# Path loss effect on BER

Does including log distance path loss to a communication system cause a drastic difference to the BER of the system?

In other words, if I have a simulation for a communication system without path loss, does the BER vs SNR curve differ drastically when I add path loss or should both the BER vs SNR curves(with and without path loss) look similar?

• If I normalize my receiver power at the receiver to unity and then calculate the noise power (based on SNR) and the BER performance, does it ensures that performance is independent of the path loss??
– user18288
Nov 15, 2015 at 14:31
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– JRE
Nov 16, 2015 at 12:11

Generally speaking, the BER only depends on the SNR. If the received signal power $P_\mathrm{S}$ is reduced due to path loss, while the noise power $P_\mathrm{N}$ remains constant, then the SNR will be reduced, because the SNR is defined as $$\gamma = \frac{P_\mathrm{S}}{P_\mathrm{N}}$$ Consequently, the BER will be increased and the answer to your first question is: yes. However, this should not influence your BER vs SNR curves. Thus the answer to your second question is: no.
If your simulation behaves differently, i.e. if introducing a path loss "shifts" your BER curves, then the SNR is probably not calculated correctly. I suggest that you estimate the received signal power $\hat P_\mathrm{S}$ at the receiver (just before the sampler). Then the power of the additive noise should be calculated by $$P_\mathrm{N}=\frac{\hat P_\mathrm{S}}{\gamma}.$$ Then add noise with mean power $P_\mathrm{N}$ to the received signal. With this setup, your BER/SNR curves should be independent of path loss.