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 …