Data transmission is disclosed over a transmission channel that is subject to narrowband interferers. An increased overall bit or data transmission rate is achieved by an exemplary method of determining a channel capacity of plural sub-channels of the transmission channel based on a net background noise power estimation. The net background noise power contains only white noise-like contributions and excludes, to a reasonable extent, noise contributions or signal power from narrowband interferers. Hence, the net background noise power can be reduced. For example, an Orthogonal Frequency Division Multiplex (OFDM) signal code construction or bit allocation scheme can be chosen that provides for optimized data transmission at a data rate that approximates or approaches the more realistic channel capacity of an individual sub-channel, resulting in an increased overall bit or data transmission rate.