[Network]Wireless and Mobile

[Network]Wireless and Mobile



1 Introduction

1.1 Elements

1. Wireless Hosts
Wireless does not mean mobility.
2. Base Station
Typically connect to wired network.

1.2 Modes

1. Infrastructure mode

base station connects mobiles into wired network.
Handoff: mobile changes base station

2. ad hoc mode

no base station
nodes orgnize themselves into a network: route among themselves.

2 Characteristics

2.1 Differences from wired link

1. signal strength
2. interference
3. multipath propagation

2.2 SNR versus BER

SNR: signal-to-noise rate
BER: bit error rate
The higher SNR, the lower BER.

2.3 Multiple Access

1. Hidden terminal problem
[Network]Wireless and Mobile

2. Signal attenuation
[Network]Wireless and Mobile

2.4 CDMA: Code Division Multiple Access

The algorithm is as what I have recapped before

(1)先将资料的0转成 -1
A = [1,-1,1], B = [1,1,-1]
(2-1) A使用Walsh Transform的第一个channel [1,1,1,1,1,1,1,1](即其第一个basis,矩阵的第一个row)来做调制
A_m = [1,1,1,1,1,1,1,1,|-1,-1,-1,-1,-1,-1,-1,-1,|1,1,1,1,1,1,1,1,]。
(2-2) B使用Walsh Transform的第二个channel [1,1,1,1,-1,-1,-1,-1](矩阵的第二个row)来做调制
B_m = [1,1,1,1,-1,-1,-1,-1,|1,1,1,1,-1,-1,-1,-1,|-1,-1,-1,-1,1,1,1,1,]。
(3)将调制的结果相加M = A_m + B_m
M = A_m + B_m = [2,2,2,2,0,0,0,0,0,0,0,0,-2,-2,-2,-2,0,0,0,0,2,2,2,2]
(1-1) M和 第一个channel [1,1,1,1,1,1,1,1]做内积得到
前八码内积:[2,2,2,2,0,0,0,0] \cdot [1,1,1,1,1,1,1,1] = 8
中间八码内积:[0,0,0,0,-2,-2,-2,-2] \cdot [1,1,1,1,1,1,1,1] = -8
后八码内积:[0,0,0,0,2,2,2,2] \cdot [1,1,1,1,1,1,1,1] = 8
(1-2) M和 第二个channel [1,1,1,1,-1,-1,-1,-1]做内积得到
前八码内积:[2,2,2,2,0,0,0,0] \cdot [1,1,1,1,-1,-1,-1,-1] = 8
中间八码内积:[0,0,0,0,-2,-2,-2,-2] \cdot [1,1,1,1,-1,-1,-1,-1] = 8
后八码内积:[0,0,0,0,2,2,2,2] \cdot [1,1,1,1,-1,-1,-1,-1] = -8
(2)内积结果出来若为8,则解调为1;若为 -8,则解调为 -1
(2-1)第一个channel解调出信号为[8, -8, 8] \to [1, -1, 1]
(2-2)第二个channel解调出信号为[8, 8, -8] \to [1, 1, -1]
(3)最后,将 -1还原回0
(3-1)因此。第一个channel成功还原信号为[1, 0, 1]
(3-2)因此。第二个channel成功还原信号为[1, 1, 0]

3 Wi-Fi: IEEE 802.11 Wireless LAN

There is a family of 802 wireless LAN. They all:

1) use CSMA/CA for multiple access

2) have base-station and ad-hoc network versions

3.1 Architecture

1. Basic Service Set: contains 

1) wireless hosts

2) access point: base station

3) ad hoc mode: hosts only

2. Channel

1) divided into 11 channels

2) interference possible: neighboring AP chooses same channel.

3. Association

host must associates to a AP

4. Passive/Active Scanning

1) Passive

[Network]Wireless and Mobile

beacon -> request -> response

2) Active

[Network]Wireless and Mobile

request -> reponse -> assocation request -> assocation response

3.2 Multiple Access – Avoid Collisions

1. reasons: why not collision detection

1) signal weak
2) can not sense all collisions: hidden terminal problem

2. Avoiding collisions

1) Idea: allow sender to reverse channel. Sender first send request-to-send(RTS) packets to base station using CSMA. BS broadcast clear-to-send(CTS) in response to RTS.

CTS heard by all nodes.

