Second hand wisdom

MIMO at last

2011-10-19T21:03:00.000-07:00

I have posted the final (nearly so) version of my MIMO tutorial.

www.complextoreal.com

It took a while. In the writing of this paper, I relied heavily on a few books and papers. The three books I often found myself thumbing through, in order are: Wireless Communications by Andrea Goldsmith, Fundamentals of Wireless Communications by D. Tse and P. Viswanath and Digital Communications by Proakis, 5th Edition. The examples used in this paper are inspired by the Andrea Goldsmith book, the one I consider the best. She has a lot of examples in her book which truly help with understanding.

The other three books that I also found helpful were: Digital Communications by Barry, Less and Messerschmitt, Introduction to Space-Time Wireless Communications by Paulraj, Nabar and Gore and MIMO-OFDM Wireless Communications with Matlab book by Yong Soo-Cho, and Won Young Yan. I used the Matlab code in this book to create some of the graphs.

With papers, the one I read several times was by Gesbert’s and the one by Foschini. I read many others but these two standout. Agilent also has an excellent tutorial online. And of course the David Tse video lectures are fantastic. (See link below) He is quite funny! IEEE also has an audio lecture that is excellent.

http://cp.literature.agilent.com/litweb/pdf/5989-8973EN.pdf
http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=550

It took me a while to get all my ideas together and I read many papers and checked nearly all the books written on the topic. While writing about these, I often could not figure out who the original source was. This is not good as I do want to credit to whom it is is due. If you the reader feel that I have not properly credited you or someone else in this paper, please do let me know.

In writing, Bernard wrote the first draft and then I added and subtracted from it. We are to do a book for Prentice Hall but the schedule is all gone out the window now. Hopefully it happens to other authors too.

The MIMO paper is now nearly 50 pages long but it is still lacking in many areas. I was not able to cover STC decoding, nor the code performance issues. The section on multi-user is also short. But I hope that what is here will help illuminate the topic and get you started.

Charan Langton

MIMO Tutorial - Part One

2011-08-11T19:33:00.000-07:00

I have posted part one of the MIMO tutorial. The first part is mostly concentrated on the capacity issues. You may think why even worry about capacity; We don't seem to worry about the capacity of the traditional SISO links. We have to worry about the capacity possible with MIMO because that is the only way to know if this new-fangled technique requiring lots of antennas and receivers is even worth doing. And the conclusion is, no surprise, that MIMO is very much worth doing.

For same power that we might use in a regular link, if we just replace the transmitter and the receiver with a MIMO transmitter and a MIMO receiver, we have got ourselves as much as 3 to 4 times higher capacity. This is what we see when we went from 802.11 N to G. The gains came from the application of MIMO. You are already using MIMO in your router with its two antennas.

But what is MIMO, is it Multiple Access, NO. Is it modulation, No. Is it a type of receive signal processing like a rake receiver, No, again. It is just increasing the number of transmitters and receiver from one to many. The signal processing actually gets simpler, believe it or not.

MIMO is the future, but not for all applications. Line of sight links do not benefit from MIMO. So MIMO's application is primarily in wireless phone and home networking.
As a topic to study, it seems complex and it is. Because you have to back track and start at the beginning by first looking at what it can offer. Then it very quickly leap frogs to trellis coding, block coding and these are not even for the purposes of error-correction. I will cover these in the next part.

Please let me know if it is easy to understand. MIMO does have a whole lot of new ideas, or actually old ideas combined in a new way. So it is confusing. Two books that I referred to a lot and like in order of preference are by Andrea Goldsmith (Stanford) and David Tse(Berkeley). David Tse actually has some terrific video movies on MIMO. Find them and watch them.

There are several other books that I used while writing this tutorial and I shall provide a list of these in part two.

BTW, if you have younger siblings or kids, be sure to look at my new Verbal Math books for kids. We have them in Kindle format now.

2010-11-24T01:14:00.000-08:00

MIMO

I have been trying to write a section on MIMO for a while. Wow what a difficult subject this is to tackle. There are so many issues, despite having read nearly every book on the topic, I still can not decide how to organize the chapter. Calculation of capacity is a big issue. But for that we have: ergodic channel, channel with outage, we have fading channels, with slow frequency selective, slow non-frequency selective, fast and selective and fast and non. Then there are channel with some correlation and channels that are random. Then there is space-time coding, and multi user MIMO and it keeps going. Fascinating subject but also messy. Hope I can do it justice.

There are some graphs in the Proakis book in the MIMO chapter that I would like to reproduce, by replotting. But the equations are complicated, with gamma functions and derivatives of gamma functions. One person must have done these long time ago and now every one copies the same pictures. Maybe I will end up doing the same thing. But I hope not. Plan on finishing the MIMO chapter by end of December.

Happy Thanksiving.
My special thanks to all of you who write to me with your appreciation of my website. I don't always answer each email but please know that your comments make my day!

ग़्रदुअतिओन स्पीच अत कल पोली सन लुईस ओबिस्पो

2010-06-04T08:52:00.000-07:00

I am giving a talk tonight at Cal Poly, San Luis Obsipo Aerospace Engineering Graduation Banquet. It is taking place at the same restaurant where I had my graduation so many years ago, Madonna Inn.
Why was I invited to give this talk?
It is because I was the first woman ever to graduate from that department.
Over the years, from being the only women in my classes and at work, I saw more women join the ranks as engineers. But women still continue to avoid engineering as a career.
Surprising, since it is a great desk job, pay extremely well and has a lot of flexibility. It is easier to integrate with a home life and having children than are many other careers.
My company Loral has been exceedingly supportive over the years when I had young children and did not want to work full time.
But yet, women continue to be afraid of it. Why?

My math books for children

2010-05-28T23:36:00.000-07:00

I am announcing the publication of my two new math books. These are for children in middle schools. My daughter still continues to fear percents, so I guess even some adults might find them useful. The books are: VERBAL FRACTIONS and VERBAL PERCENTS.

The idea is for children to learn these procedures verbally, i.e. doing all work done in head, without any writing. The process builds conceptual understanding and speed. The books will be available in bookstores and of course at the big online places such as Barnes and Noble and Amazon.com. Please check them out, or at website www.mathlesson.com.

Complex Confusing Confounding Codes

2010-05-25T09:19:00.000-07:00

I am trying to edit and fix my tutorial on Turbo codes, at www.complextoreal.com. I remember what a difficult time I had writing that section. The editing is not much easier. Many of you have written me about errors and points of confusion in the Turbo Tutorial. Please do so again. I keep replacing my computer every one-two years and keep losing all my saved emails. So if you have specific ideas about improvement, changes, please let me know.

I am also wondering who the main developers are of the Turbo (using MAP and SOVA decoding algorithms) are? If you have companies that make these chips, write.

Charan Langton