20 - Voltage Standing Wave Ratio (VSWR) and Return Loss

 So now that we have a grasp of what a voltage standing wave is, the next step is to understand the degree of its impact. Is it minor bouncing or something more significant? To measure this, we use the Voltage Standing Wave Ratio, or VSWR, as our metric. This will also tie into our discussion of line loss.

As we previously discussed, a voltage standing wave assumes a sinusoidal pattern, with bouncing effects causing fluctuations in amplitude around the origin, typically from positive to negative voltages. In our example, this ranges from +6 volts to -6 volts, and +4 volts to -4 volts around 0 volts.

To quantify the severity of this bouncing, we calculate the VSWR using a straightforward mathematical equation. It involves dividing the maximum voltage on the line by the minimum voltage. In our example on the positive voltage side, it's 6 volts divided by 4 volts, which equals 1.5. Since VSWR is expressed as a ratio, the denominator is typically 1 to keep it simple, resulting in a 1.5 to 1 VSWR ratio. This ratio provides a measure of how pronounced the voltage standing wave is and its impact on the system.

In our example, a VSWR of 1.5 to 1 is quite good, considering that achieving a perfect 1 to 1 ratio, with no reflected voltage, is an ideal but practically unattainable scenario. A VSWR of 1.5 to 1 falls between the ideal and a very good real-world situation, making it favorable.

However, we need to set our expectations based on some common VSWR values. The best-case scenario is around 1.1 to 1, which represents an outstanding VSWR. A pretty good VSWR is about 2 to 1, and a satisfactory value could be a 3 to 1 ratio. Ideally, we aim to keep the VSWR below the 2 to 1 threshold. Anything better than this is acceptable.

The significance of maintaining a lower VSWR becomes apparent when we consider the amount of reflected energy, which directly correlates with power loss. With a 2 to 1 VSWR, about 11% of the total power is reflected back towards the source. This may not seem favorable, but it's considerably better than a 3 to 1 VSWR, which reflects approximately 25% of the power. Thus, striving for a 2 to 1 VSWR is essential to keep reflected energy and power loss within acceptable limits.

Now, let's delve into the concept of return loss, which provides a more comprehensive perspective on power loss due to voltage standing waves. Return loss is a mathematical expression that quantifies this loss.

We're now transitioning from discussing VSWR to exploring the concept of return loss, which provides a more comprehensive perspective on power loss due to voltage standing waves.

Return loss is a mathematical expression that quantifies the loss experienced when power is reflected. To calculate return loss, we start with the input power and subtract the reflected power. At this point, we're converting the power values into dBm (decibel-milliwatts), which is a common way to express power levels.

For instance, let's say our transmission power is 20 dBm, which is similar to how we assess the transmission levels of access points. We then subtract the power reflected back towards the source. If, in our case, the reflected power is -5 dBm, the return loss would be 25 dB.

In return loss, a higher value is better. We want the return loss to be as high as possible. Generally, in the industry, we aim for return loss values greater than 20 decibels. Anything above 10 decibels is considered acceptable. If the return loss falls below 10 decibels, it becomes a significant concern.

As we conclude this discussion on electrical RF concepts, our primary takeaways are to understand the importance of minimizing power loss due to VSWR and the role of return loss in quantifying this loss. While we don't need to be electrical engineers for this exam, having a grasp of these concepts and their significance in wireless networking is essential.

 

In summary, let's revisit some key takeaways regarding voltage standing wave ratio (VSWR) and return loss, which have been the focal points of this skill.

• VSWR Goals:

Aim for a VSWR of 2 to 1 or better. A lower VSWR indicates better performance and less power loss.

Matching impedances between components is crucial. Components with similar impedance values minimize signal loss.

Ensure connectors are properly tightened and the system is correctly installed to avoid increased resistance and impedance mismatches, which can lead to unexpected power loss.

• Return Loss:

Return loss quantifies power loss due to reflected waves in the system.

The higher the return loss value, the better. In general, aim for a return loss greater than 20 decibels (dB), with anything above 10 dB considered acceptable.

Return loss is determined by comparing the input power level to the reflected power level..       

Understanding and managing VSWR and return loss are essential aspects of ensuring the efficiency and performance of wireless communication systems. These concepts help us assess the quality of our RF transmission lines and make informed decisions for optimal signal transmission.

In summary, here are the practical takeaways to ensure optimal performance in wireless communication systems regarding voltage standing wave ratio (VSWR) and return loss:

• Match Impedances:

Whenever possible, aim for components with similar impedance values. This minimizes reflected power and helps reduce signal loss.

• Secure and Tighten Connections:

Ensure that all connectors, cables, and other system components are securely tightened and properly installed. Loose or poorly connected components can lead to unexpected power loss and impedance mismatches.

• Focus on Outdoor Designs:

These concepts are particularly relevant in outdoor wireless deployments. Pay special attention to impedance matching when designing and installing outdoor systems to achieve optimal performance.  

By carefully designing and maintaining your wireless communication systems, you can effectively manage VSWR and return loss, ensuring that your systems operate at their best and minimize signal loss. Thank you for your attention, and I hope you found this information valuable.

19 - Voltage Standing Waves (VSW)

 In the previous discussion, we explored how AC voltage is applied directly to two dipole antennas, creating wireless waveforms. However, in practical applications, we usually don't connect our power source, such as a radio transmitter, directly to the antenna. There's a series of components, including connectors, cables, and other elements, that can introduce losses and affect how cleanly the signal is delivered to the antenna. In this blog, we will delve into the concept of voltage standing waves, which will set the stage for our discussion on the voltage standing wave ratio in the next blog. This ratio will play a significant role in understanding the losses incurred when delivering power to antennas.

So, let's dive in. Imagine we have an AC power source, and we want to deliver this power to the two antenna elements within our dipole antenna. However, we can't simply connect it directly, as there are various components, such as cables, connectors, and lightning arrestors, in the signal's path from the power source to the antenna. These components introduce resistance, known as impedance, into the circuit. For instance, the cable might have an impedance of 200 ohms, while a connector could have an impedance of 75 ohms.

 

The issue arises when these impedance values are mismatched. To illustrate this, let's consider an analogy.

Sure, let's continue. The analogy I'd like you to consider is thinking about water flowing through a pipe. Imagine we have a large pipe that allows a substantial amount of water to flow through, much like low resistance in an electrical circuit. Now, as we reach an abrupt change in the pipe size, the water is forced into a smaller pipe. This represents a change in impedance from an electrical perspective.

In the world of water, some of the water will impact the wall of the smaller pipe and bounce off it. This results in a combination of backflow in the system and a smaller amount of water being pushed through the narrower pipe. The purpose of this analogy is to illustrate the reflection concept. Just as water reflects off the change in resistance in the pipe, electricity behaves similarly. When an electrical signal encounters different impedance levels, a portion of the signal is reflected, creating what we call a voltage standing wave.

So, what is a voltage standing wave? It's essentially the interaction of two different voltages working against each other. One voltage is our input voltage, which is represented as a sinusoidal waveform. Let's say this AC voltage fluctuates between positive 5 volts and negative 5 volts. This waveform is moving in a certain direction. However, when this voltage encounters impedance changes in the circuit, some of it gets reflected back. We'll label this reflected voltage as V-reflect.

