It even makes sense to start with minimum power and increase it until the necessary area is covered.
0. Wi-Fi is about sharing, not competing
In a congested environment it doesn’t matter if your access point is stronger than the neighbor’s. If your AP can receive other APs then it will share the air time with them by taking turns. All APs on the same channel will give other APs equal access to the spectrum. This is how 802.11 was written.
[Edit: I added this point as an afterthought, since this isn’t obvious to many users.]
1. Full power doesn’t increase coverage
Mobile devices like phones and tablets have very limited batteries. To minimize power consumption their radios typically max at 15mW (12dBm), while access points max at 100mW (20dBm) on 2.4GHz and 200mW (23dBm) on 5GHz. However, WiFi connection is always bidirectional. It does no good if the client can receive the AP if the AP can’t receive the client. Have you ever been unable to connect – even though you appear to have good signal? This is the reason.
The bidirectional connection is symmetrical. It doesn’t matter if the AP has a better antenna or is located higher up. The antenna gain and any attenuation factors work symmetrically in both directions. So a good antenna and good location will improve the connection in both directions. Unilateral transmit power increase will only work in one direction.
2. Roaming
In WiFi the client devices decide which access point they want to associate with and when to switch to next. (This is contrary to the mobile telephone network, where access points decide which one will serve which client.) Many devices are very reluctant to roam to another AP. They hold on to the first chosen one even when there is a much stronger AP next to the device. Only when the connection breaks will they associate with the next AP – and keep that connection to the end. This results in clients using far away access points with poor connections. By lowering the transmit power the connection will break sooner and the client will roam to a better access point.
This behaviour affects access point utilisation as well. In the worst scenario the access point by the entrance covers the entire office just barely. When users arrive their devices will associate with the entrance AP and keep using it for the rest of the day. The entrance AP is overloaded while other APs are idle.
3. Battery life
The access point informs the clients what its transmit power is (802.11h TPC, 802.11k TPC or Cisco DTPC). Mobile devices will adjust their transmit power level to match to save battery. The logic is that if the mobile device can receive the AP at that power level, the same applies in reverse as the symmetry was explained earlier. By setting the AP transmit power to 5mW (7dBm) for example, you can increase the battery life of the clients. Such a weak signal won’t penetrate walls, so you need more access points – see the next section Performance…
4. Performance
Back then access points were expensive and they were placed far apart. Now the price is no longer an issue, but WiFi performance is. By adding more access points there will be less clients per AP, hence more bandwidth per client.
Keep in mind that wires are always more efficient than radio waves. The faster and closer you can move the data from radio to wires, the better. That’s why increasing the number of low-powered access points is the key to a high performance WiFi network. Why low-power? See the next section Interference…
5. Interference
A powerful signal will interfere with neighbouring devices even if they are on different channels (frequencies). At high signal levels the whole device will act as an antenna and induction will cause superfluous signals in the circuits. This is why you need to keep access points at least 10′ (3m) apart or have a thick concrete wall in-between, preferably both.
Access points can still interfere with each other, even if there is enough distance. The WiFi channels are not absolute. While the transmission is on a certain channel, the signal bleeds to the neighbouring channels as well, albeit weaker. At high transmit power this weak signal will be strong enough to interfere.
6. Distortion
If you drive an amplifier at full power the output will distort. This is easy to test with a car radio: turn it on full blast and try to make sense of the lyrics. A distorted signal is hard to decode and in WiFi parlance this means transmission errors and retransmissions, which will slow down the network. You can increase performance by lowering the transmit power.
7. Neighbourliness
A strong signal will cause interference in a large area. Even though the extra milliwatts won’t benefit you, they will consume limited air time and interfere with all other WiFi networks in the area (look back at point 0 at the beginning of the article).
Think about it security wise as well: Why should anyone across the street be able to receive your WiFi signal?
