Thursday, June 7, 2007

Question 8

A code X1X2X3X4X5X6X7 which consists of information bits X1X2X3X4 and redundant bits X5X6X7 satisfying

( X1+X2+X3+X5 ) mod 2 = 0
( X1+X2+X4+X6 ) mod 2 = 0
( X2+X3+X4+X7 ) mod 2 = 0
is transmitted.

If the received code Y1Y2Y3Y4Y5Y6Y7 differs from the transmitted code by no more than one bit, then it is possible to determine the correct information bits X1X2X3X4 according to whether or not each of the following becomes zero:

( Y1+Y2+Y3+Y5 ) mod 2 = 0
( Y1+Y2+Y4+Y6 ) mod 2 = 0
( Y2+Y3+Y4+Y7 ) mod 2 = 0

If Y1Y2Y3Y4Y5Y6Y7 = 1100010,
which of the following indicates the correct information bits? In this example, a mod b denotes the remainder when a is divided by b

a) 0100
b) 1000
c) 1100
d) 1101

answer

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