The Method of Types for the AWGN Channel

For the discrete-time AWGN channel with a power constraint, we give an alternative derivation of Shannon’s sphere-packing upper bound on the optimal block error exponent and prove for the first time an analogous lower bound on the optimal correct-decoding exponent. The derivations use the method of types with finite alphabets of sizes depending on the block length n and with the number of types sub-exponential in n.