While I don’t have a video for you to watch the entire presentation, I do have some pictures, and I’ll post the paper and slides I presented in case any one is interested. If you have any questions feel free to post on here or email me directly and I’ll be happy to answer any of them.

J.B. Ernst and M.K. Denko, “Cross-Layer Mixed Bias Scheduling for Wireless Mesh Networks,” in Proc. IEEE International Conference on Communications (ICC), Cape Town, South Africa, 2010.

Abstract—In this paper we propose a mixed bias approach which makes use of cross layer optimization. The cross-layer parameters are based on conditions in the network from multiple layers and are used to determine resource and time allocation for nodes in the network. Unlike existing proposals, we propose to bias against several parameters such as link quality and queue size in addition to node distance. We also propose a combined mixed bias approach which takes into account multiple parameters together. The scheme is evaluated using simulation experiments. The performance results are reported in this paper.

Download the paper (pdf)
Download the presentation slides (pdf)

The following instructions explain how to install the latest stable version of ns3 (as of April 14th, 2010) on windows 7 with cygwin. I will try to include any common problems I have encountered, or those of users who comment on the post experience in order to make your install easier.

Step 1:
Download & install cygwin. (note: I install it in the recommended directory “{System Root}/cygwin/”). Make sure you select “install” for python and devel. This will ensure you have python and gcc/g++ as well as all of the dependencies. You can do this by clicking on the word default in the list of packages. I left all of the other package options on default for the install.

Step 2:
Download ns3.7.1. Save the file to “{System Root}/cygwin/home/{your-username}”

Step 3:
Start cygwin. At the cygwin prompt type: “tar xvf ns-allinone-3.7.1.tar.bz2″. This will unpack the ns3 archive so you can use it.

Step 4:
After it has unpacked, change directory to the new ns3 directory with the following: “cd ns-allinone-3.7.1″. Then build ns3 by typing the following: “./build.py”. You can probably grab a coffee or tea while it compiles.

ns3 on windows 7 with cygwin

Step 5:
You should be good to go. You can validate the install by changing directory again to the ns-3.7.1 directory (“cd ns-3.7.1″) and running “./test.py”. It will let you know with a PASS / FAIL for each test case. You can now edit the files yourself. The scenario files are located in “” and the source files are located in “”. Good luck!

The lab where I TA the C programming class

I’ve definitely learned a lot from my last attempt at TA-ing the previous semester. That time around I helped with an m68k assembly language class. It was quite difficult, especially since it was a class that many students found challenging. It ended up being a good experience though because it helped teach me the importance of being prepared for the weeks labs. The biggest challenge was trying to anticipate what types of questions would be asked and how to prepare myself. By the end of the first couple of labs, I started to get the hang of it and made myself a routine. Since it had been sometime since I last worked with m68k assembly, I decided the best way to prepare was to fully complete the labs myself before the students. While it made for quite a bit of work, I got to learn quite a bit, and I could answer the questions with confidence. In the C class, since I work with it quite a lot more often than assembly, I didn’t need to review the labs nearly as much. I found just bringing a textbook that I could quickly reference was always useful.

It’s amazing how ta-ing helps you to remember and cement concepts in your mind. Certain things that might have been a bit fuzzy or hard to remember have been recalled and re-clarified since I am forced to know the material in-depth in order to prepare for the weekly labs and assignments. Also the questions from the students help me to consider things I wouldn’t normally. I would definitely recommend being a TA for any CS grad student (or upper year undergrad) who might be considering it!

The biggest lesson I’ve learned this semester is that the profs in undergrad were always right. Math is very important in CS. While it may not have been apparent at the time, (I always questioned the relevance of much of it since it was all presented very abstractly and disconnected from anything I was doing in undergrad) I now find some of my math skills to be my greatest weakness as a CS researcher. This is why this past semester I have gone out of my “comfort zone” and tried a couple of courses which I would generally shy away from. First is discrete optimization (Classifications of Optimization Problems, VRP, TSP, Bin-Packing, Cutting Stock, Simplex Method, PSO, Tabu Search, Branch & Cut etc). Second is a system performance and evaluation course (Queuing Theory, Markov models, Operational Analysis, etc). In each case, I have been pushed to the limits of what I know (and what I remember from my undergrad days). On the other hand, it has been easy to identify my weakest areas in my knowledge so that I can hopefully improve in them significantly before my quals in a couple of semesters. As an added benefit, perhaps because of the perspective I have gained as a grad student, I have started to realize the larger picture and see how many of the mathematical ideas can be applied to improve the state of the art in a particular problem area.

Lastly, I have been working at formulating my research and solidifying what it is I am working towards with this PhD. The very general description is “heterogeneous wireless networks”. Within this area, I am interested in particular type of heterogeneous wireless network. It is made up of a wireless mesh network as the backbone. Instead of traditional client nodes such as laptops, pdas etc, the clients are actually other types of wireless networks, for example: 802.11 WLAN, RFID, 3g Mobile etc. There are many problems when this type of network is considered. One is the gateway placement problem (where to place gateways between the types of networks, how many etc.). Also in each sub-network, there may be a particular set of parameters which cause the sub-network to perform very well. However when the sub-networks are joined, this set of parameters may not be optimal for the entire network as a whole. The problem then is how to optimize these sets of parameters with respect to the entire network.

