Wifi networks: Are you immune to RF Fields exposure ? (part 2)
Today’s world is mobile and most of our modern devices are permanently linked to the Internet by the use of radio waves.
Since we receive sometimes alarming messages about the consequences of being exposed to RF fields from Wifi or mobile base stations, you may wonder how to behave when you are potentially subject to such emissions, and whether or not there are some preventive actions you could consider.
In part I of this article, we went quickly through a few current health considerations and in summary, we discovered as of today, there aren’t any risk evidence or definitive studies about the body exposure to RF fields.
The next step:
If the health experts cannot give us any clear guidance, what can we do?
The goal of this article is to provide you a minimum amount of knowledge about the way the WiFi devices work and spread radio waves, so you can take some actions against unnecessary exposure, or even choose a more appropriate equipment.
As you will see, RF fields are really a weird science for human beings, so most of our day to day experience won’t help, unless we invest some time to understand how it works.
As for the ultraviolet emissions (think about the sun beam), we can mainly influence two parameters :
- the power level of the emission (indirectly, the amount of energy finally hitting us),
- and the exposure duration.
Show me the main RF source!
Let’s start with the transmission power topic.
Switzerland follows the ETSI regulation (refer to www.etsi.org), which is enforced all over European countries. One important part of the enforcement is related to the transmission power, either to protect other radio equipments (think about radars) or human beings.
Most of wifi devices have omnidirectional antennas, and that type of antenna spreads the RF energy in all directions like if the transmitter was in a middle of a sphere. If you move away from the transmitter, the sphere gets bigger, and you receive only a small amount of the initial RF signal.
Rule 2: RF energy decreases very quickly based on the distance from the source
Experiments show that in a closed environment, like a building for example, even without any obstacle, the RF power is divided by ten if you double the distance from the source! Walls, glass walls have a significant mitigation effect, so the signal will be even weaker if the transmitter isn’t in line of sight.
So, can we rule that it should be enough to stay away from any wifi access-point ?
It depends … To understand why, we need to understand the second rule.
Rule 3: all WiFi devices shall respect the same transmission limits,
whatever type they belong to: mobile devices, fixed devices, access-points, WiFi routers, (or even radio wave ovens).
All wifi devices are equal in regard to the RF emissions. The access-point is the conductor in the WiFi cell (the area where all WiFi devices share the same radio frequency band – or channel) and it has a few prerogatives, however, it is not allowed to use higher transmission power than the other end-devices.
When one access-point is part of an enterprise deployment, it will most likely lower the transmission power, because such a deployment usually supposes a global wifi coverage, and the AP tends to avoid interferences with its neighbours.
On the client side, this is a total mess! None of them will exceed the local regulation limit, however, you may have some of them using the maximum transmission levels, while others (often mobile devices) trying to save the battery and using lower values. It’s totally dependant on the vendor, the device firmware revision, etc…
In addition to the access-point, and the clients, you have also other sources than WIFI devices sending radio signals in the same frequency band ; from the WIFI perspective, they are considered as interferences, and sum up with the WIFI traffic (you have a few examples given on Apple support page here: Potential sources of Wi-Fi and Bluetooth interference)
In conclusion, my Rule 3 states that there are a lot of devices in our hands, in our pockets or around us in the office or at home which usually generate as much (or sometimes, even more) RF signals than the access-point you see a few meters away, usually with that suspicious blinking LED you don’t like at all.
Now, I assume you are not totally convinced about my Rule 3, because your personal experience is that most of the time, your WiFi router, or the corporate WiFi access-point is much bigger than your own mobile WiFi end point. Why should we have such a big and intrusive device on the wall or on the ceiling if it isn’t more powerful than a smaller, much discreet WiFi client you can put in your pocket?
It is more performant (usually, there is a huge difference), but the benefit is seen on the sensitivity side (i.e. the reception), or on the quality of the emission (more antenna elements, with a better signal pattern), since the regulation limits the maximum power value anyway.
Based on Rule 2 and 3, we should take care about the closest active WIFI device, and not worry particularly about the size or the aspect of it!
A WIFI device transmits radio frames only when needed, and remains silent otherwise.
The access-point needs to advertise its presence, so there is a small amount of traffic generated for that purpose, otherwise the transmission is totally dependant:
- on the amount of data sent over the channel,
- on the signal quality, because a lower signal quality means disturbances and the need for retransmissions, so that increases the traffic overall.
Each WIFI client negotiates the fastest possible connection with the access-point, based on the access-point signal and the RF noise levels, and that speed can evolve easily in a range of 100 (from the lowest to the highest values).
And most often, the highest speed is reached when remaining very close to the access-point.
That means your device may take 100 times longer to receive a web page when remaining away from the access-point than if you were close to it.
Now the most disturbing fact: if your phone transmits data (an image for example, the conversation during a web call, or all the small frames you have to send also when acknowledging the data you receive), it will take 100 times longer to do it if you are far away from the access-point compared to a situation where you are close to it.
During all that time you device transmits WIFI signals very close to you, so you are much more exposed to RF energy by your own device when you are far away from the access-point than if you come closer to it!
That leads to the most important rule :
Rule 1: most RF or WiFi rules are counter-intuitive to human beings.
Don’t forget about this one, because you can refer to it again and again.
We have covered the emission levels, the sources, and the amount of radio energy we receive in various scenarii. So, in the next and latest article, we will propose a few possible recommendations we can follow to limit the WIFI exposure.Tags: