Apparently, no information could pass through plasma, therefore during descent of spacecraft, no information can be transmitted. Why so?
Plasma is "electrically neutral medium of unbound positive and negative particles". As it's got charge carriers floating about, it's electically conductive. In a sense, you can think of it as a metal sheet. If a metal sheet fully encloses the spacecraft, you'd get a Faraday Cage. Similarly, if the plasma sheath fully encloses the space craft, you end up with a Faraday Cage. Faraday Cages massively attenuate EM signals attempting to pass through them, resulting in loss of RF communications.