This is an important functionality I use in my simulations but when I want it I always have to search for it because I forget the Matlab function name. There are lots of loopy ways using random numbers to get this done, but there is an in-built Matlab function you can use: randperm(n). I often need to choose a set of values from a vector. For example, randomly choosing a set of users. Random numbers cannot be used because they can give you identical numbers. Need a method that would generate different numbers. What randperm does is scrambling a sequence of numbers. For example; randperm(5) = 3 1 4 2...

For some reason I prefer Ubuntu on my iMac 27″ compared to my normal desktop. It just looks good in it. The installation is straight forward. Lucid is still alpha but it feels solid (only one more month to go anyway) and it looks good. The purple theme is gorgeous. I first installed 9.10 and then upgraded. Below I post some pics. For a detailed installation guide refer to my earlier post on the iMac here. But note that MacBook Pro installation is less troublesome, because you do NOT need to go to the safe graphics mode to install. Just hit install Ubuntu. There is a documentation you can...

This is a follow up to the Cyclic Prefix (CP) I did here. There I gave a graphical explanation and here I will discuss how it happens theoretically. I recently came across the derivation in a text [1]. So here goes. Considering an N-point FFT system, a block of data points , is to be transmitted during a symbol time. The data vector is sent to an IFFT module. The operation of the FFT, i.e. the discrete Fourier Transformation (DFT) is given by the following matrix: where denotes the -th entry in the DFT matrix . Then the transmitted data vector after the IFFT operation is. . The normalization factor ...

Just yesterday got Ubuntu 9.10 installed on a iMac 27 incher. Here is small guide to the installation. Step 1: You need to partition your hard drive. Use the pre-installed Boot Camp Assistant program (Applications->Utilities->Boot Camp Assistant) for this. You probably will need to divide the drive in half because the other option of 32GB (I think) will not be enough. Step 2: Install rEFIT. This will give you a boot menu at startup where you can choose between Ubuntu and Mac OS X. Below is a screen shot of what you will see at start up (note: This is after Ubuntu installation). Step 3:...

This column will briefly explain how cyclic prefix (CP) in OFDM works by illustration. I decided to add this topic because the I seldom found a text that simply discussed the operation of CP and its usage. First, lets define a property of Discrete Fourier Transform (DFT) : If x(n) and h(n) time-domain signals, circular convolution between them x(n) © h(n) is equivalent to multiplication in the frequency-domain, X(k).H(k). That is, if we circularly convolve two time-domain signals, it is equivalent to multiplying the respective DFT’s of the time-domain signals in the frequency-domain. Now lets...

Do you even remember this? (http://www.mylivesearch.com/). I didn’t until a moment ago when I saw a cover of a TV series and remembered about this in an eerie way. Whatever became of this, I think I can safely say this is pretty much dead. It came out back in May 2007 and more than 2 years later it is still in beta. And a Google search gives less hits than it would give on my name (Don’t believe me? try it). This came as a direct opponent to Google search. It touted to redefine the way search results are found. It complained that Google results are outdated and it will give you the most...

Linux doesn’t always enjoy the love of hardware manufacturers. But it is blessed with an enthusiastic group of engineers who make life that much easier for the rest of us. BTNX-Button Extension (http://www.ollisalonen.com/btnx/) is such application. This nifty application maps mouse buttons with any combination of keys you want. Days of 3-button mouses are gone (except for Apple who are trying to do without buttons). Mouses now come with lot more buttons now.. I never realized the usefulness of this until I got myself a Logitech MX 1100 which has 8 buttons + scroller (except the 2 dpi buttons)....

Came along this handy web site on a Twitter post and thought it’s interesting to share. Started creating my own. It’s getting into shape. Why I thought of posting a short note on this is because I think this will get big. Soon. If you Google for “resume writing” it will give you a big list of pay sites where they provide you different levels of services. From resume writing templates to personal live assistance in providing you with a personalized resume. And these can cost you something around $1000! or more. For many of us starting out, what we need is a nice looking template...

This is a brief introduction to the Iptables. In the most basic terms, iptables can be thought of as a firewall. Basically, there are two components in an iptable: Chains Rules The incoming packets are flown through Chains. You can define many chains as you like and then connect the chains together so the packets are flown continuously. For the normal use, we can do without defining additional chains but I will show one with a chain to grasp the idea. First of all, there are few (among many) keywords that are of importance to learn. INPUT: All the incoming data packets come to this chain OUTPUT:...

I decided to add this little piece seperately becasue the last column was a little long. In this part-2 of securing the SSH connection, I will discuss how to further secure your SSH connection. To recap on the last part, we secured the (already secure) SSH connection by: Using RSA keys to login Disbaling the password login Restricting connections from Iptables We will pick up from there. So now nobody can log into your server (or computer) without having the private key. But this key is just a file that resides in your local computer. So suppose your local computer is in your office or your...