telekomünikasyon trafiği...
TRANSCRIPT
Telekomünikasyon Trafiği Gelişimi
Haberleşme
Servislerindeki
Artış
Electronic Communications: Telephone, wireless phone, TV, radar, etc.
Concept and Model of Communications
General Communication Model
Source Transmitter Transmission
System Receiver Destination
Microphone Telephone Computer Scanner
Transformer Encoder Compress Modulator
Line/Cable Fiber/Air Satellite Network
Transformer Decoder Uncompress Demodulator
Speaker Earphone Computer Printer
Basic Communication Criteria: Performance, Reliability, Security
Important Reasons for Modulation:
• Ease of Radiation: c=l×f
• Simultaneous Transmission of Several Signals
FDM/TDM
• Effecting the Exchange of SNR with B
Channel Capacity Channel Bandwidth
Signal-to-Noise Ratio: S_
N
Modulation
Carrier: Acos(2πfct+φ) where fc is called carrier frequency
Modulation: change or modify values of A, fc, φ according to input signal m(t) - modify A A[m(t)]: Amplitude Modulation (AM)
- modify fc fc[m(t)]: Frequency Modulation (FM) - modify φ φ[m(t)]: Phase Modulation (PM)
Modulator m(t)
Acos(2πfct+φ)
modulated signal: s(t)
• Sayısal sinyaller analog sinyallere göre gürültü ve parazit sinyallerinden
daha az etkilenirler.
• Sayısal sinyallerdeki bozulmalar tekrar ediciler (regenerative repeaters)
tarafından giderilebilir.
• Hata sezme (error detection) ve düzeltme (correction) teknikleri sayesinde az hata
oranlı sinyal iletimi yapılabilir.
• Sayısal sinyallere parazit ve karıştırıcı sinyal etkilerinden korunabilmek için
güvenlik ve kriptolama gibi sinyal işleme teknikleri uygulanabilir.
• Sayısal devreler analog devrelere göre daha esnek, daha dayanıklı, ve daha az
maliyetli olarak tasarlanabilir.
Neden
Sayısal
Haberleşme?
Sayısal Haberleşme Alıcı-Verici Birimi
Sayısal Haberleşme Çoklu-Atlama Kanalı
Sayısal Tekrarlayıcı
Modulator, Demodulator & Modem
Modulator accepts bit sequence and modulates a carrier.
Demodulator accepts a modulated signal and regenerates bit sequence.
Modem is a single device which includes both modulator and demodulator.
Multiplexing, Multiplexer & Demultiplexer
Multiplexing is a technique that allows simultaneous transmissions of multiple
signals across a single data link.
CompA1
CompB1
CompC1
Da
Db
Dc D ≥ Da+Db+Dc
D E M U X
CompA2
CompB2
CompC2
1 shared link: rate D
Multiplexer Demultiplexer
FDM – Frequency Division Multiplexing
- A set of signals are put in different frequency positions of a link/medium. - Bandwidth of the link must be larger than the sum of signal bandwidths. - Each signal is modulated using its own carrier frequency. - Examples: radio, TV, satellite, etc.
A1
B1
C1
Mod
Mod
Mod
1
2
3
+
f
Dem
Dem
Dem
1
2
3
A2
B2
C2
1
2
3
1
2
3
f1
f2
f3
TDM – Time Division Multiplexing
- Multiple data streams are sent in different time in single data link/medium. - Data rate of the link must be larger than a sum of the multiple streams. - Data streams take turn to transmit in a short interval. - Widely used in digital communication networks.
CompA1
CompB1
CompC1
CompA2
CompB2
CompC2
D E M U X
… C1 B1 A1 C1 B1 A1 …