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
卫星轨道平面与地球赤道平面
的夹角示意图
地球赤道

赤道轨道
θ = 0° ，赤道轨道卫星
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
卫星轨道平面与地球赤道
平面的夹角示意图
地球赤道
倾斜轨道

0°< θ < 90°,倾斜轨道卫星
卫星轨道平面与地球赤道平面的
夹角示意图
θ=90° 极轨道
0<θ<90°倾斜轨道
θ=0赤 道轨道
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
静止卫星
35786KM
AB 间 弧 长
18100KM
B
A
地球
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
P1
P2
P3
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 Categorize
Communications Satellites

Coverage area


Service type




Global, regional, national
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



Orbit around earth in different planes




Circular with center at earth’s center
Elliptical with one foci at earth’s center
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



Earth stations take turns using uplink channel


Sends data in assigned time slot
Satellite repeats incoming transmissions


Each frame is divided into a number of time slots
Each slot is dedicated to a particular transmitter
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
蜂窝—频率复用方式
FDMA 频率复用
2
2
6
CDMA 频率复用
1
1
1
3
4
2
6
5
7
1
1
1
1
1
1
1
1
FDMA—蜂窝覆盖
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
扇区的裂变
Sector-1
Sector-1
Sector-6
Sector-2
Sector-5
Sector-3
Sector-3
Sector-2
Sector-4
G = 3 x 0.85 = 2.55
* 扇区的重叠按 15 %记
G = 6 x 0.85 = 5.1
蜂窝在通信网的位置
Radio tower
EXCHANG
Radio tower
Radio tower
Radio tower
RNC
MSC
Radio tower
Radio tower
RNC
EXCHANG
Radio tower
蜂窝系统的小区切换
Base 2
Base 1
Base 3
移动通信网络结构
PSTN
PSTN
AUC
GMSC
H
C
HLR
D
E
VLR
MSC
VLR
MSC
A
BSS
A
BSS
BSC
BSC
Abis
Abis
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
BTS
Radio tower
Radio tower
Radio tower
Radio tower
BTS
Radio tower
Radio tower
Radio tower
Radio tower
BTS
Radio tower
BTS
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
Radio tower
终端用户漫游
AUC
H
HLR
PSTN
GMSC
E
MSC
A
BSS
BSC
Abis
BTS
BTS
H
C
C
D
VLR
AUC
GMSC
HLR
D
VLR
VLR
MSC
MSC
A
A
BSS
BSC
Abis
BTS
E
BTS
BSS
BSC
Abis
BTS
BTS
VLR
MSC
A
BSS
BSC
Abis
BTS
BTS
移动通信的信号传输处理技术
 编码技术
语音编码（信源编码）
信道编码（卷积编码、Turbo编码）
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
信源
信源编码
信道编码
调制
解调
信道解码
信源解码
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
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
系统卷积编码技术
g
c
0
Information Bits
(Input)
0
Code Symbols
(Output)
g
1
c
1
（前向链路卷积编码：编码率＝1/2，约束长度＝9）
Turbo编码技术
Systematic 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
64 kbps
Output
Parity Path
64 kbps
Input
+
+
D
D
+
64 kbps
Output
+
64 kbps
Output
D
+
Interleaver
Parity Path
+
+
D
D
D
+
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
写出
写入
a1 a2
b1 b2
an
bn
m1 m2
mn
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
ASK(幅移键控）
非恒定包络 QAM（正交幅度调制）
MQAM（星座调制）
数字调制
BFSK(二进制频移键控）
FSK
(频移键控） MFSK（多进制频移键控）
BPSK（二进制相移键控）
DPSK（差分二进制相移键控）
PSK
OQPSK(参差QPSK）
QPSK
恒定包络 （相移键控）
(正交四相 л/4QPSK
相移键控） DQPSK（差分QPSK）
MSK（最小频移键控）
CPM
GMSK（高斯成型MSK）
（连续相位调制）
TFM（平滑调频）
移动通信中的调制技术
模拟调制技术---FM
应用：第一代模拟蜂窝移动通信系统
恒定包络调制技术---FSK、MSK、GFSK、GMSK
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
MSK调制/解调技术
调制器
ak码
解调器
差分
编码
b k码
串/并
转换
GMSK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
BPSK调制技术
调制器
m（t）


