[Network] Wireless and Mobile

Wireless1 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 strength2 interference3. Multipath Propagation

2.2 SNR versus BER

snr:signal-to-noise rateber:bit Error ratethe higher SNR, the lower BER.

2.3 Multiple Access

1. Hidden terminal problem
2. Signal Attenuation

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2.4 Cdma:code Division multiple Access

The algorithm is as-I have recapped before

 modulation (modulation) (1) First 0 of the data into -1a = [1,-1,1], B = [1,1,-1] The advantage is that when demodulation, can be different from 0 and 1, and the demodulation error rate decreased. (2-1) A uses the first channel of Walsh Transform [1,1,1,1,1,1,1,1] (that is, its first basis, the first row of the matrix) to do modulation 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 uses the second channel of the Walsh Transform [1,1,1,1,-1,-1,-1,-1] (second row of the matrix) to do the modulation 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) Add the result of the modulation M = a_m + b_mm = 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] (4) The last signal sent out is M, together with 24 bit. 

Demodulation (demodulation) (1) will receive the data respectively and channel to do the inner product (1-1) m and the first channel [1,1,1,1,1,1,1,1] do the inner product to obtain the first eight yards of the inner product: [2,2,2,2,0,0,0,0] \cdot [ 1,1,1,1,1,1,1,1] = 8 middle eight yards inside product: [0,0,0,0,-2,-2,-2,-2] \cdot [1,1,1,1,1,1,1,1] = 8 after eight yards: [0,0,0,0,2,2,2,2] \cdot [ 1,1,1,1,1,1,1,1] = 8 (1-2) m and the second channel [1,1,1,1,-1,-1,-1,-1] do the inner product to get the inner product of the first eight yards: [2,2,2,2,0,0,0,0] \cdot [1,1,1,1,-1,-1,-1,-1] = 8 middle Eight yards inside product: [0,0,0,0,-2,-2,-2,-2] \cdot [1,1,1,1,-1,-1,-1,-1] = 8 after eight yards: [0,0,0,0,2,2,2,2] \cdot [1,1,1,1,-1,-1,-1,-1] =- 8 (2) If the inner product result is 8, then the demodulation is 1; if 8, then demodulation is-1 (2-1) The first channel to the signal is [8,-8, 8] \to [1,-1, 1] (2-2) The second channel solution signal is [8, 8,-8] \to [1, 1, -1] (3) Finally, restore-1 back to 0 (3-1) so. The first channel successfully restores the signal as [1, 0, 1] (3-2) so. The second channel successfully restores the signal as [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) has 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:h OSTs only

2. Channel

1) divided into one channels

2) Interference possible:neighboring AP chooses same channel.

3. Association

Host must associates to a AP

4. Passive/active scanning

1) Passive

Beacon--Reque St-Response

2) Active

request--reponse-&G T 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 Termina L 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.

3.3 Frame

1. Addressing

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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 would see frame from H1 and remember which switch can is used to reach H1

2. Advanced Capabilities

1) rate adaptation

BER vs. SNR

2) Power management

If there is no MSG to being sent to this node. This node would sleep. When the node receive ' Beacon frame ', the node would 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

4 Cellular Internet Access

4.1 architecturelike The other architecture, it's hierarchical and consists a list of base station, users, and link s or protocols. In Cellular Internet:the hierarchical Arch was formed by Mobile switching Center. and Cell denotes the components, BS, users, Air-interface (protocols)

1. Hops:two techniques1) fdma/tdma:divide spectrum2) cdma:bit dot algorithm (see before)

4.2 Standards

2G, 2.5G, 3G

GSM-GPRS

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Mobility1 principles:addressing and routing

1.1 Address

First I need to clarify some address definations:

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.

1.2 Routing

1. Registrationmobile moves to a visited network, and connects to home agent telling it some mobility Information.H Ere is three important components:

1) mobile2) foreign Agent3) Home Agent

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2. Indirect Routingmobile requests to connect with correspondent through Home agent. Then correspondent transfers the PKT to mobile through home agent. Mobile replies directly to correspondent.

Triangle Routing problem on-going connection can be maintains

3. Direct Routing

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Correspondent need to get care-of-address when mobile moves to another visited network. Some Improvement Accommdation Mobility with direct Routingwhen mobile moves, new FA gets pkt from old FA (Chaining)

2 Mobile IP

2.1 Indirect Routing

In indirect or direct routing network, Frame should is encapsulated into addresses.

Such as indirect routing network:

1) Correspondent:mobile Permanent Address

2) Home Agent:add care-of-address (theaddress 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 would put out the registration request to foreign agent. And then foreign agent forwards the request to the home agent and gets the reply for the mobile.

Note:

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

3.2 Anchor MSC:

Like the machanism mentioned above.

[Network] Wireless and Mobile