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Research and Publications: A Personal Perspective. Bo Li Hong Kong University of Science and Technology Microsoft Research Asia. Outline. What about research? How much does one have to learn? PhD research What is procedure of publications? How to write technical papers?.
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Research and Publications:A Personal Perspective Bo Li Hong Kong University of Science and Technology Microsoft Research Asia
Outline • What about research? • How much does one have to learn? • PhD research • What is procedure of publications? • How to write technical papers?
Research is easy! • You have done this many times in course projects • Take a known problem, and apply a known technique • Obtain results, and write a report
Research is difficult! • Is it technically correct? • Does it make intuitively sense? • Is it publishable, where and why? • Does it offer some insights beyond what we have known? • Does it have any impact? • …
Research • There are basically four types of research works: • New problem and new solution • New problem and old solution • Old problem and new solution • Old problem and old solution
Research • Case I comes rarely, perhaps something you could only wish, once a life-time experience • Shannon theory • Cases II and III are the ones that you should target for • Packet scheduling: weighted fair queuing • Geographical routing in ad hoc networks • Case IV is where you can start • Plenty of out there under the category of “Yet another paper on … “
Where do ideas come from? Drink a beer, relax, ideas will come to you The ideas fall from the sky! Understanding the existing works, build upon that incrementally
Where do ideas come from? • Ideas in most cases come from the deep understanding of a subject, and possess of broad knowledge • This is not a technical training, i.e., this is not about solving a bipartite graph, or differential equations • This is about relating them to real world problems • This is about providing new insight beyond known • This is about your creativity!
Research: What is it? • Research = Re (repeat) + search • Much of the research has been built upon existing works, therefore a thorough understanding of those is the basis • Too many smart people in each area, so if an idea seems to be too good to be true, it likely is -> rethink that again • Each idea needs iterations: what is it? why has it not been done? what is the logical connection with the existing approaches?
Research: Engineering Problem • Each solution to an engineering problem is only a trade-off; it is not a cure for all, it definitely has side-effect. • Networking coding • Potential capacity gain under loaded system • Is it really? Is there any alternative? What is the penalty for doing so? Can we handle that in system design? • P2P • Facilitate the voluntary file sharing • Can this be extended beyond that?
Case I: Adaptive Video Multicast • The need for multicast - efficiency • Multiple-unicast Multicast • Fundamental problem: users’ heterogeneity and network dynamics
Case I: Adaptive Video Multicast • Layered video encoding and transmission • Cumulative layered coding (Scalable coding) • Base layer: most important feature, low rate, low quality • Enhancement layers: progressively refine quality
Case I: Adaptive Video Multicast • Existing solutions • Multiple multicast tree, each for a layer • Receiver adaptation: user’s joining and leaving groups (receiver) • Adaptation is performed at receivers only: fixed layer rates and limited num of layers • Fundamental Problem • The mismatchbetween the fixed sending rate and the dynamic and heterogeneous rate requirement from receivers
Case I: Adaptive Video Multicast • End-to-end adaptive video multicast • Optimal rate allocation for each layer: formulation and solution • End-to-end transmission protocol and whether TCP friendly • Complexity analysis • Practical issues: feedback explosion (sampling), RTT estimation (open and closed loop)
Sample References • B. Li and J. Liu, “Multi-Rate Video Multicast over the Internet: An Overview,” IEEE Network,(17)1: 24-29, January-February 2003. • J.-C. Liu, B. Li and Y.-Q. Zhang, “Adaptive Video Multicast Over the Internet,” IEEE Multimedia, (10)1: 22-33, January-March 2003. • J. Liu, B. Li, and Y.-Q. Zhang, “An End-to-End Adaptation Protocol for Layered Video Multicast Using Optimal Rate Allocation, IEEE Transactions on Multimedia, (6)7: 87-102, February 2004.
Summary • Identify a general category of problems • The idea should be intuitively simple • Publications can be “easier”
Outline • What about research? • How much does one have to learn? • PhD research • What is procedure of publications? • How to write technical papers?
