the the GEO orbit

No problem with frequency changes Tracking of the satellite is simplified High coverage area

Disadvantages of the GEO orbit Weak signal after traveling over 35,000 km Polar regions are poorly served Signal sending delay is substantial

LEO Satellite Characteristics Circular/slightly elliptical orbit under 2000 km Orbit period ranges from 1.5 to 2 hours Diameter of coverage is about 8000 km Round-trip signal propagation delay less than 20

ms Maximum satellite visible time up to 20 min System must cope with large Doppler shifts Atmospheric drag results in orbital deterioration

LEO Categories Little LEOs

Frequencies below 1 GHz 5MHz of bandwidth Data rates up to 10 kbps Aimed at paging, tracking, and low-rate messaging

Big LEOs Frequencies above 1 GHz Support data rates up to a few megabits per sec Offer same services as little LEOs in addition to voice

and positioning services

MEO Satellite Characteristics Circular orbit at an altitude in the range of 5000 to

12,000 km Orbit period of 6 hours Diameter of coverage is 10,000 to 15,000 km Round trip signal propagation delay less than 50

ms Maximum satellite visible time is a few hours

Frequency Bands Available for Satellite Communications

Satellite Link Performance Factors Distance between earth station antenna and

satellite antenna For downlink, terrestrial distance between earth

station antenna and “aim point” of satellite Displayed as a satellite footprint (Figure 9.6)

Atmospheric attenuation Affected by oxygen, water, angle of elevation, and

higher frequencies

Satellite Footprint

Satellite Network Configurations

Capacity Allocation Strategies Frequency division multiple access

(FDMA) Time division multiple access (TDMA) Code division multiple access (CDMA)

Frequency-Division Multiplexing Alternative uses of channels in point-to-point

configuration 1200 voice-frequency (VF) voice channels One 50-Mbps data stream 16 channels of 1.544 Mbps each 400 channels of 64 kbps each 600 channels of 40 kbps each One analog video signal Six to nine digital video signals

Frequency-Division Multiple Access Factors which limit the number of

subchannels provided within a satellite channel via FDMA Thermal noise Intermodulation noise Crosstalk

Forms of FDMA Fixed-assignment multiple access (FAMA)

The assignment of capacity is distributed in a fixed manner among multiple stations

Demand may fluctuate Results in the significant underuse of capacity

Demand-assignment multiple access (DAMA) Capacity assignment is changed as needed to respond

optimally to demand changes among the multiple stations

FAMA-FDMA FAMA – logical links between stations are

preassigned FAMA – multiple stations access the

satellite by using different frequency bands Uses considerable bandwidth

DAMA-FDMA Single channel per carrier (SCPC) – bandwidth

divided into individual VF channels Attractive for remote areas with few user stations near

each site Suffers from inefficiency of fixed assignment

DAMA – set of subchannels in a channel is treated as a pool of available links For full-duplex between two earth stations, a pair of

subchannels is dynamically assigned on demand Demand assignment performed in a distributed fashion by

earth station using common-signaling channel (CSC)

Reasons for Increasing Use of TDM Techniques Cost of digital components continues to

drop Advantages of digital components

Use of error correction Increased efficiency of TDM

Lack of intermodulation noise

FAMA-TDMA Operation Transmission in the form of repetitive sequence of

frames Each frame is divided into a number of time slots Each slot is dedicated to a particular transmitter

Earth stations take turns using uplink channel Sends data in assigned time slot

Satellite repeats incoming transmissions Broadcast to all stations

Stations must know which slot to use for transmission and which to use for reception

FAMA-TDMA Uplink

FAMA-TDMA Downlink

4.2 Cellular Wireless Networks

蜂窝移动通信的基本概念蜂窝移动通信的基本概念

蜂窝系统 ---“小区制”系统 - 将所要覆盖的地区划分为若干个小区，每个小区的半径可视用户的分布密 度在 1-10km左右 , 在每个小区设立一个基站为本小区范围内的用户服务。

- “频率复用”的概念

- 特点：用户容量大，服务性能较好，频谱利用率较高，用户终端小巧且电池使用时间长，辐射小等

- 问题：系统复杂，越区切换，漫游，位置登记；更新和管理以及系统鉴权等 蜂窝分类 - 宏蜂窝 (Macro-cell) 2-20km - 微蜂窝 (Micro-cell) 0.4－ 2 km - 微微蜂窝 (Pico-cell) <400m - 分层蜂窝 ( 由多种蜂窝组成 )

移动通信系统的全球覆盖移动通信系统的全球覆盖

蜂窝—频率复用方式

FDMA 频率复用

1

11

1

1

11

11

1

3

6

2

62

2

1

45

7

CDMA 频率复用

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FDMA— 蜂窝覆盖

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Sector-1

Sector-2

Sector-3

Sector-4

Sector-5

Sector-6Sector-1

Sector-3

Sector-2

G = 3 x 0.85 = 2.55 G = 6 x 0.85 = 5.1

* 扇区的重叠按 15 % 记

扇区的裂变

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RNC

RNC

MSC

EXCHANG

EXCHANG

蜂窝在通信网的位置

Base 1

Base 2

Base 3

蜂窝系统的小区切换

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VLRMSCMSC

VLRMSCMSC

GMSCGMSC

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSS

AUCAUC

HLRHLR

PSTN

E

D

CH

A

PSTNPSTN

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSS

A

移动通信网络结构

VLRMSCMSC

VLRMSCMSC

GMSCGMSC

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSS

AUCAUC

HLRHLR

E

D

CH

A

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSSA

PSTNPSTN

VLRMSCMSC

VLRMSCMSC

GMSCGMSC

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSS

AUCAUC

HLRHLR

E

DC

H

A

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSSA

终端用户漫游

移动通信的信号传输处理技术移动通信的信号传输处理技术

调制技术

数字频率调制技术（ FSK 、 MSK 、 GMSK 、 GFSK)数字相位调制（ PSK 、 QPSK 、 /4 － QPSK)正交振幅调制（ QAM ）自适应调制扩频调制

编码技术 语音编码（信源编码）信道编码（卷积编码、 Turbo编码）

信源编码 信道编码 信道解码 信源解码调制 解调信源

语音编码技术语音编码技术语音编码技术是数字移动通信的基础，是第一代与第二代移动通信的主要区别语音编码技术是数字移动通信的基础，是第一代与第二代移动通信的主要区别

意义：提高通话质量（数字化＋信道编码纠错）提高频谱利用率（低码率编码）提高系统容量（低码率，语音激活技术）

移动通信对语音编码的要求：编码速率低，话音质量好抗噪声干扰和抗误码的能力强编译码延时小编译码器复杂度低，便于大规模集成功耗小，以便应用于手持机

语音编码技术在移动通信中的应用语音编码技术在移动通信中的应用

系统卷积编码技术系统卷积编码技术

Information Bits (Input)

Code Symbols (Output)

