Analog-to-digital conversion (ADC) is an electronic process in which a continuously variable, or analog, the signal is changed into a multilevel digital signal without altering its essential content.

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Chapter 4.3: ANALOG-TO-DIGITAL CONVERSION
A digital signal is superior to an analog signal because it is more robust and noise can easily be recovered, corrected and
amplified.
For this reason, the tendency today is to change an analog signal to digital data. In this section, we describe two
techniques:
1. Pulse Code Modulation (PCM)
2. Delta Modulation (DM)
PCM is a method that is used to convert an analog signal into a digital signal so that the modified analog signal can be
transmitted through the digital communication network.
PCM consists of three steps to digitize an analog signal:
• Sampling
• Quantization
• Binary encoding
Sampling: Sampling is a process of measuring the amplitude of a continuous-time signal at discrete instants. Sampling
also recognized as Pulse Amplitude Modulation (PAM).
Quantization: In the quantization process, every sampled amplitude value is assigned with fixed values.
Binary encoding: Binary encoding is the process where a quantized value is converted to the binary signal format.
Types of Sampling: Three different sampling methods for PCM
1. Ideal sampling Amplitude
2. Natural sampling Amplitude
3. Flat-top sampling Amplitude
According to the Nyquist theorem, the sampling rate must be at least 2 times the highest frequency contained in the
signal.
Example: Telephone companies digitize voice by assuming a maximum frequency of 4000 Hz. The sampling rate
therefore is 8000 samples per second.
We want to digitize the human voice. What is the bit rate, assuming 8 bits per sample?
The human voice normally contains frequencies from 0 to 4000 Hz. The sampling rate and bit rate are calculated as
follows:
Sampling rate= 4000 X 2 = 8000 samples/s
Bit rate = 8000X 8 = 64000 bps = 64 kbps
Transmission modes: data transmission refers to the process of transferring data between two or more digital devices.
There are two modes used to transmit data between digital devices:
1. Serial transmission: Serial data transmission sends data bits one after another over a single channel.
2. Parallel transmission: Parallel data transmission sends multiple data bits at the same time over multiple channels.
Serial transmission occurs in one of three ways:
Asynchronous:
• Usually 1-byte of Data send at one time
• Start and Stop bit are exist
• Data transmission speed and cost slow and low
Synchronous:

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• Usually Multiple bytes of Data send at one time
• Start and Stop bit aren’t exist
• Data transmission speed and cost slow and low fast and high
Isochronous:
• Transmission occurs at regular intervals
• Fixed gap between transmission of two data items
Chapter 5.1: DIGITAL-TO-ANALOG CONVERSION
We need to convert analog to digital and digital to analog signal because most of the devices operate with digital
signals. Concerning them, data in analog form needs to be modified in a digital signal. Besides, we can't send a digital
signal by air because most of the communication channel uses air as a communication medium. Therefore, we need to
change a digital signal to an analog to make it travel by air.
A carrier signal or carrier wave is a sine wave that is modulated with an input signal to carry information because the
carrier signal contains a higher frequency than the given input signal.
Amplitude-Shift Keying (ASK), Frequency-Shift Keying (FSK), and Phase-Shift Keying (PSK) is Digital-to-
Analog conversion techniques.
In ASK, carrier signals amplitude modifies proportionally with the information signal and produces a digitally
modulated signal.
And if frequency modifies proportionally with an information signal than frequency shift keying (FSK) is produced.
Alike, the phase of the carrier signals modifies proportionally with the information signal than phase-shift keying (PSK)
is produced.
Advantages of ASK:
• Modulation and de-modulation both processes are easy
• It has a simple receiver design
Disadvantages of ASK:
• Error probability is high
• Performance in the presence of noise is poor
Advantages of FSK:
• It has a lower probability of error.
• Performance in the presence of noise is better than ASK
Disadvantages of FSK:
• FSK modulation and de-modulation both processes are moderately complex.
• It uses larger bandwidth compared to other modulation.
Advantages of PSK:
• Performance in presence of noise better than FSK
• Error probability is low
Disadvantages of PSK:
• It has lower bandwidth efficiency.
• Detection and recovery algorithms are very complex.
Compare ASK, PSK & FSK systems:
ASK FSK PSK

