DIGITAL MODULATION AND DATA ENCODING (MINGGU KE 4)

Digital Modulation gives more data limit, high information security, faster framework accessibility with incredible quality correspondence. Consequently, computerized regulation methods have a more noteworthy interest, for their ability to pass on bigger measures of information than simple ones. 

    

There are numerous kinds of computerized regulation strategies and we can even utilize a blend of these procedures also. In this section, we will talk about the most unmistakable computerized regulation methods. 

A. Amplitude Shift Keying 

The amplitude of the resultant yield relies on the info information whether it ought to be a zero level or a variety of positive and negative, contingent on the transporter recurrence. 

Amplitude Shift Keying (ASK) is a kind of Amplitude Modulation that addresses the paired information as varieties in the plentifulness of a sign. 

Following is the outline for ASK tweaked waveform alongside its information. 

Any tweaked signal has a high recurrence transporter. The double flag when ASK is regulated, gives a zero incentive for LOW information and gives the carrier output yield for HIGH information. 

B. Frequency Shift Keying 

The frequency of the yield signal will be either high or low, depending on the information applied. 

Frequency Shift Keying (FSK) is the advanced adjustment method wherein the frequency of the carrier signal fluctuates as indicated by the discrete computerized changes. FSK is a scheme of frequency modulation. 

Following is the outline for FSK tweaked waveform alongside its information. 

C. Phase Shift Keying (PSK)

PSK is the digital modulation technique where the phase of the carrier signal is varried by the sine and cosine inputs at a particular time. PSK technique is mainly used in wireless LAN, bio-metric, contactless operations, along with Bluetooth communications.

DIGITAL SIGNAL ENCODING FORMATS

Non- Return-to-Zero (NRZ)

NRZ encoding is used in slow-speed synchronous and asynchronous transmission interface. With this format, 1 bit is sent as a high value and 0 as a low value without complex encoding. The receiver in this case may lose synchronization when using NRZ which may cause consecutive bits with the same value with no change in voltage.

Advantage of NRZ

ü                                  Easy to streamline bandwidth usage

ü                                  More immune to noise

Weaknesses of NRZ

o   The presence of a dc component

o   Lack of sync capability

Applications

- Commonly used for digital magnetic recording

- Not widely used for signal transmission

2.1. Nonreturn-to-Zero-Level (NRZ-L)

·                    Displays the two voltage differences for bits 0 and 1

·                    The voltage remains constant throughout the bit interval

·                      No transition at the beginning of an interval (no return to voltage level zero)

·                       For example there is no voltage level for returns to binary 0

·                      More generally negative voltage is used for displays binary 1 and a positive voltage to show others.

·                       This code is often used to generate or interpret digital data via terminal or other

 

2.2. Nonreturn-to-Zero Inverted (NRZI)

Nonreturn to zero inverted on ones

·       Maintains constant voltage pulses to bit time duration

·       The data itself is indicated as presence or absence present transition

·       There is a transition (low to high or high to low) at the start of the bit time indicates binary 1, no transition indicates binary 0

·       As an example of differential coding

MULTILEVEL BINARY

Uses more than two signal levels

Ø  Two examples are Bipolar-AMI and Pseudoternary

i)                Bipolar-AMI

                        Binary 0 is displayed via signal on line

Binary 1 is displayed via positive pulse or negative

The binary pulse 1 must change polarity

Loss of synchronization will not occur if appears a string of length 1 s

·       There is no pure dc component

·       The bandwidth is narrower than the NRZ bandwidth

·       Widely used as a tool for detecting errors

ii)             Pseudoternary

            Binary 1 is displayed via signal on line

Binary 0 is displayed via positive pulse or negative

There is no special advantage over coding bipolar-AMI and each being 

the basis to apply to the appropriate application

 

Conclusion between the Multilevel Binary over NRZ Coding

a.     Not as efficient as NRZ coding

b.     Each signal element is only displayed in bit 1

c.      The signal path receives one of three levels, but each signal element can display log23 = 1.58 bits information, contains only one bit of information

d.     The receiver must distinguish between the three levels (+ A, -A, 0) than just two levels in the previous signaling

e.     Due to this, a signal power of approx. 3dB is requiredto achieve the same bit error probability

f.      Multilevel is widely used for Digital Subscriber Line(DSL) and Gigabit Ethernet.

SuSource:

        Jain, Raj. 2005. Signal Encoding Techniques. Washington University

        

S

S