0g

1g

1c

0c

（前向链路卷积编码：编码率＝（前向链路卷积编码：编码率＝ 1/21/2 ，约束长度＝，约束长度＝99 ））

TurboTurbo 编码技术编码技术

Interleaver

+

D D D

+

+

+

64 kbpsOutput

64 kbpsOutput

64 kbpsInput

D D D

+

+

+ + 64 kbpsOutput

Systematic Path

Parity Path

Parity Path

Uses the Same Coder for Both Parity Generators

Second Parity Generator Input is Interleaved

Yields 0.5 dB Improvement Relative to Convolution Encoder for High Speed Data

交织技术交织技术目的：把一个较长的突发差错离散成随机差错，再利用纠正随机差

错的编码技术消除随机差错原因：

深度衰落，较长时间人为干扰，大自然突发噪声交织器结构：

－交织深度－交织深度越大， 抗突发差错能力越强

a1

a2

an

b1 b2 bn

m1 m2 mn

写入写出

调制技术调制技术

目的：使传输的数字信号与信道特性相匹配，以便有效进行信息传输分类：

调制信号：模拟调制、数字调制相位连续性：相位连续调制、相位不连续调制信号包络：恒定包络调制、非恒定包络调制

数字调制技术分类数字调制技术分类

BFSK( 二进制频移键控）MFSK （多进制频移键控）

FSK( 频移键控）

ASK( 幅移键控）QAM （正交幅度调制）MQAM （星座调制）

非恒定包络

OQPSK(参差 QPSK ）л/4QPSK

DQPSK （差分 QPSK ）

QPSK

( 正交四相相移键控）

DPSK （差分二进制相移键控）BPSK （二进制相移键控）

PSK（相移键控）

CPM（连续相位调

制）

MSK （最小频移键控）GMSK （高斯成型MSK ）TFM （平滑调频）

恒定包络

数字调制

移动通信中的调制技术移动通信中的调制技术

模拟调制技术模拟调制技术 ---FM---FM

应用：第一代模拟蜂窝移动通信系统

恒定包络调制技术恒定包络调制技术 ------FSKFSK 、、 MSKMSK 、、 GFSKGFSK 、、 GMSKGMSK特点：

对线性要求低，可使用 C 类放大器，功率效率高带外辐射低可达 -60 -70dB

可使用限幅器 ---鉴频器检测系统结构简单，实现容易限幅器可克服随机噪声和瑞利衰落导致的信号幅度的变化，抗干扰和衰落能力强具有较好的解调门限

MSKMSK 调制调制 // 解调技术解调技术

差分编码

串 / 并转换

ak 码 bk 码调制器

解调器

GMSKGMSK 调制技术调制技术目的：抑制高频分量，防止过量的瞬时频率偏移，满足相干检测的需要要求：带外辐射功率为－ 60～－ 80dB

特点：实现简单，在原MSK 调制器的基础上增加前置滤波器 高斯滤波器：带宽窄且为锐截止型

较低的过脉冲响应

输出脉冲的面积不变

应用： GSM 系统

高斯成型滤波器

BPSKBPSK 调制技术调制技术

调制器

解调器

m （ t ）

S（ t ）

x （ t ）

cosct

y （ t ）

S（ t ）

r （ t ）

cosct

LPF ∫dtT1 T

0

星座图Q

I

调制器

解调器

QPSKQPSK 调制技术调制技术

LPFRb/2

LPFRb/2

串并变换 本振

90° 相移﹢ BPF

输入Rb

QPSK信号

LPF

LPF

载波恢复电路

90° 相移

BPF接收信号 恢复电路符号时

序恢复

判决电路

判决电路

复用

QPSKQPSK 调制技术调制技术

星座图Q

I

Q

I

载波相位为(0 ， /2 ， ， 3/2)

载波相位为(/4 ， 3/4, 5/4,

7/4)

OQPSKOQPSK 调制技术调制技术

调制器

解调器

QPSKQPSK 调制技术调制技术

星座图Q

I

Q

I

载波相位为(0 ， /2 ， ， 3/2)

载波相位为(/4 ， 3/4, 5/4,

7/4)

分集技术分集技术

接收多路不相关的信号并合并。

空间分集技术 --- 用 2 个以上的天线接收同一个信号

频率分集技术 --- 用 2 个以上的载波频率传输

时间分集技术 --- 在不同时间接收同一个信号

极化分集技术 --- 接收垂直和水平极化信号

常用的分集技术常用的分集技术

常用的分集技术常用的分集技术

空间分集技术 --- 用 2 个以上的天线接收同一个信号

频率分集技术 --- 用 2 个以上的载波频率传输

时间分集技术 --- 在不同时间接收同一个信号

极化分集技术 --- 接收垂直和水平极化信号

最大比合并

直射路径

反射路径

合并合并

RAKERAKE 接收机技术接收机技术

CDMACDMA 系统系统

CDMACDMA 扩频技术原理扩频技术原理

扩频原理：以频带换取信噪比

香农理论： C=Bw log2 (1+S//N)

扩频系统的优点： 抗干扰能力强，可抗白噪声、人为干扰、多径干扰等 保密性好。扩频信号频谱近似白噪声，若不知 PN序列生成方法就难以获取原始信息

隐蔽性好。扩频信号近似白噪声，难以检测，宽带扩频信号功率谱密度很低，难以监听

易于实现大容量多址通信 易于精确定时和测距 易于采用各种先进的分集技术，如 RAKE 接收、智能天线等

Interference Sources

Long & ShortCodeSpreading

Encoding &Interleaving

Long &Short CodeCorrelator

Decode &Deinterleaving

BasebandData

BasebandData

Background Noise External Interference Other Cell Interference Other User Noise

CDM A Transm itter CDM A Receiver

fc

M Hz BW

fc

390 kHz BW

0

kHz BW

0

1.25 M Hz BW

fc

1.25 M Hz BW

fcfc

-100 dB/Hz

fc

Spurious Signals

Interference Sources

Long & ShortCodeSpreading

Encoding &Interleaving

Long &Short CodeCorrelator

Decode &Deinterleaving

BasebandData

BasebandData

Background Noise External Interference Other Cell Interference Other User Noise

CDM A Transm itter CDM A Receiver

fc

1.25

fc

9.6 kHz BW

0

9.6 kHz BW

0

fc

M Hz BW

fcfc

-100 dB/Hz

fc

Spurious Signals

M Hz BW1.25

CDMACDMA 直接序列扩频技术直接序列扩频技术

CDMACDMA 多址码多址码

码分：用户、信道和基站均依靠多址码识别针对不同的多址码需求，分别使用不同类型的码组

基站的识别 --- 不同相移的 PN序列，码元周期为 215 － 1

信道的识别 --- 正交的 Walsh函数，完全正交的 64 阶 Walsh 码用户的识别 ---周期足够长的 PN序列，码元周期为 242 － 1

公共掩码：移动台电子序列号（ ESN ）专用掩码：移动台识别号（ MIN ）

卷积编码和重复：解决多速率业务的矛盾在 IS-95 系统中采用低速率重复和高速率并行选通发送在 WCDMA 系统中采用层间可变速率扩频正交码（ OVSF ），多信道并行发送

块交织：抗快衰落

功率控制技术功率控制技术

意义：减小干扰，增加系统容量， CDMA 系统是个干扰受限系统减小远近效应，提高 QoS

对抗阴影效应，消除慢衰落提高电池使用寿命

准则：在接收端收到的有用信号功率相等上行：各个移动台到达基站的信号功率相等

下行功率控制：用于小区呼吸

IS95 CDMA IS95 CDMA 功率控制功率控制

{反向功率控制

前向功率控制

{开环功率控制

闭环功率控制{内环功率控制

外环功率控制

基站的识别 --- 不同相移的 PN序列，码元周期为 215 － 1

信道的识别 --- 正交的 Walsh函数，完全正交的 64 阶Walsh 码

用户的识别 ---周期足够长的 PN序列，码元周期为 242 －1

公共掩码：移动台电子序列号（ ESN ）

专用掩码：移动台识别号（ MIN ）

IS95 CDMA IS95 CDMA 地址码的选择地址码的选择

直接序列扩频直接序列扩频—— PNPN 码长码发生器码长码发生器

ESN =

(E 31 , E 30 , E 29 , E 28 , E 27 , E 26 , E 25 , . . . E2 , E 1 , E0)

