Which forward error correction code employs a shift-register based encoder and produces a continuous stream of encoded bits?

Which forward error correction code employs a shift-register based encoder and produces a continuous stream of encoded bits?

• A. Hamming code
• B. Reed-Solomon code
• C. Convolutional code
• D. Shannon limit

Answer: (C)

Convolutional codes are defined by a shift-register based encoder that treats the input as a continuous stream and produces encoded output bits on the fly. In a convolutional encoder, each output bit is formed by combining the current input bit with several past input bits stored in memory elements arranged as shift registers. The pattern of which bits are combined is set by generator polynomials (the taps), so the encoder’s output depends on the current bit plus a window of previous bits. Because the encoder keeps accumulating past bits, encoding happens continuously as long as data is flowing, yielding a steady stream of encoded bits rather than fixed-size blocks. This real-time, memory-based structure is exactly what makes convolutional codes suitable for streaming data in SATCOM links and other channels, with decoding often performed by the Viterbi algorithm. Hamming codes are block-based; they encode fixed-size data blocks with parity bits, not as a continuous stream tied to past bits. Reed-Solomon codes are also block-based and operate on symbols rather than bit streams. The Shannon limit is a theoretical bound on error performance and capacity, not a type of code or encoder.

Convolutional codes are defined by a shift-register based encoder that treats the input as a continuous stream and produces encoded output bits on the fly. In a convolutional encoder, each output bit is formed by combining the current input bit with several past input bits stored in memory elements arranged as shift registers. The pattern of which bits are combined is set by generator polynomials (the taps), so the encoder’s output depends on the current bit plus a window of previous bits. Because the encoder keeps accumulating past bits, encoding happens continuously as long as data is flowing, yielding a steady stream of encoded bits rather than fixed-size blocks. This real-time, memory-based structure is exactly what makes convolutional codes suitable for streaming data in SATCOM links and other channels, with decoding often performed by the Viterbi algorithm.

Hamming codes are block-based; they encode fixed-size data blocks with parity bits, not as a continuous stream tied to past bits. Reed-Solomon codes are also block-based and operate on symbols rather than bit streams. The Shannon limit is a theoretical bound on error performance and capacity, not a type of code or encoder.