NTRU and one failed example
I've searched about this problem these two days, considering the paper cygnusv mentioned, and finally after reading the problem related to the pqc implementation, I guess that's the condition which is not formally mentioned in NTRU papers. And this condition 
$$q &gt; p(6d + 1)$$
must be true in order for the probability of unrecoverable messages to be less than $2^{-80}$.