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This article is reproduced from the official account of Wechat, "those things about Wireless CCIE" (ID:passcciew). By Xie Qing.

The location and method of wireless access point deployment cannot be compromised.

As mentioned earlier, achieving high-quality coverage requires professional RF knowledge, which you may not be proficient in, and a network engineer may not know about RF. But it doesn't matter, while studying hard, some general guidelines can help you achieve good and consistent signal coverage for common deployment scenarios. The most important of these is the reasonable location and method of deploying wireless access points.

When it comes to the location and method of deploying wireless access points, many people mistakenly think that it is very simple, but there is a lot of knowledge in it. The location and method of deploying a wireless access point looks "simple" (in fact, it is also very simple. You just have to follow one important principle: let the electromagnetic and radio frequency signals of communication between the wireless access point and the client reach each other easily). However, in practice, you will encounter a variety of scenarios, horizontal installation or vertical installation? Is it installed above the ceiling, under the ceiling or directly on the table? Do you use an internal omni-directional antenna or an external omni-directional antenna or directional antenna? These problems have been bothering many people.

Here are some basic principles you need to know that can help you avoid making low-level mistakes:

1. The wireless access point should be installed horizontally and securely so that it does not wobble or move. The following figure shows the wrong installation and deployment method:

two。 Wireless access points should be deployed away from metal objects, and radio frequency signals will have a strong reflection effect when they encounter metal just like light meets a mirror, especially when the main lobe signal meets metal as soon as it is emitted from the wireless access point. the strong reflection will greatly counteract the normal signal.

In the deployment above, the wireless access point is surrounded by a variety of metal objects, air conditioning pipes, metal bridges, and fluorescent lights, all of which strongly reflect the main lobe of the wireless signal and eventually affect normal signal coverage.

The common metals in deployment environment are: metal ceiling, anti-theft door, pipe, protective net and so on. In particular, do not deploy wireless access points behind metal cages. In addition, many lightweight walls are metal mesh keels, which will also have a negative effect on the transmission of wireless network signals. The following installation pictures are incorrect locations and methods of deployment.

3. Wireless access points should not be deployed too high (especially those with built-in antennas at a height of more than 4 meters). For example, the wireless access points in the following figure are deployed too high and surrounded by metal objects.

The right thing to do is to deploy the wireless access point below the obstacle, at least 1 meter away (according to the Fresnel zone principle). For example, the deployment location of the wireless access point can be lowered through the boom.

If the above picture is not so obvious, please look at the following figure:

Here is a more "obvious" one:

Although it may seem a bit "excessive", the principle is similar. Another reason not to deploy wireless access points with built-in antennas too high is the "black under the light" effect. When deploying wireless access points on a large scale, considering the cost of configuration and maintenance, it is often necessary to enable automatic radio frequency management. If the location of wireless access points is too high, the transmission power between wireless access points will be reduced in order to reduce co-channel interference. At this point, the downward signal propagation of the wireless access point will be affected by the signal weakening. At this time, even if the client directly below the wireless access point receives a weak signal from the wireless access point, it is not conducive to the efficient communication between the two.

4. Cisco recommends that wireless access points be deployed horizontally (antennas are typically vertically polarized).

Since the antennas of Cisco wireless access points are generally vertically polarized, it is recommended that the installation method be level with the ground in order to provide consistent signal coverage.

But sometimes you will see the installation shown in the following figure:

This approach is not recommended. First of all, its signal coverage and consistency cannot be guaranteed. The following site survey heat map is a coverage comparison of the two deployment methods in the same environment:

Secondly, the installation of walls perpendicular to the ground in a multi-floor office environment is not conducive to the formation of consistent signal coverage, especially on the signals of the upper and lower adjacent floors. Most of the wireless access points you often see "jump" between multiple floors are caused by this installation method.

In some deployment scenarios, the wireless access point cannot be deployed on the ceiling and needs to be installed on the wall. for the wireless access point with a dipole external antenna, the direction of the antenna should be adjusted (left below). Or you can use some third-party installation accessories to achieve the correct installation (bottom right):

5. Choose the correct antenna and use the same type of antenna to keep the main lobe coverage of the antenna consistent.

If you choose a wireless access point with an external antenna during deployment, remember to use the same type of antenna and keep the main lobe coverage of the antenna consistent. Here is the incorrect way to deploy:

Dipole antennas with different types of gain are configured:

Mixed use of omnidirectional and directional antennas:

The target coverage area of the external dipole antenna is inconsistent:

It may seem regular, but with the same mistake, the target coverage area of the external dipole antenna is inconsistent:

6. The distance between the wireless access points is greater than 3 meters (10 feet), even if they operate on different channels.

