Successive Interference Cancellation for Bandlimited Channels with Direct Detection

Oversampling increases information rates for bandlimited channels with direct detection, but joint detection and decoding (JDD) is often too complex to implement. Two receiver structures are studied to reduce complexity: separate detection and decoding (SDD) and successive interference cancellation (SIC) with multi-level coding. For bipolar modulation, frequency-domain raised-cosine pulse shaping, and fiber-optic channels with chromatic dispersion, SIC achieves rates close to those of JDD, thereby attaining significant energy gains over SDD and classic intensity modulation. Gibbs sampling further reduces the detector complexity and achieves rates close to those of the forward-backward algorithm at low to intermediate signal-to-noise ratio (SNR) but stalls at high SNR. Simulations with polar codes and higher-order modulation confirm the predicted rate and energy gains.