センサネットワークSensor Networks

担当：山内規義 教授Prof. Noriyoshi Yamauchi

April 17, 2008

April 14, 2007History of telecommunications

Basics of telecommunications-Information-Networks-Communication-Data-Analog vs. digital-Digital signal-Encode, decode

Class schedule (tentative)4/10 Orientation, Introduction4/17 Basics of telecommunications (1)4/24 Basics of telecommunications (2) 5/1 Basics of wireless communications5/8 International standards of wireless communications5/15 protocols5/22 ZigBee5/29 Blue Tooth6/5 Applications of WSN (1)6/12 Future trends of WSN (2)6/19 Applications of WSN to automobiles6/26

What is information

Communication network

Logical components of network

node

station

link

What is network

A a wide variety of systems of interconnected componentstypically, computers.

What is communicationCommunication is the process of exchanging information usually via a common system of symbols.

Telecommunication is the extension of communication over a distance. In practice it also recognizes that something may be lost in the process; hence the term 'telecommunication' covers all forms of distance and/or conversion of the original communications, including radio, telegraphy, television, telephony, data communication and computer networking.

What is data

Expression of information using a certainformat.

Container of information

Datum (singular単数 )

Data (plural複数 )

Analog Signal and Digital Signal

Analog signal:振幅が時間とともに連続的に変化する信号Continuous change withtime

Digital signal：離散的な時間に対し，離散的な値しかとらない信号．一般に” 0”と“ 1”の 2値で表される．Discrete value for discrete time.Usually expressed using 0 and 1

Voltage Voltage

Periodic Signal and Aperiodic Signal

f(x)=f(x+T)

T ： period

Periodic Aperiodic

Sine Wave

y=sin T2 t( ) t:時間（秒）

AmplitudeMaximum value

Minimum value

Time

Period

Relation between Frequency and Period

Frequency Period

t = 1/f

Sine Wave with Different Phase

y=sin T2 t( + ) :位相 (phase)

Amplitude

Time

Changes of Amplitude, Frequency and Phase

Amplitude change Frequency change

Phase change

Time Domain and Frequency Domain

Time domain Frequency domain

Time and Frequency Domain Including DC

Complicated Wave Forms

Frequency Spectra of Periodic and Non-Periodic Signals

Frequency Spectrum

信号に含まれる周波数成分がどのくらいあるかを表したグラフ

Bandwidth （周波数帯域）

周波数帯域：信号が含む周波数の範囲（何 Hzから何 Hzまで）帯域幅：周波数スペクトルの幅Bandwidth: f1 – f2

Amplitude

Frequency

Digital Signal

bit 　“ 1” または“ 0”1 bit

0.5 bits8 bits = 1 Byte

Transmission Speed （ビットレート， bit rate ）1秒間に伝送できるビット数のことThe number of bits transmitted in 1 sec

Unit: bps (bit per second)

Transmission Speed

Unit： bit per second bpsIn this case, the bit rate is 8 bps

Bandwidth

アナログ信号の場合：周波数スペクトルの幅のこと， Hzを単位とするIn analog signal: f1 – f2 (Hz)

ディジタル信号の場合：信号の伝送速度のこと， bpsを単位とするIn digital signal: Transmission speed (bps)

Transmission Speed and Frequency Spectra

伝送速度を早くすればするほど，信号の伝送にはより広い周波数帯域幅が必要になる．The faster the bit rate, the wider bandwidth we need.

Information and Transmission Rate

Telephone

Fax

TV phone

TV conferenceHDTV

Signal Distortion

Analog and Digital Signal TransmissionAnalog

Digital

通信容量（ Channel Capacity ） ある通信路を通過できる最大の伝送速度のことThe maximum bit rate allowed in theTransmission medium

符号化（エンコード， Encode ） 情報を伝送路に適した形式の信号に変換することTo transform the information to signal whichfits the transmission media.

復号化（デコード， Decode ） 符号化された信号を元の情報に変換することTo return the signal to the original Information.

Signal TransmissionInformation Signal Signal Information

Encode Decode

Information source

Noise

Transmitter Receiver Recipient