PhD Defense: "Millimeter Wave MIMO: Design and Evaluation of Practical System Architectures"

Eric Torkildson

December 1st (Wednesday), 10:00am
Harold Frank Hall (HFH), Rm 4164

Unlicensed spectrum at 60 GHz and the E-band frequencies spans multiple GHz, enabling wireless links to reach multi-Gb/s speeds. In this work, we propose increasing speeds further by leveraging spatial multiplexing gains at millimeter (mm) wave. To this end, we design and evaluate practical MIMO architectures that address the unique challenges and opportunities associated with mm wave communication. We begin by recognizing that the mm wave channel is predominantly line-of-sight (LOS), and develop arrays that provide robust spatial multiplexing gains in this environment. Noting that the cost and power consumption of ADCs become limiting factors as bandwidths scale to multiple GHz, we then propose a hierarchical approach to MIMO signal processing. Spatial processing, including beamforming and spatial multiplexing, is performed on a slow time scale and followed by separate temporal processing of each of the multiplexed data streams. This design is implemented in a four-channel hardware prototype.

We then investigate mm wave spatial multiplexing for short range indoor applications, first by quantifying fundamental limits in LOS environments, and then by investigating performance in the presence of multipath and LOS blockage. For linear arrays with constrained form factor, an asymptotic analysis (as the number of antenna elements gets large) based on properties of prolate spheroidal wave functions shows that a sparse array producing a spatially uncorrelated channel matrix effectively provides the maximum number of spatial degrees of freedom in a LOS environment, but that substantial beamforming gains can be obtained by using a denser array. This motivates a system architecture that utilizes arrays of subarrays to provide both directivity and spatial multiplexing gains. The performance of this system is evaluated in a simulated indoor environment using a ray-tracing model that incorporates multipath effects and potential LOS blockage. Our numerical results provide insight into the spatial variations of attainable capacity within a room, and the combinations of beamsteering and spatial multiplexing used in different scenarios.

Hosted by: Professor Upamanyu Madhow