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studentspace:labs [2007/11/05 16:53] – created cs242003studentspace:labs [2007/11/06 05:24] (current) cs233257
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 Hassan Hassan
  
 +
 +===============================================================
 +Hi Hassan,
 +
 +The definition of a symbol is what you can transmit through the channel at a given instance... In both cases in our lab our Baud rate is 1 symbol/second. I think you are confusing the physical make up of the signal (such as sine waves and matched filters) with the more abstract "Digital symbol". In the case of QPSK you transmit two digital bits at any given moment, thus you are sending 2 bits per symbol. In the case of 16-APSK you are sending 4 bits per symbol (analogous to sending a single hexadecimal digit per second). Now in both cases the bit error rate may be the same, but in the case symbol error rate, you are expecting to have more symbol mismatches in the case where each symbol carries more bits.
 +
 +Example:
 +
 +Source data:
 +
 +1  0  1  0  0  0  1  1  1  0  1  0  0  1  0  1
 +
 +1  0  1  0  1  0  1  1  1  1  1  0  1  1  0  1
 +
 +Where the error rate is 3/16 errors per bit
 +
 +Now in the first case each symbol is two consecutive bits:
 +
 +The error rate is 3/8 errors per symbol.
 +
 +Now in our second case each symbol is four consecutive bits:
 +
 +The error rate is 3/4 errors per symbol.
 +
 +Hope it helps, and hope someone will correct me if I am wrong :)
 +
 +Regards,
 +
 +Ron  
 +
 +=================================================================
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