Question

Suppose we want to transmit the message 0010 1101 and detect transmission errors using the CRC divisor polynomial (x3+x2+1).

A.) [15 marks] Determine the bit string that should be transmitted.

B.) [15 marks] If the leftmost 1-bit of the transmitted string is inverted due to noise on the link, what is the result of the receiver's CRC calculation?

Answer 1

A)

The CRC polynomial given is x3+x2+1=1101

The message given is 00101101

The number of bits in the divisor that 1101 is 4.

So,number of 0's to be appended to three

message = 4-1 = 3.

Thus the data to be transmitted is original message appended with the remainder obtained.

The data to be transmitted are 00101101010.

B)

These transmitted data 00101101010.

If the leftmost 1- bit is inverted due to noise during transmission, then

The transmitted data =10101101010.

The divisor using CRC polynomial is 1101.

So, to check the data from the receiver end append three 0's to the transmitted and divide it by the divisor.

The remainder obtained by the reciever is 101 and not 000. So, this implies that there is an error in the message.