Radio for IoT draws tenth the power of Wi-Fi

Researchers at Belgium-based Imec and Holst Centre in the Netherlands have demonstrated a low power radio technology which they claim will operate over long distances.

They claim a 10-fold reduction in power over traditional 802.11 Wi-Fi based on OFDM (orthogonal frequency-division multiplexing) radio transmission in a paper at IEEE International Solid-State Circuits Conference (ISSCC 2016) which took place in San Francisco earlier this month.

The fully digital polar transmitter consumes only 13 nano-joules per bit, said the researchers.

It was demonstrated running the long range Wi-Fi protocol – IEEE802.11ah – which is intended for internet-of-things applications.

The 802.11ah protocol operates in the 868MHz unlicensed frequency band. This is the same as rival IoT radio standard LoRaWAN 1.0 but which differentiates it from Bluetooth the other Wi-Fi radios operating at 2.4GHz. It has 1MHz/2MHz channel bandwidths and supports long range data links of up to 2.1Mbit/s.

The 802.11ah standard uses OFDM to improve the link robustness against fading and to achieve a high spectral efficiency i.e. maximising the data rate in a given radio channel.

Imec and Holst Centre’s approach has been slightly different they have designed a fully-digital polar transmitter but meets the requirements of conventional Wi-Fi standards in terms of spectral mask and error vector-magnitude (EVM).

For example, the measured phase noise at 1.5MHz offset for the Imec radio is -115dBc/Hz which is 15dB lower than the spectral mask requirement for the IEEE 802.11ah standard.

At 1MHz/2MHz with 64-QAM OFDM data packets, both the far-out and close-in spectrum pass the mask with at least 4.8dB margin. The EVM is below 4.4%.

The power consumption of the transmitter is as low as 7.1mW, when delivering 0dBm output power and operating from a 1V supply.

This claims Imec is a 10x power reduction compared to other OFDM transceivers.