重新排列的 ESN = (E 0 , E 31 , E 22 , E 13 , E 4 , E 26 , E 17 , E 8 , E 30 ,

E 21 , E 12 , E 3 , E 25 , E 16 , E 7 , E 29 , E 20 , E 11 ,

E2 , E 24 , E 15 , E 6 , E 28 , E 19 , E 10 , E 1 , E 23 ,

E 14 , E 5 , E 27 , E 18 , E 9)

+

+

+

+

+

+

1

2

3

4

5

6

7

8

9

10

39

40

41

42

x

1

x2

x3

x4

x5

x6

x7

x8

x9

x39

x40

x41

x42

x10

Long Code

4242-bit Long Code Mask

Mod

ulo

-2 A

dd

itio

n

MSB

LSB

M41 ～ M32 = 1100011000

M31 ～ M0 = 重排的 ESN

公用长码掩码：

前向链路用于扰码反向链路用于扩频

PNPN 码短码发生器码短码发生器

PI(x) = x15 + x13 + x9 + x8 + x7 + x5 + 1

PQ(x) = x15 + x12 + x11 + x10 + x6 + x5 + x4 + x3 + 1

前向链路用于区分机站反向链路用于扩频

WalshWalsh函数函数

H1 = 0 H2 = 0 00 1

H4 =

0 0 0 00 1 0 10 0 1 10 1 1 0

H2N = HN HN

HN HN

构造： 特性： 是一类取值于 1 和－ 1 的二元正

交函数系 多种等价定义，常用 Hadamard

矩阵法 两个 Walsh函数相乘仍为 Walsh

函数 函数集合是完备的 同步时正交，不同步时自相关和互相关性能不好

WalshWalsh函数函数

1111

1111

1111

1111

x

1

1

1

1

=

0

0

4

0

前向链路信道结构前向链路信道结构

Pilot Chan

Paging Ch 1

Paging Ch 7

Sync Chan

Traffic Ch 1•••

W1W32 W7 W8W0Up to

FORWARD CDMA CHANNEL (1.23 MHz channel

transmitted by base station)

Traffic Ch 25

Traffic Ch 55•••Traffic

Ch 24

W31 W33 W63Up to

Traffic Ch N••• •••

Up to

Mobile Power Control Sub-Channel

W = Code Channel Number

Traffic Data

Frequency DomainFrequency Domain

User #3

User #2

User #1

SynchPaging

Pilot

1.2288 MHzfreq

Code DomainCode Domain

0 1 2 3 4 5 6 7 8 9 32

40 63Use

r1

User3

User2

Walsh Code

Pilot

Paging

Synch

IS-95IS-95 系统：信号在频域和码域上的分布情况系统：信号在频域和码域上的分布情况

前向链路信道调制前向链路信道调制

前向链路导频信道调制前向链路导频信道调制

＋

＋

＋ 基带滤波 ×

Q 信道序列1.2288Mcps

I 信道序列1.2288Mcps

sin （ 2fc t ）

基带滤波 ×

cos （ 2fc t ） ∑ s （ t ）

I （ t ）

Q （ t ）

I

Q

导频信道

W0

215

215

全 0（无数据）

前向链路同步信道调制前向链路同步信道调制

卷积编码器R ＝ 1/2， L ＝ 9

码符号重复 块交织

1.2kb/s 2.4kb/s 4.8kb/s 4.8kb/s

码符号 码符号码符号

＋

＋

＋ 基带滤波 ×

Q 信道序列1.2288Mcps

I 信道序列1.2288Mcps

sin （ 2fc t ）

基带滤波 ×

cos （ 2fc t ） ∑ s （ t ）

I （ t ）

Q （ t ）

I

Q

同步信道幀结构

W32

215

215

前向链路寻呼信道调制前向链路寻呼信道调制

卷积编码器R ＝ 1/2， L ＝ 9

码符号重复 块交织9.6kb/s4.8kb/s

码符号 码符号

＋

＋

＋ 基带滤波 ×

Q 信道序列1.2288Mcps

I 信道序列1.2288Mcps

sin （ 2fc t ）

基带滤波 ×

cos （ 2fc t ） ∑ s （ t ）

I （ t ）

Q （ t ）

I

Q

寻呼信道幀结构

Wk

k ＝ 1 ， 2 ，… 7

215

215

19.2kb/s9.6kb/s

19.2kb/s

＋

242 长码发生器抽样器： 64个码片抽样一个

19.2kb/s

前向链路业务信道调制前向链路业务信道调制

＋

＋

＋ 基带滤波 ×

Q 信道序列1.2288Mcps

I 信道序列1.2288Mcps

sin （ 2fc t ）

基带滤波 ×

cos （ 2fc t ） ∑s （ t ）

I （ t ）

Q （ t ）

I

Q

Wj

215

215

＋

242 长码发生器

抽样器： 64个码片抽样一个

19.2kb/s

MUX

复用定时控制抽样

功率控制位800Hz

业务信道信息比特

增加 8bit尾比特

卷积编码器R ＝ 1/2， L ＝ 9

码符号重复 块交织

9.2kb/s4.4kb/s2.0kb/s0.8kb/s

28.8ks/s 14.4ks/s7.2ks/s3.6ks/s

28.8ks/s

码符号 码符号码符号

9.6kb/s4.8kb/s2.4kb/s1.2kb/s

对 9600&4800增加幀质量指示比8.6kb/s

4.0kb/s2.0kb/s0.8kb/s

前向链路卷积编码前向链路卷积编码

Information Bits (Input)

Code Symbols (Output)

0g

1g

1c

0c

r ＝ 1/2 ， k＝ 9

I-channel

Q-channel

(0,0)(1,0)

(1,1) (0,1)

(I,Q)I Q Phase

0 0 π/4

1 0 3π/4

1 1 -3π/4

0 1 -π/4

前向前向 CDMACDMA 信道调制信道调制—— QPSKQPSK

I 、 Q 映射 星座和相位转移图

反向链路信道结构反向链路信道结构

Access Ch 1

Traffic Ch 1

Traffic Ch m

• • • Access Ch n

REVERSE CDMA CHANNEL (1.23 MHz channel received

by base station)

• • • • • • • • • • • • • • • • • • • • • • • •

Addressed by Long Code PNs

反向接入信道调制反向接入信道调制

增加 8bit尾比特

卷积编码器R ＝ 1/3， L ＝ 9

码符号重复 块交织 64-阶正交调制4.4kb/s

4.8kb/s 14.4ks/s 28.8ks/s 28.8ks/s

307.2kcps

码符号 码符号码符号 调制符

＋

242 长码发生器

长码掩码

＋

＋ D 基带滤波 ×

Q 信道序列1.2288Mcps

I 信道序列1.2288Mcps

sin （ 2fc t ）

基带滤波 ×

cos （ 2fc t ） ∑ s （ t ）

I （ t ）

Q （ t ）

I

Q延时 1/2PN码片＝ 406.9ns

接入信道幀结构

PN 码片1.2288Mcps

反向业务信道调制反向业务信道调制

s （ t ）

307.2kcps

业务信道信息比特

＋

242 长码发生器

长码掩码

＋

＋ D 基带滤波 ×

Q 信道序列1.2288Mcps

I 信道序列1.2288Mcps

sin （ 2fc t ）

基带滤波 ×

cos （ 2fc t ） ∑

I （ t ）

Q （ t ）

I

Q延时 1/2PN码片＝ 406.9nsPN 码片

1.2288Mcps

增加 8bit尾比特

卷积编码器R ＝ 1/3， L ＝ 9

码符号重复 块交织 64-阶正交调制

9.2kb/s4.4kb/s2.0kb/s0.8kb/s

28.8ks/s 14.4ks/s7.2ks/s3.6ks/s

28.8ks/s 28.8ks/s

码符号 码符号码符号 调制符

9.6kb/s4.8kb/s2.4kb/s1.2kb/s

对 9600&4800增加幀质量指示比8.6kb/s

4.0kb/s2.0kb/s0.8kb/s

数据突发随机化

幀速率数据

Sample masking streams shown are for the 14-bit PN sequence:

