PhD Defense: "Diversity and Equalization for MultiGigabit Millimeter Wave Communications over a Sparse Multipath Channel"

Hong Zhang

November 30th (Friday), 2:00pm
Engineering Science Building (ESB), Room 2001

We undertake a fundamental investigation of diversity and equalization over highly directional links in the millimeter(mm) wave band. The particular focus is on outdoor links, using 60 GHz unlicensed spectrum. Such links could be used to form wireless mesh networks with multiGigabit data rates. We find that the sparse multipath channels induced by the use of directional transmission and reception require new design approaches, relative to design of conventional wireless links in rich scattering environments.

We investigate spatial and frequency diversity for such highly directional links for which the number of dominant paths is significantly smaller than for the scattering environments seen by omnidirectional links. While fading can still be severe, we observe that the channel statistics are very different from classical Rayleigh or Rician fading models, and are characterized by the variations in a small number of parameters characterizing the propagation geometry. While our findings are quite general, our specific focus is on modeling outdoor millimeter wave lamppost-to-lamppost links in an urban environment (e.g., for multiGigabit mesh networks using 60 GHz unlicensed spectrum). We show that it is possible to design quasi-deterministic diversity strategies such that geometric configurations which result in destructive interference are unlikely. The rules of thumb regarding antenna spacing and bandwidth differ significantly from those for standard rich scattering models.

Commercial exploitation of such multiGigabit mesh network at 60 GHz band requires that we take advantage of the low-cost digital signal processing (DSP) made available by Moore’s law. A key bottleneck, however, is the cost and power consumption of high-precision analog-to-digital converters (ADCs) at the multiGigabit rates of interest in this band. This makes it difficult, for example, to apply traditional DSP-based approaches to channel dispersion compensation such as time domain equalization or Orthogonal Frequency Division Multiplexing (OFDM), since these are predicated on the availability of full-rate, high-precision samples. We investigate the use of analog multitone for sidestepping the ADC bottleneck: transmissions are split into a number of subbands, each of which can be separately sampled at the receiver using a lower rate ADC. We investigate linear equalization strategies corresponding to different combinations of: (a) combining samples from both arrays/choosing the stronger array and (b) equalizing the subbands independently/jointly. We find that exploiting spatial diversity completely by combining samples from both arrays is critical for combating fading and inter carrier interference.

About Hong Zhang:

photo of hong zhang Hong Zhang received her B.S. degree in Electrical Information Engineering from Wuhan University, Wuhan, China in 2003. She received her M.S. degree in Electrical Engineering from Beijing Institute of Technology, Beijing, China in 2006. She received her M.S. degree in Electrical and Computer Engineering from University of California Santa Barbra in 2008. Hong is currently pursuing a Ph.D. degree in Electrical and Computer Engineering under the guidance of Prof. Upamanyu Madhow. Her current research interests lie in wireless communications focusing on the 60 GHz band. She interned at Mentor Graphics, Denali Software and Broadcom Inc., during the summer of 2008, 2009 and 2012, respectively.

Hosted by: Professor Upamanyu Madhow