Many students I have encountered feel that this low level knowledge is not useful and that the particular assembly language is obsolete. They see the course as too difficult and a waste of time. I feel I can weigh-in on this debate is a slightly new light from many of the parties interested. I was recently a student in a similar course myself so I am not so far removed as some of the professors. On the other hand, I have had the experience of being involved in the instruction process of the course, I have completed an undergraduate degree and spent some time working so I am aware of the larger picture as well. Perhaps the problem of the course being difficult for students speaks to the state of the primary and secondary education system in Ontario / Canada, but that’s a whole different story.

In my opinion, this course is an absolute necessity for a degree in computer science, or even computer engineering. A big part of computer science to me is about being able to determine why and how a particular solution is faster or slower than another one and how we can improve existing solutions. Understanding the core principles taught in this type of course significantly help in understanding operating system concepts, distributed systems, compilers and many other higher-level topics in computer science. It also allows the student to see some of the limitations in current computer architectures and even how the existing / past architectures work. From a software engineering point of view, the difficulty in getting error feedback and troubleshooting is perfect for learning why it is a good idea to carefully plan and conceptualize your programs before writing. The more complicated topics in these type of courses require good conceptual knowledge of addressing, stacks, interrupts etc. Students can learn the benefit of visualizing the concepts with diagrams, memory maps and flow-charts. The same people who fail to understand memory concepts in this type of class likely have problems with malloc/free and recursion in c classes. Without knowing how the underlying concepts work, how can you be convinced that a particular high level implementation is faster than another one. You would be taking for granted what is happening at a lower level and making serious assumptions about how the system is working.

To me learning only high level languages without any assembly would be like skipping Newton’s physics models and going straight to quantum mechanics. You can probably describe many phenomenon much easier and better than with Newtons models, but without learning about Newton first you would not understand how quantum physics really works. You would not be convinced that certain properties are true and you would loose some of the ability to question what is really happening in some ways. It would be more difficult to extend ideas and even challenge existing paradigms. It really removes much of scientific component of program.

The first part of the talk showed a network learning how to recognize written characters. The approach was unique (at least to what I’ve encountered in my soft computing class) in that it didn’t assign and back-propagate the labels from the start. The network learned “features” based on the input patterns and then assigned the labels after the pattern had been learned. The coolest feature was being able to “visualize what the network is thinking” by doing the process sort of in reverse. The second part of the talk applied a similar technique to the motion of person wearing sensors. The network could be trained to recognize the style of motion of the person and then from that, new styles of walking could be “imagined” by the network. For example the network could image the person changing walking styles midwalk through the visualization even though it hadn’t been trained in this way. In all it was very interesting. It would be fun to try to apply some of these techniques to wireless networks. Perhaps the motion modeling could be applied to mobile wireless devices to help with hand-offs?

Anyway, if anyone is interested and you are at one of the Universities which is a part of the groups putting these on, they happen every other week. You can see at schedule at the SHARCNET website, or probably at the group you are a part of at your school. As far as I know, anyone can attend!

In a slightly related note, I am attending two wireless network conferences in Ontario in the upcoming weeks. At the end of September I am volunteering at the adhocnets 2009 conference in Niagara Falls. I am quite excited about one of the keynote speakers (Prof. Ian Akyildiz) who has written some excellent survey papers in the area. The same week I am attending the IEEE TIC STH conference at Ryerson University in Toronto. I am presenting a paper on cross layer scheduling and resource allocation in wireless mesh networks.

Update: The paper from the TIC STH Conference is available via IEEE Xplore here.

Update: Here are some pictures from the conference:

Conference Venue, Ryerson University

Welcome to the conference!

Tea break

One of the talks

There were people from 40 different countries there and I feel like I met someone from almost every one of them at some point. There were over 300 people at AINA this year, which apparently is down from the last couple of years (where they had 4-500) but it was still a great conference for me. I will post my slides from my presentation in this post in case anyone is interested, along with a link to the paper once it is available. I submitted another paper last night for a conference in Toronto and am working on two more papers, so hopefully I’ll be travelling soon. I am trying to aim for ICC in South Africa next year.

Here are a few pictures from the conference.

Abstract:
This paper addresses the problem of scheduling in Wireless Mesh Networks (WMNs). The paper first discusses existing scheduling algorithms and classifies them based on the technique they use and their implementation frameworks.Then detailed discussions of the proposed scheduling method are presented. Simulation experiments are conducted to compare the performance of fair scheduling with the method that does not use fair scheduling. The simulation results confirm that the proposed scheduling method has better performance with respect to the metrics used for performance evaluation.

J.B. Ernst, M.K. Denko, “Fair Scheduling with Multiple Gateways in Wireless Mesh Networks”, in Proc. of the 22nd IEEE Int. Conf. on Advanced Information Networking and Applications (AINA 2009), Bradford UK, 2009.

The paper itself is available through IEEE Xplore

Here are some pictures from the day:

Preparing for the Defense before Everyone Arrives

Some Members of Pervasive Computing and Wireless Network (PerWin) Research Group, University of Guelph

Answering Questions from the Committee at Guelph

After some relaxing, a conference in UK and some business related projects I will finally have some time (hopefully) to update the site with all the projects, articles and source I have been slowly working on the past few months in between working like crazy on my M.Sc. This fall I start my Ph.D. which will likely at least start from the work I just worked on.