(b0, b1, ..., b13) = 0 0 1 0 1 1 0 1 1 0 0 1 0 0

9600 bps frame

Power Control Group Number

Previous Frame

0 1 2 3 4 5 6 7 8 9 11 12 13 14 151015141312

4800 bps frame

Previous Frame

0 1 2 3 4 5 6 7 8 9 11 12 13 14 151015141312

2400 bps frame

Previous Frame

0 1 2 3 4 5 6 7 8 9 11 12 13 14 151015141312

1200 bps frame

Previous Frame

1514 0 1 2 3 4 5 6 7 8 9 11 12 13 14 15101312

192 bits = 576 code symbols = 96 modulation symbols = 16 Power Control Groups20 ms ={

PCG 14 PCG 15

b1 3

b1 2

b1 1

b1 0

b9

b8

b7

b6

b5

b4

b3

b2

b1

b0

PN bits used for scrambling

1.25 ms = {12 bits = 36 code symbols = 6 modulation symbols = 1 Power Control Group

Code Symbols Transmitted: 1 33 65 97 ... 481 513 545 2 34 66 98 ... 482 514 546

Code Symbols Transmitted: 1 17 33 49 ... 241 257 273 2 18 34 50 ... 242 258 274

Code Symbols Transmitted: 1 9 17 25 ... 121 129 137 2 10 18 26 ... 122 130 138

Code Symbols Transmitted: 1 5 9 13 ... 61 65 69 2 6 10 14 ... 62 66 70

反向反向 CDMACDMA 信道可变数据速率传输信道可变数据速率传输

c

c

c

Code Symbols (Output)

Information Bits (Input)

g

g

g

0

1

2

1

0

2

反向链路卷积编码反向链路卷积编码

r ＝ 1/2 ， k＝ 9

I-channel

Q-channel

(0,0)(1,0)

(1,1) (0,1)

(I,Q)I Q Phase

0 0 π/4

1 0 3π/4

1 1 -3π/4

0 1 -π/4

反向反向 CDMACDMA 信道调制信道调制—— OQPSKOQPSK

I 、 Q 映射 星座和相位转移图

f0

2

1

10

fp f s

20log10

| S(f)|

基带滤波基带滤波

频率响应限值频率响应限值

基带滤波基带滤波

分集技术分集技术

最优相干合并

前向链路多径 / 基站分集

非相干最大比合并

反向链路多径 / 基站分集

符号判决 维特比译码器

天线 1 天线 2

直射路径

反射路径

径 1 径 2径 3 径 4

反向链路基带解调

反向链路基带解调

软切换技术软切换技术概念：移动台开始与一个新的基站通信时，并不中断与前一个基站之间的通信特性： 软切换发生在具有相同频率分配的 CDMA 信道之间 软切换提供在基站边界处的前向业务信道和反向业务信道的路径分集

非相干最大比合并符号判决和译码

天线 1 天线 2

小区位置 1

非相干最大比合并符号判决和译码

天线 1 天线 2

小区位置 2

选择更好的幀进行声码器处理 到声码器

语音幀 1 语音幀 2

使用相同参考偏移的 PN 码

Base 1

Base 2

Base 3

小区软切换

小区软切换

Mobile Station Base Station

• Detects user-initiated call

• Sends Origination Message > Access Channel > • Sets up Traffic Channel

• Begins sending null TrafficChannel data

• Sets up Traffic Channel < Paging Channel < • Sends Channel AssignmentMessage

• Receives N5m consecutive

valid frames

• Begins sending the TrafficChannel preamble

• Acquires the Reverse TrafficChannel

• Begins transmitting nullTraffic Channel data

< Forward TrafficChannel

< • Sends Base StationAcknowledgement Order

• Begins processing primarytraffic in accordance withService Option 1

< Forward TrafficChannel

< • Sends Service OptionResponse Order

Optional Optional

• Sends OriginationContinuation Message

> Reverse TrafficChannel

>

Optional Optional

• Applies ring back in audiopath

< Forward TrafficChannel

< • Sends Alert With InformationMessage (ring back tone)

Optional Optional

• Removes ring back fromaudio path

< Forward TrafficChannel

< • Sends Alert With InformationMessage (tones off)

(User conversation) (User conversation)

Simple Call Flow, Mobile Station Origination Example

WCDMA 技术

Core Network

D-RNC S-RNC

Node Bcell cell cell

Node Bcell cell cell

Node Bcell cell cell

Node Bcell cell cell

Iub Iub IubIub

IurIu

UTRANUTRAN 结构结构

UE

NodeB

CRNC SRNC CN

Uu Iub Iur Iu

UMTS UMTS 接口接口

2G 与 3G 网络结构

VLRMSCMSC

VLRMSCMSC SGSNSGSN

GMSCGMSC

BSCBSC

BTSBTS BTSBTS

Abis

BSSBSSBSCBSC

BTSBTS BTSBTS

Abis

BSSBSS

AUCAUC

HLRHLR

EIREIR

PSTN

E

D

C

F

H

A

PSTNPSTN GGSNGGSN PDNPDN

Gb

Gp

Gc

Gf

GnGr

Gs

Other PLMNOther PLMN

RNCRNC

NodeBNodeB NodeBNodeB

Iub

RNSRNSRNCRNC

NodeBNodeB NodeBNodeB

Iub

RNSRNSIur

Iu-CSIu-PS

Iu-PSIu-CS

Gi

PLMN: Public land mobile network UMTS:Universal Mobile Telecommunication System

WCDMA 网络结构

Node Bcell

cellcell

ME

US

IM

SIM

ME

US

IM

SIM

ME

US

IM

SIM

Node Bcell

cellcell

Node Bcell

cellcell

RNC

RNC

MSC

SGSN

GMSC

GGSN

VLR

EIR HLR AuC

UEUE

Iur

IubUu

E

E

DPSTNB

F C

Gs Gf

Gr

Gn

Gi

Gp

Gc

Iu

IuCSCN:Core NetworkCN:Core NetworkRNSRNS

RNSRNS

IuPS

FDD Mode only

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

WCDMAWCDMA空中接口协议结构空中接口协议结构

S -P

30 ksps

30 kspsPilot, PowerControl and TFCI

18 kbps

Time Multiplexer

60 kbps

OVSFCodeGen

3840 kcps

3840 kcps

I 3840 kcps

Q

218 ComplexScramble Code

Generator

Q

I+

+

+

-10 ms segment

Spreading42 kbps

Qscramble

Iscramble

SF=128

Iscramble

Add CRC & Tail Bits

268 bits244 bits1/3 Rate

Conv. Coder

804 bits 688 bits 344 bits688 bitsFrame

SegmentTrCHMux

DTCHData Bits

42 kbps

120 bits96 bits 360 bits 304 bits 76 bits304 bits

20 ms Frames

40 ms Frames

10 ms Frames

34.4 kbps

Add CRC & Tail Bits

1/3 RateConv. Coder

7.6 kbps

Segment& Match

DCCHData Bits

DPCCH

RateMatching

RateMatching

1stInterleaver

1stInterleaver

DPDCH

Frame Segment

CCTrCH

2ndInterleaver

ComplexScrambling

下行下行 DPCHDPCH 编码编码

下行下行 DPCHDPCH 调制调制

T

Im{T}

Re{T}

cos(t)