Now, let's explore the properties of this reflected voltage. First, the reflected voltage has a much smaller amplitude compared to the input voltage. Let's say, for our example, it's approximately plus or minus 1 volt.

However, a crucial point to understand is that the reflected voltage maintains the same frequency as the input voltage. This means that these two waveforms directly impact each other, similar to the concept of wireless interference when the frequencies align.

Here's where it gets interesting. We effectively add these two waveforms together, just as we discussed with wireless interference. The result is a standing voltage pattern, which means it's not traveling in any direction. This standing wave is essentially a pulsating wave, varying with time. The pulsations depend on whether the crests of the waves align with each other or if a crest lines up with a trough.

Remember, the individual waves are still moving in their respective directions, but the combined standing wave doesn't move. Sometimes, the amplitude might reach positive 6 volts when the crests align, adding the 1 volt to the 5-volt input. Other times, it could subtract from the 5 volts, resulting in a pattern representing 4 volts. This back-and-forth pattern is what creates the pulsations in the standing wave.

The phase and frequency of the standing wave remain constant, which is why it's called a "standing wave" – it doesn't move. Instead, it pulsates between positive 6 and positive 4 volts (at least on the positive side of the origin) and bounces between negative 4 and negative 6 volts on the other side of the origin.

Describing a standing wave without visual aid can be challenging. I recommend conducting a Google search for "voltage standing waves animation" to find some enlightening animations. These animations will illustrate how the waves pulsate, with the maximum amplitude varying slightly above and below the input voltage.

What's important to understand is that the standing wave ratio quantifies how much the waveform pulsates. We'll delve deeper into this in the next blog. The overarching goal of this entire course is to grasp voltage standing wave ratios because they directly relate to signal loss in our transmission lines. Minimizing this pulsation is crucial, and this can be achieved through matched impedances.

The root cause of this situation is the varying impedances along the electrical path, which result in reflected behavior, similar to the water pipe analogy. Imagine a scenario where a radio is connected to a connector represented by a pipe of a certain size, which then connects to a cable with the same impedance, leading to another connector with matching impedance. In this ideal scenario, the electrical signal, the AC voltage, flows seamlessly without any reflection.

However, it's important to note that achieving this level of impedance matching is mostly theoretical. In real-world scenarios, it's nearly impossible to achieve perfect impedance matching. There are several reasons for this:

1. Cable Length: The cable length is a variable that can't always be cut to an exact length to match different connector types.
2. Variance: Even if two components are both rated at 50 ohms, for example, there may be slight variances due to manufacturing or other factors. One component might have an impedance of 50.5 ohms, while the other might be at 49.7 ohms, leading to a mismatch.

So, despite our efforts to buy components with the same rated impedance, there can still be impedance variations that lead to reflections and voltage standing waves. This variance is one of the challenges faced in real-world RF systems. In the next blog, we'll delve deeper into the Voltage Standing Wave Ratio (VSWR) to understand how these reflections affect our systems.

And so, in summary, it's generally considered impossible to perfectly match all impedances within a complex RF system due to the various components involved, such as connectors, cables, arrestors, attenuators, and signal boosters. These components have their own impedance levels, and achieving perfect matching in a real-world scenario is highly challenging.

As we've discussed, this impedance mismatch results in reflected voltage and the formation of a standing wave. The input voltage and the reflected voltage combine, and as they move in opposite directions, they cancel each other out, creating a standing wave. The wave fluctuates between higher and lower amplitudes, depending on how the waveforms align at any given moment.

While achieving perfect impedance matching is often unattainable, it remains a goal in wireless system design to minimize impedance mismatches as much as possible. This is critical for reducing reflected voltage and standing waves, which can impact the performance and efficiency of RF systems.

18 - AC Voltage and Wi-Fi

As we've hinted at a few times, wireless antennas don't operate within the closed circuit framework where electrical current flows from the power source and returns to it through the antenna. So how exactly do we manage to convert electrical signals into wireless signals, regardless of the open or closed circuit concept? That's what we're about to delve into, with the core idea being alternating current or AC power, as discussed in the previous blog.

Now, electricity comes in two primary forms: direct current (DC) and alternating current (AC). In the case of direct current, you have a constant voltage; for instance, you could apply a steady 5 volts to a circuit that remains unchanging, which is what we typically expect in many scenarios. On the other hand, alternating current, or AC, follows a different pattern. It allows us to propel electrons through a circuit by oscillating back and forth, pushing the electrons both forward and backward rather than in a continuous direction, as in the case of direct current.

So, instead of having a constant voltage along the line, we apply voltage in a pattern resembling a sinusoidal waveform, which should sound familiar, especially in the context of wireless communications. In this pattern, the voltage fluctuates between positive and negative values. For example, it could reach +5 volts at one moment, then swing down to -5 volts, and take on values in between at various points in time. This alternating voltage is a fundamental aspect of how we generate wireless signals.

Zero volts on the line is also a possibility, and it's entirely acceptable because, in this context, what matters more is the current. While a constant voltage would result in a continuous current flow, alternating current exhibits a back-and-forth nature. At this point, electrons are technically in motion, but they are moving back and forth, ultimately achieving the same power transmission.

These two types of power, direct current (DC) and alternating current (AC), are commonly used in different applications. Most of our electronic devices require DC power to operate. However, when it comes to power transmission, we often use AC power, which allows us to transmit electricity over longer distances and take advantage of devices like power transformers.

In practice, when we use electronic devices, we typically plug them into an AC power source. This could be a wall outlet. Often, you'll see a power brick on the cord, and you plug this assembly into the wall, which provides AC power. Alternatively, you might have an AC adapter, a larger device, which you plug into the wall. The AC power is then converted to DC to supply the necessary voltage to the electronic device.

Additionally, when we use batteries, they always provide power in the form of DC. Consequently, there's no need to convert between AC and DC in such situations.

So, why are we studying this? Because antennas are unique in that we usually talk about electricity in the context of a circuit. If we have a DC power source, we need to establish a circuit to utilize it.

In a typical circuit with a direct current (DC) power source, you'd connect a load, like a resistor, and current would flow in one direction from positive to negative. However, when dealing with an alternating current (AC) power source, you don't need a closed circuit. In fact, you can create an open circuit where power flows back and forth between the two poles. This is precisely what happens in an antenna.

To illustrate this, let's focus on the dipole antenna. A dipole antenna, as the name suggests, involves two poles. You can depict it as having one pole extending in one direction and the other pole going in the opposite direction, creating an antenna element in between. To power this antenna, you connect it to your AC power source.

This antenna conforms to the same pattern we discussed. There are two poles: pole 1 and pole 2. You can connect the positive end of your AC source (for simplicity, we'll refer to it as positive for now, although it alternates) to one pole and the negative end to the other pole.

The key thing to understand is that, due to the alternating current nature of the power source, the voltage alternates back and forth. As a result, current begins to flow, and initially, all the electrons are evenly distributed on the two dipole antennas. This sets the stage for how antennas work to transmit wireless signals.

