Power in comm.AWGNChannel

Hello,

I am using comm.AWGNChannel to simulate the effect of AWGN channel on 8 signals that represents my symbols. Each symbol has 1002 samples. My AWGN channel object is created by

channel = comm.AWGNChannel('NoiseMethod', 'Signal to noise ratio (Es/No)', 'EbNo',20, 'SamplesPerSymbol' , 1002, 'SignalPower', Px);

I couldn’t understand the impact of SignalPower parameter on the resulted signal. When I omit it, I got low perfrmance system. When I set it to the everage signal power of the eight symbols, the performance is little bit improved. When I set it to small valuse, such as 0.002 watts, the performance is improved. My questions are how we can find the correct value of the SignalPower that is referenced to 1 ohm (watts). Is it in dB?

What is the relation between Es/No and SNR? Does the following relation apply or not? Es/No(dB)=10log10(Tsymb*Fs)+SNR(dB)