Complex-valuedchip sequencefrom summingoperations

-sin(t)

Splitreal &imag.parts

Pulse-shaping

Pulse-shaping

G1

G2

GP

GS

S-SCH

P-SCH

(point T in

I

Any downlinkphysical channelexcept SCH

SP

Cch,SF,m

j

Sdl,n

Q

I+jQ S

下行下行 DPCHDPCH 调制星座图调制星座图

Add CRC & Tail Bits

268 bits

Pilot, Power Control, &TFCI

DPCCHData Bits 15 kbps

3840 kcpsSF=256

Data OVSF Generator

3840 kcpsSF=64

244 bits1/3 Rate

Conv. Coder

804 bits1st

Interleaver

804 bitsRate

Matching

490 bits

Gain = - 6 dB

Gain

ComplexScrambling

I+

+

+

-OVSF 2Generator

1,-1

Deciby 2

I 3840 kcps

225 Scramble Code

Generator

Q 3840 kcpsQ

402 bitsFrame

Segment

60 kbps

Control OVSF Generator

Cch,256,

0

Cch,64,16

I Scramble Code

I Scramble Code

Q

Q

DTCHData Bits

60 kbps120 bits96 bits 360 bits 360 bits 110 bits90 bits

DPDCHData Bits

20 ms Frames

40 ms Frames

10 ms Frames

49 kbps

Add CRC & Tail Bits

1/3 RateConv. Coder

1stInterleaver

RateMatching

11 kbps

Segment& Match

DCCHData Bits

TrCHMux

60 kbps

CCTrCH2nd

Interleaver

上行上行 DPCHDPCH 编码编码 // 调制调制

上行上行 DPCHDPCH 调制调制

I

j

cd,1

d

Sdpch,n

I+jQ

DPDCH1

Q

cd,3

d

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Cellular Network Organization Use multiple low-power transmitters (100 W or

less) Areas divided into cells

Each served by its own antenna Served by base station consisting of transmitter,

receiver, and control unit Band of frequencies allocated Cells set up such that antennas of all neighbors are

equidistant (hexagonal pattern)

Frequency Reuse Adjacent cells assigned different frequencies to

avoid interference or crosstalk Objective is to reuse frequency in nearby cells

10 to 50 frequencies assigned to each cell Transmission power controlled to limit power at that

frequency escaping to adjacent cells The issue is to determine how many cells must

intervene between two cells using the same frequency

Approaches to Cope with Increasing Capacity Adding new channels Frequency borrowing – frequencies are taken from

adjacent cells by congested cells Cell splitting – cells in areas of high usage can be

split into smaller cells Cell sectoring – cells are divided into a number of

wedge-shaped sectors, each with their own set of channels

Microcells – antennas move to buildings, hills, and lamp posts

Cellular System Overview

Cellular Systems Terms Base Station (BS) – includes an antenna, a

controller, and a number of receivers Mobile telecommunications switching office

(MTSO) – connects calls between mobile units Two types of channels available between mobile

unit and BS Control channels – used to exchange information

having to do with setting up and maintaining calls Traffic channels – carry voice or data connection

between users

Steps in an MTSO Controlled Call between Mobile Users Mobile unit initialization Mobile-originated call Paging Call accepted Ongoing call Handoff

Additional Functions in an MTSO Controlled Call Call blocking Call termination Call drop Calls to/from fixed and remote mobile

subscriber

Mobile Radio Propagation Effects Signal strength

Must be strong enough between base station and mobile unit to maintain signal quality at the receiver

Must not be so strong as to create too much cochannel interference with channels in another cell using the same frequency band

Fading Signal propagation effects may disrupt the signal and

cause errors

Handoff Performance Metrics Cell blocking probability – probability of a new

call being blocked Call dropping probability – probability that a call

is terminated due to a handoff Call completion probability – probability that an

admitted call is not dropped before it terminates Probability of unsuccessful handoff – probability

that a handoff is executed while the reception conditions are inadequate

Handoff Performance Metrics Handoff blocking probability – probability that a

handoff cannot be successfully completed Handoff probability – probability that a handoff occurs

before call termination Rate of handoff – number of handoffs per unit time Interruption duration – duration of time during a

handoff in which a mobile is not connected to either base station

Handoff delay – distance the mobile moves from the point at which the handoff should occur to the point at which it does occur

Handoff Strategies Used to Determine Instant of Handoff Relative signal strength Relative signal strength with threshold Relative signal strength with hysteresis Relative signal strength with hysteresis and

threshold Prediction techniques

Power Control Design issues making it desirable to include

dynamic power control in a cellular system Received power must be sufficiently above the

background noise for effective communication Desirable to minimize power in the transmitted signal

from the mobile Reduce cochannel interference, alleviate health concerns, save

battery power In SS systems using CDMA, it’s desirable to equalize

the received power level from all mobile units at the BS

Types of Power Control Open-loop power control

Depends solely on mobile unit No feedback from BS Not as accurate as closed-loop, but can react quicker to

fluctuations in signal strength Closed-loop power control

Adjusts signal strength in reverse channel based on metric of performance

BS makes power adjustment decision and communicates to mobile on control channel

Traffic Engineering Ideally, available channels would equal

number of subscribers active at one time In practice, not feasible to have capacity

handle all possible load For N simultaneous user capacity and L

subscribers L < N – nonblocking system L > N – blocking system

Blocking System Performance Questions Probability that call request is blocked? What capacity is needed to achieve a certain

upper bound on probability of blocking? What is the average delay? What capacity is needed to achieve a certain

average delay?

Traffic Intensity Load presented to a system:

= mean rate of calls attempted per unit time h = mean holding time per successful call A = average number of calls arriving during average

holding period, for normalized

hA

Factors that Determine the Nature of the Traffic Model Manner in which blocked calls are handled

Lost calls delayed (LCD) – blocked calls put in a queue awaiting a free channel

Blocked calls rejected and dropped Lost calls cleared (LCC) – user waits before another attempt Lost calls held (LCH) – user repeatedly attempts calling

Number of traffic sources Whether number of users is assumed to be finite or

infinite

First-Generation Analog Advanced Mobile Phone Service (AMPS)

In North America, two 25-MHz bands allocated to AMPS

One for transmission from base to mobile unit One for transmission from mobile unit to base

Each band split in two to encourage competition

Frequency reuse exploited

AMPS Operation Subscriber initiates call by keying in phone number

and presses send key MTSO verifies number and authorizes user MTSO issues message to user’s cell phone

indicating send and receive traffic channels MTSO sends ringing signal to called party Party answers; MTSO establishes circuit and

initiates billing information Either party hangs up; MTSO releases circuit, frees

channels, completes billing

Differences Between First and Second Generation Systems Digital traffic channels – first-generation systems are

almost purely analog; second-generation systems are digital

Encryption – all second generation systems provide encryption to prevent eavesdropping

Error detection and correction – second-generation digital traffic allows for detection and correction, giving clear voice reception

Channel access – second-generation systems allow channels to be dynamically shared by a number of users

Mobile Wireless TDMA Design Considerations Number of logical channels (number of time slots

in TDMA frame): 8 Maximum cell radius (R): 35 km Frequency: region around 900 MHz Maximum vehicle speed (Vm):250 km/hr Maximum coding delay: approx. 20 ms Maximum delay spread (m): 10 s Bandwidth: Not to exceed 200 kHz (25 kHz per

channel)

