In iterative turbo decoding I am having a problem when the Eb_No values are negitive. I get an error of .21*10^-4 but for the second or third iterationit still remains the same where as for the positive Eb_No values it works fine i.e error decreases with itterations....
This is the result for various db calues

1.0e-004 *
Eb_No
-2 0.2168 0.2295 0.2100 0.2305 0.2207
-1 0.1777 0.1953 0.1738 0.1846 0.1689
0 0.0830 0.0801 0.0811 0.0986 0.0820
1 0.0547 0.0078 0.0029 0 0
2 0.0205 0 0 0 0


can some please help me............

thank you,
Arun