Transcript Basics of telecommunications (1)[PPT:0.694MB]

April 17, 2008
センサネットワーク
Sensor Networks
担当：山内規義 教授
Prof. Noriyoshi Yamauchi
April 14, 2007
History of telecommunications
Basics of telecommunications
-Information
-Networks
-Communication
-Data
-Analog vs. digital
-Digital signal
-Encode, decode
Class schedule (tentative)
4/10 Orientation, Introduction
4/17 Basics of telecommunications (1)
4/24 Basics of telecommunications (2)
5/1 Basics of wireless communications
5/8 International standards of wireless communications
5/15 protocols
5/22 ZigBee
5/29 Blue Tooth
6/5 Applications of WSN (1)
6/12 Future trends of WSN (2)
6/19 Applications of WSN to automobiles
6/26
What is information
Logical components of network
Communication network
node
link
station
What is network
A a wide variety of systems of interconnected components
typically, computers.
What is communication
Communication 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 certain
format.
Container of information
Datum (singular単数)
Data (plural複数)
Analog Signal and Digital Signal
Voltage
Voltage
Analog signal:
振幅が時間とともに連続
的に変化する信号
Continuous change with
time
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
Periodic Signal and Aperiodic Signal
Periodic
f(x)=f(x+T)
T：period
Aperiodic
Sine Wave
Amplitude
Maximum value
Time
Period
Minimum value
2p
(
t)
y=sin
T
t:時間（秒）
Relation between Frequency and Period
Period
Frequency
t = 1/f
Sine Wave with Different Phase
Amplitude
Time
2p
(
t + f)
y=sin
T
f:位相(phase)
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）
Amplitude
Frequency
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
Digital Signal
bit “1”または“0”
1 bit
0.5 bits
8 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
bps
In 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
TV phone
Fax
Telephone
HDTV
TV conference
Signal Distortion
Analog and Digital Signal Transmission
Analog
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 the
Transmission 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 which
fits 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 Transmission
Information
Signal
Signal
Encode
Information
Decode
Receiver
Transmitter
Information source
Noise
Recipient