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Encoding vs Modulation | Difference between Encoding and Modulation

This page compares Encoding vs Modulation and mentions difference between Encoding and Modulation used in data communication with examples including advantages.

Introduction: There are two types of signals viz. analog and digital. They are used for various purposes. Often it is required to convert one form of the signal to the other form for certain applications. Encoding and modulation are used for these conversions.

Hence four possible combinations of data and signal are as follows.
• Encoding of analog data as analog signals (Telephone).
• Encoding of digital data as analog signals (Modem).
• Encoding of analog data as digital signals (Codec).
• Encoding of digital data as digital signals (Digital Transmitter).

Data communication system consists of transmitter, channel and receiver.

Encoding process

Encoding converts analog data to digital signal form. Analog data is converted to digital data format using sampling and quantization process as used in PCM. It uses encoder at the transmitter end and decoder at the receiver end. Encoder makes digital data suitable to be transmitted on digital transmission lines. They are used to transmit encoded data using DSL (Digital Subscriber line) or ethernet cables used between stations connected on LAN (Local Area Network).

Encoding Decoding process
Figure-1 : Encoding decoding process

Digital signals are voltage/current pulses having few discrete levels such as 2 levels are used in binary. Each pulse is known as signal element. Binary data is encoded into these signal elements using encoder.

Example of encoding: Following are the different types of schemes used for encoding of digital data as digital signals.
Unipolar : NRZ
Polar : NRZ, RZ, Bi-phase (Manchester, Differential Manchester)
Bipolar : AMI (Alternate Mark Invert) , Pseudoternary Multilevel : 2B1Q, 8B6T and 4D-PAM5
Multitransition : MLT-3

Polar NRZ Polar RZ
Figure-2 : Polar encoding for NRZ and RZ signal

• Unipolar : In the unipolar signaling type, binary one ('1') is encoded as presence of pulse where as binary zero ('0') is encoded as absence of pulse. Hence it is known as "ON-OFF Keying". It is categorized into unipolar NRZ and unipolar RZ types as described below.
• Polar : In the polar signaling type, one ('1') is encoded as positive pulse where as zero ('0') is encoded as negative pulse. It is further categorized into polar NRZ and polar RZ types.
• Bipolar : In the bipolar signaling type, there are three voltage levels viz. positive, negative and zero. Binary '0' is encoded as neutral zero voltage. Binary '1' is encoded either as positive pulse or as negative pulse based on its alternate positions. It is also called Duobinary signal. Binary ones are mapped by alternatine positive and negative voltages. Hence it is called as Alternate Mark Inversion (AMI). It is further categorized into Bipolar NRZ and Bipolar RZ.

Advantages of Encoding process

Following are the advantages of encoding techniques.
➨It provides self synchronization by eliminating long string of zeros and ones and incorporating more transitions in the data. Hence it is easy for receiver to match bit intervals with transmitter and recover the bit pattern. Line encoding techniques prevent baseline wandering.
➨It incorporates error detection capability in the code. This helps to detect some or all the errors.
➨It doesn't create any DC components i.e. low frequencies.
➨Some encoders are immune to noise and interference.
➨Based on number of levels encoding techniques are simple or complex to implement.
➨Refer advantages and disadvantages of Unipolar, Polar and Bipolar coding and NRZ and RZ coding techniques.

Modulation process

The process of shifting baseband signals to higher frequency region is known as modulation. Modem performs modulation at the transmitter end and demodulation at the receiver end. There are two types of modulation viz. analog and digital. The modulated analog signal can be transported using optical fiber cables and unguided media.

Analog modulation takes analog baseband signal and gives modulated analog signal as output. Digital modulation takes digital baseband signal and gives modulated analog signal.

Modulation Demodulation process
Figure-3 : Modulation demodulation process

Example of Modulation : Following are the different types of schemes used for modulation based on their input data type (analog or digital).
Analog modulations include AM, FM, PM etc.
Digital modulations include ASK, FSK, BPSK or PSK, QPSK, 16-QAM etc.

Amplitude modulation
Figure-4 : Analog Modulation (AM-Amplitude Modulation)

The figure depicts amplitude modulation in which input is analog baseband frequency and output is analog carrier frequency.

ASK modulation
Figure-5 : Digital Modulation (ASK-Amplitude Shift Keying)

The figure depicts digital modulation in which input is digital data and output is analog modulates signal.

Advantages of modulation process

Following are the genetic advantages of modulation techniques.
➨Modulation converts low frequency baseband signal to high frequency carrier signal suitable for transmission over air without any noise or interference.
➨It overcomes need of large antenna required in low frequency transmission. Higher frequencies after modulation require smaller antannas.
➨Higher level digital modulation schemes such as QPSK, QAM reduces bandwidth requirement and increases spectrum efficiency.
➨Higher level modulation schemes increases data rate as more number of data bits are mapped on single signal elements. For example QPSK maps 2 bits on single symbol or signal element where as 16-QAM maps 4 bits on single symbol or signal element and so on.
➨It reduces error probability.
➨Refer advantages and disadvantages of AM and FM, ASK modulation, FSK modulation and PSK modulation.

Line coding techniques

Difference between Unipolar Polar and Bipolar coding    RZ vs NRZ vs Manchester coding    RZ vs NRZ pulse shapes    Advantages and disadvantages of NRZ encoding    RZ encoding    2B1Q coding    8B6T coding    4D PAM5 coding    MLT-3 coding    4B/5B encoding    8B/10B encoding    R8ZS scrambling    HDB3 scrambling   

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