An Upper Bound for the Capacity of Amplitude-Constrained Scalar AWGN   Channel
  This paper slightly improves the upper bound in Thangaraj et al. for the capacity of the amplitude-constrained scalar AWGN channel. This improvement makes the upper bound within 0.002 bits of the capacity for $\frac{E_b}{N_0}\leq 2.5$ dB. 
Borazon Rassouli and Bruno Clerckx
cs.IT math.IT