8. Longer lifetime
Lower transmit power equals lower energy consumption equals less heat. Operating at lower temperature increases equipment lifetime. While access points are inexpensive, they tend to break at the most inconvenient time and place. You won’t notice the energy savings on your electricity bill, though.
Great post. Learnt a lot and remembered some almost truly forgotten and valuable and important information.
Thanks metis.
AlienC
Is this forum still active?
This is not a forum exactly, but a collection of articles with commenting enabled. The latest comments on this article are from May, which is IMO quite impressive since I wrote the article four years ago. It has aged well and is still relevant.
Your comments are appropriate for congested apartment blocks, but the unavoidable fact is that the 802.11 standard was cursed from the start with inadequate transmit power, with difficulty getting getting through a few interior walls. There is no end to articles online extolling the virtues of low WiFi transmit power, but that doesn’t cut it when the router can’t provide a reliable connection 50 or 60 feet away.
Since upgrading to a new router with 1 watt of transmit power, all my 2.4 GHz range problems are over. My neighbors are not close enough to care one way or the other. My devices all connect immediately with flawless high speed bidirectional communication. Everywhere, with a single access point and no messy handoffs.
Yes, upgrading to a full watt of transmit power at the AP will increase coverage, I agree. How did you achieve flawless high speed bidirectional communication, though? How did you increase the coverage of your cell phone? If the AP can’t receive the client device through the walls, there is no link.
Very helpfull. Thank you.
You are welcome!
As your points, number 3 and 8, reducing the transmit power will increase the battery lifetime. Will you explain this with a numerical example?
Power is the product of current and voltage (Watt=Ampere*Volt). The operating voltage is (close to) constant, so reducing the transmit power by 3dB (=halving it) will reduce the current by half. Battery capacity is the product of current and time (Ampere*hour). Halving the current will double the time (=battery life). Of course the mobile device will also use power for other purposes than WiFi radio, so the total battery life will not double. Battery lifetime extension is not the reason to reduce the tx power, but rather a by product – a pleasant one!
Thank you for explaining in a very clear way.
Um, you are AWESOME!!!
I van’t believe how much I just learned reading your posts!
Thank you!
You are welcome! 😁
This is really helpful. I’m hoping it helps with my network. I live in an apartment with lots of wifi signals in the building causing a lot of interference, and my connection drops frequently. I’ve been trying to figure out how to fix it. I’ve tried optimizing for channel interference, but that hasn’t helped, I think, because every channel is being used by several SSIDs on my floor and neighboring floors.
The router I have is a modem + router with 5ghz and 2.4ghz. Should I lower the radio power on both 5ghz and 2.4ghz? The options are 100%, 70%, 50%, 35%, 15%. Any recommendations on what to go with or just experiment? Thanks!
If you have an Android phone then you should install Wifi Analyzer. It will show you the neighboring networks and which channels they use. If a neighboring network is visible then your access point will share the air time with it. 802.11 is based on sharing, not competing. It doesn’t matter if your AP is stronger, it will yield to the other AP as long as it can receive it. Too bad Wifi Analyzer can’t show the utilization of the networks. You can share a channel with many low activity networks while a single high traffic network can gobble up most of the air time.
In your case I’d look at the environment. Most probably you’ll find the 2.4GHz very congested and in that case I would disable it on my router and use only 5GHz. 5GHz doesn’t penetrate walls as well so you need to check if you have the coverage. Increasing power doesn’t help because phones and laptops have very low transmit power. To match the mobile devices the 15% should be enough, don’t go above 35%. If all your neighbors would also turn down their transmitters we wouldn’t have any congestion problem at all, would we.
Look at the channels on 5GHz. Quite often the Auto setting will pick a channel in the 36–48 or 36–64 range only. The upper channels (100+) are often vacant or at least not so congested. Which channels are available depends on your local regulations. If you can’t get the coverage on 5GHz then you should consider adding another AP. It can be any brand or model. As long as the network name and security settings are identical you can use them as a single network. It could be that your problems are caused by poor coverage in the first place anyways.
Start at the lowest option and increase power as needed to find the optimal coverage for your apartment.
Exactly! This could be the TL;DR summary for the whole post.
You are amazing! I was trying to research on this and you have answered what I am really pondering about. Thank you.
You almost say it, but not quite: We could all get better performance if our neighbours did the same. Technically proficient (and diplomatic) folk could help those next door to do this.
Or some really clever guy could write software that optimises everyone’s router power, then sell it to all the broadband suppliers. A win for everyone!
No, it wouldn’t work. Everyone wants to have “full power” and all bars coverage. Just the same as car engines, so many horses under the hood with little practical value.
“Or some really clever guy…”
Huh?
I don’t get the joke here?
yes!
WHAT IS THE NAME OF YOUR ROUTER?
Am using 50% and it seams more than good
-50% is only a 3dB decrease. -75% would be a 6dB decrease. That’s why I dislike percentages. Nobody wants to set their power to 10% even though it only equals 10dB decrease.
Next question is: What is the original power level? If it is 200mW for 5GHz, then 10% is 20mW, which is still plenty for most devices. Cell phones and tablets typically max out at 15mW.
how do i get more clients to use 5ghz , I run a meraki dual band with 2.4ghz power set at 6-12 minimum bit rate 12 and 5ghz set at 15-24 minium bitrate 24
I want to optimize for best wifi calling experience
I’m not familiar with Merakis, but can’t you lower the power even more? I would like to turn off 2.4 altogether.
If my customer insists on having a 2.4GHz network, I usually name it like CompanySlow. That way the users can always see which network they are connected to. If somebody complains, I just ask which network they are connected and explain: “There is a hint in the name..”
This has been awesome!! I’m having challenges with roaming while using Wi-Fi calling. My AP’s are all at full power. I feel that if I bring them down just a fraction that it may improve the “handoff” between AP’s and perhaps the overall utilization. I’m going to put the suggestions in your 8 steps into practice!!
I always suggest you start with the lowest power setting. If you find coverage holes then think which AP you should turn up a notch to fill the hole. Using the least amount of RF power is good design.
Thanks!
“Using the least amount of RF power is good design.” What a wonderful world this would be if more people understood this.
Great post! I work for a retail store in Canada and many of our stores have issues with their wifi. When i use a wifi analyser I can see how badly saturated the waves are. Every store in the mall has a wifi, I can see dozens of them. I was thinking of replacing the access point with a more powerful antenna but I think putting multiple wifis and lowering their power might be a better solution.
Let me know what you think.
The best solution would be to get all stores (or at least your neighbors) to reduce their transmit power. If there is a suitable forum you should open discussion by asking how they feel their Wi-Fi networks perform.
Multiple access points may be difficult to set up if all the channels are saturated. I usually suggest turning 2.4GHz off altogether so none of your users will ever connect to it by accident. Using the higher channels on 5GHz might be a solution to a working Wi-Fi. Malls and especially food courts are difficult environments.
Thank you. This was a great article!
9: Security… Reducing power means hackers need to be physically closer to your access point making it harder to attack your wifi network from outside the building.
So true. I did mention it as a side note to #7.
Thats totally incorrect, having less power, it increases the chances of a man in the middle attack, since hacker would be able to set a rouge ap, and clients would try to connect to it, sending wifi passwords to the rouge ap granting the hacker the information it needs to access the target wifi
I’m sorry but you are completely wrong. You can’t fight rogue APs by increasing tx power. I believe you are referring to an evil twin, which is a malicious kind of a rogue AP.
First of all, evil twins don’t know the pre-shared key, so they can’t offer WPA/WPA2 to begin with. In WPA/WPA2 the key is not transferred (or revealed to the evil twin) but the client just proves it knows the secret. Since the evil twin doesn’t know the key it can’t verify the client’s key. Typically evil twins offer the same SSID with open authentication since some clients will happily just connect if the SSID is familiar. Then the evil twin can access the data flow from and to the client (a.k.a. man-in-the-middle). But it won’t learn the Wi-Fi password. This of course requires that the evil twin is connected to the wired network so the clients can communicate over it.
I’m no networking expert but based on basic hacking principles I would assume Jose is right. Just because you think you have some amazingly secure key, doesn’t mean I can’t compromise that via a range of other methods and then exploit the weak signal by doing a man in the middle attack to compromise further data that I wouldn’t be able to automatically compromise if the signal were stronger. Don’t act like your key creates perfect security and that all further layers of security are irrelevant.
Jose’s idea of overpowering the evil twin is flawed. Wi-Fi devices will take turns, they won’t transmit on top of each other. You can’t “exploit” a weak signal. As long as the signal is decodable it is as good as a strong signal.
Yes, multiple layers of security is a good idea. If you want to use transmit power as a security feature, reduce the power as this will make your signal more difficult to decode. See point #7.
Yes. But how do i reduce power on lumia windows phone im asking, huh? Tell me people if you’re so smart.
You can’t control the transmit power on client devices, the article is about access points.
However, if you turn down the transmit power on access points, client devices will turn down theirs to match. Access points announce the power they are using and since the device is receiving the AP it can trust the same power suffices to reach the AP. This is known as Transmit Power Control or TPC.
You showed great restraint. Well done.
Yes, agreed. It’s great to keep these discussions on a higher consciousness level, even though some forget that.
Nice pro-answer Petri !
*
I would like to find a helpful site to show how to turn down these power levels.
I also use: http://www.FLFE.net to harmonize the EMF’s emitted from wifi’s to calm down the emf-intensity.
Thanks, Don.
Do the Google WiFi access points use the electrical wiring in the building to transmit signals? Do the Google WiFi access points adjust their power automatically as needed? Are access points always on or do they sleep when there are no requests for transmission? I’m wondering if mesh systems used with cable modems actually reduce RF in my home by being more efficient on each exchange. Thank You
1) No, Google Wifi uses wireless connections known as mesh. Read this if you want to learn more about meshing.
2) I am not familiar with them, but they probably will use as much power as they can. There can always be some client trying to connect at the edge of the coverage. They may adjust power according to their reception of each other.
3) Access points are always on since they can’t predict when some client will want to transmit or connect. They will transmit a beacon ten times every second for example.
4) If you want to reduce RF noise in your home then you should wire the access points and all stationary devices (printers, desktop computers etc.)
Thank you!
Does it make sense to set the power for 2.4Hz low, while keeping the 5Ghz at High, to have as many clients select the 5Ghz band as possible?
Yes – and it is the recommended way to do band steering. Theoretically 6dB difference will make the signals equally strong and most devices will choose 5GHz over 2.4GHz in that case. Make it 7dB and you are on the winning side.
Band steering is also better accomplished by naming both the 2.4 GHz & 5 GHz wifi networks the same. In other words instead of “jones-2.4” & “jones-5” name both “jones” and use the same password for both.
There can’t be any AP based band steering if the SSIDs are different, it is a requirement. However, band steering causes all kinds of problems, so I avoid it when I can. I prefer to name the networks “Jones” for 5GHz and “JonesSlow” for 2.4GHz. It is incredible how well this kind of band steering works 😁
I have both 2.4 and 5g turned down to 25% power, have no problems with reception. Wish I could turn them lower, but that’s as low as it goes.
Your WiFi can be optimized by adjusting to max power and conduct throughput test in all your desired coverage areas. Take the worst case location and reduce the power then check the performance. Repeat as necessary.
I prefer to start with the approximated minimum power level and go up from there. Theoretically we will end up with the same transmit power – either way.
Now if I could just convince my neighbours to do the same thing…
Exactly! On the commercial side this is often the case in shopping malls where each and every store has their own Wi-Fi. You could try by passing the link around if your neighbours are technically savvy at all. If not, you could offer to “fix” or “optimize” their Wi-Fi for free.
