what does mean quasi-static channel When I read papers about channels, I usually see something Quasi-static Channel, 

Does "Quasi-static Channel" mean "time-variant channel" or "time-invariant channel"?
Quasi-static channels can be said as "block-wise" time (in)variant. For example, your channel has no variations over time (not in delay domain) for some time-period, e.g., 1 ms, but the channel may change after 1 ms.