A network interface device includes i) a separator circuit configured to separate data into a plurality of frequency bands, ii) a first multiple input, multiple output (MIMO) processing circuit configured to multiplex the data into a plurality of spatial channels, and iii) a first analog front end circuit. The first analog front end circuit is configured to, for each spatial channel of the plurality of spatial channels: i) combine data in the plurality of frequency bands, including combining data in a first frequency band with data in a second frequency band different from the first frequency band, into a respective combined signal for simultaneous transmission over the plurality of frequency bands, and ii) transmit the combined signal via a transmission medium. Transmission of symbols in the first frequency band is synchronized with transmission of symbols in the second frequency band.