# Can I estimate Wi-Fi's power transmission in function of the amount of data transmitted?

For a specific device connected to specific AP. Can I estimate the differences in radiation power (mWh) depending on the data transmitted (2KB/s vs 200KB/s)?

If so, how?

• Have you read the Wifi spec to determine if there is a relationship? Have you made any measurements? – John U Mar 14 '14 at 9:46
• Power would be mW not mWh. mWh could be energy. – Brian Drummond Mar 14 '14 at 10:48
• Transmission power it is not related with bandwidth, but it is related with the receiver sensitivity and modulation schemes (dBm at x Mbps in DFM, QPSK, CCK, OFDM…) at a range of –68dBm to –94dBm. Then you can calculate propagation losses, Tx antenna gain, Transmitter power… – GR Tech Mar 14 '14 at 14:49

## 1 Answer

If two radio systems are operating at broadly the same frequency, using the same type of antennas and over the same distance and terrain, a theoretical comparative judgement can be made. The judgement is based on the assumption that a receiver (at a lower data rate) requires less received power at its antenna compared to the receiver operating at the higher data rate.

The required power for a receiver is -154dBm + 10log$_{10}$ (bit rate)

Ignoring the -154dBm (because we are making comparisons) it can be seen that: -

10log$_{10}$ (200,000) = 53 dBm and

10log$_{10}$ (2,000) = 33 dBm

I've ignored "B" (bytes) and assumed "b" (bits) in the equation but it makes no difference; 2 kbps requires a power level at the antenna that is 20 dB smaller than 200 kbps for the same bit error rate.

In real money, that means one-hundredth of the power is required to be transmitted for 2kbps, all other things being equal.