Let's dive deeper into how this process works. Imagine that I apply the electrical charge in such a way that all the electrons on one side of the dipole antenna rush to the other side. This results in a concentration of electrons on one pole, leading to a very negative charge on that side, while the other side is left with a deficit of electrons, resulting in a positive charge.

However, this is not the end of the story. Since the power source alternates, we'll soon transition from the positive voltage state to a negative voltage state. Consequently, all the electrons will rush to the opposite side, turning it into the negative pole and leaving a bunch of positive charges on the other side.

So, over time, you have a positive charge on one side of the dipole antenna and a negative charge on the other side. Then, this situation flips, and you have a positive charge on the opposite side. This pattern continues, constantly shifting between positive and negative charges in accordance with the cycles of the AC power source. It's this continual oscillation of positive and negative charges that ultimately generates the wireless waves emanating from the antenna.

The underlying physics behind this phenomenon is quite complex, and we won't delve into it in detail. However, it's important to grasp that wireless radiation occurs due to this ongoing reversal of charges. But how does this translate to real-life scenarios?

Often, in the context of wireless networking, you'll see access points with two rubber duck antennas protruding from the top. These are typically dipole antennas, similar to what we've been discussing. If we were to take one of these dipole antennas and expand and open it up, we would find a metal antenna encased in plastic, creating the familiar antenna configuration used in wireless networking.

This metal antenna is designed in a way that a wire splits into two parts, forming two antenna elements. One element extends upward, and the other extends downward, neatly folded inside the rubber casing.

An interesting aspect of dipole antennas is that their length is significant. The length of the dipole, from one element to the other, should be half of the wavelength of the wireless transmission being utilized. As a reminder, the frequency directly determines the wavelength. We can calculate the wavelength based on the frequency of operation.

For instance, in the 2.4 gigahertz range, the wavelength should be around 125 millimeters. However, in the 5 gigahertz range, with more than double the frequency, the wavelength is considerably shorter, roughly 60 millimeters. Therefore, for a half-wavelength dipole antenna in the 2.4 gigahertz range, it should be about 62.5 millimeters in length. In contrast, for the 5 gigahertz range, a half-wavelength dipole antenna should be approximately 30 millimeters in length.

This length measurement is specific to the metal components inside the antenna. Keep in mind that there are various types of antennas with different designs. A dipole antenna serves as a great example for study due to its physical properties, which can be linked back to AC voltage. Nevertheless, all antennas leverage AC power but do so in different ways.

It's also worth noting that there are dual-band antennas available, which can receive both 2.4 and 5 gigahertz radio waves. These antennas provide versatility when dealing with various frequencies.

When considering the ideal length of dipole antennas for specific frequencies, it's important to understand that the calculations are based on ideal scenarios and are not strictly required. For example, a 2.4 gigahertz dipole antenna should be around 62.5 millimeters, while a 5 gigahertz dipole antenna should be approximately 30 millimeters in length. However, in practice, the length of the antenna can be adjusted to suit specific deployment needs, even if it's not the ideal half-wavelength length. For instance, a 2.4 gigahertz antenna that is 115 millimeters long would still work but might not be as efficient as an antenna with the ideal length.

Additionally, dual-band antennas are designed to work with multiple frequency bands. These antennas compromise by having a length typically between 40 and 50 millimeters to accommodate both the 2.4 and 5 gigahertz bands. While they provide versatility, dual-band antennas may not perform as well as single-band antennas designed for a specific frequency range.

In conclusion, this discussion began by explaining the difference between alternating current (AC) and direct current (DC). AC alternates between positive and negative voltages in a sinusoidal wave pattern. It was noted that AC is applied to open circuits to create wireless waveforms, as demonstrated with the dipole antenna. This back-and-forth movement of electrons and the shifting of positive and negative charges generate wireless signals. Understanding these concepts is essential for working with wireless technologies.

While it is ideal for antennas to have a length that corresponds to half the wavelength of the desired frequency, this requirement is not strictly mandatory. For example, when creating 2.4 gigahertz waveforms, it's not necessary to use an exactly 62.5-millimeter dipole length. However, the closer the antenna's dimensions are to this ideal length, the higher the quality of the signals and the better the receive sensitivity are likely to be. When working with dual-band antennas or other variants, there are additional considerations to consider.

Understanding the construction of a dipole antenna and the ideal dimensions associated with different frequencies is valuable for those dealing with wireless technologies.

17 - Electricity Concepts

I often playfully tell young people that, sooner or later, they'll find themselves in the world of Information Technology (IT). It's a light-hearted way of pointing out a common trend: many of us in IT come from diverse backgrounds. Some of us began our academic journeys studying subjects unrelated to IT, while others had entirely different careers before making the shift into the world of IT.

In my case, I originally embarked on the path of studying electricity as an aspiring electrical engineer. I obtained a degree in electrical engineering with the expectation that this would be my lifelong pursuit. However, life had other plans, and I found myself in the field of IT, guided by a series of interesting events. It's quite amusing for me to be here now, studying the intricate relationship between wireless technology and electricity, as it feels like a full-circle journey.

I must confess that I have a genuine enthusiasm for delving into the intricacies of electricity, whether it's exploring the principles of voltage, current, or resistance. These foundational concepts are essential for understanding how wireless waves are generated. Therefore, as we embark on this educational journey, it's crucial that we establish a strong foundation in these basic electricity principles.

As previously mentioned, our primary focus is on wireless networking and the nature of wireless waves in communication. Nevertheless, it's important to remember that even within the realm of wireless systems, there are wires involved. The connection between the transmitter or radio and the antenna necessitates the transmission of an electrical signal to generate the wireless waves.

In essence, while we delve into the world of wireless technology, it's vital to maintain an appreciation for the fundamental electrical principles that underpin this field. So, let's dive in and witness these concepts in action.

To delve into this subject, we must first introduce electricity into the equation. As we progress, our aim is to gain a comprehensive understanding of the inevitable power loss that occurs along this electrical pathway. For wireless engineers, it's crucial to comprehend both the process itself and the methods used to estimate and mitigate this power loss.

Our journey begins with electricity on this pathway, and we will conclude this discussion by honing in on strategies to minimize the resultant power loss. To lay the foundation for this, we need to explore basic concepts in electricity. When discussing electricity, three primary factors come into play: voltage, current, and resistance. It's worth noting that occasionally resistance is referred to as impedance, which is a more technical term often used in the field.

So, what do these concepts entail? Voltage can be thought of as the driving force that propels electricity through the circuit. However, it's important to clarify that voltage isn't precisely a force; it's technically the energy per charge. For a deeper understanding of voltage, it's essential to grasp this more accurate description. Nevertheless, for practical purposes and to facilitate mental visualization, it's often simplistically viewed as a driving force that generates current.

Now, let's take a closer look at the concept of current. Current refers to the flow of electrons, essentially the movement of electric charge. From a physics standpoint, what's happening is that we are setting the electrons inside a conductor into motion. Here's a brief aside for a deeper understanding.

