1. KOMUNIKASI DATA
Materi Pertemuan 10

2. Encoding and Modulation Techniques
Have already noted in Ch 3 that both analog and digital information can be encoded as either analog or digital signals:
Digital data, digital signals: simplest form of digital encoding of digital data
Digital data, analog signal: A modem converts digital data to an analog signal so that it can be transmitted over an analog
Analog data, digital signals: Analog data, such as voice and video, are often digitized to be able to use digital transmission facilities
Analog data, analog signals: Analog data are modulated by a carrier frequency to produce an analog signal in a different frequency band, which can be utilized on an analog transmission system
Stallings DCC8e Fig 5.1 emphasizes the process involved in this. For digital signaling, a data source g(t), which may be either digital or analog, is encoded into a digital signal x(t). The basis for analog signaling is a continuous constant-frequency fc signal known as the carrier signal. Data may be transmitted using a carrier signal by modulation, which is the process of encoding source data onto the carrier signal. All modulation techniques involve operation on one or more of the three fundamental frequency domain parameters: amplitude, frequency, and phase. The input signal m(t) may be analog or digital and is called the modulating signal, and the result of modulating the carrier signal is called the modulated signal s(t).
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3. Digital Signaling Versus Analog Signaling
Digital or analog data is encoded into a digital signal
Encoding may be chosen to conserve bandwidth or to minimize error
Analog Signaling
Digital or analog data modulates analog carrier signal
The frequency of the carrier fc is chosen to be compatible with the transmission medium used
Modulation: the amplitude, frequency or phase of the carrier signal is varied in accordance with the modulating data signal
by using different carrier frequencies, multiple data signals (users) can share the same transmission medium
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4. Digital Signaling Digital data, digital signal
Simplest encoding scheme: assign one voltage level to binary one and another voltage level to binary zero
More complex encoding schemes: are used to improve performance (reduce transmission bandwidth and minimize errors).
Examples are NRZ-L, NRZI, Manchester, etc.
Analog data, Digital signal
Analog data, such as voice and video
Often digitized to be able to use digital transmission facility
Example: Pulse Code Modulation (PCM), which involves sampling the analog data periodically and quantizing the samples
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5. Analog Signaling Digital data, Analog Signal
A modem converts digital data to an analog signal so that it can be transmitted over an analog line
The digital data modulates the amplitude, frequency, or phase of a carrier analog signal
Examples: Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK)
Analog data, Analog Signal
Analog data, such as voice and video modulate the amplitude, frequency, or phase of a carrier signal to produce an analog signal in a different frequency band
Examples: Amplitude Modulation (AM), Frequency Modulation (FM), Phase Modulation (PM)
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6. INTRODUCTION

7. DIGITAL TO ANALOG TRANSMISSION

8. Types of Digital to Analog Conversion

9. Modulation in wireless communication
Translate digital data to analog signal (baseband)
Shifts center frequency of baseband signal up to the radio carrier
example carrier frequency
802.11b/g: 2.4 GHz, a (5 GHz), GSM: 1.9 GHz
Why?
Antenna size: on the order of signal’s wavelength
More bandwidth available at higher carrier frequency
Medium characteristics (path loss, shadowing, reflection, scattering, diffraction) depend on signal’s wavelength

10. Modulation at sender modulation analog baseband signal digital data
radio
carrier
analog
baseband
signal

11. Amplitude Shift Keying (ASK)
Pros: simple
Cons: susceptible to noise
Example: optical system, infra-red 1 1 t

12. Describe Amplitude Shift Keying
Amplitude-shift keying (ASK) is a form of modulation that represents digital data as variations in the amplitude of a carrier wave.

13. Amplitude Shift Keying (ASK)
The simplest and most common form of ASK operates as a switch, using the presence of a carrier wave to indicate a binary one and its absence to indicate a binary zero.
This type of modulation is called on-off keying,

14. Frequency Shift Keying (FSK)
Pros: less susceptible to noise
Cons: requires larger bandwidth 1 1 t

15. Describe Frequency Shift Keying (FSK)
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK (BFSK).

16. Describe Frequency Shift Keying (FSK)
Two binary digits represented by two different frequencies near the carrier frequency
where f1 and f2 are offset from carrier frequency fc by equal but opposite amounts

17. Phase Shift Keying (PSK)
Pros:
Less susceptible to noise
Bandwidth efficient
Cons:
Receiver must synchronize in frequency and phase w/ transmitter t 1 1

18. Describe Phase Shift Keying (PSK)
Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave).

19. Describe Phase Shift Keying (PSK)
Uses two phases to represent binary digits

20. Variant of phase shift keyingQ I 1
BPSK (Binary Phase Shift Keying):
bit value 0: sine wave
bit value 1: inverted sine wave
very simple PSK
low spectral efficiency
robust, used in satellite systems 11 10 00 01 Q I A t
QPSK (Quadrature Phase Shift Keying):
2 bits coded as one symbol
needs less bandwidth compared to BPSK
symbol determines shift of sine wave
Often also transmission of relative, not absolute phase shift: DQPSK - Differential QPSK

21. Quadrature Amplitude Modulation (QAM)
combines amplitude and phase shift keying
It is possible to code n bits using one symbol
2n discrete levels
bit error rate increases with n
0000
0001
0011
1000 Q I
0010 φ a
Example: 16-QAM (4 bits = 1 symbol)
Symbols 0011 and 0001 have the same phase φ, but different amplitude a and 1000 have same amplitude but different phase
Used in Modem

22. What is transmitted in air?
radio wave (baseband modulated w/ carrier radio)
high-frequency, short wavelength
wave length * frequency = speed of light  3x108m/s
e.g., b, wavelength 0.1m

23. Frequency range (bandwidth)
need a wide spectrum
e.g., b bandwidth 20 MHz
w/o noise: Nyquist’s result
w/ noise (e.g., thermal noise, background radiation)
Shannon’s channel capacity theorem: the maximum number of bits that can be transmitted per second by a physical channel is:
W: frequency range
S/N: signal noise ratio

24. Frequencies for communication
twisted pair
coax cable
optical transmission
1 Mm
300 Hz
10 km
30 kHz
100 m
3 MHz
1 m
300 MHz
10 mm
30 GHz
100 m
3 THz
1 m
300 THz
VLF LF MF HF
VHF
UHF
SHF
EHF
infrared
visible light UV
VLF = Very Low Frequency UHF = Ultra High Frequency
LF = Low Frequency SHF = Super High Frequency
MF = Medium Frequency EHF = Extra High Frequency
HF = High Frequency UV = Ultraviolet Light
VHF = Very High Frequency

25. Frequency regulation
ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences)