10 - RF Interference

While it would be ideal if our only concern in wireless signal propagation was free-space path loss, the reality is that wireless signals can encounter other wireless signals on their journey to the receiver. The way these signals interact depends on various factors, and this is what we refer to as wireless interference. In essence, it's the idea that the wireless waveforms I've just transmitted might collide with other wireless waveforms, whether from other devices or even reflections of my own transmission.

Let's delve deeper into the concept of interference, something we need to grasp early in our Wi-Fi explorations. It's crucial to understand that we often serve a multitude of clients, such as laptops, tablets, and phones, all communicating with a single access point. However, they must take turns, which may not be immediately intuitive.

In my early days of learning about wireless technology, I too believed that the access point could somehow distinguish and manage all these simultaneous communications. The truth is, that these devices must take turns at incredibly short intervals, measured in microseconds and nanoseconds, time frames that are beyond human perception but routine for computers.

For those familiar with Ethernet, you might have encountered the concept of hubs or shared Ethernet mediums. In the realm of Ethernet, we use a protocol known as carrier-sense multiple access with collision detection (CSMA/CD). This protocol ensures that only one device can transmit data at any given time.

Similarly, in Wi-Fi, multiple devices must share the same medium—the airspace. They must take turns to communicate, and this process occurs at an incredibly rapid rate. The challenge arises when multiple devices attempt to transmit simultaneously on this shared medium.

This need to 'take turns' is fundamental to avoiding interference and ensuring efficient communication. It might seem like all devices are communicating at the same time from a human perspective, but they are taking turns on an extremely fine-grained timescale.

So, while wireless interference is an inevitable part of the wireless communication landscape, understanding this concept is essential for optimizing Wi-Fi performance. It underscores the need for devices to coordinate and share the medium efficiently to minimize interference and maintain reliable communication.

This concept applies similarly. If one device begins transmitting and, simultaneously, another device starts transmitting, all devices involved will receive each other's information, leading to a collision. To avoid this, we employ a similar idea—when one device starts transmitting, others should refrain from sending until the initial transmission is complete.

The advantage of this approach is evident when we consider Ethernet hubs, which were later replaced by switches. Switches managed the collision domain and improved network performance. In a wired network, we operate within a bounded domain defined by cables. Multiple cables can coexist without significant interference, except for potential electromagnetic interference, which we should be mindful of.

In contrast, Wi-Fi operates in an unbounded environment, where multiple devices share the same wireless medium—the airspace surrounding them. Like Ethernet hubs, these devices must still take turns because, in this shared medium, only one speaker can transmit at a time, while others must listen.

This mechanism works seamlessly when all devices adhere to the same communication standard, especially in the context of Wi-Fi. Wi-Fi devices take turns efficiently and cooperate. Even if there are instances of accidental overlap, there are built-in mechanisms to address such issues, which we'll explore in more detail later.

However, the challenge arises when non-Wi-Fi devices are present in the same area. These devices, such as Bluetooth-enabled devices, microwaves, cordless phones, or proprietary communication devices, do not follow the same rules. They don't take turns and can disrupt the shared medium, leading to communication problems.

In both cases, these non-Wi-Fi devices emit wireless signals that traverse the same space as Wi-Fi signals, leading to a phenomenon known as interference. Interference occurs when these wireless waveforms collide, affecting their propagation and the information they carry.

To illustrate, imagine standing on a beach and throwing rocks into the water, creating ripples. Initially, these ripples don't intersect, freely influencing the water around them. However, when they do eventually cross paths, they create complex patterns due to their interaction. This analogy applies to wireless waveforms as well.

When two waveforms collide, we can analyze the result through a mathematical approach. Consider two waveforms with the same frequency but 180 degrees out of phase, essentially mirror images of each other. Each waveform has energy levels relative to its origin, with regions above and below the origin. When we add these waveforms together, areas of positive and negative energy cancel each other out, resulting in a net sum of zero.

This explanation simplifies the concept of interference, where colliding waveforms interfere with each other, potentially rendering the signals unusable.

When two waveforms align perfectly and cancel each other out, they result in a straight line with zero net energy. However, in practical scenarios, this perfect alignment is rare. When waveforms are slightly out of phase, such as by 45 or 90 degrees, they don't cancel out entirely. Instead, their energies combine, resulting in a distorted waveform. Creates waveforms that are no longer readable by receiving devices.

Interference is the consequence of these distorted waveforms colliding with each other. It renders signals unusable and can lead to frustrating experiences. For instance, I recall an early experience in my Wi-Fi career when I played an online video game with a wireless controller connected to my system. Every time I moved, the game lagged, and I attributed it to poor game coding. It took a while to realize that the controller, operating on the same frequency as my Wi-Fi but using a proprietary communication method, constantly interfered with my Wi-Fi signals.

Interference is a significant concern, especially in the 2.4-gigahertz range, but it can also occur in the 5-gigahertz range and, in the future, the 6-gigahertz range.

Interference is a challenge we can mitigate but not eliminate entirely. It's crucial to understand that waveforms of similar or the same frequencies are more likely to interfere with each other. When two waveforms share frequencies, they can collide and disrupt each other.

However, it's worth noting that if waveforms are slightly offset in phase and share similar frequencies, they may still impact each other but not to the extent of rendering signals unusable. This tolerance allows for multiple devices to communicate simultaneously in the same area without causing significant interference.

For instance, in a room, you can have one access point communicating on one frequency while another operates on a different frequency. Devices connected to these access points may also communicate simultaneously without major issues. This concept relies on the use of different channels and sometimes different frequency bands to minimize interference.

In upcoming blogs, we'll delve into various frequency bands, such as 2.4 GHz, 5 GHz, and 6 GHz, as well as specific channels like 36, 40, and 44, to explore how they affect wireless communication.

Happy Learning!!