Within an atom, you have a nucleus containing both neutrons (with no charge) and protons (with a positive charge). In an ideal scenario, you would also find electrons orbiting the nucleus. You can think of these electrons as if they're in orbit around the nucleus, somewhat akin to planets orbiting the sun, although the reality is more intricate.

What's crucial for us to grasp is that these electrons are present in a quantity that cancels out the positive charge of the protons. When we apply electricity to a material that contains a multitude of these atoms (a conductor), we essentially excite these electrons, prompting them to move. It's important to note that the nucleus and the atoms themselves remain stationary. However, the electrons within these atoms begin to shift and flow in a specific direction.

In essence, electricity is the movement of electrons through a material, which we typically refer to as a conductor. Now, resistance and impedance represent essentially the same concept but are expressed using different terminology. You can think of them as the friction that must be overcome to set these electrons in motion. This resistance or impedance determines how easily or difficultly the electrons can flow through the material.

Electrons naturally prefer to remain attached to their current nucleus, and as a result, the more resistance we introduce into a circuit, the harder it becomes to set those electrons in motion. In simpler terms, applying the same voltage to two different circuits, the one with higher resistance will have lower current, and vice versa. This relationship between voltage, current, and resistance is so well-established that it's expressed in Ohm's law.

Ohm's law states that voltage (V) is equal to current (I), often denoted as "I," times resistance (R) or impedance. Therefore, V = IR is a fundamental expression in the world of electricity. Thanks to this equation, we understand the nature of this relationship. For instance, if we want to double the current, we'd need to halve the resistance, assuming the voltage remains constant in both scenarios.

It's important to note that when we view the equation from the perspective of current, it becomes voltage divided by resistance (I = V/R). This underscores the fact that resistance cannot be zero in a practical circuit because it would lead to an infinite amount of current. This situation is what's referred to as a short circuit. A common science experiment illustrating this concept involves connecting a single wire across the two leads of a 9-volt battery. However, it's crucial to exercise caution when doing so, as the voltage generates an immense amount of current, resulting in significant heat production.

The generation of this heat isn't just potentially harmful to us; it could also lead to the wire itself burning through. Therefore, it's of utmost importance that we never undertake this science experiment without taking extensive safety precautions. A short circuit in such conditions generates a significant amount of heat as the current escalates rapidly.

I mention this because, in practical terms, we aim for the opposite of a short circuit. Instead, we need to introduce a load into every circuit. This load provides a level of resistance. In many cases, a circuit configuration looks like this: we have a battery, often represented by this symbol, and we connect it to a resistance component, typically indicated by an angled squiggly line. This squiggly line represents the resistance element, while the battery provides the voltage source. A standard battery, like a AA or AAA battery, features a positive and negative side that you're likely familiar with.

This setup introduces a fundamental concept in the world of electricity: the concept of a circuit. I've used this term a few times, but what exactly does it mean? If we break down the word, "CIRC" shares its root with the word "circle." Essentially, a circuit implies that we need some form of a loop for electricity to flow, and this is the case in most scenarios.

I say "in most cases" because antennas are a fascinating exception to this rule, and we'll delve into why that is shortly. For now, it's vital to understand that, typically, a circuit, or a closed loop, is necessary for the flow of electricity. Electricity always flows from the positive end of a source, like our battery, through the circuit it's connected to.

Electricity flows from the positive side of the battery to the negative side. However, what's interesting is that the actual direction in which electrons move is the opposite of this flow. Electrons, being negatively charged, move from the negative side (minus) of the battery to the positive side (plus). So, in essence, electricity flows from positive to negative, while the electrons themselves move from negative to positive. The distinction between these two directions can sometimes be puzzling, but it's generally more important to understand the concept in terms of the electricity flow.

To summarize, when we refer to an electrical current, it's always discussed in the context of the direction of the electricity itself, rather than the movement of electrons. Now, it's crucial to recognize the units of measurement for each of these electrical components, as they each have their specific units. Voltage is measured in volts (V), current is expressed in amperes (A), and resistance is quantified in ohms (Ω). It's worth noting that the unit for ohms is often represented using the Greek letter omega (Ω) rather than the letter "O."

Let's illustrate this with an example based on Ohm's law. If we have a voltage of 120 volts and apply a resistance of 60 ohms, we can calculate the current. Using Ohm's law, we find that current (I) is equal to voltage (V) divided by resistance (R). In this case, it's 120 volts divided by 60 ohms, which equals 2 amperes (A). Two amperes represents a significant amount of electricity. In many applications, particularly in electronics, current is expressed in milliamperes (mA), which are 1/1,000th of an ampere, much like milliwatts are 1/1,000th of a watt.

Ampere, the unit for current, is named after a scientist whose last name was Ampère, and as a result, it's represented with a capital 'A'. Therefore, when we denote current in milliamperes (mA), you'll see a lowercase 'm' alongside the capital 'A'. It's fascinating to delve into the world of electricity and explore the fundamentals that underlie all these electrical circuits.

Let's revisit the "why" behind our discussion. We're talking about these concepts because wireless signals originate from electrical signals. To generate wireless radiation, we first need to create electrical signals. Conversely, if an antenna is receiving wireless signals, we must translate those signals back into electricity. Understanding these fundamental electrical principles is crucial for comprehending their impact on the world of wireless technology, a theme we'll continue to explore in this learning module.

The foundations of electricity revolve around three key concepts: voltage, current, and amperes (amps). We need to grasp the principles of these components and recognize that Ohm's law provides the equation that defines their interrelationships.

16 - Loss and Link Budgets

In the previous blog, we introduced the concept of power loss in wireless systems. We discussed how various factors, such as connectors, cables, and other components, can result in a reduction of the power that ultimately reaches the antenna. In this blog, we will delve deeper into this topic and also explore the concept of the link budget, which provides a comprehensive view of power considerations across the entire system.

While we often emphasize the gains achieved in a wireless system, typically through the addition of antennas to boost the signal, it's equally important to address losses, as we did in our last blog.

To recap, the fundamental idea is that the presence of connectors and longer cables contributes to power losses. This means that not all the transmitted power makes it to the antenna intact.

In the context of cables, their length plays a significant role in power loss. Longer cables introduce more electrical resistance, causing a greater power loss during transmission. Additionally, we mentioned the use of lightning arrestors. Lightning arrestors are devices designed to safeguard access points from electrical surges resulting from lightning strikes, whether they are direct hits or occur in proximity.

When discussing power losses, we typically quantify them in decibels (dB). The losses from these components are typically less than one dBm (decibel-milliwatt) per device. For instance, connectors may lead to a loss of around half a dB, while cables might result in a quarter of a dB loss. The specific loss also depends on the type and quality of the devices being used. To understand the expected decibel loss for a particular component, you can refer to its specification sheet when making a purchase decision.

This brings us to the important concept of the link budget. The link budget is a way to account for the power losses and gains that occur as a wireless signal travels through the environment. It's essentially a comprehensive analysis that covers the entire path from the transmitter to the receiver.

In this end-to-end conversation, we consider the journey of the transmitting radio as it traverses the wireless system, passes through the airspace, and reaches the receiving end. To illustrate this, we can break it down into several key components:

Let's consider a scenario in which we have an intentional radiator power of 18.5 dBm, and our antenna provides a gain of 5 dBi. To calculate the effective isotropic radiated power (EIRP), we add these values, resulting in a total EIRP of 23.5 dBm.

