# Correct scaling for AWGN noise in OFDM system after adding Preambles

I have a two-part question:

• Question 1

I wonder if anyone can explain about the scaling factor that is used for AWGN noise in OFDM system. For example I know about the scaling factor for normal OFDM system for wasted energy due to cyclic prefix. For example assume \begin{align} \textrm{N}&=64\quad\text{is the number of subcarriers}\\ \textrm{CP}&=16\quad\text{Cyclic prefix length} \end{align}

then we usually boost the signal energy by $\sqrt{80/64}$ to compensate for the wasted energy then we add a noise to the signal.

Now my question is assume I have short, long preamble and signal filed (L-sig) and I concatenate it with OFDM symbols. Do I need to have extra scaling factor due to short, long preamble and signal field since I am thinking that AWGN noise is added to the entire packet plus the preamble?

If an expert can comment on correct method of adding noise to this system and how to take these field into account and compensate for the wasted energy.

• Question 2

Does MATLAB command awgn(TX_signal,SNRdB,'measured') already takes the correct scaling factor into account or not? I have seen many simulations in the web are using this command for OFDM system.