[Network]Wireless and Mobile

3.3 Frame

1. Addressing

[Network]Wireless and Mobile
[Network]Wireless and Mobile

1) Address 1: receiver

2) Address 2: sender

3) Address 3: router

2. In frame control
1) Frame type: RTS, CTS, ACK, data

3.4 Other Characteristics

1. Mobility within same subnet

Self-learning: switch will see frame from H1 and remember which switch can be used to reach H1

[Network]Wireless and Mobile

2. advanced capabilities

1) Rate adaptation


2) Power management

If there is no msg to be sent to this node. This node will sleep. When the node receive ‘beacon frame’, the node will wake up.

3. Personal area network

ad box mode: master/slave/parked device

3.5 802.16: WiMax

antenna: unlike 802.11, it has a large range

downlink/uplink scheduling

[Network]Wireless and Mobile

4 Cellular Internet Access

4.1 Architecture

like the other architecture, it is hierarchical and consists a list of base station, users, and links or protocols.
In Cellular Internet: the hierarchical arch is formed by Mobile Switching Center. And Cell denotes the components, BS, users, air-interface(protocols)

1. Hops: two techniques

1) FDMA/TDMA: divide spectrum
2) CDMA: bit dot algorithm(see before)

4.2 Standards

2G, 2.5G, 3G


[Network]Wireless and Mobile


1 Principles: addressing and routing

1.1 Address

First I need to clarify some address definations:

[Network]Wireless and Mobile[Network]Wireless and Mobile

1) mobile: 

care-of-address, in visited network known by home network

permanent address, in home network known by correspondent to communicate

2) home:

home agent: function entity for mobile

3) correspondent:

who mobile want to contact with.

1.2 Routing

1. Registration

Mobile moves to a visited network, and connects to home agent telling it some mobility information.
Here are three important components:
1) mobile
2) foreign agent
3) home agent
[Network]Wireless and Mobile

2. Indirect Routing

Mobile requests to connect with correspondent through home agent. Then correspondent transfers pkt to mobile through home agent. Mobile replies directly to correspondent.
[Network]Wireless and Mobile

Triangle routing Problem
On-going connection can be maintains 

3. Direct Routing

[Network]Wireless and Mobile

Correspondent need to get care-of-address when mobile moves to another visited network.
Some Improvement
Accommdation mobility with direct routing
when mobile moves, new FA gets pkt from old FA(Chaining)
[Network]Wireless and Mobile

 2 Mobile IP

2.1 Indirect routing

In indirect or direct routing network, frame should be encapsulated into addresses.

Such as indirect routing network:

[Network]Wireless and Mobile

1) correspondent: mobile permanent address

2) home agent: add care-of-address(the address of foreign agent address) to find visited network 

3) foreign agent: dissolve to a permanent address.

2.2 Agent discovery

agent advertisement: foreign/home agents advertise service by broadcasting ICMP msg.

Registration Example

foreign agent broadcast ICMP msg. And a new mobile will put out registration request to foreign agent. And then foreign agent forwards the request to the home agent and gets the reply for the mobile.

[Network]Wireless and Mobile


Mobile maintains the home agent address consistantly.

3 Handoff within Mobile Switching Center

3.1 Common: 

like mobile move to another foreign network and update the information between BSS and MSC

[Network]Wireless and Mobile

3.2 Anchor MSC: 

like the machanism mentioned above.

[Network]Wireless and Mobile

版权声明:本文内容由互联网用户自发贡献,该文观点仅代表作者本人。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如发现本站有涉嫌侵权/违法违规的内容, 请发送邮件至 举报,一经查实,本站将立刻删除。


【正版授权,激活自己账号】: Jetbrains全家桶Ide使用,1年售后保障,每天仅需1毛

【官方授权 正版激活】: 官方授权 正版激活 支持Jetbrains家族下所有IDE 使用个人JB账号...



  • Paxos算法详解


  • idea修改快捷键方法总结


  • 做oj好还是做leetcode好_序列的子序列

    做oj好还是做leetcode好_序列的子序列给出矩阵 matrix 和目标值 target,返回元素总和等于目标值的非空子矩阵的数量。子矩阵 x1, y1, x2, y2 是满足 x1 <= x <= x2 且 y1 <= y <= y2 的所有单元 matrix[x][y] 的集合。如果 (x1, y1, x2, y2) 和 (x1’, y1’, x2’, y2’) 两个子矩阵中部分坐标不同(如:x1 != x1’),那么这两个子矩阵也不同。示例 1:输入:matrix = [[0,1,0],[1,1,1],

  • php跨域访问的session_php跳转到另一个php


  • 一个Python小白5个小时爬虫经历


  • ubuntu解决vim打开文件时报错E325ATTENTION「建议收藏」