How much does one have to learn? • I have learnt all the mathematics, and I am loaded • Discrete algorithms, partial differential equations, dynamic control, probabilistic modeling, information theory and etc. • I still don’t have a clue what to do in research. • Where in the world is research topic?
How much does one have to learn? • I have read all papers out there from journals and conferences • Can I do research now? • There is no way you can cope with all of them • Majority of the published works are junks, and can cause brain damage and can be misleading
The minimum needed for research • Logical thinking, after all we are in engineering world • Basic skills • You have to know the Dijstra algorithm in order to understand the OSFP (?) • the ability to learn • Life long learning process, esp. in CS
The minimum needed for research • Abstraction. Take a problem, you have to know • What is/are the fundamental problem(s) • You have to see both “forest and trees” • What have been done, why? • What are seemingly undoable? • Understand your strength and weakness
The minimum needed for research • Open mind • We are not dealing with math problem in that there exists perfect solutions • Engineering solutions are subject to argument and debate, i.e., each solution is a trade-off, and it only works in a constrained environment • Critical mind • When you read others, it is equally important to understand what circumstance that it does not work as in which it works • If you can not identify such scenario, you are not understanding the problem
Case II: Proxy Placement • How to place the proxy (mirror sites) in the internet • B. Li et al., “On the Optimal Placement of Web Proxies in the Internet,” Proc. IEEE Infocom'99 • ACM Communications Review (2001) cited as the 1st ever work on this topic
Case II: Proxy Placement • Formulation: graph theory problem, k-median problem: given N nodes, how to select K nodes to place the content so certain optimal criterion can be met • For general graph, this is NP-hard • For tree, we solved this using a known dynamic programming technique • This turns out to be the fundamental problem for object replication in DB, which has been cited over 300 times since then
Sample References • J.-L. Xu, B. Li and D. Lee, “Placement Problems for Transparent Data Replication Proxy Services,” IEEE Journal Selected Areas in Communications, 20(7): 1383-1398, 2002 • A. Vigneron, L. Gao, M. Golin, G. Italiano and B. Li, “An Algorithm for Finding a k-Median in a Directed Tree,” Information Processing Letter, 74(1-2): 81-88, 2000 • B. Li, “Content Replication in a Distributed and Controlled Environment,” Journal of Parallel and Distributed Computing, 59(2), pp. 1-21, Nov. 1999
Summary • Finding a problem is more important, and difficult than solving a problem • You need out-of-box thinking
Outline • What about research? • How much does one have to learn? • PhD research • What is procedure of publications? • How to write technical papers?
PhD Research • Make a plan earlier, for 3-4 years • The research topics must be of current interest, and state-of-the-art • Don’t work on packet scheduling, and IEEE 802.11 MAC protocol • Beating the performance of Ethernet is like kicking a dead horse! • It has to be something that within your capability • You need to understand your strength and weakness, and be realistic (don’t shoot stars) • You should know your interest, self-motivation is one of the single most important factors
PhD Research • Read top 10 or 20 papers in the area • Understand the basics, fundamental problems, and open issues • Think and read • Put all papers into perspective • Start from a small yet concrete problem • Build you skill and confidence • Discussions generates ideas
Reading • Top conference or workshop first • ACM Sigcomm, ACM Mobicom, IEEE Infocom • IEEE ICNP, IWQoS, MobiHoc • Second tier conference only for reference • IEEE Globecom, ICC • Avoid bad conferences • Regional, and less reputable ones • Read journal papers only it has not been published else where, or when it contains more detailed and complete treatment
PhD Research • Focus! • Don’t over-estimate your ability • Don’t diversify too much • Start with small idea(s), publish in an easy conference in the 2nd year • Working plan: target at 2 conferences (20 or less acceptance rate) and one journal paper per year (in 2-3 years) • The thesis is a collection of the papers • So you need to have a focus!
