Chapter 4 / 4.17

4.17 REVISION QUESTIONS

1. Identify the principal satellite-channel impairments that motivate the use of FEC, and classify them as random, burst, or erasure-type errors.

1. Explain why source coding and encryption increase the need for channel coding in practical systems.

1. For a link dominated by scintillation and occasional blockages, which error patterns dominate and why?

1. Explain why commercial providers often specify a guaranteed BER rather than a fixed coding scheme.

1. Define code, codeword, and explain how restricting valid sequences enables error detection.

1. Give a real-world example where natural redundancy enables error detection without formal coding.

1. What is the difference between systematic and non-systematic codes?

1. Briefly define the following: Hamming distance, minimum distance, minimum free distance, and constraint length of a code.

1. Briefly describe what is meant by a block-coding technique.

1. Construct an odd-parity (5,4) code for the data word 1010.

1. In the book example, why does adding a parity bit reduce undetected error probability so dramatically?

1. Describe how a checksum is formed and verified.

1. Why would a (7,4) Hamming code mis-correct some 2-bit errors?

1. Using the generator matrix in Equation (4.17), what is the code word for an input data word d=[1010]? (c=[1010010])

1. Consider an encoder using the generator matrix in Equation (4.17). If the received code word r=[1011011], what is the corrected input data word? (d=[1011])

1. For the data word d=0111 use the generator polynomial g(X)=1+X+X ³ to generate a (7,4) cyclic systematic and non-systematic codeword. (non-systematic—0100011; systematic—0010111)

1. Briefly describe what is meant by a convolutional-coding technique.

1. Briefly describe what is meant by interleaved codes.

1. Briefly describe what is meant by punctured codes.

1. Briefly describe what is meant by concatenated codes.

1. List the three principal families of compound code and a hallmark of each.

1. Briefly describe what is meant by coding gain.

1. Briefly describe the issues associated with the selection of a suitable channel coding technique for satellite communications.

1. Briefly describe forward error correction (FEC) and automatic repeat request (ARQ).

1. Why is pure ARQ ill-suited to GEO broadcast?

1. Give a LEO use case where ARQ is practical.

1. Briefly describe the purpose of channel coding.

1. What is the difference between systematic and non-systematic codes?

1. Briefly describe what is meant by a block code.

1. Briefly describe what is meant by a convolutional code.

1. Briefly describe what is meant by the Hamming distance and constraint length of a code.

1. Briefly describe what is meant by interleaved codes.

1. Briefly describe what is meant by concatenated codes.

1. Briefly describe the issues associated with the selection of a suitable channel-coding technique.

1. Briefly describe forward error correction (FEC) and automatic repeat request (ARQ).