星座图
Q
x（t）
cosct
S（t）
I
解调器
y（t）

cosct
LPF

S（t）
1 T
0
T∫dt
r（t）
QPSK调制技术
调制器
Rb/2
输入
Rb
串并
变换
接收
信号
90°相移
载波恢
复电路
QPSK
信号
判决电路
LPF
符号时
序恢复
90°相移

BPF

LPF

BPF
﹢
本振
Rb/2
解调器

LPF
LPF
判决电路
复用
恢复电路
QPSK调制技术
星座图
Q
Q
I
I
载波相位为
载波相位为
(0，/2， ， 3/2)
(/4， 3/4, 5/4, 7/4)
OQPSK调制技术
调制器
解调器
QPSK调制技术
星座图
Q
Q
I
I
载波相位为
载波相位为
(0，/2， ， 3/2)
(/4， 3/4, 5/4, 7/4)
分集技术
接收多路不相关的信号并合并。
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
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
合并
直射路径
反射路径
最大比合并
RAKE接收机技术
CDMA系统
CDMA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
CDMA直接序列扩频技术
390
9.6 kHz BW
1.25 MHz BW
fc
0
fc
0
CDMA Transmitter
Baseband
Data
Encoding &
Interleaving
-100 dB/Hz
9.6 kHz BW
1.25 MHz BW
CDMA Receiver
Long & Short
Code
Spreading
Spurious Signals
Long &
Short Code
Correlator
Decode &
Deinterleaving
1.25 MHz BW
fc
fc
fc
Background Noise
External Interference
Other Cell Interference
Interference Sources
1.25
Baseband
Data
MHz BW
fc
Other User Noise
CDMA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
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 功率控制
{
前向功率控制
反向功率控制
{
开环功率控制
闭环功率控制
{
内环功率控制
外环功率控制
IS95 CDMA 地址码的选择
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）
42
x41
41
x40
40
x39
39
10
9
8
+
7
+
x10
x9
x8
x7
x6
Modulo-2 Addition
x42
前向链路用于扰码
直接序列扩频—PN码长码发生器
反向链路用于扩频
MSB
ESN = (E 31 , E 30 , E 29 , E 28 , E 27 , E 26 , E 25 , . . . E 2 , E 1 , E 0 )
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 ,
Long Code
E 14 , E 5 , E 27 , E 18 , E 9 )
6
+
x5
5
x4
4
+
公用长码掩码：
x3
3
+
M 41 ～ M32 = 1100011000
重排的ESN
M 31 ～ M0 =
x2
2
+
E 2 , E 24 , E 15 , E 6 , E 28 , E 19 , E 10 , E 1 , E 23 ,
x
1
1
42
LSB
42-bit Long Code Mask
PN码短码发生器
PI(x) = x 15 + x13 + x9 + x8 + x7 + x5 + 1
PQ(x) = x 15 + 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
Walsh函数
特性：
构造：
H1 = 0
0
0
H4 =
0
0
0
1
0
1
H2 =
0
0
1
1
0
1
1
0
00
01
HN HN
H2N =
HN
HN
 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
Walsh函数
1 1 1 1
1 1 1 1
1 1 1 1
1 1 1 1
x
1
1
=
1
1
0
4
0
0
前向链路信道结构
FORWARD CDMA CHANNEL
(1.23 MHz channe l
transmi tted by base stati on)
Pi lot
Chan
W0
Paging Traffi c
Sync Paging
•••
Ch 1
Chan Ch 1
Up Ch 7
to
W32
W1
W7
W8
c
Traffi c
••• Traffi
•••
Ch N
Ch 24
W = Code Channel
Numbe r
Traffi c Data
Up
to
W31
Mobile Power
Control
Sub-Channel
Traffi c