The next factor to account for is the free space path loss, which depends on several variables. First, it is influenced by the frequency used, as higher frequencies experience faster attenuation in free space, as previously discussed. Secondly, it depends on the distance between the transmitter and receiver. For our example, let's assume a free space path loss of 90 dB, which means we lose 90 dBm across the airspace.

Subtracting this loss from our total EIRP, we get a received power level of -66.5 dBm (23.5 dBm - 90 dB). However, we must also consider the gain on the receiver's side. Assuming both the transmitter and receiver use antennas with a 5 dBi gain, the signal is boosted by the same amount on the receiving end, resulting in a new power level of -61.5 dBm (-66.5 dBm + 5 dB).

Nonetheless, there will be additional losses in the system. Let's assume we experience a loss of 1.5 dBm during transmission. This brings our total received power level to -63 dBm (-61.5 dBm - 1.5 dB).

We can represent this power variation over distance in a graph, with positive dBm on one side and negative dBm on the other. As the signal travels, we'll observe fluctuations in power. For instance, the transmitter itself might initially emit a power of 20 dBm, but due to losses in cables and connectors, the power decreases gradually along its path.

This explains the fluctuations in power levels as the wireless signal propagates through the environment, helping us understand the signal's strength at various points along the way. It's a critical aspect of designing and optimizing wireless communication systems.

What can we practically gather from all of this? Well, one key takeaway is that when it comes to outdoor wireless systems, it's imperative to pay closer attention to link budgets, although this concept isn't irrelevant for indoor systems either.

The distinction lies in the complexity of the components involved. In indoor setups, we usually have fewer components to contend with. For instance, we typically don't require lightning arrestors, and our cable lengths, if we're using cables at all, are minimal. Additionally, indoor environments may utilize internal antennas, which essentially involve negligible cable lengths and minimal connector losses, even though there are technically conductors involved.

Conversely, outdoor wireless systems often necessitate more extensive considerations. This is partly due to the need for weatherproofing and the various elements that outdoor systems must endure. In outdoor setups, we commonly use larger connector types, which can introduce higher losses.

Moreover, outdoor systems frequently require longer cables. This is because outdoor access points and antennas may need to be positioned at greater distances from each other. This flexibility is essential for accommodating various environmental factors. Outdoor setups also demand the inclusion of lightning arrestors to protect against electrical surges.

All these factors contribute to greater losses in outdoor wireless systems when compared to indoor systems. When selecting and ordering components for these systems, it's crucial to refer to the technical specifications of the devices being installed. These specifications provide valuable information about factors such as cable lengths, connector types, and other losses, helping you design and configure effective outdoor wireless systems.

To ensure the success of our wireless designs, we must thoroughly understand and quantify the potential losses within our system. This means we need to be able to predict and calculate what these losses will be. For example, if we initially plan for a three-dBi antenna but find that our anticipated losses are one dB higher than expected, we should be prepared to consider using a more powerful four-dBi antenna to compensate for these losses. This decision-making process is an integral part of wireless system design.

Another crucial consideration is the impact of frequency. As mentioned earlier, higher frequencies lead to greater signal degradation in terms of free space path loss. However, it's important to note that this principle also applies to the electrical components of the system. Even when the signal is in the form of an electrical current traveling through cables and other components, higher frequencies will result in more significant losses. This highlights the importance of selecting the appropriate frequency for a given wireless application.

In summary, it's essential to recognize that wireless system design isn't just about adding antennas and focusing on gains. Every component within the system plays a role in the overall signal loss. The goal is not to eliminate all losses but to understand and manage them effectively. By doing so, we can optimize our wireless systems for the best possible performance.

15 - IR, EIRP, and Power Limits

As we delve into the intricacies of our wireless system, we encounter varying power levels throughout its components. Starting with the radio, it possesses a certain power output. Along the way, we may experience power loss through the cables, but the antenna plays a critical role in reshaping the signal propagation, effectively providing gain to our power output. Understanding this is crucial because there are regulations governing the maximum power output of wireless transmitters. You can't simply deploy a massively powerful radio that emits an excessive amount of energy in any environment.

To comply with these regulations, it's imperative to comprehend the guidelines regarding the connection of specific antenna types to radios. Let's delve deeper into these terms, such as IR (Intentional Radiator) and EIRP (Effective Isotropic Radiated Power), and explore the associated power limits.

When we discuss wireless devices, we often depict them as radiating energy, but it's vital to deconstruct this into individual components. One of these components is the radio, which serves as the source of the wireless signal. In technical jargon, the radio is referred to as the intentional radiator (IR). An intentional radiator signifies a device explicitly designed to generate RF waves and characterizes the power output from the entire system.

The intentional radiator, or radio, connects to other components via connectors and cables. These connectors can be either internal or external to the device, and the cables extend towards the antenna.

The components between the transmitter and the antenna that make up the IR include:

the transmitter
all cables
connectors
grounding
lightning arrestors
amplifiers
attenuators

In many scenarios, the signal path consists of a series of components, often starting with a single cable leading to another connector, followed by the antenna element. However, this signal path can incorporate additional components. For instance, in the case of an outdoor access point, there might be a lightning arrestor in the middle. Alternatively, there could be cable extensions or other elements along the line.

The critical aspect we're discussing here is the power delivered to the antenna, known as the power level of the intentional radiator. It's intriguing because we may initially think the radio is transmitting at, say, 20 dBm. However, as our conversation progresses, we'll discover that each of these connectors and even the cable itself introduces signal loss. This means that as the signal traverses this pathway, we'll experience power reduction.

For example, there might be a 0.5 dBm loss at the first connector, a 0.25 dBm loss in the cable, and another 0.5 dBm loss at the final connector. When we tally up these losses, it totals to a negative 1.25 dBm. Consequently, after the calculations, the power received by the antenna (IR power) is 18.75 dBm.

This represents the actual transmission value that the antenna will subsequently emit. For now, it's important to grasp that we commence with a certain power level, but by the time it reaches the antenna, this power level undergoes some reduction/loss.

If we were simply radiating the power in all directions from the radio, it would distribute evenly in an ideal asymmetric sphere. However, the antenna alters this signal, potentially focusing it on a particular direction or even compressing it to a confined area around itself, rather than following a perfect spherical pattern.

Regardless of how the antenna manipulates the signal, the outcome is an increase in decibels. It's crucial to note that this power increase is not due to the antenna adding power to the signal – the antenna doesn't draw power from a source. Instead, it shapes and directs the signal, akin to how a flashlight concentrates its beam in a particular direction. Think of it as the contrast between a lantern casting light in all directions and a flashlight creating a focused, brighter beam while leaving areas behind it unlit.

Consequently, the combined effect of the original power level, accounting for the discussed losses, and the antenna's influence introduces a new concept we need to understand – the equivalent isotropically radiated power or EIRP.

