1.2.2 Fast Fading Channels Definition:the fading coefficients vary relatively fast with respect to the duration of communication,we call it fast fading. Feature:coherence time is much shorter than coding delay. Performance measure:ergodic capacity. erg =lim N→0 p.之e+AlH.） ∑RsP 二 sup((hdh ∫Q(h)pH(h)dh≤P 1818 1.2.2 Fast Fading Channels Definition: the fading coefficients vary relatively fast with respect to the duration of communication, we call it fast fading. • Performance measure: ergodic capacity. • Feature: coherence time is much shorter than coding delay.     1 1 2 2 1 2 2 ( ) ( ) 1 = lim sup log 1 = sup log 1 ( ) ( ) N k k H C P N N erg k k N P k H C Q h p h dh P C P H N Q h h p h dh              