A Study of Discrete Multitone Modulation for Wireline Links Beyond 100 Gb/s

To overcome the severe losses beyond 28 GHz in low-cost electrical channels, 4-level pulse-amplitude modulation (4-PAM) wireline links targeting 112 Gb/s incorporate resource- or power-intensive equalization schemes such as decision-feedback equalizers (DFE) with many taps. Alleviating the timing constraints that cause DFEs to balloon in size and power, discrete multitone (DMT) modulation involves independent sub-channels that can be equalized in the frequency domain without feedback. DMT allows flexibility in assigning bits to each sub-channel, thereby potentially avoiding lossy parts of the frequency spectrum. This article presents behavioural modeling results and an experimental setup used to study DMT transceivers. Our simulations show 200 Gb/s operation at a bit error rate (BER) of less than {10^{-5}} over an IEEE P802.3ck channel with 21 dB of loss at 50 GHz and assuming 150~\mathrm{fs_{rms}} of jitter, 1.26~{\mathrm{ mV}}_{\mathrm{ rms}} of noise at the receiver's input, and 7-bit 80 GS/s data converters. An updated bit-loading algorithm led to BER values 1-2 orders of magnitude below our previous results. The estimated power and area of the associated digital signal processing are comparable to those of DFE. We also present an experimental DMT setup achieving 61.6 Gb/s at a BER of {8.6 \times 10^{-4}} over a physical channel with severe notches that is very challenging for 4-PAM.