Yair Carmon Shlomo Shamai Tsachy Weissman Comparison of the Achievable Rates in OFDM and Single Carrier Modulation with I.I.D. Inputs. 1795-1818 2015 61 IEEE Trans. Inf. Theory 4 https://doi.org/10.1109/TIT.2015.2403354 db/journals/tit/tit61.html#CarmonSW15