Frequently (Un)Asked Questions – Pt. 4

In this installment of FUAQ, I will talk about two main types of Wi-Fi interference that can cause headaches in the homes and offices. In fact, you have probably fallen prey to these issues without even realizing it! Consider the following scenario:

At a hotel conference, people go into two ballrooms that are next to each other and start up conversations with each other. With only two people per ballroom, it is very easy for them to hear what the other is saying. Also, there is good noise separation between each ballroom at this point.

Now let’s add more people to the ballrooms. The sound grows. If two people want to hear each other, they must either get closer or talk louder. As the room gets louder still, fewer people can actually have complete conversations. Not only can the people in one ballroom no longer hear, but the sound also starts to bleed over into nearby rooms, making it harder for those people to hear each other as well.

OFDM and You

For the past couple weeks, I have been wrestling with a question: To what are the waves compared when using OFDM and QAM? This took me on a long journey that ended in a simple question: nothing. Here is how I got there.

For those of you who are long time readers, you will remember when I talked about types of digital modulation. At the end of said blog, the additional reading lead to quadrature amplitude modulation. Recently, I was explaining phase shift keying to someone and got to thinking, “When using phase shift keying, the signal is compared to itself in the past.” (admittedly, I was wrong, but bear with me.) So how does an 802.11 radio compare all the subcarriers in an OFDM signal? And to what are they compared?!