The EIRP defines the net output of the entire system, representing the maximum power achievable from any point within the signal coverage area. Fundamentally, it boils down to a mathematical equation. We start with the intentional radiator power, which we've already discussed. This factor accounts for both the initial power and any losses incurred, so remember that. The EIRP is calculated by adding the IR power to the antenna gain, which represents pure gain. Therefore, EIRP equals IR + antenna gain.

For instance, consider a scenario where the antenna has a gain of 4 dBi. In our previous example, we calculated the intentional radiator power level to be 18.75 dBm. By adding this 4 dBi value from the antenna, the total EIRP for the system is 22.75 dBm. This is how we compute the EIRP when provided with transmitter power, losses, and antenna gains.

Understanding the values of IR and EIRP is essential because regulations stipulate specific power limits. Regulatory bodies establish rules for the use of Wi-Fi, ensuring that it operates within defined parameters. For instance, if someone intended to cover their entire house with Wi-Fi, they could potentially find a manufacturer willing to produce a 1-megawatt radio, which would transmit at 60 dBm (equivalent to 1 million watts). Such a device would indeed provide extensive Wi-Fi coverage, potentially reaching the entire neighborhood.

Nevertheless, it has been decided that such high-power Wi-Fi is not allowed, and there are several reasons for this restriction. Let's consider some of them. First, Wi-Fi is primarily designed for close-range communication. If we were to create Wi-Fi devices with a range extending over a mile, it could lead to an arms race of sorts, where wireless clients and access points push their range capabilities even further, potentially causing interference and other issues.

Furthermore, the safety of Wi-Fi is a priority. People are exposed to Wi-Fi radiation regularly. It's important to remember the concept of the electromagnetic spectrum and how Wi-Fi operates at a much lower frequency than even visible light. The more dangerous types of radiation, such as X-rays and gamma rays, are associated with higher frequencies. Visible light, while it has a frequency, is significantly higher than that of Wi-Fi. To illustrate, Wi-Fi operates in the 5 gigahertz range, while visible light operates in the 400,000 gigahertz range. This is why we consider Wi-Fi to be safe from a frequency perspective. However, we still want to ensure its safety from a power-level perspective. Exposing people to excessive Wi-Fi power is something we aim to avoid.

Lastly, there aren't many practical benefits to increasing Wi-Fi power substantially. In fact, in contemporary times, we prefer to keep our cell sizes small, meaning that we want to control the range and coverage of Wi-Fi networks to provide efficient and manageable services.

One of the strategies we employ to achieve controlled coverage is by reducing the power output of access point radios while increasing their quantity. This approach allows us to create a softer and more evenly distributed coverage throughout a building, ensuring that even the corners are reached and accommodating a higher number of clients.

Considering the world, we live in, with a multitude of wireless clients, we often require high-density deployments in various scenarios. However, there's a balance to be struck because the larger we make ourselves in terms of coverage, the fewer clients we can effectively support. These power limits are enforced from two perspectives.

First, we have a power limit related to the intentional radiator power level. For instance, on a particular band and channel, there might be a restriction like, "You can only broadcast at 23 dBm," factoring in the associated losses. Generally, these losses are insufficient to allow us to increase the power output beyond the prescribed level. For instance, you might find that 23 dBm is a common limit for several channels, but it can vary depending on the band, channel, and even the region in the world.

Now, here's the key point: if we only had a rule governing the amount of power we can transmit, we could manipulate the antenna to an extreme degree, potentially adding a substantial gain like 20 dBi or more, thereby concentrating the signal into an exceptionally focused beam.

While significantly increasing antenna gain might not be particularly practical, it's important to remember that the primary aim is safety. We want to avoid directing high levels of Wi-Fi power toward individuals, which is why there are rules concerning EIRP (Equivalent Isotropically Radiated Power). These EIRP rules vary based on the band, channel, and region.

When deploying Wi-Fi, it's crucial to exercise caution and adhere to these rules. Thankfully, most Wi-Fi vendors are diligent in ensuring compliance. You can't typically purchase a wireless system from a vendor that exceeds the regulated radiated power limits.

However, as a wireless designer, you must be cautious when selecting antennas. You have the authority to deploy an access point with a specific power output and pair it with an antenna that possesses higher gain. This can potentially lead to EIRP violations. Therefore, it's imperative to have a solid understanding of the EIRP regulations in your region to ensure that your wireless systems do not breach these rules.

Happy Learning!!

14 - Antenna Propagation Video

This video provides a visual guide to understanding Antenna Signal Propagation.

Video Credit: The National Film Board of Canada for the Canadian Air Forces.

Happy Learning!!

13 - Antenna Gain

Let's discuss the gains and losses involved in building a Wi-Fi system. We aim to transmit signals across a range of frequencies within a single channel. To achieve this, we must ensure that the signal reaches the receiver with sufficient power. Our discussion begins with antennas, their potential gains, and their functioning.

Let's view some antenna types first:

Indoor Access Points Antenna Placement

By default, a transmitting device, such as a radio, radiates its signal equally in three dimensions, forming a spherical energy field around it. However, in practical scenarios, we connect the radio to an antenna to control the signal direction. A perfect spherical radiation pattern is not realistic. The closest approximation is an omnidirectional antenna, which creates a circular pattern when viewed from above.

Yet, when considering the three-dimensional nature of signal propagation, the pattern looks more like a doughnut when viewed from the side. We shape the signal radiation to suit our needs, like how a directional antenna narrows the signal into a beam, resulting in higher signal strength measured in decibels.

When assessing antennas for power levels, we need to understand how to measure their effectiveness and what we are comparing them to. Decibels (dB) represent a relative value, so to increase our radio's power in a specific direction, we must determine the gain introduced into our system.

Initially, one might consider using dBm, a decibel related to milliwatts, but this is not suitable for antennas. Antennas are passive devices composed of metal that receive and propagate signals based on their design. Since they don't generate power themselves, we can't rate them in dBm. Instead, we use dBi, where the "i" signifies isotropic behavior.

Isotropic behavior serves as a reference point. We modify the signal pattern from the antenna, typically compressing it into a directional pattern, to strengthen it in some way. For instance, a 3-dBi antenna, when added to a radio transmitting at x dBm, results in a power level equal to x plus 3. This measurement accounts for how the antenna focuses and strengthens the signal in a specific direction or pattern.

We're effectively adding 3 decibels (dB) of power to the radio's transmit power, regardless of its specific value, be it 20 dBm, 17 dBm, or 1 dBm. The antenna's gain remains consistent at 3 dBm.

Antennas are sometimes rated using a different value known as dBd, where the "d" stands for dipole antenna. Dipole antennas are common, often seen as rubber-covered antennas on access points. They aim to approximate the theoretical spherical radiation pattern, though not perfectly. Typically, a dipole antenna has a rating of about 2.2 dBi, or sometimes seen as 2.14 dBi.

In terms of the relationship between dBi and dBd, a dipole antenna is considered 0 dBd, equivalent to its 2.2 dBi rating. Therefore, if you purchase a 3 dBd antenna, it's effectively a 5.2 dBi antenna. This relationship is straightforward: to convert from dBd to dBi, add 2.2, and to convert from dBi to dBd, subtract 2.2. While both ratings may appear on antenna specs, dBi is more common these days, with dBd occasionally encountered.

i.e. dBi=dBd+2.2 and dBd = dBi-2.2

Let's delve into what we can anticipate from antenna gain. Our initial assumption might be that higher dBi values correspond to an increased range, and to some extent, this is true. A high-gain antenna can indeed extend the range.

