The possible solutions for having minimum probability of error are good modulation schemes, good encoding schemes, or a combination of modulation and encoding schemes. If I consider only the models and the schemes one of the optimal methods by means of which modulation schemes can be implemented is in the form of block orthogonal signalling; where one can find out that the priority of error expression is bounded by the expression on the right hand side, where the value of K will be 1 for BPSK. The value of K will be 2 = for QPSK, etc., and therefore, if we want to keep the exponent positive, than the E_b/N₀ must not be greater than 1,4 dB.