Even if the wireless access point does not work in the same channel, but if the deployment distance is too close (less than 3 meters), it will also cause electromagnetic interference and affect the signal coverage. The following figure shows the wrong way to deploy:

7. Environmental factors should be considered when outdoor wireless access points are deployed outdoors.

When deploying wireless access points outdoors, in addition to dustproof and waterproof, other factors need to be considered, such as whether the dead weight of the equipment will cause installation instability. Will the wind affect the installation of the equipment?

A common misunderstanding is that the outdoor wireless access point is waterproof, so when installing carelessly, remember to apply waterproof cement and wrap it with waterproof tape at the seams of all devices connected to the wireless access point, such as antennas.

Also, do not deploy indoor wireless access points to the outside.

The indoor wireless access point with suitable working temperature can be deployed in the outdoor environment by using the protective box, but the location and mode of deployment should also be considered.

A flexible grasp of the above principles can help you achieve good and consistent signal coverage in a typical deployment scenario. There are also a few typical questions to be answered here.

Should I choose an internal antenna wireless access point or an external antenna wireless access point?

It can be said that 90% of installation and deployment scenarios use built-in antenna wireless access points to provide coverage. For example, the office space in the most common carpet environment. Some special scenarios require the use of external antennas (usually directional antennas) wireless access points, such as high lobby, storage environment, production workshop and so on.

Users have very high requirements for the beauty of the installation, how to ensure it? The installation and deployment is beautiful and the signal quality is good? The two are not contradictory. Sometimes the best installation location is not the most suitable installation location, which requires compromise and persistence, and sometimes the location that seems impossible to install can also achieve reasonable installation and provide good signal coverage through your creativity.

For example:

Can you see that the wireless access point is in the light?

Install the wireless access point above the ceiling and secure the antenna below the ceiling.

Install wireless access points in the pendant of the mall!

Install wireless access points and antennas under the office floor!

Can only say, there is no impossible, only unexpected! Use your ingenuity! Remember that in any case, you have to go through the site survey and verification before you can be finally confirmed!

Finally, a question that people often ask: how far does your wireless access point (or antenna) cover?

Well, to answer this seemingly simple question, you need to determine two important prerequisites: what is your target client? What is the bandwidth requirement of your application?

Why do you need to confirm these two premises? for example, your wireless access point and wireless client can establish the data rate of 1Mbps at a distance of 100m, but it can not meet the needs of your application.

These two premises determine what kind of reception sensitivity you use when calculating the coverage (different wireless clients have different reception sensitivities when establishing different data connection rates). What kind of client transmit power and antenna gain (wireless access point reception sensitivity, transmission power, antenna gain information is often easy to get) participate in the calculation.

First of all, we need to evaluate the transmission loss of the wireless signal in the medium. We can use the free space propagation model of google or baidu wireless to calculate the transmission loss at a given frequency (different channel frequencies) and distance, and then subtract the wireless access point transmission power, antenna gain and wireless client antenna gain to match the reception sensitivity of the wireless client at different data connection rates. And come to a general conclusion.

There are many variables here that will affect the final result: radio transmission in free space is an ideal model, and there will be many variables in real deployment. If you want to study further, you can refer to the IEEE or ITU documentation. In addition, in the real deployment, the transmission power of wireless access points and wireless clients is not constant.

Therefore, we will not provide a "coverage" value that is full of variables and different results for different users, in case you are misled. As mentioned earlier, the current WLAN has evolved from the one-sided pursuit of connection and coverage to the stage of high-capacity access. At this time, the number of wireless access points deployed in a given area is much denser than simply pursuing signal coverage. a practical experience is that the distance between wireless access points should not be less than 10 meters, and it is more appropriate to be about 15-20 meters. At this time, the wireless client can basically establish a high data connection rate between the wireless access point and the wireless access point.

Finally, I'd like to recommend an interesting website (https://badfi.com/), where you can see all kinds of interesting ways to deploy wireless access points, and take a warning from the wrong deployment methods in fun.

The previous review:

(1) adhering to correct planning and design is the first step towards successful deployment.

(2) pay attention to key performance indicators (part I)

(3) pay attention to the key performance indicators (part two)

(4) the best guarantee of 5GHz spectrum, and the best effort of 2.4GHz spectrum.

(5) any design plan that ignores client capabilities will fail in deployment!

(6) correctly understand the function of 802.11ac.

(7) it is not easy to achieve high quality wireless coverage.

(8) the location and method of wireless access point deployment should not be compromised.

(9) We should both talk on paper and keep our feet on the ground.

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