However, it's not that straightforward. We must consider how the antenna achieves this. Picture the ideal spherical radiation pattern, which we then compress into a more focused form, resulting in greater power radiating away from the antenna.

Now, take a directional antenna as an example. Say we have a lower-gain 5-dBi directional antenna. It can project its signal quite a distance, which is beneficial for directing the signal in a specific direction. But what if we upgrade it to an 8-dBi antenna? The higher gain narrows the signal focus, potentially increasing the range but also reducing the beam width significantly.

The key question is: Do we prefer the broader coverage of the lower-gain antenna or the narrower yet extended reach of the 8-dBi antenna? This illustrates the importance of considering our specific needs and available power.

Since antennas are passive devices and don't generate power, they merely alter power distribution. This concept becomes clearer as we explore antenna spec sheets later in these blogs, revealing various examples of how antennas affect signal performance.

We measure antenna gain in two ways: dBi, where "i" stands for isotropic, and dBd, where "d" refers to dipole antennas. With dBi, a 5-dBi antenna, for instance, alters the spherical radiation pattern. Think of it as adding power to the radio transmitter.

For dBd, we relate it to a dipole antenna, which is 2.2 dB more powerful than an isotropic one. So, a 0-dBd antenna is equivalent to a 2.2-dBi antenna. The math is straightforward—add 2.2 to the dBd rating to get the dBi rating.

Remember, antennas are passive; they shape the signal sent by the powered radio. Higher-gain antennas can extend the range but narrow the beam width. It's crucial for wireless engineers to select the right antenna for specific needs.

Passive Gain

Passive gain refers to the redistribution of energy around an antenna without increasing the total emitted energy. It alters the distribution pattern without changing the overall energy output.

Active Gain

Active gain, on the other hand, is a type of gain attained through the use of an amplifier. It boosts the energy output without altering the coverage area's shape or characteristics

Happy Learning!!

12 - Channels and Bands

In wireless communication, the allocation of radio frequency (RF) bands and channels is vital to prevent interference and efficiently manage communication. When multiple devices share the same frequency, interference, and contention for access become concerns. Therefore, understanding frequency is crucial for practical RF management.

Frequency plays a dual role in interference mitigation and bandwidth allocation. Interference can occur when multiple devices transmit on the same frequency, leading to waveform collisions and the need for contention resolution. Additionally, frequency is tied to bandwidth, which can be expanded by using different channels. To increase available bandwidth, one approach is to deploy more access points using various channels. Alternatively, channel bonding combines channels to enhance throughput on a single channel.

In wireless communication, different frequencies are like valuable real estate, each represented by distinct channels. Imagine having three channels available. When you deploy an access point on one channel, it's as if that channel is "occupied real estate." In a scenario where you need more coverage and deploy multiple access points, you must ensure that each access point resides on an unused channel.

However, situations can arise where you need more access points than there are available channels. In such cases, you might have to share channels among access points. For instance, you could have two access points using the same channel, which can work if their coverage areas don't overlap significantly. Still, interference concerns arise, so it's essential to carefully manage power levels to minimize conflicts.

This concept of mapping channels to real estate helps us grasp the limitations and challenges of channel allocation in wireless networks. Sharing the same "real estate" (channel) with multiple "tenants" (access points) can lead to interference and performance issues.

Understanding the concept of dividing frequencies into channels begins with recognizing different bands or spectrums. These bands encompass a wide range of frequencies, which are further divided into specific channels.

In the context of Wi-Fi, there are three primary bands: the 2.4 gigahertz band, the 5 gigahertz band, and the newly introduced 6 gigahertz band (Wi-Fi 6E). Each band covers a range of frequencies. For instance, the 2.4 gigahertz band spans from 2,401 to 2,473 megahertz in the United States (with variations in other regions), while the 5 gigahertz band ranges from 5,150 to 5,895 megahertz.

Despite the apparent width of these bands, their usable spectrum is limited due to regulatory constraints. For example, the 2.4 gigahertz band offers only 72 megahertz of available space, and the 5 gigahertz band experiences gaps and restrictions within its range, making certain frequencies unsuitable for Wi-Fi.

Understanding the specifics of these frequency bands and their constraints is crucial for effective Wi-Fi channel selection and network planning.

The allocation of frequencies into channels is a fundamental concept in wireless networking. It's crucial to grasp as it influences the design and performance of Wi-Fi networks.

In the Wi-Fi landscape, we have three primary frequency bands: the 2.4 gigahertz (GHz) band, the 5 GHz band, and the 6 GHz band (Wi-Fi 6E). Each band covers a range of frequencies. For example, the 2.4 GHz band spans from 2,401 to 2,473 megahertz in the United States, though this may vary in other regions. The 5 GHz band ranges from 5,150 to 5,895 megahertz.

The 6 GHz band is considerably larger, starting at 5,945 megahertz and extending up to 7,125 megahertz, providing a spectrum width of 1,180 megahertz. Comparatively, the 5 GHz band offers a more extensive channel space than the 2.4 GHz band, and the 6 GHz band surpasses both by a significant margin.

The concept of channels comes into play as we subdivide these bands to facilitate Wi-Fi communication. Wi-Fi transmissions employ a range of frequencies, not just a single frequency. These channels employ technologies like Dynamic Frequency Selection (DFS) and Orthogonal Frequency Division Multiplexing (OFDM) to efficiently use a portion of the available spectrum. Depending on the band, channels are typically 20 or 22 megahertz wide.

For instance, in the 2.4 GHz band, there are typically three non-overlapping channels represented as distinct segments within the band. Understanding channels and their characteristics is essential for designing and optimizing Wi-Fi networks effectively.

In the context of channel allocation in the 2.4 gigahertz band, it's important to note that channels are typically 22 megahertz wide. These channels employ technologies like Orthogonal Frequency Division Multiplexing (OFDM) to transmit Wi-Fi signals efficiently.

Each channel is associated with a primary frequency, often referred to as the center frequency. For instance, in the 2.4 gigahertz band, channel 1 spans from 2,401 to 2,423 megahertz, with a center frequency of 2,412 megahertz.

However, in practice, not all available channels are non-overlapping. In this band, we commonly use channels 1, 6, and 11 as non-overlapping channels. This is because adjacent channels are typically separated by approximately 5 megahertz. Therefore, while channels like 2 and 8 exist, they overlap with other adjacent channels, making them unsuitable for use in scenarios where non-overlapping channels are essential to minimize interference. Understanding which channels are non-overlapping is critical for Wi-Fi network planning and design.

In wireless communications, we encounter the concept of channel overlap, which has implications for Wi-Fi network planning. Channels in the 2.4 gigahertz band, for example, are designed to overlap with one another. As we draw channels 3, 4, and 5, we see that they overlap with adjacent channels 1, 2, and 6.

