0
$\begingroup$

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"?

$\endgroup$
  • 1
    $\begingroup$ Hello Marcus, First, thank you for your downvoting !! .. Yes I understand what you mean but I need the answer to be in general. If I cited such reference the answer will be according to that citation. What I need is a general description. Exactly as below answers. Thank you for your understanding. please, cancel your downvoting. $\endgroup$ – New_student Aug 19 '18 at 16:15
  • $\begingroup$ sorry, that's dumb. "we need the answer to be in general". Great, so if I answer "quasi-static is when you have a bear dancing in front of your antenna", it's right, too? Because I wrote a paper where "quasi-static" means exactly that. $\endgroup$ – Marcus Müller Aug 19 '18 at 16:27
  • $\begingroup$ I.e. the answers you've gotten aren't "in general". They are just a specific understanding of the term, in a context that their authors don't mention. In that sense, they aren't correct at all. $\endgroup$ – Marcus Müller Aug 19 '18 at 16:28
  • 1
    $\begingroup$ I think that the motivation behind the question may have originated from the definition of the term itself. In general, anything "quasi" is "not exactly". Another example would be "quasi real-time" systems. So, "quasi static" is time-variant with the rate (of change) being relatively slow. But how much and by how much depends on the application. "Quasi" originates in Latin, like "et al, i.e., a priori, de facto, in vivo" and others. From this point of view, the question would be off topic but... $\endgroup$ – A_A Aug 19 '18 at 16:55
  • 1
    $\begingroup$ I am sorry, I voted to close the question too quickly from the review panel, without noticing that it had already receive an accepted answer. In any case, I have found this a very useful and helpful community. $\endgroup$ – A_A Aug 19 '18 at 17:07
1
$\begingroup$

Quasi-static is almost-static. In other words, for a block (or window) period of time, you could assume that your channel is static. Below, i attach a figure that depicts this scenario. As you can see the channel could be assumed static for around 100 ms.

enter image description here

$\endgroup$
  • $\begingroup$ Thank you so much .. got it. It means the channel is time invariant during block period but it might be time variant otherwise. we can say it's a special case of time-variant channel. $\endgroup$ – New_student Aug 19 '18 at 16:17
  • $\begingroup$ Yeah its as if you got piecewise static functions. $\endgroup$ – Ahmad Bazzi Aug 19 '18 at 16:19
2
$\begingroup$

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.

$\endgroup$
  • $\begingroup$ Thank you so much .. got it. It means the channel is time invariant during block-wise but it might be time variant otherwise. $\endgroup$ – New_student Aug 19 '18 at 16:16

Not the answer you're looking for? Browse other questions tagged or ask your own question.