Traffi c
•••
Ch 25 Up Ch 55
W33 to W63
IS-95系统：信号在频域和码域上的分布情况
Pilot
Synch
Paging
Frequency Domain
User #3
User #2
User #1
freq
1.2288 MHz
Code Domain
Walsh Code
0
1
2
Pilot Paging
3
4
5
6
7
8
9
User User
1
2
32
Synch
40
User
3
63
前向链路信道调制
前向链路导频信道调制
215
导频信道
I信道序列
1.2288Mcps
＋
全0
（无数据）
I
基带滤波
×
I（t）
cos（2fc t）
＋
＋
W
0
215Q信道序列
1.2288Mcps
Q
基带滤波
×
Q（t）
sin（2fc t）
∑
s（t）
前向链路同步信道调制
码符号
同步信道幀结构
卷积编码器
码符号重复
R＝1/2，L＝9
1.2kb/s
码符号
2.4kb/s
215
I信道序列
1.2288Mcps
＋
码符号
块交织
4.8kb/s
I
基带滤波
4.8kb/s
×
I（t）
cos（2fc t）
＋
＋
W
32
215Q信道序列
1.2288Mcps
Q
基带滤波
×
Q（t）
sin（2fc t）
∑
s（t）
前向链路寻呼信道调制
242长码发生器
码符号
寻呼信道幀结构
卷积编码器
9.6kb/s
4.8kb/s
R＝1/2，L＝9
抽样器：64个
码片抽样一个
码符号
码符号重复
215
块交织
I信道序列
1.2288Mcps
＋
I
基带滤波
＋
k＝1，2，…7
×
I（t）
cos（2fc t）
＋
k
＋
19.2kb/s
19.2kb/s
9.6kb/s
W
19.2kb/s
215Q信道序列
1.2288Mcps
Q
基带滤波
×
Q（t）
sin（2fc t）
∑
s（t）
前向链路业务信道调制
业务信道 对9600
信息比特 &4800
增加幀
质量
8.6kb/s 指示比
4.0kb/s
2.0kb/s
0.8kb/s
码符号
增加8bit
尾比特
卷积编码器
28.8ks/s
14.4ks/s
7.2ks/s
3.6ks/s
215
功率控制位
800Hz
＋
19.2kb/s
242长码
发生器
抽样器：64个
码片抽样一个
复用
定时
控制
抽样
码符号重复
R＝1/2，L＝9
9.6kb/s
4.8kb/s
2.4kb/s
1.2kb/s
9.2kb/s
4.4kb/s
2.0kb/s
0.8kb/s
I信道序列
1.2288Mcps I
＋
M
U
X
码符号
基带滤波
＋
j
块交织
28.8ks/s
×
I（t）
cos（2fc t）
＋
W
码符号
215Q信道序列
1.2288Mcps
Q
基带滤波
×
∑
s（t）
Q（t）
sin（2fc t）
前向链路卷积编码
g
c
0
Information Bits
(Input)
0
Code Symbols
(Output)
g
1
r＝1/2，k＝9
c
1
前向CDMA信道调制—QPSK
星座和相位转移图
I、Q 映射
Q-channel
I
Q
Phase
0
0
π/4
1
0
3π/4
1
1
-3π/4
0
1
-π/4
(1,0)
(0,0)
(I,Q)
I-channel
(1,1)
(0,1)
反向链路信道结构
REVERSE CDMA CHANNEL
(1.23 MHz channel re ce i ved
by base stati on)
Acce ss • • • Acce ss T raffi c • • • • • • • • • • • • • • • • • • • • • • • •
Ch 1
Ch n Ch 1
Addre sse d by Long Code PNs
T raffi c
Ch m
反向接入信道调制
码符号
接入信道幀结构
增加8bit
4.4kb/s 尾比特
卷积编码器
码符号重复
R＝1/3，L＝9
4.8kb/s
码符号
14.4ks/s
I信道序列
1.2288Mcps
＋
＋
PN码片
1.2288Mcps
242长码发生器
长码掩码
码符号
Q信道序列
1.2288Mcps
28.8ks/s
307.2kcps
I
基带滤波
延时1/2PN码片＝406.9ns
Q
基带滤波
＋
D
64-阶
正交调制
块交织
28.8ks/s
调制符
×
I（t）
cos（2fc t）
×
Q（t）
sin（2fc t）
∑
s（t）
反向业务信道调制
业务信道 对9600
信息比特 &4800
增加幀
质量
8.6kb/s 指示比
4.0kb/s
2.0kb/s
0.8kb/s
码符号
增加8bit
尾比特
卷积编码器
28.8ks/s
14.4ks/s
7.2ks/s
3.6ks/s
I信道序列
1.2288Mcps
幀速率数据
数据突发
随机化
码符号重复
R＝1/3，L＝9
9.6kb/s
4.8kb/s
2.4kb/s
1.2kb/s
9.2kb/s
4.4kb/s
2.0kb/s
0.8kb/s
码符号
＋
＋
PN码片
1.2288Mcps
242长码发生器
长码掩码
码符号
Q信道序列
1.2288Mcps
28.8ks/s
307.2kcps
I
基带滤波
延时1/2PN码片＝406.9ns
Q
基带滤波
＋
D
64-阶
正交调制
块交织
28.8ks/s
