Wi-Fi coverage and router placement⚓︎

If you use your Turris as a Wi-Fi access point you can read something about signal coverage and optimum router placement.

About Wi-Fi⚓︎

Wi-Fi (originally Wireless Fidelity) is a popular technology used for wireless networking. It can be used for accessing the Internet as well as for communication between devices in the same local network (computers, mobile phones, tablets, smart TV sets, smart home appliances…).

Wi-Fi is based on electromagnetic waves. These waves spread from their source (ie. a communicating device) to the space. Their intensity drops with distance (with its square; thus double distance means four times lower intensity) and are absorbed in matter.

For Wi-Fi communication, sufficient level of signal (ie. intensity of electromagnetic waves) has to be available. Lower levels cause lower transmission speed, lower reliability (transmitted packets are more likely damaged and must be retransmitted) and more frequent outages.

Transmission power of Wi-Fi is limited by regulatory rules. It is both due to health concerns and prevence of interference between different networks and other devices (because the same frequency range is used also for other purposes like Bluetooth, microwave ovens or some medical equipments).

It means that suitable placement of each Wi-Fi device is very important. And if your Turris acts as a Wi-Fi access point it applies even more for it.

Absorption in materials⚓︎

Different materials have different absorption rate. You should keep this in mind when you search for the optimum place for your router or another Wi-Fi device.

Some materials with heavy absorption⚓︎

• reinforced concrete (steel concrete); e.g. in carrying walls or floors
• steel lathing; e.g. on mortared wooden walls
• metal plates or metallized sheet covering; e.g. on roofs
• metallic lattices or shutters; e.g. at windows
• thick layer of stonework; e.g. in walls
• anti-sun glass or anti-sun foil; e.g. in windows
• soil; e.g. around cellars
• electronic devices; e.g. TV sets or audio systems

Some materials with medium absorption⚓︎

Various materials used in walls, floors, ceilings etc., for example:

• plain or areated concrete
• brick
• thick layer of wood
• thin layer of stonework

Some materials with light absorption⚓︎

• glass; e.g. in windows
• plasterboard/drywall; e.g. in thin walls
• thin layer of wood; e.g. in doors or furniture
• asphalt sheet covering; e.g. on roofs
• plastics; e.g. in furniture
• fabrics (both natural and artificial); e.g. in curtains
• papier-mâché or paper composites; e.g. in thin walls, doors or furniture

The above list is only illustrative. There are many and many materials and their absorption rate may differ according to their composition. Porous materials like bricks or wood can sponge up water and their absorption rate will rise.

Interference between devices⚓︎

All Wi-Fi and other devices which emit radio signal can mutually interfere. It applies especially on devices working on identical or near frequencies. This interference can lead to lower trasmission speed, outages or other problems.

Your router should be as far as possible from such devices and/or to a place where such signal sources are somewhat shielded e.g. by a wall. Another approach is to try different frequency channels.

Where to place your router⚓︎

There are several criterions which should be considered:

1. As lower distance to the farest point (where you want to use some Wi-Fi device) as possible. It usually means that the router should be placed near the center of your flat and on the middle level of your house.

2. As little of heavy (and medium) absorbating materials as possible. It’s often not easy but even so useful. For example, find a position where the signal can pass through wooden doors instead of thick stonework walls.

3. As far as possible from other devices emitting radio signals. See above for details.

4. Availability of the uplink. It depends whether you can/may modify the building (if it is necessary) or accept the uplink cable in bulk.

5. Avalability of electricity. It is similar to point no. 4. But if you have got a MOX there is possibility to add a PoE add-on and supply it over the uplink cable.

6. Omnia and MOX mPCIe Wi-Fi can cover much larger area than MOX SDIO Wi-Fi. If you have only the SDIO consider to buy the mPCIe add-on.

7. Your router should be avoided too high or too low temperatures (below 0 °C or 40 °F and over 40 °C or 104 °F) as well as direct sun. Because it produces some heat itself so fresh air should have free access to it.

How to measure signal⚓︎

If you try to find the best place for your router you can utilize measurement of the Wi-Fi signal. There are many tools but probably the most suitable for many situations is WiFi Analyzer.

WiFi Analyzer is a simple mobile application for Android which measures and visualizes signal levels and displays other useful Wi-Fi data. It can be installed from:

• F-Droid
• Google Play

The application is distributed under the GNU GPLv3.

You can install the application and move your mobile device to the places where you want to use Wi-Fi the most often. The measured values could be interpreted as follows:

• -50 dBm or more: excellent level
• -60 up to -50 dBm: good level, suitable for the most of work
• -70 up to -60 dBm: moderate level, suitable for regular work
• -80 up to -70 dBm: low level, sufficient only for unpretending use
• less than -80 dBm: mostly unusable

Keep in mind that different devices would have various levels of the signal, according to their antennas and Wi-Fi interfaces. Thus if one device works it needn’t mean that another device will work too.