| Pretty much all WiFi transceivers are indeed power-intensive, but it is actually receiving that often takes more juice. ESP8266 consumes ~70mA with both CPU and WiFi running but idle, and 15mA with CPU idling and WiFi powered down [1]. That's 55mA or (@3.3v) ~180mW for _idle_ (i.e. receiving) WiFi circuitry. Again - that's WiFi only, with exactly zero RF power transmitted. Now transmit. EU restricts amount of RF power radiated by a WiFi station/AP to 100mW. In US and few other places you can go slightly higher, but then other challenges arise, so for practical purpose most WiFi chipsets top out at 100 mW (a.k.a. 20dBm). Assuming RF power amplifier has efficiency of 32% [2], transmit duty cycle of 50% (that's transmitting half of the time and receiving for another half - pretty intense traffic here), we get: (100/32%)*50% = just 156mW consumed towards "blasting out" some RF. Clearly, receiving WiFi takes more. And there is a good reason for that. Most modern designs implement Rx as: Low-noise amplifier with some bandpass filtering -> Zero-IF mixer -> quadrature ADC -> DSP. It's the latter that does FFT, I/Q constellation tracking, demodulation, forward error correction, etc. essentially in software. And that takes a lot of power. [1] http://bbs.espressif.com/viewtopic.php?t=133 [2] http://ww1.microchip.com/downloads/en/DeviceDoc/75003C.pdf |
TIL :)