Arizona State University Network Science Seminar Series
|Speaker||Gireeja Ranade (Microsoft Research, Redmond)|
|Date||1:30 p.m., Feb 27, 2017|
|Gireeja Ranade is a postdoctoral researcher at Microsoft Research, Redmond. Before this she was a lecturer in EECS at UC Berkeley working on designing and teaching the pilot version of novel lower-division EECS classes (16AB). She received an MS and PhD in EECS from UC Berkeley and an SB in EECS from MIT. She has worked on topics in brain-machine interfaces, information theory, control theory, wireless communications and crowdsourcing.|
|Developing high-performance cyber-physical systems requires a deep understanding of how uncertainty and unpredictability impair performance. In this talk, I discuss some theoretical perspectives to understand uncertainty in systems as well as practical protocols to mitigate it. I will first introduce a notion of "control capacity," which parallels the notion of Shannon communication capacity, and provides a fundamental limit on the ability to stabilize a system with random time-varying parameters (modeled as multiplicative noise). Further, it can be used to quantify the value of side-information in control. We contrast systems with noisy actuation (e.g., when motors on a drone cannot precisely execute control actions) to noisy sensing (e.g., miscalibrated cameras). In the first case, we show that linear control strategies are optimal, while in the second, we show that non-linear strategies can outperform them. Further, we use techniques from information-theory and probability-theory to bound the improvement that non-linear strategies can bring. Finally, I will shift from quantifying the effect of uncertainty to methods for reducing uncertainty. With the aim of enabling industrial automation, I will discuss the development of highly-reliable low-latency wireless communication protocols for machine-to-machine communication. The talk will include joint work with Jian Ding, Yuval Peres, Govind Ramnarayan, Anant Sahai, Sahaana Suri, Vasuki Narasimha Swamy, and Alex Zhai.|
Upcoming Seminar: Orthogonal precoding for sidelobe suppression in DFT-based systems using block reflectors
|Speaker||Vaughan Clarkson (University of Queensland)|
|Date||1:30 p.m., Mar 3, 2017|
|Location||To be updated|
Bachelor of Science (Mathematics), UQ, 1989
Bachelor of Engineering (Computer Systems; Hons I), UQ, 1990
Doctor of Philosophy, ANU, 1997
Sidelobe suppression has always been an important part of crafting communications signals to keep interference with users of adjacent spectrum to a minimum. Systems based on the discrete Fourier transform, such as orthogonal frequency-division multiplexing (OFDM) and single-carrier frequency-division multiple access (SC-FDMA) are especially prone to out-of-band power leakage. Although many techniques have been proposed to suppress sidelobes in DFT-based systems, a satisfactory balance between computational complexity and out-of-band power leakage has remained elusive.
Orthogonal precoding is a promising, linear technique in which the nullspace of a precoding matrix with orthonormal columns is designed to suppress the sidelobes. Orthogonal precoders have been proposed that yield excellent out-of-band suppression. However, they suffer from high arithmetic complexity—quadratic in the number of active subcarriers—which has limited their application.
In this talk, we find that the arithmetic complexity can be made linear instead of quadratic if a block reflector is used to perform the precoding instead of an otherwise unstructured unitary transformation. There is no penalty to be paid in achieved bit-error rate. We show by numerical simulation that the penalty in peak-to-average power ratio is also very small for OFDM.