Archive for the 'Miscellaneous' Category

EE Wins the Nobel Prize for Physics

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Charles K. Kao, who got his PhD in Electrical Engineering from Imperial College London, and founded the Electrical Engineering Department at Chinese University of Hong Kong, was just awarded the Nobel Prize in Physics for his pioneering work on fiber optic communications.

This is really amazing to me, a trained engineer winning this award. Yes, John Bardeen won two of these, but he was really trained as a physicist. I’m willing to bet money that physicists don’t like this decision.

Sanity Checks for Complex Proofs

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I ran into this article today: Ten Signs a Claimed Mathematical Breakthrough is Wrong. While the author is writing from the perspective of quantum mechanics, I think we can extend many of the sanity checks to problems in communication theory and signal processing as well.

I really like the first point: “the authors don’t use TeX”. I don’t know why but there seems to be such a correlation but I have seen this time and again.

Inventor of frequency hopping

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A very interesting play, perhaps most amusing for wireless engineers, centered around the story of frequency hopping.
http://www.sciam.com/article.cfm?id=hedy-lamarr-not-just-a-pr

I like how they use the music analogy. Perhaps the first hopping algorithm was something like “Scott Joplin’s Entertainer” since Bach would be easily recognized by the Germans.

High SNR distribution of eigen-values of a Wishart Matrix

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Today I came across a nice result on the distribution of eigen values of matrix $HH^{\dag}$, where the entries of $H \in {\mathcal C}^{m\times n}$ are i.i.d. Gaussian distributed. The result says that the $k^{th}$ eigen value $\lambda_k$ (in the decreasing order) of $HH^{\dag}$ has the following distribution, $P(\lambda_k\le x) = x^{(m-k+1)(n-k+1)},$ for small $x$.
Its quite useful for analysing many MIMO techniques, such as MRC, MRT.
The reference is a recent IT Paper: http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=4544985&isnumber=4544949

Finding a Good Research Topic

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A student from China recently asked me about how I got interested in relay selection and started obtaining (publishable) results. Since I have some free time on my hands now, I figured I’d share some thoughts on this topic.

I actually don’t think that the way I got interested in relay selection was the ideal strategy in terms of “finding a good research topic.” Instead, I’ll discuss what I think is a better way of “finding a good research topic.” Note that the following is especially relevant for graduate students researching wireless communications (for the obvious reasons).

It’s fairly common for a new graduate student to be overwhelmed by the plethora of potential research topics. When I was starting work on my masters degree, I wanted to do research involving some aspect of wireless networks, since I felt (wrongly, as it turned out) that all of the good point-to-point problems had already been solved. During the summer of 2004, I worked on beamforming for MIMO ad hoc networks, but that ended up being a major dead end. On a related note, I recently perused my research notebook and found that during January 2006, I was interested in cooperative diversity for OFDM networks (my, how things have changed).

This brings up the key question: how should a new graduate student sort through the morass of potential research topics and come up with a good one? I’ll discuss two potential answers.

One approach is to have your advisor answer this question for you, assuming that you have an advisor. In general, you can assume that your advisor has a strong grasp of the current state of research in wireless communications. This knowledge can help him/her determine a topic for you that is 1) interesting, so you won’t be bored stiff for approximately 5 years and 2) worthy of a Ph.D. dissertation, so you will have made a fundamental contribution of some sort by the time you graduate.

The second approach, which I highly recommend, is to take the initiative. To start off, you should do a significant amount of reading. Survey articles in journals such as the IEEE Communications Magazine and the IEEE Signal Processing Magazine can be valuable starting points for the interested yet relatively inexperienced grad student.

A particularly well-written survey article can provide the reader with a good grasp of “what’s been done” on a topic such as “OFDMA power allocation for relay-based networks” and suggest various open problems that are both interesting and important. When reading through these survey articles, one should also scan the list of references to learn about the key papers (and researchers, so you can bookmark their home pages) in a particular area.

It’s then important to read through these key papers to grasp the nuances of the topic that you’re learning about and ask yourself tough questions along the way. For example, do you understand the (technical) paper that you’re reading? Can you justify all of the authors’ assumptions? Can you re-derive every expression (especially the proofs of key theorems) in the paper? I should note that sometimes papers contain typos/gross errors, so you shouldn’t automatically trust everything you read.