Steps in Design of TDMA Timeslot

GSM Network Architecture

Mobile Station Mobile station communicates across Um interface

(air interface) with base station transceiver in same cell as mobile unit

Mobile equipment (ME) – physical terminal, such as a telephone or PCS ME includes radio transceiver, digital signal processors

and subscriber identity module (SIM) GSM subscriber units are generic until SIM is

inserted SIMs roam, not necessarily the subscriber devices

Base Station Subsystem (BSS) BSS consists of base station controller and

one or more base transceiver stations (BTS) Each BTS defines a single cell

Includes radio antenna, radio transceiver and a link to a base station controller (BSC)

BSC reserves radio frequencies, manages handoff of mobile unit from one cell to another within BSS, and controls paging

Network Subsystem (NS) NS provides link between cellular network and

public switched telecommunications networks Controls handoffs between cells in different BSSs Authenticates users and validates accounts Enables worldwide roaming of mobile users

Central element of NS is the mobile switching center (MSC)

Mobile Switching Center (MSC) Databases Home location register (HLR) database – stores

information about each subscriber that belongs to it Visitor location register (VLR) database –

maintains information about subscribers currently physically in the region

Authentication center database (AuC) – used for authentication activities, holds encryption keys

Equipment identity register database (EIR) – keeps track of the type of equipment that exists at the mobile station

TDMA Format – Time Slot Fields Trail bits – allow synchronization of transmissions

from mobile units Encrypted bits – encrypted data Stealing bit - indicates whether block contains data or

is "stolen" Training sequence – used to adapt parameters of

receiver to the current path propagation characteristics Strongest signal selected in case of multipath propagation

Guard bits – used to avoid overlapping with other bursts

GSM Speech Signal Processing

GSM Signaling Protocol Architecture

Functions Provided by Protocols Protocols above the link layer of the GSM

signaling protocol architecture provide specific functions: Radio resource management Mobility management Connection management Mobile application part (MAP) BTS management

Advantages of CDMA Cellular Frequency diversity – frequency-dependent

transmission impairments have less effect on signal

Multipath resistance – chipping codes used for CDMA exhibit low cross correlation and low autocorrelation

Privacy – privacy is inherent since spread spectrum is obtained by use of noise-like signals

Graceful degradation – system only gradually degrades as more users access the system

Drawbacks of CDMA Cellular Self-jamming – arriving transmissions from

multiple users not aligned on chip boundaries unless users are perfectly synchronized

Near-far problem – signals closer to the receiver are received with less attenuation than signals farther away

Soft handoff – requires that the mobile acquires the new cell before it relinquishes the old; this is more complex than hard handoff used in FDMA and TDMA schemes

Mobile Wireless CDMA Design Considerations RAKE receiver – when multiple versions of a

signal arrive more than one chip interval apart, RAKE receiver attempts to recover signals from multiple paths and combine them This method achieves better performance than simply

recovering dominant signal and treating remaining signals as noise

Soft Handoff – mobile station temporarily connected to more than one base station simultaneously

Principle of RAKE Receiver

Types of Channels Supported by Forward Link Pilot (channel 0) - allows the mobile unit to acquire

timing information, provides phase reference and provides means for signal strength comparison

Synchronization (channel 32) - used by mobile station to obtain identification information about cellular system

Paging (channels 1 to 7) - contain messages for one or more mobile stations

Traffic (channels 8 to 31 and 33 to 63) – the forward channel supports 55 traffic channels

Forward Traffic Channel Processing Steps Speech is encoded at a rate of 8550 bps Additional bits added for error detection Data transmitted in 2-ms blocks with forward

error correction provided by a convolutional encoder

Data interleaved in blocks to reduce effects of errors

Data bits are scrambled, serving as a privacy mask

Forward Traffic Channel Processing Steps (cont.) Power control information inserted into traffic

channel DS-SS function spreads the 19.2 kbps to a rate of

1.2288 Mbps using one row of 64 x 64 Walsh matrix

Digital bit stream modulated onto the carrier using QPSK modulation scheme

ITU’s View of Third-Generation Capabilities Voice quality comparable to the public switched

telephone network 144 kbps data rate available to users in high-speed

motor vehicles over large areas 384 kbps available to pedestrians standing or moving

slowly over small areas Support for 2.048 Mbps for office use Symmetrical / asymmetrical data transmission rates Support for both packet switched and circuit switched

data services

ITU’s View of Third-Generation Capabilities An adaptive interface to the Internet to reflect

efficiently the common asymmetry between inbound and outbound traffic

More efficient use of the available spectrum in general

Support for a wide variety of mobile equipment Flexibility to allow the introduction of new

services and technologies

Alternative Interfaces

CDMA Design Considerations Bandwidth – limit channel usage to 5 MHz Chip rate – depends on desired data rate, need for

error control, and bandwidth limitations; 3 Mcps or more is reasonable

Multirate – advantage is that the system can flexibly support multiple simultaneous applications from a given user and can efficiently use available capacity by only providing the capacity required for each service

4.3 Cordless Systems and Wireless Local Loop

Cordless System Operating Environments Residential – a single base station can

provide in-house voice and data support Office

A single base station can support a small office Multiple base stations in a cellular

configuration can support a larger office Telepoint – a base station set up in a public

place, such as an airport

Design Considerations for Cordless Standards Modest range of handset from base station,

so low-power designs are used Inexpensive handset and base station,

dictating simple technical approaches Frequency flexibility is limited, so the

system needs to be able to seek a low-interference channel whenever used

Time Division Duplex (TDD) TDD also known as time-compression

multiplexing (TCM) Data transmitted in one direction at a time,

with transmission between the two directions Simple TDD TDMA TDD

Simple TDD Bit stream is divided into equal segments,

compressed in time to a higher transmission rate, and transmitted in bursts

Effective bits transmitted per second:

R = B/2(Tp+Tb+Tg)

R = effective data rate B = size of block in bits Tp = propagation delay Tb = burst transmission time Tg = guard time

Simple TDD Actual data rate, A:

A = B /Tb

Combined with previous equation:

The actual data rate is more than double the effective data rate seen by the two sides

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TDMA TDD Wireless TDD typically used with TDMA

A number of users receive forward channel signals in turn and then transmit reverse channel signals in turn, all on same carrier frequency

Advantages of TDMA/TDD: Improved ability to cope with fast fading Improved capacity allocation

DECT Frame Format Preamble (16 bits) – alert receiver Sync (16 bits) – enable receiver to

synchronize on beginning of time slot A field (64 bits) – used for network control B field (320 bits) – contains user data X field (4 bits) – parity check bits Guard (60 bits) – guard time, Tg

A Field Logical Control Channels Q channel – used to broadcast general system

information from base station to all terminals P channel – provides paging from the base station

to terminals M channel – used by terminal to exchange

medium access control messages with base station N channel – provides handshaking protocol C channel – provides call management for active

connections

B Field B field transmits data in two modes

Unprotected mode - used to transmit digitized voice

Protected mode - transmits nonvoice data traffic

DECT Protocol Architecture

DECT Protocol Architecture Physical layer – data transmitted in TDMA-TDD

frames over one of 10 RF carriers Medium access control (MAC) layer – selects/

establishes/releases connections on physical channels; supports three services: Broadcast Connection oriented Connectionless

Data link control layer – provides for the reliable transmission of messages using traditional data link control procedures

