Exam-style question
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A communication system receives three copies of a four-bit sequence: 1101, 1001 and 1101. Explain how majority voting can be used to produce the corrected sequence. Then explain how a checksum could be used to check a block of numerical data and how a check digit could be used to check an identifier.
Model answer
What a good answer should say
- For each bit position, the receiver compares the three copies and chooses the value that appears at least twice.
- The first position is 1 in all three copies, the second is 1, 0 and 1, the third is 0 in all three copies, and the fourth is 1 in all three copies.
- The corrected sequence is therefore 1101.
- For a checksum, the sender calculates a value from the data values and sends that value with the data.
Explanation
Why this works
The majority-voting calculation shows how a differing copy can be corrected using the two matching copies. The checksum and check-digit explanations correctly describe generating an additional checking value and comparing a recalculated value with it.
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