Ch0:1 Tseng:WirelessNet Chapter 0: Chances of Wireless Communications Yu-Chee Tseng Dept of Computer...

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Chapter 0:Chances of Wireless Communications

Yu-Chee Tseng

Dept of Computer Science and Information Engr.

National Chiao-Tung University

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Wireless Network Architectures

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Wireless Network Models

With Infrastructure: Without Infrastructure (ad hoc networks):

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Cellular: Infrared:

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無線隨意網路（ Multi-hop Ad Hoc Network ）

Laptop

PDA

LaptopLaptop

Laptop

A

B

C

D

E

PDA

Laptop

Laptop

Laptop

PDA

PDA

C'

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感測網路（ Sensor Network ）

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Bluetooth Technology

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Applications of Wireless Communications

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Mobile Computing

Wireless Communication Technology

Portable Computer Technology appearance of light-weight computing devices

Vision: Ubiquitous Computing / Nomadic Computingcomputers everywhere; information anywhere anytime

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Features of Wireless Communication

one global bandwidth shared by all users fortunately channels, such as (frequency, time-slot) pairs, can be reuse

d Radio-based

low bandwidthhigh latency radio communication linkshigher bit error rate (BER)

fading short-term multipath fading (Rayleigh effect)

due to same signal taking different paths and arriving at the receiver shifted in phase

long-term fading (radio shadow) topology of the terrain (like mountains) can cause signal dropouts solution: deploying multiple antenna sites

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Features of Portable Computers

Limited resources: limited energy (battery life) limited CPU speed limited memory

Less reliable, less secure

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Mobile System Architecture

Cellular-based Ad hoc Relaying link Wireless ATM Packet Radio Network Sensor Networks

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Mobile Computing Applications/Services

Wireless information services: Pico-service: local parking lot availability, layout of a buildi

ng Micro-service: train and bus station information, local traffic

information Macro-service: weather information, local news service Wide Area Service: stock market information

Real-time multimedia applications tele-medicine tele-computing collaborative environments

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Research: Hardware Aspects

power saving display, LCDlow-voltage CPUs

AT&T's Hobbit chip: 5,000 times less power consumption in doze mode than active mode

radio: IEEE 802.11 power consumption example:

transmit: 1400 mW receive: 1000 mW idle: 830 mW sleep: 130 mW

size, user interface (wearable computers)

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Research: Software Aspects

mobile communication protocolsWAPwireless TCPMobile IPMAC protocols

Energy-efficient protocolrelated to the above send/receive/idle/sleep model

... and many others

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Research: Algorithmic Aspects

Bandwidth saving Data caching for broadcast channel allocation communication scheduling math. analysis