MATLAB: How to specify AWGN Input Signal Power for a signal generated by WLAN Toolbox

Communications ToolboxWLAN Toolbox

I am using the WLAN Toolbox to generate a signal, and then I am using that signal in a Simulink model, where I add noise to it with the AWGN Channel block. Since my signal is coming from the WLAN Toolbox, I do not know how to specify the "Input Signal Power" parameter of the block:

I have a few questions:
1) Should it be the power of the whole imported signal or just of one 802.11p packet? Note that I am using an OFDM/802.11p signal.
2) Should the idle time of the packet also be taken into account to obtain the signal power?
3) The parameter says the input signal power is referenced to 1 ohm. How can you tell whether the imported signal from WLAN toolbox is referenced to 1 Ohm?

Best Answer

You can calculate Input Signal Power however you would like for your particular application. For a WLAN waveform, defining the SNR during the active portion of the waveform (during a packet) is probably the most useful definition, but ultimately it depends on your requirements.
You could compute the average power of the waveform over the length of the whole waveform including the idle time. Since the power is averaged over the whole waveform, the idle time between packets has an impact on the total power of the waveform. However, in some cases the idle time between packets is small as compared to the packet length so the power of the waveform remains more or less the same even with more NumPackets in the waveform. Note than the WLAN standard normalizes the packet, therefore, the power of a each packet created by wlanWaveformGenerator should be ~0dBW (assuming 1 Ohm).
In addition, in the WLAN Toolbox, we assume the output from wlanWaveformGenerator function as voltage signal in volts with 1ohm resistance. For example:
cfg = wlanNonHTConfig;
tx = wlanWaveformGenerator(1,cfg);
tx = var(tx); % In watts
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