Consider the wireless channel. It is mult-path - means that signal is sum of sent signals with some delay and fadings. The standard models for "impulse response" for multi-path channel in wireless is:
$ h(t) = c_1 \delta(t - t_1) + c_2 \delta(t - t_2) + ... + c_N \delta(t - t_N) $,
where $t_i$ are path-delays and $c_i$ are fadings.
Question I wonder is this model realistic ? Is it really reasonable to assume "delta"-functions for each path or may be it we need to assume something more smooth ? What is good reference, where the results of real measurements can be found ?
[EDIT] in response to comment.
I am interested in cellur telephone links. I know that the standard e.g. channel 3GPP models assume 6-9 paths with delta-functions. I am suspicious about this assumption. So I want to see results of real measurements which support this model.
[EDIT 2] More details. I am interested in channel estimation for OFDM system cellur system. Assume carrier frequency is something like 1GHz - 2GHz. One user typically may have ~100 OFDM elements. Each element is about 15kHz. So the user bandwidth 1.5MHz.
What am suspicious about is that if we have 9 paths and we have about 100 pilot symbols, then our channel estimation would be quite good , and BER will be close to ideal ch.est. Because we need to estimate ~9*2 unknowns from 100 of data - so we get good quality of estimation. This is in theory, but I am afraid if will test such system in practice we mail fail, cause in practice it might be not 9 paths but 90 paths ...
So let me stress the following part of the question:
Where to find results of real measurements in urban requirement for channel response ?
I guess that should be old stuff may be from 60-ies ? Cause many modern literature concern MIMO channels and pay attention to angular spread and so on - while I need more simple information.