In this paper, we propose a novel superreceiver architecture for Nyquistwavelengthdivision multiplexing （WDM） superchannel optical coherent systems. As opposed to a conventional coherent receiver, where each subchannel is demodulated independently, the proposed superreceiver jointly detects and demodulates multiple subchannels simultaneously. By taking advantage of information from side channels that use joint DSP to cancel interchannel interference （ICI）, the proposed super receiver performs much better than a conventional receiver. This architecture also has the potential to compensate for crosschannel impairments caused by linear and nonlinear effects. We examine the proposed architecture through experiment and simulation. OSNR is improved by more than 5 dB after 1280 km fiber transmission with narrow channel spacing.