[ 데이터통신 ] chapter 5. Analog Transmission

 

안녕하세요. 개알못입니다~~

이번 포스터는 데이터통신 과목에서 Analog transmission 에 관하여 다루겠습니다.

 

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5.1 Modulation of Digital Data

- Modulation

Converting binary data or a low-pass anlalog signal to a band-pass analog signal

Characteristics ofs a sine wave : Amplitude, frequency, phase

 

- Bit rate vs baud rate

Bit rate : bits transmitted during one second

Baud rate : signal units per second = bit rate x bits represented by a signal unit

Baud rate is less than or equal to the bit rate

 

- Carrier signal

A high-frequency signal that acts as a basis for the information signal in an analog transmission.

Digital information modulates the carrier signal by modifying one or more of its characteristics.

 

- ASK (Amplitude Shift Keying)

Change the strength of a carrier signal

Highly susceptible to noise ( Problematic for ASK)

On/off keying

Bandwidth = (1+d) x N     (d : a factor related to the modulation process)

 

- FSK (Frequency Shift Keying)

Change the frequency of a carrier signal

Avoid the problems from noise

Limiting factor : physical capability of a carrier

Bandwideth = Fc1 - Fc0 + N

 

- PSK (Phase Shift Keying)

the phase of the carrier is vared

Peak amplitude and frequency remain constant

Not susceptible to noise : reliable detection

No bandwidth limit problem as in FSK

Bandwidth : same with ASK

Usually higher bit rates than ASK

2PSK or binary PSK (the same rate as ASK)

4PSK, QPSK : dibit

8PSK : tribit

 

- QAM (Quadrature Amplitude Modulation)

A combination of ASK and PSK

A maximum contrast between each signal unit

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5.2 Telephone Modems

- A telephone line has a bandwidth of almost 2400 Hz for data transmission.

- Modems stands for modulaot/ demodulator.

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5.3 Modulation of Analog Signal

- Analog-to-analog modulation

 

- Amplitude Modulation (AM)

The total bandwidth required for AM can be determined from the bandwidth of the audio signal

BWt = 2 x BWm

 

- Frequency Modulation (FM)

The total bandwidth required for FM can be determined from the bandwidth of the audio signal.

BWt = 10 x BWm

 

참고자료 : Data Communications and Networks, fourth edition by Behrouz A, Forouzan

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