调制符
×
I（t）
cos（2fc t）
×
∑
s（t）
Q（t）
sin（2fc t）
反向CDMA信道可变数据速率传输
20 ms
=
bits = 576 code s ymbol s =
{ 192
96 modul ation s ymbo ls = 16 Powe r Co ntrol
1.25 ms
bits = 36 code s ymbols
{ 12
6 modula tion s ymbol s = 1
=
G roups
=
Powe r Control Gro up
Pre v ious Fr ame
12
13
14
15
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
9600 bps
frame
11
12
13
14
15
4800 bps
frame
11
12
13
14
15
2400 bps
frame
12
13
14
15
1200 bps
frame
Pow e r Con trol Gro up Numbe r
Cod e Symb ols T ra nsmitte d:
1 33 65 97 ... 481 5 13 545 2 34 6 6 98 ... 482 51 4 546
Pre v ious Fr ame
12
13
14
15
0
1
2
3
4
5
6
7
8
9
10
Cod e Symb ols T ra nsmitte d:
1 17 33 49 ... 241 2 57 273 2 18 3 4 50 ... 242 25 8 274
Pre v ious Fr ame
12
13
14
15
0
1
2
3
4
5
6
7
8
9
10
Cod e Symb ols T ra nsmitte d:
1 9 17 25 .. . 121 12 9 137 2 10 18 26 ... 1 22 130 138
Pre v ious Fr ame
12
13
14
15
0
1
2
3
4
5
6
7
8
9
10
11
Cod e Symb ols T ra nsmitte d:
1 5 9 13 ... 61 65 6 9 2 6 1 0 14 ... 62 66 7 0
Sample mas kin g s tre ams s hown
are for th e 14-bit PN s e que nce :
(b0, b1, . .., b13) = 0 0 1 0 1 1 0 1 1 0 0 1 0 0
PN b its use d
for s crambl ing
b
0
b
1
b
2
b
3
b
4
b
5
b
6
b
7
b
8
PCG 14
b
9
b
1
0
b
1
1
b
1
2
b
1
3
PCG 15
反向链路卷积编码
g0
Informati on
Bi ts
(Input)
c0
Code
Symbols
(Output)
g
1
g2
r＝1/2，k＝9
c1
c2
反向CDMA信道调制—OQPSK
I、Q 映射
星座和相位转移图
Q-channel
I
Q
Phase
0
0
π/4
1
0
3π/4
1
1
-3π/4
0
1
-π/4
(1,0)
(0,0)
(I,Q)
I-channel
(1,1)
(0,1)
基带滤波
2 0log
0
10
| S (f)|
1
1
2
0
fp
fs
频率响应限值
f
基带滤波
直射路径
分集技术
天线1
反射路径
径1
最优相干合并
径2
天线2
径3
非相干最大比合并
符号判决
前向链路多径/基站分集
径4
维特比译码器
反向链路多径/基站分集
反向链路基带解调
反向链路基带解调
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
使用相同参考偏移的PN码
天线1
天线2
天线1
天线2
小区位置1
小区位置2
非相干最大比合并
符号判决和译码
非相干最大比合并
符号判决和译码
语音幀1
语音幀2
选择更好的幀进行声码器处理
到声码器
小区软切换
Base 2
Base 1
Base 3
小区软切换
Simple Call Flow, Mobile Station Origination Example
Mobile Station
Base Station
• Detects user-initiated call
• Sends Origination Message
>
Access Channel
>
• Sets up Traffic Channel
• Begins sending null Traffic
Channel data
• Sets up Traffic Channel
<
Paging Channel
<
• Sends Channel Assignment
Message
• Receives N5m consecutive
valid frames
• Begins sending the Traffic
Channel preamble
• Acquires the Reverse Traffic
Channel
• Begins transmitting null
Traffic Channel data
<
Forward Traffic
Channel
<
• Sends Base Station
