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?! Continue reading “OFDM and You”
Consider the following scenario:
Two APs can hear each other. AP1 is set to use channel 36+40+44+48 (primary channel 36+40) while AP2 is set to use channel 44+48. Due to the nature of 802.11 and co-channel interference, AP1 cannot transmit while AP2 is transmitting.
In this scenario, the APs will forever dance the dance of CCI, waiting for the other to finish transmitting before taking over the medium itself. Wouldn’t it be better if instead of waiting, they could both transmit at the same time?
This is a scenario brought to you by 802.11ac, an infrequently discussed issue known as: Overlapping BSS (OBSS). OBSS is defines as two BSSs that, well, overlap, because their channel configurations occupy some of the same space. Continue reading “On OBSS Interference”
Whilst reading CWSP, I came across a phrase multiple times that was never explained, so I took it upon myself to dive in and figure out- what is a Diffie-Hellman exchange?
Lets start from the beginning. Since the dawn of wireless communications, security has been a priority due to the boundless medium through which all information travels. Naturally, encryption was chosen as the choice for securing wireless communications.
But with (symmetric) encryption, both parties need the same keys to encrypt and decrypt information. How do you agree on keys over a public medium to which anyone can listen? A Diffie-Hellman key exchange. Continue reading “What is a Diffie-Hellman exchange?”
In this edition of The Wi-Fi Rabbit Hole, I don’t go “down the rabbit hole”. Instead, I just felt inspired to share my love of sending information through the modulation of waves.
To get started, lets go over what a wave has to offer: wavelength, amplitude, and frequency. If we alter any of these aspects of a wave, we can encode information. Consider the following scenario:
Example: We have a door and we want to use it to send secret messages to our roommate. First, we agree that we are going to send messages in binary. This makes it easier to understand, because all we need to differentiate between is one and zero.
Continue reading “Types of Digital Modulation”
Have you ever read an article or blog and a topic piqued your interest? I have. When such an idea or topic arises, I tend to set aside everything else and delve into the depths of knowledge until I satisfy my thirst for understanding.
Recently, I began my journey towards obtaining my CWNE. The study guides are chalk full of interesting topics that have sent me down the rabbit hole numerous times. I created this blog in hopes of sharing my trips spawned by this long journey. Continue reading “What’s this all about?”