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Source Coding in Communications

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Questions and Answers

What type of encoding method is used when source symbols are not equally probable?

Variable-length code words

What property is required from any variable-length code to ensure proper decoding?

Unique decodability

What is a prefix code and what distinguishes it?

A prefix code is a code system with the 'prefix property' where no code word is a prefix of another.

Give an example of a prefix code.

{a=0, b=110, c=10, d=111} Signup and view all the answers

What are the two important properties to consider when using variable length codes?

Unique decoding and instantaneous decoding Signup and view all the answers

Can you explain the prefix property in the context of coding?

The prefix property requires that no code word in the system is a prefix of any other code word. Signup and view all the answers

Define source encoding and list two functional requirements of an efficient source encoder.

Source encoding is the process of representing data generated by a discrete source efficiently in binary form. Two functional requirements of an efficient source encoder are: code words produced in binary form and uniquely decodable source code. Signup and view all the answers

Explain the formula for entropy H(Y) for a source with statistically independent symbols.

The formula for entropy H(Y) for a source with statistically independent symbols is: H(Y) = -∑(P(y_j) * log_2(P(y_j))), where P(y_j) is the probability of symbol y_j. Signup and view all the answers

Define code efficiency η and how it is calculated.

Code efficiency η is defined as (H(Y) / max[H(Y)]) * 100. It is calculated by dividing the entropy by the maximum entropy and multiplying by 100. Signup and view all the answers

What is the formula for the overall code length L in terms of the average code word length?

The formula for the overall code length L in terms of the average code word length is: L = ∑(P(x_j) * l_j) bits/symbol, where l_j is the length of the code word for symbol x_j. Signup and view all the answers

Explain the concept of fixed-length code words and provide an example.

Fixed-length code words have a constant length for each symbol in the source alphabet. For example, the code C(a) = 000, C(b) = 001, C(c) = 010, ..., C(g) = 110 uses fixed-length code words for symbols a to g. Signup and view all the answers

How is a source sequence encoded using fixed-length code words?

A source sequence is encoded using fixed-length code words by assigning the corresponding code word to each symbol and concatenating the code words together. Signup and view all the answers