Netgroup’s Lunch Talks


Special events

October 4th 2012

Department of Electronic Engineering

“Tor Vergata” University

Mihaela van der Schaar (University of California)


Meeting room R2 – 10:00 – 11:00 a.m. :

Talk 1: Structural solutions and online learning for delay-critical communication over dynamic, unknown wireless networks


Delay-sensitive communications (e.g. multimedia transmission) are booming over a variety of wireless and wired networks. However, the concepts and methods that have dominated multi-user communication and networking research in recent years are not well suited for efficiently designing and implementing systems aimed at supporting delay-sensitive applications. The problem is that this application class demands new theories, methods and metrics as compared to classical information theory (which ignores delay requirements and complexity limitations), queuing theory (which only considers stationary traffic and service processes and does not optimally control the queues), stochastic control theory (which does not exploit the structure of specific interaction scenarios to improve the devices’ ability to adapt online as well as to reduce their complexity) and online learning theory (which often suffers from slow convergence rates). In this talk, we will present a new foundation for systematically designing and optimizing multi-user wireless networks and distributed systems aimed at supporting delay-critical applications. This foundation rests on several structural results and three associated separation principles, which enable devices to autonomously (i) minimize the delay experienced by the various delay-critical applications sharing the network infrastructure; (ii) learn to operate optimally in time-varying and a priori unknown environments by deploying low-complexity online learning algorithms; and (iii) coordinate with each other in an informationally-decentralized manner in order to optimally utilize the available network resources and maximize the overall network performance. Preliminary results demonstrate that use of this foundation leads to (a) savings of up to 70% in transmission energy under the same delay constraints as state-of-the-art stability constrained solutions; (b) improvements of video quality for real-time wireless streaming scenarios by up to 5 dB peak signal-to-noise ratio (PSNR) compared to state-of-the-art rate-distortion optimized solutions for streaming of multi-modal traffic; and (c) improvements of video quality for multi-user wireless video transmission scenarios by 3-4 dB PSNR or more compared to. state-of-the-art static Network Utility Maximization (NUM)-like solutions.


Meeting room R3 – 15:00 – 16:00:

Talk 2: Medium Access Control Protocols with Memory


Many existing medium access control (MAC) protocols utilize past information (e.g., the results of transmission attempts) to adjust the transmission parameters of users. This paper provides a new, general, mathematical framework to express and evaluate distributed MAC protocols utilizing a finite length of memory for a given form of feedback information. We define protocols with memory in the context of a slotted random access network with saturated arrivals. We introduce two performance metrics, throughput and average delay, and formulate the problem of finding an optimal protocol. We first show that a time-division multiple access (TDMA) outcome, which is the best outcome in the considered scenario, can be obtained after a transient period by using a protocol with -slot memory, where is the total number of users. Next, we analyze the performance of protocols with one-slot memory using a Markov chain and numerical methods. Protocols with one-slot memory can achieve throughput arbitrarily close to 1 (i.e., 100% channel utilization) at the expense of large average delay by correlating successful users in two consecutive slots. Finally, we apply our framework to wireless local area networks (WLANs).


Mihaela van der Schaar bio:


She is Chancellor’s Professor of Electrical Engineering at University of California, Los Angeles. Her research interests include engineering economics and game theory, strategic design, expert and social networks, online reputation and social media, dynamic multi-user networks and system designs, wireless networks, online learning, real-time stream mining, meta-learning and multimedia networking and systems. She is an IEEE Fellow, a Distinguished Lecturer of the Communications Society for 2011-2012, the Editor in Chief of IEEE Transactions on Multimedia and a member of the Editorial Board of the IEEE Journal on Selected Topics in Signal Processing. She received an NSF CAREER Award (2004), the Best Paper Award from IEEE Transactions on Circuits and Systems for Video Technology (2005), the Okawa Foundation Award (2006), the IBM Faculty Award (2005, 2007, 2008), the Most Cited Paper Award from EURASIP: Image Communications Journal (2006), the Gamenets Conference Best Paper Award (2011) and the 2011 IEEE Circuits and Systems Society Darlington Award Best Paper Award. She received three ISO awards for her contributions to the MPEG video compression and streaming international standardization activities, and holds 33 granted US patents. She is also the founding director of the UCLA Center for Engineering Economics, Learning, and Networks (see For more information about her research visit: