Next-Generation Digital Radio Circuits

Increasing demand for wireless communication has made spectrum a scarce commodity. Mobile data traffic in Canada is slated to increase 7-fold over 2014 levels by 2019. In response, Industry Canada is trying to make new spectrum available around 600MHz and 3500MHz for commercial providers, but this will require commissioning and deploying new equipment at great expense. At the same time, our use of unlicensed spectrum (around 2.4 GHz and 5 – 6 GHz, for example) is growing even faster than that of the licensed spectrum, and therefore seeing tremendous congestion. The number of wirelessly connected devices is growing 14% annually, and the 260+ TWh/yr worldwide energy consumption of communication infrastructure continues to grow at a frightening 10.4% annually.

Our research is focused upon developing high speed transceiver circuits to exploit larger bandwidths, make more efficient use of spectrum, and decrease power consumption.  Specifically, we are currently focused upon the design of the analog-to-digital converters for these applications. For example, a primary challenge in wireless communication is the so-called “near-far” problem whereby many transmitters occupy adjacent channels – some nearby, some faraway.  Therefore, a tremendous dynamic range is required to receive signals from a faraway source in the presence of much larger interference signals from nearby “blockers” overwhelm the receiver.  In mobile devices, the objective is to isolate the desired channels from adjacent blockers.  In the infrastructure (i.e. cell tower), circuitry is required to process all signals, near and far, simultaneously.  Both are exciting research opportunities.

Another objective of this research program is to address the fundamental IC implementation problems associated with new wireless communication technologies that rely upon a massive plurality of signal paths through the transmitter and receiver.  Specifically, “massive MIMO” (multi-input multi-output) is a wireless technology that relies upon hundreds or even thousands of antennas at the fixed terminals (i.e. central router or base-station) while maintaining only 1-4 antennas in each mobile device.  All antennas in the fixed terminal transmit and receive signals in concert to hundreds of users simultaneously using the same frequencies, thereby permitting tremendous reuse of available spectrum.  Orders-of-magnitude increases in bandwidth are achievable without increasing spectrum or radiated-power limits.  The excellent directivity of massive arrays can also be used to increase the reach of wireless communication, a great benefit for Canada’s remote geographies.  The tremendous potential of massive MIMO has made it a key part of wireless technology roadmaps worldwide and implicit in Canada’s wireless regulatory policies, yet that potential is being questioned because the assumed analog signal processing required at the fixed terminals for straightforward implementation of massive MIMO is impractical.  Specific challenges include the need for 100’s of precise RF clocks, 100’s of parallel broadband data converters, and their manufacture in low-cost CMOS which is subject to tremendous variability.  The proposed program seeks analog integrated signal processing technologies to address these challenges in future wireless infrastructure, enabling practical and inexpensive massive MIMO communication.