Java Architecture for XML Binding (JAXB) is method to convert your class objects in to XML files. I came across this concept while looking for a way to share the architecture of exchanges and queues in an AMQP system. Although Java object serialization would’ve worked I wanted a much more ‘standard’ way to share this …
Oct
02
Theory behind Doppler frequency shift
Doppler frequency shift plays a major part in wireless communications, radar and many other systems. Sometimes Doppler shift is useful, like in radar detection systems, but sometimes it’s harmful, like in mobile wireless communications systems. Calculating the Doppler shift is very trivial. , where v is the relative speed between transmitter and receiver, and the …
Sep
17
Introduction to Virtual functions, Virtual Tables and Virtual Pointers in C++
If coming from Java to C++, it could be slightly confusing how function inheritance works in C++. C++ uses the notion of “virtual” functions. In C++, unless a function is declared as virtual, polymorphism will not work. Lets see how this works with a simple Base class and a Derived class. #include <iostream> #include <string> …
Apr
24
Arduino with 20×4 Liquid Crystal
It seems that Arduino’s LiquidCrystal library isn’t playing that nice with 4 row displays. I was having trouble getting a 20×4 VFD to work with an Arduino on a parallel connection. It would properly display the first line, but then second line starts from the 3rd row of the display. So it goes, row 1, …
Sep
25
Android Activity lifecycle demo code – with Intents and multiple Activity switching
It can be a little confusing to understand where Android Activities are started and which methods are invoked and what happens when Intents are sent and returned, restarted, etc. So in this code I overrode all the Activity lifecycle methods and put a Toast so I can see which methods are invoked at what time. …
Sep
23
Android Activity Life Cycle Demo
I’m just starting with Android, and if you are a beginner like me, you probably want to understand two of main concepts of Android: Activities and Intents. You probably start off with a “Hello, World.”, so in Android that is an Activity. Anything you can see on the screen is handled by an Activity. And …
Mar
06
Ubuntu Lucid Lynx (10.04) Alpha2 on MacBook Pro.
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 …
Mar
10
RANDPERM: Randomly choosing a subset of values in Matlab
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 …
Jan
28
How the Cyclic Prefix (CP) works in OFDM – Part II – The Theory.
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 …
Dec
20
How the Cyclic Prefix works in OFDM
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 …
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