Capacity approaching scheme

hi, all I have question about capacity since I am only familiar with deriving capacity.

The question is:

Consider a 2-state channel in which the received SNR is 20dB when the channel is good and 0dB when the channel is bad. Assume that the channel state changes frequently and the long term state probabilities for the good and bad states are 0.2 and 0.8, respectively, Assuming CSIR only and no latency requirement, describe a capacity-approaching scheme in detail (including encoding, power, and decoding) and evaluate the corresponding spectral efficiency.