You generally wouldn’t compare Wi-Fi bands to lawn sprinklers, but that’s precisely what Keith Parsons, one of the world’s top authorities on all things Wi-Fi, does in this webinar Comparing the 2.4GHz, 5GHz, and 6GHz Bands. The founder of WLAN Pros acknowledges this isn’t a perfect analogy, but it breaks things down in a way that’s easy to understood.
The “junk band,” 2.4GHz, is a small sliver on a frequency chart containing many things that cause issues. It was unused for a long time. It can be used it for Wi-Fi, ZigBee, and Bluetooth, with “sliced” frequency based on usage – but all share the same frequency. The throughput is lower where there is overlap.
The 3.5GHz set of frequencies is common in Wi-Fi for private LTE and CBRS and most mobile phones.
The 5GHz frequency uses much more spectrum. Like all frequencies used, each channel has a center frequency, and expanded out, it yields slightly less coverage because the frequency is physically smaller: a greater loss than 2.4GHZ over the same distance.
The 6GHz frequency is 1200 MHz wide. The spectrum is wide, but it thins out toward the end, resulting in loss of free space.
Even though these frequencies have their differences, they all follow the same curve, and the differential between 2.4GHz, 5Ghz, and 6GHz is constant across the board. If one drops, the others drop with it. The 6GHz band would drop slightly less, but it still follows the same curve.
When comparing Wi-Fi frequencies, the size matters in how to design, troubleshoot, and deal with the operation. The size of the 2.4GHz wavelength is longer than 5GHz, and the 6GHz is slightly smaller.
Measuring is fairly simple knowing the speed of light is fixed; it’s a constant. The wavelength size determines the antenna size. The frequency – in this case, 2.412 – is the specific frequency on the bottom channel. Calculating the size shows the RF wave is physically as long. A quarter wave can be created with antennas. The 4.9 turns into 1.21, and that's the size of any antenna that can hear this frequency.
RF isn’t water, and it doesn’t come out in droplets, but it’s an apt analogy to describe this scenario. The sprinklers are the antennas.
Sprinklers move back and forth or spray in patterns or in a circle, equivalent to an omni antenna. When watering a lawn, the flow is directed in one spot, but the water doesn’t go anywhere else. Turning up the water pressure makes the water go farther and spread out, but it won’t yield more water.
The SNR should be what is yielded, but sometimes Wi-Fi is simply a mass of APs – lots of water, in this analogy. It's not just the water – a specific type of it is needed. For example, several sprinklers each have its own color of water but only the red is required. The analogy falls apart because Wi-Fi doesn't work this way.
Just like sprinklers, all antennas aren't created equally. One antenna may contain 10 dB in EIRP but lose a little bit of energy. Another may have 10 dB and yield more than 10 dB, because that antenna is focused like a sprinkler.
Inefficiently designed antennas won’t meet the requirements, but those designed with effectiveness in mind will achieve the desired results. If water spurting everywhere is not the desired outcome, there is wasted water and energy.
Receive aperture is what makes 2.4GHz, 5GHz, and 6GGz different from each other. Imagine circles with rims, as the image below suggests.
The rim of each circle shows the difference between the low and high ends. The 3.5GHz has a slight band because it's not very big. In 5GHz, there is more space – a bigger band. The 6GHz has an even bigger band because the difference between the low and high ends of the 6GHz is fairly significant.
In a 2.4GHz antenna spraying 2.4GHz of water, the 2.4GHz circle in the image above represents the size of the rain cup catching the water. In contrast, the 5GHz circle represents the amount of water caught off 5GHz.
It’s important to discuss antenna aperture. Some falsely believe the 5GHz doesn't go as far as the 2.4GHz. If a 2.4GHz and a 5GHz radio each broadcast at the same time aiming toward the moon, each would hit at the exact same time and distance with the exact same of water. The difference would be that on the moon, the 5GHz would have less water because it has a smaller receive aperture. When designing a 2.4GHz versus a 5GHz, the easiest solution is to transmit less on 2.4GHz or transmit more on 5GHz. The 5GHz client receives the same amount of water as the 2.4GHz because it pushes out more.
A half-inch diameter pipe, a five-eighths inch, or a three-quarter inch pipe can be used to fill a 55-gallon drum. It takes less time to fill using the larger diameter pipe, but this is not pressure; this is water flow. With a lack of flow control in most antennas, when sending random signals, it’s like turning up the water pressure and covering more neighbors’ lawns, but not the desired one. There is a difference between a directional antenna and a receive aperture and no flow control with RF, just the pressure, which will indicate the distance it travels.
Sprinklers are available at different price points. A $10 plastic sprinkler with a quick disconnect can send water in a circle. One without a quick disconnect and attached durable brass pipe will operate in the same way but at six times the cost.
Both sprinklers do the same thing – they send water in a circle. The more expensive one sends water in a much bigger circle, it can handle a lot more pressure, and it's made of quality materials. When installing APs, something durable and more costly is preferable. Use high-quality antennas and APs for an efficient result – the water travels where it needs to. In other words, the clients receive their fill of SNR.
How do professionals obtain higher data rates and SNR? They capture more; 5GHz and 6GHz require extra. There are specific rules for 5GHz and 6GHz. In 5GHz, 20 doubles; twice as much noise is created and transmitted over a wider channel, and it’s received on a wider channel.
The SNR drops by 3dB – not because the sound changed, but because of noise increase. The FCC allows doubling the size of the channel so as not to lose the extra 3dB.
The increase in noise is offset with the transmit power so the clients still receive that amount. Having 6GHz allows transmission and maintenance of the energy received. The amount of water hit on the 6GHz is unchanged.
The FCC implemented a rule saying clients must be 6dB down from the AP’s max. So when clients talk back to the AP, they are going to be throttled and won’t have the same distance. This means APs can talk down to clients, but clients will always be throttled at 6dB lower. The design circles, therefore, have to be smaller – not because the APs can't hear the clients, but because clients can't transmit the same return power.
Remember, you can’t see or hear Wi-Fi, but 7SIGNAL can. Contact 7SIGNAL to learn more about our wireless experience monitoring platform and to get help with frequency size when designing, troubleshooting, and dealing with Wi-Fi.
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