If you want to answer these questions in the affirmative, this is a great opportunity for building your technical background. For example, let’s say that the authors are studying a MIMO wireless system and assume that a two-ring scattering model is being employed. If you don’t know what a two-ring scattering model is, you should obtain a copy of a MIMO textbook such as this one by Paulraj et al. and learn more about channel modeling.

Also, let’s say that you’re reading through this famous paper by Gupta and Kumar, and you’re having trouble deriving some (or all, as this paper is actually quite tricky to understand) of the key results. In this case, you might want to strengthen your graph theory background by taking an appropriate class, such as this one at UT-Austin. You might also want to improve your knowledge of random geometry, and you can check your university library for a helpful book such as this one by Bollobas for more coverage of this advanced topic.

As you read through the key technical papers in the area that you’re learning about, you should think of additional open problems and ask yourself more tough questions. For example, you can ponder something like, “the authors’ assumption of a zero-error feedback channel seems a bit restrictive. From my other reading it’s clear that introducing a channel estimation error at the transmitter would better model a practical system. Maybe I can’t obtain an exact expression for the sum capacity given channel estimation errors, since that seems quite complicated, but can I obtain relatively tight bounds?”

Regardless of the approach that you take in terms of finding a good research topic, it’s crucial that you interact with your advisor during this process. Your advisor, who has worked in either the general area that you’re considering or a related area, can help you determine if the open problem you’re considering is either trivial, worthy of multiple dissertations, or actually reasonable for a dissertation. Note that by adopting the second approach I discussed above, your ability to have meaningful dialogue with your advisor during this process is enhanced. In particular, you can evaluate your advisor’s suggestions and converge on a reasonable topic more quickly; this is especially important if your advisor has not worked in the general area that you’re considering.

That’s all I had to say on this subject, at least for now. I welcome comments, especially from my group-mates on this issue of “finding a good research topic.”

LTE abbreviations - Take Your Pick!!

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Light up Turn on Engage
Laptop and Terminal Euphoria
Linking The Earth
Linking Telephony Everywhere
Luscious Telephony Experience
Limitless Technology for Everyone
Limited Time Enigma
Laugh Track Escapade
Lightning-fast Transfer of Everything
Let’s Turnaround East
Late Troublesome Expensive
Look, Talk, and Enjoy
Live Telecommunication Environment
Leading Telecommunication Excellence
Loads of Traffic for Everyone
Live connection To Everyone
Live communication To Everyone
Lifeline To Everyone
Let’s Take it Easy
Life Time Eternal
Love Thy Enemy
Link Technology Enhancement
Legacy Terminal Equipment

- from LTE / LTE-A TSG RAN mailing list

Some people also say “Long Term Employment” or “Life Time Employment.” :)
But my pick is “Love Thy Enemy.” How about you?

Spring 2008 Roundup

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Although there is still a week of finals, the semester is basically finished. This has been my most eventful semester, personally, but how did the WSIL fare? Let’s take a look.

First and foremost, our dear Kaibin Huang just successfully defended his dissertation and is on his way to a post-doc at Hong Kong University of Science and Technology. Not only that, but he was awarded the WNCG Student Leadership award. A WSIL member has won this award two of the past three years.

Along the same lines, Takao Inoue is now a Ph.D. Candidate. He joins Chan-Byoung Chae and Caleb Lo as the next in line to graduate.

We also welcomed the well-known Dr. Marios Kountouris as a post-doctoral researcher.

In addition, we had eight journal papers published:

