Leuven, Belgium: IMEC, in collaboration with the Holst Centre, has developed an ultra-wideband (UWB) impulse radio solution for the globally available 6- to 10-GHz band with a receiver that uses less than 6 mW (see the figure). It’s designed for the personal network, wirelessly streaming audio and video signals between a portable device and a set of headphones.
Unlike wireless headsets for voice calls, wireless headphones for listening to music have not yet reached mass market adoption largely because a technology that can stream the quality required at the power level required has not yet been developed, said Kathleen Philips, IMEC’s principal researcher for ultra-low-power wireless systems.
Magnetic induction, the technology used in hearing aids, can provide quality but its 50-cm range was deemed insufficient. Bluetooth, which uses the 2.4-GHz band, drained the battery of a mobile device within two hours and also suffered from quality problems, Philips said.
“There’s a coexistence problem with legacy radios in the crowded 2.4-GHz band,” Philips said. “It’s not a problem for file transfers, but it’s a problem if you talk about audio streaming because you can’t afford any lost packets.”
IMEC’s solution came from an UWB technology that has been used in military radio communications for some time—the impulse radio. Though they use the 6- to 10-GHz UWB spectrum, impulse radios are very different from the complex, high-power UWB radios seen in the industry circa 2002. The impulse radio’s transmitter sends out short pulses (within the 802.15.a mask) at regular intervals, using a large bandwidth.
The receiver must switch itself on at the exact same time as the pulse to receive the data, switching itself off in between pulses, to preserve power. Synchronisation of the transmitted pulses and the receiver, not to mention the consistency of the duty cycles involved, has posed a problem for impulse radios developed for consumer applications in the past.
Because of its wideband operation, the impulse radio does not suffer from fading, a phenomenon whereby reflected signals destructively interfere with each other, adding to its reliability.
“It’s scaleable,” Philips added, “You can put more pulses in the air to increase the data rate, but this also increases the power consumption.”
IMEC’s single-chip transmitter can deliver +13-dBm peak output power while drawing an average of 3.5 mW, while the receiver front-end IC draws 3 mW and exhibits –88-dBm sensitivity at 1 Mbit/s.
The baseband, currently implemented on an FPGA but due for tapeout “soon,” Philips said, runs a digital synchronisation algorithm for the real-time duty cycling and draws around 3 mW. A receiver system could therefore draw in the region of 6 mW, which compares favourably with a similar Bluetooth receiver that draws more than 30 mW.
Philips said the range of the radio was 10 m but the team wants to double this distance in the future.
The Holst Centre