Research Topics • Theoretical vs. practical • Can this be related to a real world problem • Engineering approach • It should have a clear boundary • Focus on what can or/and can not be done • Don’t lose the bigger picture • Tree and the forest • How does it help to solve one or more pieces in the bigger problem
PhD Research • System works • System work usually involves team efforts • Building from scratch is a dangerous thing • The prototype has to demonstrate significance in that either this is a proof of a concept, or demonstrate the feasibility • Less than 5% chance being useful, yet worth the investment for technical break through • Theoretical works • Theoretical work usually provides an elegant solution to a generalized problem • The significance can be greatly enhanced if practical insight can be drawn
Advisor/Mentor • Choosing an advisor could be the single most important factor for your research • Understanding the general problem, the ability to identify the significance and yet another • Personal and professional relationship • Junior vs. senior, hands-on or hands-off • Regular guidance vs. direction • Independent and close collaboration • Group or individual effort • Time, efforts and experience
You really need an Advisor/Mentor • Can a rabbit eat a dog, fox and wolf?
You really need an Advisor/Mentor • Punch line It really does not matter what the topic is, and what you are doing, all it matters is who your advisor is
Example I: My PhD research • What you need is a jump start for confidence building • A. Ganz and B. Li “Performance of Packet Networks in Satellite Clusters,” IEEE Journal on Selected Areas in Communications, (10)6: 1012-1019, August 1992 • Be objective, don’t lose the bigger picture • The research topics are both important and not so important • The research works in PhD study is simply a training process, be realistic. • Usually the most productive period for one’s career is within the 5 years’ after one’s PhD
Example II: My student • Jiangchuan Liu • Who has written close to 20 top journal papers since 1999, largely on video multicast • Assistant Professor at Simon Fraser Univ., former with Chinese Univ. of Hong Kong. • Won the prestigious Hong Kong Young Scientist award in 2003, given to one individual annually by Hong Kong Institute of Science (HKIS) • Sometime direction is all a student needs
Collaborations leads to Productivity • Working with the right people • Skill complementary • Same interests • Working with smart people
Case III: Cellular Networks 7 3 1 6 4 1 4 5 5 2 7 7 3 1 3 1 6 6 4 1 4 5 2 2 7 1 3 1 6 4 Frequency Reuse Pattern for N=7 Number of cells per cluster: Frequency Reuse Factor, If total of S channels available, Each cell can be assigned k channel If M clusters within the system, the total system capacity:
Case III: Cellular Network • There were several fundamental problems in cellular network when moving to multi-service environment • Bandwidth within a cell have to be shared • Erlang assumption (Poisson arrival and exponential sojourn time and exponential call duration time) fails due to data traffic • Gaussian approximation for a cell capacity fails given the cell is small …
Case III: Cellular Network • Relaxing Erlang, by considering heavy tail long range dependency LRD) distribution, i.e., Pareto distribution • Failed since 1997
Case III: Cellular Network • Gaussian approximation • Particle movement and diffusion equation • S. Wu, K. Y. M. Wong and B. Li, “A Dynamic Call Admission Policy with Precision QoS Guarantee Using Stochastic Control for Mobile Wireless Networks,” IEEE/ACM Transactions on Networking, (10)2: 257-271, April 2002.
Summary • Working on hard and open problems • Persistence pays off
Summary • The idea has to be simple, this is a hard lessen we have learn • 10 years of research on ATM are pretty much a waste • Internet • POTS or PSTN
Outline • What about research? • How much does one have to learn? • PhD research • What is procedure of publications? • How to write technical papers?
Conference Paper • Start earlier for a conference submission • Deadline is the best drive for making progress • What make a good paper: content and writing! • Clear, convincing, simple and good English • This is a never-ending optimization process, do this within the time and page limits • Review process 5/30 rule • 5 minutes - Abstract, introduction, figure and conclusion • 30 minutes – understand 90% of the paper
Journal Paper • A good conference paper (10%-25% acceptance rate) can be submitted to a journal, with 30% new results • Report more complete and focused results • Give yourself a deadline • Be patient with the long review and re-review • At the earlier stage of one’s career, don’t quit if asked for major revision • But don’t do seemingly impossible
What does a reviewer look for • New problem or new solution? • Are the main results significant? • Is the paper technically correct? • Does the paper provide a fair assessment of its strength and limitation? • Is the paper clearly written, thus accessible to general readers? • Are the references adequate? • Is the paper appropriate for conference/journal? • …