Decoder-Assisted Communications over Additive Noise Channels

A number of additive noise networks are studied in the presence of a helper that observes the noise and assists the decoder by providing it with a rate-limited description of said noise. It is shown that 'flash helping' - where noise descriptions are provided infrequently but with great precision - is often optimal and typically increases capacity by the maximal allowed description rate. It requires no binning. The discrete setting of the modulo-additive noise channel is also discussed.