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Parameters of ASK is
Amplitude
Parameters of FSK is
Frequency
Parameters of PSK is Phase
Noise immunity is low Noise immunity is High Noise immunity is High
Error probability High Error probability Low Error probability Low
Modulation Complexity is
Simple
Modulation Complexity is
Moderately complex
Modulation Complexity is
Very complex
Performance in presence of
noise Poor
Performance in presence of
noise Better than ASK
Performance in presence of
noise Better than FSK
If the available channel is a bandpass channel, analog data must be converted to an analog signal by Analog-to-analog
conversion before transmission.
Bandpass is a range of frequencies that are transmitted through a bandpass filter to remove unwanted frequencies.
Baseband is the original frequency range of a transmission signal before it is modulated. It modulates carrier signals to
generate a broadband analog signal.
Analog-to-analog conversion can be done in three ways:
1. Amplitude Modulation (AM): The power level of the information signal changes the amplitude of the carrier
signal in proportion to generate the modulated signal.
2. Frequency Modulation (FM): The power level of the information signal changes the frequency of the carrier
in proportion to generate the modulated signal.
The bandwidth of frequency modulation is high, nearly 10-times higher than signal frequency.
3. Phase Modulation (PM): The power level of the information signal only changes the phase of the carrier signal
to generate the modulated signal.
Sometimes we receive one radio broadcast on another station because we know radio-wave has three parts,
frequency, amplitude, and wavelength. Each radio station produces a specific set of frequencies that radio device antenna
collects and radio tuners lockdown them to present the information. If the turner failed to lockdown or frequencies are
collided with unwanted noise, we can hear two station broadcasts in one station.
Chapter 6: Bandwidth Utilization-Multiplexing and Spreading
The bandwidth utilization is the amount of bandwidth utilized from the total bandwidth available. Multiplexing help
to reach maximum efficiency of bandwidth utilization. It is a set of techniques that combined multiple signals into one
signal over a shared medium.
We need to convert analog to digital and digital to analog signal because most of the devices operate with digital
signals. Concerning them, data in analog form needs to be modified in a digital signal. Besides, we can't send a digital
signal by air because most of the communication channel uses air as a communication medium. Therefore, we need to
change a digital signal to an analog to make it travel by air.
Types of Multiplexers: Multiplexers divided into
1. Frequency Division Multiplexing (FDM)
2. Wavelength Division Multiplexing (WDM)
3. Time Division Multiplexing (TDM)
FDM and WDM are analog multiplexing and TDM is digital multiplexing.
Difference Between FDM WDM and TDM:

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FDM WDM TDM
It requires complex connections at the
transmitter and receiver.
It requires complex connections at the
transmitter and receiver.
It does not require complex
connections.
The communication channel is
divided by frequency.
The communication channel is
divided by wavelength.
The communication channel is
divided by time.
FDM uses analog signals. WDM uses optical signals. TDM uses digital and analog signals.
A guard band is an additional part of FDM that prevents Signals from overlapping and helps each signal to remain in
separate.
Chapter 7: Transmission Media
In network communications, a Transmission Media is a physical connection or an interface between the transmitter
and the receiver. Transmission media are of two types:
1. Guided Transmission Medium: It refers a physical path for transmission.
i. Twisted pair cable
ii. Coaxial cable
iii. Fiber optics
2. Unguided Transmission Medium: It refers broadcasted through air
i. Free Space
The purpose of twisting the wire in a twisted pair cable because it eliminates EMI or electromagnetic interference. The
EMI generate noise or interference that corrupts data.
The Shielded Twisted Pair uses a metallic shield that prevents external resistance for better performance.
We use coaxial cables when the distances are high otherwise fiber optic. Coaxial cables performance is comparatively
low and its setup is easy than fiber optic.
The design of coaxial cable consists of a copper wire that surrounded by additional layers that shielding as an outer
protective jacket to prevent damage to the signal. As a result, it transmits high-frequency signals at low loss.
To pass data through the optical fiber, we use modulation of data into an analog signal and transmit it as light so it
reflects frequently until the data reached the receiver.
Registered Jack 45 or RJ45 is the most common twisted-pair connector.
Unshielded Twisted Pair Cable Vs Shielded Twisted Pair Cable:
Unshielded Twisted Pair Cable Shielded Twisted Pair Cable
UTP doesn't use an external layer as shields or jacket STP uses an external layer as shields or jacket
UTP costs cheaper and does not require much
maintenance.
STP costs moderately expensive.
UTP data rates slow comparatively STP. STP provides high data rates
Noise and error are high comparatively. Less noise and error.