Differential Quantization Speech signals tend not to change much between

two samples Transmitted PCM values contain considerable

redundancy Transmit difference value between adjacent samples

rather than actual value If difference value between two samples exceeds

transmitted bits, receiver output will drift from the true value Encoder could replicate receiver output and additionally

transmit that difference

Differential PCM (DPCM) Since voice signals change relatively slowly, value

of kth sample can be estimated by preceding samples

Transmit difference between sample and estimated sample Difference value should be less than difference between

successive samples At the receiver, incoming difference value is

added to the estimate of the current sample Same estimation function is used

Adaptive Differential PCM (ADPCM) Improve DPCM performance using

adaptive prediction and quantization Predictor and difference quantizer adapt to the

changing characteristics of the speech Modules

Adaptive quantizer Inverse adaptive quantizer Adaptive predictor

ADPCM Encoder

ADPCM Decoder

Subject Measurement of Coder Performance Subjective measurements of quality are

more relevant than objective measures Mean opinion score (MOS) – group of

subjects listen to a sample of coded speech; classify output on a 5-point scale

MOS scale is used in a number of specifications as a standard for quality

Wireless Local Loop Wired technologies responding to need for reliable,

high-speed access by residential, business, and government subscribers ISDN, xDSL, cable modems

Increasing interest shown in competing wireless technologies for subscriber access

Wireless local loop (WLL) Narrowband – offers a replacement for existing telephony

services Broadband – provides high-speed two-way voice and data

service

WLL Configuration

Advantages of WLL over Wired Approach Cost – wireless systems are less expensive due to

cost of cable installation that’s avoided Installation time – WLL systems can be installed

in a small fraction of the time required for a new wired system

Selective installation – radio units installed for subscribers who want service at a given time With a wired system, cable is laid out in anticipation of

serving every subscriber in a given area

Propagation Considerations for WLL Most high-speed WLL schemes use millimeter

wave frequencies (10 GHz to about 300 GHz) There are wide unused frequency bands available above

25 GHz At these high frequencies, wide channel bandwidths

can be used, providing high data rates Small size transceivers and adaptive antenna arrays can

be used

Propagation Considerations for WLL Millimeter wave systems have some

undesirable propagation characteristics Free space loss increases with the square of the

frequency; losses are much higher in millimeter wave range

Above 10 GHz, attenuation effects due to rainfall and atmospheric or gaseous absorption are large

Multipath losses can be quite high

Fresnel Zone How much space around direct path between

transmitter and receiver should be clear of obstacles? Objects within a series of concentric circles around the line

of sight between transceivers have constructive/destructive effects on communication

For point along the direct path, radius of first Fresnel zone:

S = distance from transmitter D = distance from receiver DS

SDR

Atmospheric Absorption Radio waves at frequencies above 10 GHz

are subject to molecular absorption Peak of water vapor absorption at 22 GHz Peak of oxygen absorption near 60 GHz

Favorable windows for communication: From 28 GHz to 42 GHz From 75 GHz to 95 GHz

Effect of Rain Attenuation due to rain

Presence of raindrops can severely degrade the reliability and performance of communication links

The effect of rain depends on drop shape, drop size, rain rate, and frequency

Estimated attenuation due to rain:

A = attenuation (dB/km) R = rain rate (mm/hr) a and b depend on drop sizes and frequency

baRA

Effects of Vegetation Trees near subscriber sites can lead to multipath

fading Multipath effects from the tree canopy are

diffraction and scattering Measurements in orchards found considerable

attenuation values when the foliage is within 60% of the first Fresnel zone

Multipath effects highly variable due to wind

Multipoint Distribution Service (MDS) Multichannel multipoint distribution service

(MMDS) Also referred to as wireless cable Used mainly by residential subscribers and small

businesses Local multipoint distribution service (LMDS)

Appeals to larger companies with greater bandwidth demands

Advantages of MMDS MMDS signals have larger wavelengths and

can travel farther without losing significant power

Equipment at lower frequencies is less expensive

MMDS signals don't get blocked as easily by objects and are less susceptible to rain absorption

Advantages of LMDS Relatively high data rates Capable of providing video, telephony, and

data Relatively low cost in comparison with

cable alternatives

802.16 Standards Development Use wireless links with microwave or millimeter

wave radios Use licensed spectrum Are metropolitan in scale Provide public network service to fee-paying

customers Use point-to-multipoint architecture with

stationary rooftop or tower-mounted antennas

802.16 Standards Development Provide efficient transport of heterogeneous traffic

supporting quality of service (QoS) Use wireless links with microwave or millimeter

wave radios Are capable of broadband transmissions (>2

Mbps)

IEEE 802.16 Protocol Architecture

Protocol Architecture Physical and transmission layer functions:

Encoding/decoding of signals Preamble generation/removal Bit transmission/reception

Medium access control layer functions: On transmission, assemble data into a frame with

address and error detection fields On reception, disassemble frame, and perform address

recognition and error detection Govern access to the wireless transmission medium

Protocol Architecture Convergence layer functions:

Encapsulate PDU framing of upper layers into native 802.16 MAC/PHY frames

Map upper layer’s addresses into 802.16 addresses

Translate upper layer QoS parameters into native 802.16 MAC format

Adapt time dependencies of upper layer traffic into equivalent MAC service

IEEE 802.16.1 Services Digital audio/video multicast Digital telephony ATM Internet protocol Bridged LAN Back-haul Frame relay

IEEE 802.16.3 Services Voice transport Data transport Bridged LAN

IEEE 802.16.1 Frame Format

IEEE 802.16.1 Frame Format Header - protocol control information

Downlink header – used by the base station Uplink header – used by the subscriber to convey

bandwidth management needs to base station Bandwidth request header – used by subscriber to

request additional bandwidth Payload – either higher-level data or a MAC

control message CRC – error-detecting code

MAC Management Messages Uplink and downlink channel descriptor Uplink and downlink access definition Ranging request and response Registration request, response and acknowledge Privacy key management request and response Dynamic service addition request, response and

acknowledge

MAC Management Messages Dynamic service change request, response,

and acknowledge Dynamic service deletion request and

response Multicast polling assignment request and

response Downlink data grant type request ARQ acknowledgment

Physical Layer – Upstream Transmission Uses a DAMA-TDMA technique Error correction uses Reed-Solomon code Modulation scheme based on QPSK

Physical Layer – Downstream Transmission Continuous downstream mode

For continuous transmission stream (audio, video) Simple TDM scheme is used for channel access Duplexing technique is frequency division duplex (FDD)

Burst downstream mode Targets burst transmission stream (IP-based traffic) DAMA-TDMA scheme is used for channel access Duplexing techniques are FDD with adaptive modulation,

frequency shift division duplexing (FSDD), time division duplexing (TDD)

4.4 Mobile IP and Wireless Application Protocol

Mobile IP Uses Enable computers to maintain Internet

connectivity while moving from one Internet attachment point to another

Mobile – user's point of attachment changes dynamically and all connections are automatically maintained despite the change

Nomadic - user's Internet connection is terminated each time the user moves and a new connection is initiated when the user dials back in New, temporary IP address is assigned

Operation of Mobile IP Mobile node is assigned to a particular

network – home network IP address on home network is static –

home address Mobile node can move to another network –

foreign network Mobile node registers with network node on

foreign network – foreign agent Mobile node gives care-of address to agent

on home network – home agent

Capabilities of Mobile IP Discovery – mobile node uses discovery

procedure to identify prospective home and foreign agents

Registration – mobile node uses an authenticated registration procedure to inform home agent of its care-of address

Tunneling – used to forward IP datagrams from a home address to a care-of address

Discovery Mobile node is responsible for ongoing discovery

process Must determine if it is attached to its home network or a foreign

network

Transition from home network to foreign network can occur at any time without notification to the network layer

