The 802.11 radio frequency signal we usually discuss is propagated horizontally by an antenna on the floor of a building. However, when deploying a wireless network in a high-rise building, you need to consider that the propagation direction of radio frequency waves needs to be perpendicular to the ground, upward or downward. This vertical propagation is sufficient to penetrate the floors and ceilings of most buildings. Conducting on-site investigations on signal propagation between floors can be complex. Here are some relevant analyses for your reference:
Analyze signal transmission between floors
Firstly, you need to understand how 802.11 signals propagate within the floor facilities where wireless networks are deployed. The structure of each building is different, so you need to conduct some tests to determine how many floors will weaken RF signals. Reminder to everyone, when developing deployment plans, you should consider that the propagation of 2.4GHz and 5GHz signals is different. If you want to deploy 802.11n first and then consider detecting 2.4GHz and 5GHz frequencies, then before testing begins, you need to have a better understanding of the location of the testing access point for cross layer signal transmission.
Here are the specific steps to complete:
1. Evaluate the structure of the building. By walking, you can observe and understand the construction between floors, including the ceiling above. This may require consulting with the building manager. After understanding, you need to make some notes about the building's architecture, such as wood, cement, steel, etc., to determine the differences in the building structure of each area, because in a multi story building, you need to test each area.
2. Activate an access point. It is best to be in the center of the building, away from the exterior walls, so that you have enough space to observe the impact of signal propagation between floors. The most ideal situation is to set the access point in a location where there are floors above and below, such as the 2nd floor. What you need to do is provide power support for the access point and ensure that it is configured with the same frequency (2.4GHz or 5GHz) and transmit power. Regarding on-site investigation testing, you need to test the signal strength of the access point and mark its position on the building chart.
3. Test the signal propagation between floors. Its main purpose is to observe how access points propagate above and below. For example, by using building charts to test the signal strength of the floors above and below the access point. In most large buildings, there is generally not much difference in signal strength between the floors above and below the access point, so you need to detect higher or lower floors. Then move the access point and repeat the test, as the structure of the building can vary greatly in different areas.
4. Record the characteristics of cross layer propagation. Take some notes on cross layer propagation (above and below the access point), such as the propagation diameter of each testing area. It is important to consider the acceptable signal coverage at the lowest level and retain this information for on-site inspection by RF.
Tip: Some tools, such as AirMagnet Survey, have special features. It allows you to record the signal coverage range and applicable range map between floors, which is very beneficial, especially when conducting on-site testing between different floors of a large building.
Determine the location of the access point
If you find that the propagation signal between floors is very good, you can reduce the number of access points in some way to save necessary facility payment costs. For example, as shown in the diagram, AP-1 and AP-4 are installed on the 2nd floor, which can provide signals for the 2nd floor and also cover the 1st and 3rd floors. AP-2 is installed on the 3rd floor and AP-3 is installed on the 1st floor, both of which provide signal coverage for the 2nd floor, leaving some space between access points (such as AP-1 and AP-4) and reducing deployment costs.
Specify RF channel
When deploying wireless networks, you should alternate the use of RF signals to minimize interference between cross layer access points. However, it is very difficult to limit three non overlapping channels in the 2.4GHz frequency band, and sometimes you cannot minimize the interference between cross layer access points in high-rise buildings, especially those that support high-capacity voice systems. Therefore, you should migrate to the 5GHz frequency band of the 802.11n standard as soon as possible. The 5GHz spectrum includes a large number of non overlapping channels, which greatly reduces the problem of channel reuse and also improves network performance.