Acknowledgement Order
• Begins processing primary
traffic in accordance with
Service Option 1
<
Forward Traffic
Channel
<
• Sends Service Option
Response Order
Optional
• Sends Origination
Continuation Message
Optional
>
Reverse Traffic
Channel
>
Optional
• Applies ring back in audio
path
Optional
<
Forward Traffic
Channel
<
Optional
• Removes ring back from
audio path
(User conversation)
• Sends Alert With Information
Message (ring back tone)
Optional
<
Forward Traffic
Channel
<
• Sends Alert With Information
Message (tones off)
(User conversation)
WCDMA技术
UTRAN结构
Core Network
Iu
Iur
D-RNC
cell
cell
cell
Node B
cell
cell
Iub
Iub
Iub
Iub
Node B
S-RNC
cell
Node B
cell
cell
cell
Node B
cell
cell
cell
UMTS 接口
Node
B
UE
Uu
CRNC
Iub
SRNC
Iur
CN
Iu
2G 与3G网络结构
PSTN
PSTN
AUC
GMSC
C
E
MSC
A
BSS
BSC
Abis
BTS
BTS
Gf
Gs
MSC
Iu-CS
RNS
Gr
EIR
F
VLR
Gn
PDN
Other PLMN
Gp
SGSN
Iu-PS
Iu-CS
RNC
Gi
Gc
HLR
D
VLR
GGSN
H
Gb
Iu-PS
RNS
Iur
RNC
Iub
Iub
NodeB NodeB
NodeB NodeB
PLMN: Public land mobile network
UMTS:Universal Mobile Telecommunication System
BSS
BSC
Abis
BTS
BTS
WCDMA 网络结构
RNS
cell
UE
IuCS
Node B
cell
ME
CN:Core Network
RNC
MSC
E
cell
SIM
USIM
GMSC
B
cell
F
C
EIR
FDD Mode
only
cell
Gs
HLR
Gf
AuC
Gc
cell
SIM
USIM
Node B
ME
PSTN
D
VLR
Iur
Gr
cell
RNC
cell
Uu
cell
SIM
USIM
Node B
ME
SGSN
IuPS
Iub
Iu
RNS
E
Gi
GGSN
Gn
Gp
WCDMA空中接口协议结构
Network Layer
Layer 3
Radio Resource Control
Radio Link Control
Data Link Layer
RRC
RLC
Logical Channels
Layer 2
Medium Access Control
MAC
Transport Channels
Physical Layer
Layer 1
Physical Channels
下行DPCH编码
20 ms Frames
10 ms Frames
244 bits
DTCH
Data Bits
268 bits
Add CRC &
Tail Bits
804 bits
1/3 Rate
Conv. Coder
688 bits
Rate
Matching
688 bits
1st
Interleaver
96 bits
DCCH
Data Bits
120 bits
Add CRC &
Tail Bits
360 bits
1/3 Rate
Conv. Coder
304 bits
Rate
Matching
304 bits
Segment
1st
& Match
Interleaver
344 bits 34.4 kbps
Frame
Segment
TrCH
Mux
76 bits
Frame
Segment
CCTrCH
2nd
Interleaver
42 kbps
7.6 kbps
40 ms Frames
DPDCH
Spreading
42 kbps
I
Pilot, Power
Control and TFCI
DPCCH
30 ksps
SF=128
Iscramble
3840 kcps
+
I
10 ms segment
-
18 kbps
60 kbps
Time Multiplexer
S -P
OVSF
Code
Gen
218 Complex
Scramble Code
Generator
Complex
Scrambling
Qscramble
+
3840 kcps
Q 30 ksps
3840 kcps
Iscramble
+
Q
下行DPCH调制
I
Any downlink
physical channel
except SCH
S

P
Sdl,n
G1
S
I+jQ
Cch,SF,m
G2
Q


P-SCH
GP
j
S-SCH
GS
cos(t)
Complex-valued
chip sequence
from summing
operations
T
Split
real &
imag.
parts
Re{T}
Pulseshaping
Im{T}
Pulseshaping
-sin(t)
(point T in
下行DPCH调制星座图
上行DPCH编码/调制
20 ms Frames
10 ms Frames
244 bits
DTCH
Data Bits
268 bits
Add CRC & Tail
Bits
804 bits
1/3 Rate
Conv. Coder
804 bits
1st
Interleaver
402 bits
Frame
Segment
490 bits
Rate
Matching
96 bits
DCCH
Data Bits
120 bits
Add CRC & Tail
Bits
360 bits
1/3 Rate
Conv. Coder
360 bits
1st
Interleaver
90 bits
Segment
& Match
110 bits
Rate
Matching
49 kbps
CCTrCH
TrCH
Mux
60 kbps
11 kbps
40 ms Frames
60 kbps
I
DPDCH
Data Bits
3840 kcps
DPCCH
Data Bits
Cch,64,16
Data OVSF
Generator
Cch,256,0
Control OVSF
Generator
3840 kcps
15 kbps
3840 kcps
SF=64
SF=256
I Scramble Code
OVSF 2
Generator
Gain
1,-1
225
Scramble Code
Generator
Q 3840 kcps
Pilot, Power Control,
&TFCI
+
-
Q
I
Complex
Scrambling
Deci
by 2
I Scramble Code
Gain = - 6 dB
2nd
60 kbps
Interleaver
Q
+
+
Q
上行DPCH调制
cd,1
d
cd,3
d
DPDCH1

DPDCH3
cd,5
I
d
DPDCH5
Sdpch,n
I+jQ
cd,2
d
cd,4
d
cd,6
d
cc
c
S
DPDCH2
DPDCH4
DPDCH6
DPCCH

Q
j
上行DPCH调制星座图
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:
A  h



 = 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 
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 lowinterference 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:
 Tp  Tg 

A  2 R1 
Tb 

The actual data rate is more than double the
effective data rate seen by the two sides
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:
R


SD
SD
S = distance from transmitter
D = distance from receiver
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  aR



b
A = attenuation (dB/km)
R = rain rate (mm/hr)
a and b depend on drop sizes and frequency
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 bindings
B—Broadcast datagrams
D—Decapsulation by mobile node
M—Minimal encapsulation
V—Van Jacobson header compression
G—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



Minimal encapsulation – new header is inserted
between original IP header and original IP payload


Original, inner IP header unchanged except TTL
decremented by 1
Outer header is a full IP header
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
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