To avoid interference and contention issues, it's crucial to select non-overlapping channels. In the 2.4 gigahertz spectrum, there are only three non-overlapping 22 megahertz channels, such as 1, 6, and 11. In contrast, the 5 gigahertz band provides more non-overlapping channels, with up to 25 in the United States, while the 6 gigahertz band offers even more options, with up to 59 channels.

These numbers can vary based on regional regulations and allowed Wi-Fi channels. Identifying non-overlapping channels and understanding how channel bonding impacts network design will be covered in more detail later in blogs. In essence, think of frequency as the real estate of wireless communications, and it's crucial to ensure that access points in the same area do not operate on the same channel to avoid interference.

In summary, to ensure effective Wi-Fi communication, it's essential to avoid interference and contention issues by selecting non-overlapping channels. Wi-Fi operates in three frequency bands: 2.4 gigahertz, 5 gigahertz, and 6 gigahertz, each subdivided into channels, which represent ranges of frequencies used for transmission.

Access points transmit data across a specific channel, which covers a frequency range. Channels in the same band can overlap, leading to interference. It's crucial for wireless engineers to choose non-overlapping channels whenever possible.

In the 2.4 gigahertz band, there are only three non-overlapping channels, whereas the 5 gigahertz band offers up to 25 non-overlapping channels (depending on regional regulations), and the 6 gigahertz band provides a generous 59 non-overlapping channels.

Selecting appropriate channels is a key aspect of optimizing Wi-Fi network performance and minimizing interference.

Happy Learning!!

11 - Noise Floor and SNR

When discussing wireless interference, it's important to consider the potential sources of disruption. This includes non-Wi-Fi devices as well as signals from distant origins that may have originally been Wi-Fi but have become unrecognizable by the time, they reach us.

These distant signals no longer adhere to our Wi-Fi protocol and essentially become part of the background noise. Understanding this concept is crucial because it's not just about clear communication between two parties: it's about maintaining communication clarity amidst surrounding noise.

Just as excessive ambient noise can make it challenging to hear someone speaking, the wireless environment can also be filled with interference. To overcome this, we use tools like the Signal-to-Noise Ratio (SNR) for analysis.

Background noise is omnipresent, both in the auditory and radio frequency realms. For instance, while writing this blog in my office, I hear the humming of my PC, the sound of the AC unit, and even kids in the background. However, most of this audio noise doesn't disrupt my conversation with my wife without her being bothered by the PC's hum.

In the wireless context, we also contend with a certain level of background RF noise originating from various sources, including natural ones.

We should also consider RF signals from various sources, including non-Wi-Fi traffic when discussing interference. However, this interference is typically in the background, originating from distant systems or Wi-Fi devices broadcasting from far away locations. By the time these signals reach our immediate vicinity, they become challenging for our wireless receivers to detect.

When addressing RF noise, we're concerned with signals that typically fall within the range of approximately negative 90 to negative 100 decibels in terms of the Received Signal Strength Indicator (RSSI). This range represents our noise floor, a critical factor to monitor.

To illustrate, imagine us standing at opposite ends of a ballroom, having a conversation without needing to raise our voices. The acoustics are favorable, and communication is clear. However, as more people join the room and engage in their own conversations, the noise level increases, making it progressively harder for us to hear each other.

Imagine a crowded ballroom where constant background conversations create a challenging environment for communication. In such a scenario, the odds of us effectively communicating from a distance are low. There are a couple of approaches we could take to overcome this situation.

One option is to raise our voices, essentially yelling or shouting at each other, which increases our power level. However, the more practical solution is for us to come closer together. As we move closer, our proximity decreases, allowing us to communicate more effectively once again.

In this illustration, we have two situations: one without noise and the other with noise. In the noise-free environment, our voices stand out as there is minimal background noise. However, even in a slightly noisy room with a distant AC system, the noise level remains low, not significantly affecting our conversation.

In contrast, when there's considerable noise in the room, speaking at the same level becomes challenging, as the noise level is high relative to our voices. The greater the noise level, the harder it is to bridge the communication gap. If the noise level surpasses our communication efforts, effective communication becomes nearly impossible.

This concept of comparing our signal to the background noise is crucial in both audio and radio frequency communication. It highlights the importance of the Signal-to-Noise Ratio (SNR), where we aim to speak above the noise floor. As mentioned, the Received Signal Strength Indicator plays a vital role in this context.

The Received Signal Strength Indicator (RSSI) measures the signal strength of wireless devices, often considered a quality signal, especially for non-real-time applications. A negative 67 dBm is typically the threshold for satisfactory performance.

However, Signal-to-Noise Ratio (SNR) is equally important. An RSSI of negative 67 dBm can represent two scenarios: one with minimal environmental noise and another with high noise levels relative to the signal strength. Companies like Aruba Networks, Cisco Systems, specializing in wireless and real-time applications, recommend a positive 25 decibel SNR for voice and video applications.

To understand this number, let's delve into some math. SNR involves dividing the signal by the noise, and since decibels are logarithmic, we manipulate the exponents. For example, dividing 10⁵ by 10³ becomes subtracting the exponents: 10^(5-3) equals 10², which is 100.

In the context of RSSI, negative 67 dBm is considered good, but assessing SNR is crucial for determining communication quality, especially in real-time applications.

To achieve a Signal-to-Noise Ratio (SNR) of 25 dB, we can simplify it into a subtraction problem. Starting with a signal strength of negative 67 dB, we need to subtract the noise level to reach 25 dB. Thus, 25 dB equals negative 67 minus noise, which leads us to find that the noise should be less than or equal to negative 92 dB relative to the signal.

In practical terms, if the RSSI is as low as negative 67 dB (our threshold), and the noise remains at negative 92 dB or lower, we maintain a 25 dB difference, which is favorable. However, if the noise worsens, such as reaching negative 88 dB, we'd require the RSSI to be no lower than negative 63 dB to maintain that 25 dB difference.

This emphasizes that while RSSI is essential, it's not the sole factor in signal quality determination. When noise levels rise significantly, alternative strategies like increasing transmission power or reducing the distance from the access point may be necessary to maintain an adequate SNR, especially for reliable voice-over wireless communication.

In wireless site surveys, considering both RSSI and SNR is crucial to establish signal strength thresholds for quality assessment, with SNR being a key takeaway for optimal wireless performance.

The Signal-to-Noise Ratio (SNR) is a crucial metric that considers both signal strength and background noise. SNR is a mathematical operation, typically a division of signal power by noise power in raw milliwatts. In the context of decibels, we can directly subtract signal strength from noise strength to calculate the SNR, which should always yield a positive decibel value. A negative SNR implies that the noise is higher than the signal, indicating poor signal quality.

When noise levels exceed the norm, it's essential to adjust our expectations for what constitutes a good Received Signal Strength Indicator (RSSI). For instance, an RSSI of negative 65 or even negative 62 may be excellent in a typical noise range of negative 90 to negative 100 dBm. However, if noise levels rise, such as reaching the negative 80s, we must reconsider our RSSI standards since they assume low noise thresholds.

Understanding SNR is vital for accurate wireless site surveys and determining whether a signal strength is adequate for various applications.

Happy Learning!!