In this paper, we derive the minimum noncoherent distance of block-coded 16QAM, and propose noncoherent block-coded 16QAM (NBC-16QAM) accordingly. Various noncoherent block coding schemes are compared via computer simulations. We find that for both NBC-16QAM and the noncoherent 16QAM scheme proposed in 2002 , the curves of bit error rates do not decade exponentially. When the block length is very small, NBC-16QAM performs worse due to its small minimum noncoherent distance. However, if the block is not short, NBC-16QAM has the best error performance because the codewords with small noncoherent distances are rare.