  • R. C. Daniels R. W. Heath, Jr., “60 GHz Wireless Communications: Emerging Requirements and Design Recommendations,'’ IEEE Vehicular Technology Magazine, vol. 2, no. 3, pp. 41-50, Sept. 2007. [IEEE Xplore]
  • J. G. Andrews, W. Choi, and R. W. Heath, Jr., “Overcoming interference in spatial multiplexing MIMO cellular networks,'’ IEEE Wireless Communications, vol. 14, no. 6, pp. 95-104, Dec. 2007. [IEEE Xplore]
  • W. Choi, A. Forenza, J. G. Andrews, and R. W. Heath, Jr., “Opportunistic space division multiple access with beam selection,'’ IEEE Trans. on Communications, vol. 55, no. 12, pp. 2371-2380, Dec. 2007. [IEEE Xplore]
  • K. Huang, R. W. Heath, Jr., and J. G. Andrews, “Uplink SDMA with Limited Feedback: Throughput Scaling,'’ EURASIP Journal on Advances in Signal Processing, special issue on MIMO Transmission with Limited Feedback, vol. 2008, Article ID 479357, 17 pages, doi:10.1155/2008/479357, 2008. [EURASIP Website]
  • B. Mondal and R. W. Heath, Jr., “A Diversity Guarantee and SNR Performance for Quantized Precoded MIMO Systems,'’ EURASIP Journal on Advances in Signal Processing, special issue on MIMO Transmission with Limited Feedback, vol. 2008, Article ID 594928, 15 pages, doi:10.1155/2008/594928, 2008. [EURASIP Website]
  • Kyung Seung Ahn, R. W. Heath, Jr., and H. K. Baik, “Shannon Capacity and Symbol Error Rate of Space-Time Block Codes in MIMO Rayleigh Channels with Channel Estimation Error,'’ IEEE Trans. on Wireless Communications, vol. 7, no. 1, pp. 324-333, Jan. 2008. [IEEE Xplore]
  • C. B. Chae, T. Tang, R. W. Heath, Jr., and S. Cho, “MIMO Relaying with Linear Processing for Multiuser Transmission in Fixed Relay Networks,'’ IEEE Trans. on Signal Processing, vol. 56, no. 2, pp. 727-738, Feb. 2008. [IEEE Xplore]
  • D. Piazza, N. J. Kirsch, A. Forenza, R. W. Heath, Jr., and K. R. Dandekar, “Design and Evaluation of a Reconfigurable Antenna Array for MIMO Systems,'’ IEEE Trans. on Antennas and Propagation, vol. 56, no. 3, pp. 869-881, Mar. 2008. [IEEE Xplore]

In addition, our fearless leader Prof. Heath, along with Prof. Andrews, won the WNCG Spring 2008 Bocce Ball tournament.

And finally, a long semester of ups and downs concludes with a nice week in the U.S. Virgin Islands for the IEEE Communication Theory Workshop, with Prof. Heath as General Chair.

Please add more here if I forgot something.

One “disadvantage” of getting a PhD in the U.S.

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For U.S. PhD-degree holders, don’t use the title “Dr.” in your business cards when you visit Germany. If not, you may face a year behind bars.

News from Washington Post

Note: this news was not posted on April 1st.

AMD Design Contest

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Many of you might know that over the weekend there was a AMD design contest. I was under the impression that such contests are coding heavy and it goes without saying that a potential turnoff for me. Thanks to my roommate, however, my impression changed significantly and I found out that majority of the problems were basically algorithmic puzzles. More importantly it turned out that once you found out the trick involved, the coding required was minimal.
I will give an example shortly. There are offcourse some problems on compiler design and related areas on which we have minimal knowledge. So to form an ideal team for these contests a partner majoring in CE/CS is a must.
Over the weekend me and my roommate (major CE) were able to solve 4 and half problems out of 5. Unfortunately, we were not able to submit our solution to the contest, since my roommate had to fly out of town and due to my “extraordinary” coding skills.
I am writing this post in hope that next year we would see someone from WNCG and especially from WSIL appearing on the LCD TV on the first floor as the winner of such a contest.

Example problem: Let z, l and m be a natural numbers, l less than m. Let p be a prime which appers in the prime factorization of z, e.g. 2 and 3 appear in the prime factorization of 24. The problem is to find out the number of natural numbers between l and m (including l and m) that have p ones in their binary representation.

IEEE 802.16j Draft 3 in balloting

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Draft 3 of IEEE 802.16j has been finished and letter ballot voting has begun. Voting closes March 15th. While Draft 2 officially passed letter ballot, resolutions to comments made with “Disapprove” votes need to be made before moving on in the process. The official announcement is available online, and you can monitor voting progress as well. The document is not available for free to the public, but in due time it will be available for purchase.