If I didn't know better, I would have thought you are punishing me
for starting this thread!
Actually, this one is easy, almost elementary. (I suspect you read
"impulse response" as "impulse", and the 7th cup of coffee made you
quickly pull the trigger...)
Still, here goes. Simple models of communications links assume the
channel to be linear, time-invariant. "Channel" is copper cable,
fiber, air, whatever. In time domain, we describe its behavior with
an impulse response. If this impulse response, the h(t) curve, is
the same no matter when you look, we call it a time-invariant
response. The impulse response of a singlemode fiber, for example,
can be called time-invariant. If not, it's time-variant. (Purists,
please cut me some slack; I know, nothing is truly time-invariant.)
If it is time-variant, we have to ask if it varies randomly or
My contention was that a multimode fiber with DMD can be viewed as a
channel whose impulse response is changing with time in a random
fashion. Hence the phrase "randomly time-variant impulse response".
> -----Original Message-----
> From: Jonathan Thatcher
> Sent: Thursday, July 20, 2000 3:07 PM
> To: 'vipul.bhatt@xxxxxxxxxxx'; HSSG
> Subject: RE: Equalization
> You have really caught my attention on this one. What
> exactly is a "
> time-variant impulse?"