An Upper Bound for the Capacity of Amplitude-Constrained Scalar AWGN Channel

This letter slightly improves the upper bound in Thangaraj et al. for the capacity of the amplitude-constrained scalar Additive White Gaussian Noise (AWGN) channel. This improvement makes the upper bound within 0.002 bits of the capacity for (E
_b
/N
₀
) ≤ 2.5 dB.