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GATE 2022 EC – Question 62

Communications · Information Theory · 2 marks · Numerical answer

Consider communication over a memoryless binary symmetric channel using a (7, 4) Hamming code. Each transmitted bit is received correctly with probability $(1-\epsilon)$, and flipped with probability $\epsilon$. For each codeword transmission, the receiver performs minimum Hamming distance decoding, and correctly decodes the message bits if and only if the channel introduces at most one bit error.

For $\epsilon=0.1$, the probability that a transmitted codeword is decoded correctly is ________ (rounded off to two decimal places).

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Correct answer: 0.84 to 0.86

Explanation

Decoding is correct when there are 0 or 1 bit errors among the 7 bits: $P=(0.9)^7+7(0.1)(0.9)^6=0.4783+0.3720=0.8503\approx0.85$.