# What is the meaning of the small power of the signal at the receiving end

I experimentally transmit an OFDM signal through 2 meters channel. When I estimate the channel at the receiving end, I find the channel coefficients very small. An example of the channel I find is:

h = [0.0823 + 0.0167i 0.0017 + 0.0033i 0.0010 + 0.0023i 0.0008 + 0.0018i 0.0004 + 0.0011i 0.0001 + 0.0001i -0.0004 + 0.0010i -0.0002 + 0.0006i];

In idea case, I supposed to get the first value 1 and all others zeros, but I do not know why that coefficients becomes very small. does that mean the signal is losing its power?

When I directly decode the signal without channel equalization, I get very small value of my signal. Is there a common reason or explanation for that signal deterioration?

NP The transmitted signal is optical in free space transmission. I am using LED as light source with 2.25 Voltage.

• Please edit your question to describe what your channel is and post a picture or a sketch. Include not just the medium that's 2m long, but the receiving and transmitting apparatus. Is it two feet of coax, two feet of string, free space transmission with two antennas separated 2m apart, etc. If it is antennas, are they simple dipoles, 1/4-wave with ground plane, Yagis, etc. Also, if it's free space transmission, tell us the frequency. Commented Oct 2, 2022 at 15:24
• Floating point numbers are often… floating. I.e. the absolute magnitude of the number lacks a physical reference and it is up to the application to normalize if neded. Commented Oct 2, 2022 at 15:52
• And without detail on the channel, there's no way of knowing what's reasonable. Commented Oct 2, 2022 at 16:01
• @TimWescott I have updated the question. Commented Oct 2, 2022 at 17:31

It sounds like your path can be described as: computer #1 $$\to$$ some electronics $$\to$$ LED $$\to$$ free space $$\to$$ photodiode $$\to$$ some electronics $$\to$$ computer #2. (And it may be just one computer without loss of generality).