Chapter 6: Digital Encoding

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In a digital communication system, the first step is to convert the information into a bit stream of ones and zeros. Then the bit stream has to be represented as an electrical signal. In this chapter, we will study the various representations of the bit stream as an electrical signal.

6.1 REQUIREMENTS FOR DIGITAL ENCODING

Once the information is converted into a bit stream of ones and zeros, the next step is to convert the bit stream into its electrical representation. The electrical signal representation has to be chosen carefully for the following reasons:

• The electrical representation decides the bandwidth requirement.

• The electrical representation helps in clocking— the beginning and ending of each bit.

• Error detection can be built into the signal representation.

• Noise immunity can be increased by a good electrical representation.

• The complexity of the decoder can be decreased.

The bit stream is encoded into an equivalent electrical signal using digital encoding schemes. The encoding scheme should be chosen keeping in view the bandwidth requirement, clocking, error detection capability, noise immunity, and complexity of the decoder.

A variety of encoding schemes have been proposed that address all these issues. In all communication systems, the standards specify which encoding technique has to be used. In this chapter, we discuss the most widely used encoding schemes. We will refer to these encoding schemes throughout the book, and hence a good understanding of these is most important.

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