IMEC and the Holst Centre have successfully developed a low power impulse radio UWB system suitable for streaming music to consumer wireless headphones. Impulse radio has long been used in military radio applications but has proved too difficult to implement in consumer electronics suitable versions, until now.
Presenting at the IMEC Technology Forum in Leuven, Belgium this week, Kathleen Philips, Principal Researcher for ultra-low power wireless systems, said that impulse radio could fill a gap between Bluetooth, ZigBee and magnetic induction (the technology used in hearing aids) for consumer headphones applications. Wireless headphones are not widespread in the market because Bluetooth uses too much power for battery powered systems, ZigBee cannot achieve the data rate required for music, and magnetic induction technology is limited to a 50cm range, she said.
Where conventional radios use modulated waves to transmit data, impulse radio is pulse based. The transmitter sends out a short wideband pulse of data (in the globally-available 6-10GHz UWB band) which is less susceptible to interference and fading because of its wideband nature. It avoids destructive interference caused by multi-path propagation on a particular channel by using many different channels. Turning the transmitter off between pulses radically reduces power consumption.
The hard part so far has been the timing. To maintain the low power consumption, both the transmitter and receiver must switch off between pulses. This means they have to be very closely synchronised and the duty cycles absolutely consistent.
Imec and Holst Centre’s solution consists of a transmitter, receiver front-end, and receiver digital baseband. The transmitter delivers 13dBm peak power, with an average power consumption of 3.3mW. The receiver front-end shows -88dBm sensitivity at 1Mbps. A digital synchronization algorithm enables real-time duty cycling, resulting in a mean power consumption of 3mW. A DCO with 100ppm frequency accuracy and a baseband frequency tracking algorithm ensure the coherent reception. A 75dB link budget with a data rate of 1Mbps is achieved.