Mobile node listens for agent advertisement messages Compares network portion of the router's IP address with the

network portion of home address

Agent Solicitation Foreign agents are expected to issue agent

advertisement messages periodically If a mobile node needs agent information

immediately, it can issue ICMP router solicitation message Any agent receiving this message will then

issue an agent advertisement

Move Detection

Mobile node may move from one network to another due to some handoff mechanism without IP level being aware Agent discovery process is intended to enable the agent to

detect such a move

Algorithms to detect move: Use of lifetime field – mobile node uses lifetime field as a

timer for agent advertisements Use of network prefix – mobile node checks if any newly

received agent advertisement messages are on the same network as the node's current care-of address

Co-Located Addresses If mobile node moves to a network that has

no foreign agents, or all foreign agents are busy, it can act as its own foreign agent

Mobile agent uses co-located care-of address IP address obtained by mobile node associated with

mobile node's current network interface

Means to acquire co-located address: Temporary IP address through an Internet service, such

as DHCP May be owned by the mobile node as a long-term

address for use while visiting a given foreign network

Registration Process Mobile node sends registration request to

foreign agent requesting forwarding service Foreign agent relays request to home agent Home agent accepts or denies request and

sends registration reply to foreign agent Foreign agent relays reply to mobile node

Registration Operation Messages Registration request message

Fields = type, S, B, D, M, V, G, lifetime, home address, home agent, care-of-address, identification, extensions

Registration reply message Fields = type, code, lifetime, home address,

home agent, identification, extensions Note: S—Simultaneous bindingsB—Broadcast datagramsD—Decapsulation by mobile nodeM—Minimal encapsulationV—Van Jacobson header compressionG—GRE (Generic routing encapsulation) encapsulation

Registration Procedure Security Mobile IP designed to resist attacks

Node pretending to be a foreign agent sends registration request to a home agent to divert mobile node traffic to itself

Agent replays old registration messages to cut mobile node from network

For message authentication, registration request and reply contain authentication extension Fields = type, length, security parameter index (SPI),

authenticator

Types of Authentication Extensions Mobile-home – provides for authentication of

registration messages between mobile node and home agent; must be present

Mobile-foreign – may be present when a security association exists between mobile node and foreign agent

Foreign-home – may be present when a security association exists between foreign agent and home agent

Tunneling Home agent intercepts IP datagrams sent to

mobile node's home address Home agent informs other nodes on home

network that datagrams to mobile node should be delivered to home agent

Datagrams forwarded to care-of address via tunneling Datagram encapsulated in outer IP datagram

Mobile IP Encapsulation Options IP-within-IP – entire IP datagram becomes payload in

new IP datagram Original, inner IP header unchanged except TTL

decremented by 1 Outer header is a full IP header

Minimal encapsulation – new header is inserted between original IP header and original IP payload Original IP header modified to form new outer IP header

Generic routing encapsulation (GRE) – developed prior to development of Mobile IP

Wireless Application Protocol (WAP)

Open standard providing mobile users of wireless terminals access to telephony and information services Wireless terminals include wireless phones, pagers

and personal digital assistants (PDAs) Designed to work with all wireless network

technologies such as GSM, CDMA, and TDMA Based on existing Internet standards such as IP,

XML, HTML, and HTTP Includes security facilities

WAP Protocol Stack

WAP Programming Model

Wireless Markup Language (WML) Features Text and image support – formatting and

layout commands Deck/card organizational metaphor – WML

documents subdivided into cards, which specify one or more units of interaction

Support for navigation among cards and decks – includes provisions for event handling; used for navigation or executing scripts

Wireless Markup Language (WML) Features Text and image support – formatting and layout

commands Deck/card organizational metaphor – WML

documents subdivided into cards, which specify one or more units of interaction

Support for navigation among cards and decks – includes provisions for event handling; used for navigation or executing scripts

WMLScript Scripting language for defining script-type

programs in a user device with limited processing power and memory

WMLScript capabilities: Check validity of user input before it’s sent Access device facilities and peripherals Interact with user without introducing round

trips to origin server

WMLScript WMLScript features:

JavaScript-based scripting language Procedural logic Event-based Compiled implementation Integrated into WAE

Wireless Application Environment (WAE) WAE specifies an application framework for wireless

devices WAE elements:

WAE User agents – software that executes in the wireless device Content generators – applications that produce standard content

formats in response to requests from user agents in the mobile terminal

Standard content encoding – defined to allow a WAE user agent to navigate Web content

Wireless telephony applications (WTA) – collection of telephony-specific extensions for call and feature control mechanisms

WAE Client Components

Wireless Session Protocol (WSP) Transaction-oriented protocol based on the

concept of a request and a reply Provides applications with interface for two

session services: Connection-oriented session service – operates

above reliable transport protocol WTP Connectionless session service – operates

above unreliable transport protocol WDP

Connection-mode WSP Services Establish reliable session from client to server and

release Agree on common level of protocol functionality

using capability negotiation Exchange content between client and server using

compact encoding Suspend and resume a session Push content from server to client in an

unsynchronized manner

WSP Transaction Types Session establishment – client WSP user requests

session with server WSP user Session termination – client WSP user initiates

termination Session suspend and resume – initiated with suspend

and resume requests Transaction – exchange of data between a client and

server Nonconfirmed data push – used to send unsolicited

information from server to client Confirmed data push – server receives delivery

confirmation from client

Wireless Transaction Protocol (WTP) Lightweight protocol suitable for "thin" clients and

over low-bandwidth wireless links WTP features

Three classes of transaction service Optional user-to-user reliability: WTP user triggers

confirmation of each received message Optional out-of-band data on acknowledgments PDU concatenation and delayed acknowledgment to

reduce the number of messages sent Asynchronous transactions

WTP Transaction Classes Class 0: Unreliable invoke message with no

result message Class 1: Reliable invoke message with no

result message Class 2: Unreliable invoke message with

one reliable result message

WTP PDU Types Invoke PDU – used to convey a request from an initiator to

a responder ACK PDU – used to acknowledge an Invoke or Result PDU Result PDU – used to convey response of the server to the

client Abort PDU – used to abort a transaction Segmented invoke PDU and segmented result PDU – used

for segmentation and reassembly Negative acknowledgment PDU – used to indicate that

some packets did not arrive

Examples of WTP Operation

Wireless Transport Layer Security (WTLS) Features Data integrity – ensures that data sent between client

and gateway are not modified, using message authentication

Privacy – ensures that the data cannot be read by a third party, using encryption

Authentication – establishes authentication of the two parties, using digital certificates

Denial-of-service protection – detects and rejects messages that are replayed or not successfully verified

WTLS Protocol Stack WTLS consists of two layers of protocols

WTLS Record Protocol – provides basic security services to various higher-layer protocols

Higher-layer protocols: The Handshake Protocol The Change Cipher Spec Protocol The Alert Protocol

WTLS Protocol Stack

WTLS Record Protocol Operation

Phases of the Handshake Protocol Exchange First phase – used to initiate a logical connection

and establish security capabilities Second phase – used for server authentication and

key exchange Third phase – used for client authentication and

key exchange Forth phase – completes the setting up of a secure

connection

Wireless Datagram Protocol (WDP) Used to adapt higher-layer WAP protocol to the

communication mechanism used between mobile node and WAP gateway

WDP hides details of the various bearer networks from the other layers of WAP

Adaptation may include: Partitioning data into segments of appropriate size for

the bearer Interfacing with the bearer network

Wireless Control Message Protocol (WCMP) Performs the same support function for WDP as

ICMP does for IP Used in environments that don’t provide IP bearer

and don’t lend themselves to the use of ICMP Used by wireless nodes and WAP gateways to

report errors encountered in processing WDP datagrams

Can also be used for informational and diagnostic purposes