4.5 Channel Capacity

Channel capacities for in-house power lines can be calculated against background and ingress noises. The received signal power is dependent on the transmit signal power and the insertion loss of a power line connection. The transmit signal power is limited by the radiation from the nearby electromagnetic field strength. By imposing a field strength of about 30 dBµV/m, the allowed PSD can be estimated to be between 72 dBm/Hz and 52 dBm/Hz according to

Equation 4.36

where we have used CFs in the range of between 65 and 45 dB at a distance of about 30 m. Figure 4.29 shows a simulated power line channel model, a simulated power line noise model, transmit signal PSDs, and received signal PSDs. In Figure 4.29, the top curve is the power line channel model, the bottom curve is the noise model, two straight lines are for transmit signal PSD of 52 and 72 dBm/Hz, and Receive1/Receive2 are for received signals with transmit PSD of 52 and 72 dBm/Hz, respectively.

Figure 4.29. Signal Level Comparison

With these simulated received signal and noise levels, channel capacity of in-house power line can be estimated using

Equation 4.37

where f₁ is 1 MHz, f₂ is 30 MHz, S(f) is the received signal level, and N(f) is the noise level. For a transmit PSD of 52 dBm/Hz, we have a channel capacity of 474.18 Mbps; for a transmit PSD of 72 dBm/Hz, we have 282.96 Mbps. They correspond to 16 and 9 bits per Hertz, respectively. We also calculated channel capacities of the power line against a flat background noise level of 145 dBm/Hz. Corresponding results are 573.05 and 380.32 Mbps for 52 and 72 dBm/Hz transmit signal PSDs, respectively. Therefore, we found that ingress noises of this noise model reduced channel capacities by 20 and 34%, respectively.