Visiting Cyber–Physical Systems Group,
University of California Los Angeles
(November 2014–January 2015)
Amir Aminifar
Department of Computer and Information Science,
Linköping University, Sweden
amir.aminifar@liu.se
I. I NTRODUCTION
I have been working on embedded control systems
since 2010. Along with our research on analysis and
design of embedded control systems, I visited the cyberphysical systems group1 of the university of California Los
Angeles (UCLA) for a period of three months. Professor
P. Tabuada, head of the cyber-physical systems group in
UCLA, is one of the main experts in the area of eventtriggered control [1] and self-triggered [2].
Before this visit, in my Ph.D. studies, all our results
were based on the traditional periodic control scheme. The
advantages of self-triggered control attracted our attention
as a potentially rich area of research. The self-triggered
control is a new paradigm for control engineers which
provides the same performance as the traditional periodic
control, while consumes considerably less resources. The
essence is that the self-triggered controller executes only
when it is needed. Although the paradigm has been proved
to be effective, the real-time scheduling problem of such
controllers is still an open issue. In the embedded systems
group (ESLAB), we are involved in the analysis and
design of embedded real-time systems, while the cyberphysical systems group in UCLA are experts in the area
of self-triggered control. The main goal of this visit was
to exchange ideas and conduct research in the area of selftriggered control, i.e., to facilitate real-time scheduling of
the self-triggered controllers.
II. C YBER –P HYSICAL S YSTEMS G ROUP AND
E LECTRICAL E NGINEERING D EPARTMENT
The cyber–physical systems group of UCLA is led
by professor P. Tabuada. There are two post-doctoral
fellows, six doctoral students, and a few master students.
Besides self-triggered and event-triggered control, other
main research areas are controller synthesis and security
in cyber-physical systems. They have weekly meetings
where everybody talks about what (s)he has been doing
and what is the main problem (s)he is dealing with.
Occasionally, there are visitors who give talks about their
research. I gave two talks while I was there, on our work in
ESLAB on control–scheduling co-design and other realtime topics. It was interesting to get their feedback and
questions.
Something I noticed is that they usually have more
visitors and collaboration in the electrical engineering de1 www.cyphylab.ee.ucla.edu
partment of UCLA than in our department. This might be
due to the fact that the electrical engineering department of
UCLA has ranked one worldwide by Microsoft Academic
Search based on H-index over ten years. 2 Although we
have SAS seminars in the division, but I believe I noticed
more interesting talks and collaboration in UCLA.
Another interesting thing was the fact that they had
many events to prepare their senior students for the future,
i.e., in finding jobs and applying for funding. In addition,
they also had a career week where the companies come
to university to recruit students.
III. R ESEARCH R ESULTS
For the first couple of weeks, I have been reading a
few papers related to self-triggered control and then we
discussed several directions for this visit. By the end of
the first month, the research direction in this visit was
clear. The ultimate goal was to do schedulability analysis
for self-triggered controllers running on a shared platform,
possibly in presence of other hard real-time tasks. The
first task, however, is to identify the self-triggered scheme
which facilitates this goal.
The first result in this visit was motivated by the following observation. The traditional self-triggered controllers
often work in a greedy fashion, i.e., they compute the latest
time that the controller should be executed in order for the
plant to remain stable. However, after this step, due to the
greedy nature of the algorithm, the control task might be
required to execute very frequently to guarantee stability,
such that it defeats the purpose of the self-triggered
control, i.e., less resource usage. This is important from
schedulability point of view because if we consider this
greedy case in our analysis, then the interference from the
self-triggered controller is considerably more than what
happens in reality, since always the worst-case scenario is
considered. And essentially, this leads to a very pessimistic
analysis method.
To remedy this, our proposed design will look into
a finite horizon in the future and avoid such catastrophic cases. Preliminary studies show that our proposed
self-triggered controller outperforms the previous results
roughly by an order of magnitude, in terms of the number
executions of the self-triggered controller.
2 http://www.engineer.ucla.edu/newsroom/featured-news/archive/
2012/electrical-engineering-ranked-no.-1-and-school-ranked-no.
-4-by-microsoft-academic-search
(a) Half Dome
(b) Top
Figure 1.
Yosemite national part
VII. ACKNOWLEDGEMENTS
I would like to acknowledge professor P. Tabuada
at UCLA for hosting my visit and embedded systems
group and CUGS (Swedish National Graduate School in
Computer Science) for funding this visit.
R EFERENCES
Figure 2.
Page museum at the La Brea Tar Pits
In addition, we have set the basis for response-time
analysis of self-triggered controllers, which is considered
to be an open problem. The plan for the future is to work
on this idea.
IV. R ECOMMENDATION
I think it is important to realize that three months visit is
in fact very short and the overhead of paperwork related to
visa/university and finding accommodation and planning
the trip might be considerable. I also recommend to do
such visits earlier in your studies, maybe in the third year
of your studies. Keep in mind that it is great if there is
a student in the host group who is working on the topic
you are interested in.
V. A DVENTURE AND S IGHTSEEING
The adventure part of this visit was going to a winter
hiking trip in Yosemite national part (see Figure 1) with
UCLA outdoor activity group for a weekend in January.
Beside the amazing nature, I got to meet many nice
students. Sleeping in tents, star gazing, and hiking to
waterfalls were some of the highlights of this trip.
I also spent one Saturday in Page museum at the La
Brea Tar Pits, one of the most famous fossil localities in
the world (see Figure 2).
VI. C ONCLUSION
During this visit, not only did I enjoy working on an
interesting topic and broaden my knowledge, but also
I got to establish contacts for future collaboration and
experienced working in another research environment.
[1] P. Tabuada, “Event-triggered real-time scheduling of stabilizing control tasks,” IEEE Transactions on Automatic Control,
vol. 52, no. 9, pp. 1680–1685, 2007.
[2] A. Anta and P. Tabuada, “To sample or not to sample: Selftriggered control for nonlinear systems,” IEEE Transactions
on Automatic Control, vol. 55, no. 9, pp. 2030–2042, Sept
2010.