Hi, I have 12 unify LR devices on a web-based controller and 6 hp Aruba on its seperate controller. My issue is the handover between different access point brands are not working properly. My hp Aruba is set to maximum transmit power. Any idea how I can have a proper handover when moving around the area?
There is no handover in PSK (WPA Personal) per se. When the client decides to roam to another AP, it will try to authenticate using the credentials it has. If the APs are broadcasting the same SSID (network name) then the client assumes it is the same network. My first worry would be DHCP. Make sure you only have one DHCP service on your network. Another cause could be the clients hanging on to the AP from too far due to the high transmit power. The solution is to lower the TX power, but that you already know.
Hi, it’s really a great post! for a small single room which dbm transmit power will be a best option for 2.4GHz? where other signals are available too.
In a single room where the signal doesn’t need to penetrate any walls I would use the Low setting, if there is one provided. The manufacturer knows its circuitry best and has some kind of idea how low it still works cleanly. Even if you could set it to 1 dBm, rather use 5-6 dBm.
I can think of one case where increasing the power would be necessary. If one of your neighbors is transmitting at full power on the same channel, it could be that your AP would take turns, but the neighbor’s AP couldn’t receive your AP’s signal. In that case it may transmit over your turns. In that case you could try Medium to see if it helps resolve the issue. The symptom would be high rate of retries. Unfortunately you can’t see this without special tools. You can always increase the power for a while and see if it improves throughput.
I’m not entirely sure that your #6 point is actually correct… but I’m only speaking from my knowledge of amplification, rather than of WiFi.
Yes, turning up an *analog* amplifier will result in distortion, but a *digital* amplifier should not. If you’re hearing distortion from a digital amp, 99% of the time the source will be the incapable-of-handling-that-volume speakers that are hooked up to it. I don’t know whether the amplification used for WiFi signals is analog or digital, but digital amplification should not result in signal distortion.
The RF amplifier is analog so it still applies.
Good article. When we built RF systems a gain antenna was always preferred over cranking up the power. However It does matter if the AP has a better antenna or is located higher up. Higher up generally = less obstructions and better antenna (ie: an omni gain or directional gain antenna) = less power is required by the AP and the AP has greater signal to receive from clients.
Yes, very true. The antennas work both ways: antenna gain and good antenna placement improves both reception and transmission equally. Transmit power only effects transmission.
I would like to see also if there are any health benefits in reducing the wifi transmit power signal.
Is it harmful if its at a higher rate for the human body?
None have been proved so far. Higher or lower data rates won’t make any difference though. Only the transmission frequency (2.4 or 5GHz) and transmit power could matter, if it matters. The energy levels are very low, though, and fade quickly with distance. That’s why you don’t need to worry about the AP at all, but your cell phone or laptop, because they are close to you.
Wi-Fi (like your car FM) use electro-magnetic waves just like light. Light waves are just very much higher in the frequency spectrum. The way electro-magnetic waves could cause health issued is by heating up your body like a microwave. That requires a lot more power than a smartphone or laptop can provide.
Ionizing radiation is a totally different matter and it is bad for health. People often confuse these.
Thank you for your reply Petri, it was always a concern of mine if the two were related and if Wi-Fi was actually harmful.
Petri,
I am learning by many of your comments- Thank you.
However Harm to the living cells- human and animal : have been the subject of extensive research on 2 sides of the issue: pro-wireless providers , and neutral or ‘clean’-scientific organizations.
Even the WHO-World Health Org. – has demanded and won many requests to clean up the science of wireless, especially in Europe.
You are correct that the EMF’s do not heat up cells- heat as being one cause of cancer. However , there are thousands of honest studies showing that many EMF waves: do affect the normal electrical functioning of living cells , heat is not involved at all.
Cells are indeed affected:
1- normal electrical activity is altered affecting the rate of cellular functioning.
2- DNA – in some cells are affected in long term studies also.( I am merely opening a new thought here- not to trash your decent input to assist others, but it does concern me that EMF’s are harmless. I am not a conspiracy theorist either- I stay away from them- for good reasons !
See these links,below to open a new discussion:
a- YouTube.com = Dr.Devra Davis . A Dr. on national board to advise on EMF hazards: simple & quick video: https://www.youtube.com/watch?v=KqAxTpJEHVs
b- also Petri , Here is an easy to read book of over 30 years research on wireless & EMF radiation : called: ”OVERPOWERED ” by Dr. Martin Blank, PhD. – very readable, interesting.
** These references above are NOT to stop all wireless & EMF devices, Just to bring awareness and help create a better future with less harmful waves.
Thank you Petri & Metis for your input here..
All the Best, Don K.
I agree this stuff can be harmful, and turning it way down can help.
Your cell phone radio uses far more power than Wi-Fi. Keep your cell phone always in flight mode if you want to play it safe.
How about the gateway transmitting the 2.4 and 5g ? I turn mine off at night because it’s in the bedroom where I sleep of course. Is that a good idea or overkill?
It decreases your carbon footprint, because the gateway won’t use electricity over night, but I don’t think it really matters. Health-wise it makes no difference (unless you keep the gateway under your pillow). The key is the distance to the gateway. The radio signal fades very quickly with distance. Doubling the distance lowers the radio energy to a quarter. Cell phones use more power and they are safe to keep next to your head.
You start at 0 and end at 8. Should this be titled _9_ reasons to turn down the transmit power of your Wi-Fi?
Yeah, I added #0 as an afterthought, but I didn’t want to change the title. I thought everybody knew 802.11 is cooperative and not competitive, but I learned it was a wrong assumption.
This was really informative. Ty 🙂
I had absolutely no idea about the shared airtime.
A follow up question if u don’t mind? 🙂
When picking channels and deciding signal power, is it just how many other ap’s that your ap can see, or is it a problem allso if the client see neighboring ap’s that your ap can’t see?
Will a client that gets connection issues because “thinks” it has a good connection (based on high transmit power from ap) que up all other clients that actually has a good connection. Thus making everyone on that ap experience the same latency as the “worst one”?
a) Yes, the client will wait for the channel to be clear before transmitting. If the AP can’t receive these remote transmitters it will transmit on top of them. It can well happen that the client can’t decipher it because of the interference.
b) The client will try to send data at some rate first, but it will retransmit and drop down the rate until the AP acknowledges the packet. This way the speed may be different in each direction (or for each packet sent, actually). All these tries and retransmissions will eat air time from other clients.
Not that helpful to me. I’ll state my opinion for every point.
0. This should not be included as a point. The focus is “Why do we have to reduce the power of the transmitter”, and clearly, this isn’t one of the reasons. Maybe add this content in the beginning, not within a point.
1. Point made.
2. Only applicable to setup with multiple routers. For single router users, this doesn’t make any sense.
3. Okay, but again, for multiple router users only.
4. Access points being cheap is subjective. For third world countries like mine, routers and internet subscription is still expensive.
5. This is the part I’m most confused. I get the point that having full power will interfere other’s APs, BUT isn’t that only benefiting the neighbor? E.g. If I set my power to 80% and my neighbor is at 100%, then I only made my signal weaker, make their AP easier to interfere my signal, giving me less performance! This will ONLY be a point if ALL people managed to do this, but with only me doing it? No thanks, effects are worse.
6. Point made. Actual test results may help for us to believe.
7. Same content to point five, same response.
0: It is not counted among the 8, it is at the beginning.. I just wanted to set straight a common misconception. Your points 5&7 reveals that you haven’t grasped its full meaning either.
2: Yes, this applies if you have multiple access points. It is common to have multiple APs even in larger homes. (You shouldn’t have multiple routers unless you have a very complicated network.)
3: The battery life consequence has nothing to do with multiple APs. This applies in a single AP scenario as well.
4: The price of APs has come down significantly. If you consider them to be expensive now then they were really expensive just a few years back.
5: This whole point is not about neighbors, though the same applies to all Wi-Fi devices regardless of the owner. This point is about multi AP environments where your own APs will interfere with each other if they are using too much power.
6: I suggested an actual test with your car radio. Amplifiers will distort the signal at max power.
7: Yes, you would benefit if your neighbor would turn down their power. The point is that there is no advantage in using excessive power. Wi-Fi is not a competition. The APs are not trying to yell louder to overcome the other. They are taking turns as long as they can detect each other. Interference or turntaking with your wall neighbors is almost inevitable. However, interference across the street is pointless. You gain nothing and you are making life harder for others.
Thank you for your input! I may edit the post at some point to clarify my intentions.
Hi Anony Resu,
I was living and working in IT for years in the third world countries such as Cambodia and Thailand. With their (yours) low-speed plans and limited access they (you) unlikely need for high-performance Wi-Fi AP (do not be confused in this IT terminology). If you need for robust and fast connection just trow a UTP cable and plug it in a cheapest gigabit TP-Link switch. I could trow cable from window to window or easily drill a hole trough a walls in Cambodia without consents and complains. BUT…
But being in New Zealand I can not do so – need for consents, certified carpenter, electrician, painter and so on. And my WiFiAnalizer shows me overcrowded 2.4GHz range and bunch of 5GHz / 80MHz networks in neighborhood as the providers send to the clients preconfigured 2.4/5GHz WiFi-routers. My WiFi-router sits at one end of the house and my workstation with 4K TV as monitor at another end and they connected by means of radio bridge (affordable MikroTik APs). I have got Gigabit Internet plan recently (950/450 Mbit/s) and it is really problem how to utilize its speed over radio and do not kill my valet with all this installations. Have bought used Cisco Aironet AP2702i for $3 on local flee auction and now trying to set it up to top of IT standards.
I found this article very helpful but your complains exaggerated. Could not stop from writing it even my time are pretty valuable for me and my family.
Most important: be patient and calm instead of being blunt and arrogant. Read, watch and do hands-on labs as much as possible before you come to teach professionals who went as far as you can not imagine and you will definitely be able to grasp more knowledge.
Cheers bro, take care!
Petry, I take my hat off before your expertise and willingness to share your skills and experience. Thanks a lot!
Can you please provide a list of routers that allow output power adjustment….. because none of mine has this feature…. thanks
No, there are so many APs on the market and new ones introduced every month. However, most of the APs I have looked at do have transmit power adjustment, even consumer grade devices. In the last few months I’ve looked at some Asus ADSL/router/firewall/Wi-Fi devices that had it hidden in the advanced configuration page. Some similar ZyXEL device had it as well, but I can’t remember where. Some let you set a decibel value, some have percentage and some have hard coded levels. In those cases you shouldn’t use more than 14dBm, 25% or medium (preferably low) setting accordingly.
Hello, and thanks for your really great posts.
A few quick questions/clarifications:
1. When in the post above you say “In those cases you shouldn’t use more than 14dBm, 25% or medium (preferably low) setting accordingly.” does this relate to Tx power for 2.4GHz band, 5.0GHz band or both? I suspect this relates to 2.4GHz band as the 14dBm/25% combination would correspond to 20dBm/100%, i.e. max Tx power for 2.4GHz, but can you confirm?
2. In that case, for the 5.0GHz band one would start from either
23dBm/100% (channels 36-64)
30dBm/100% (channels 100-140).
Applying your recommendation to set Tx Power 6dB stronger in the 5.0GHz band vs the 2.4GHz band, i.e. at about 20dBm, are the following settings correct if my Tri-band AP allows only % adjustments of Tx power?
20dBm/50% (channels 36-64)
20dBm/10% (channels 100-140)
Or does the 6dB rule apply only to channels 36-64, in which case by how much should we “pump up” further the Tx power for channels 100-140?
3. Finally, I would be very interested in another of your very hands-on posts (or a good reference) that would cover the typical attenuation losses from typical obstacles in a house, e.g. brick wall, concrete floor, wooden floor, glass window of various types, etc. There are a series of references available on the web but they are often very theoretical & not really applicable to estimating “back of the envelope” impact in a real setup. Elements of information that are missing are for example:
a. Differences in “Straight through” loss in dB for different frequency bands: 2.4GHz, 5.0GHz (36-64), 5.0GHz (100-140)
b. Impact of wall/floor thickness (1 brick vs 2 bricks, etc.)
c. Impact of angle of incidence vs “straight through”, i.e. what if direct path between AP and device is at an angle of 30° / 45° / 60° of the wall or floor instead of the usual 90° assumed in most documents?
Yours,
Sébastien
1. I would use 14dBm for 5GHz and 8dBm for 2.4GHz in most cases (indoors, rather dense user base, plenty of APs). After surveying I may need to change some local setting. My advice is to start with low power and increase it if needed. Even better if you start out with 10dBm for 5GHz and 4dBm for 2.4GHz.
2. That’s why nobody likes percentage settings: The maximums depend on the jurisdiction. Over here we max at 23dBm for UNII-I&II and 14dBm for UNII-III. I would use the same absolute (dBm or mW) power setting through all 5GHz since I don’t want my clients to choose a more distant AP in any case. I would use 6dBm less for 2.4GHz since I do want my clients to choose 5GHz over 2.4GHz.
3. There aren’t any posts or references, since there are no rules of thumb. All walls are different: a simple dry wall with gypsum boards attenuates typically 2-3dBm if the frames are wooden. Metal frames create odd patterns of attenuation. All glass panes behave differently, especially if they are tinted.
Wall thickness is simpler. Doubling the thickness doubles the loss, if the construction is the same. Same goes for angles: Waves going directly through travel the shortest distance inside the wall thus attenuate least. Deviation from straight angle increases the attenuation. Check your old trigonometry book for details 🙂
However, attenuation of a wall is simple to measure. Set up an AP on the same side of the wall as you are. Move as far from the AP as you can while keeping a clear line of sight (several yards/meters). Check the signal level with some tool. Next, move the AP just to the other side of the wall (less than a foot or 30cm). Check the signal level from the same spot. The settings on the AP doesn’t matter as long as they are the same for both measurements. You are only interested in the difference.
I have a RT-AC66U. It have settings for transmit power.
It’s a pretty old router but can handle 150mbps. It can also run custom firmwares.
But I recommend that you check out other Asus routers that’s a bit newer.
What about using thin foil between the router and the wall to “block” some of the wifi signals to reach areas it doesn’t need to?
It could also block signals from the outside.
Couldn’t it also help the router to receive signals better, like a parabolic antenna?
Yes, metal will block signals but it will also reflect. If you have a reflector close to the antenna (in terms of wavelength) you will get very interesting interference patterns. Your coverage area will be completely different from what you would expect. Place the metal sheet at least several wavelengths (12cm for 2.4GHz, 6cm for 5GHz), preferably a meter from the antenna. Look up Fresnel zone, too, and note it extends well beyond the antenna.
Designing antenna reflectors is a very complicated subject. I would assume you could google for introductory papers, but it will take years of study to learn. (I have a friend who wrote his doctorate dissertation on antenna design.)
Life would be easier if we had some handy materials to absorb microwaves, but stone and concrete are difficult to add afterwards. A body of water would also work, but is hard to place or maintain.
The main, and only meaningful, reason to reduce router transmit power is to avoid adverse health effects. Non-ionizing radiation DOES cause biological effects, even at lower signal strengths.
Yes, it actually does. It heats up tissues. That is how microwave ovens work. The difference is in the power. Ovens use typically 800 Watts while Wi-Fi devices use 0.2W at most. In the text I suggest lowering that to 0.02W range. However, the power attenuates quickly with distance. Unless you sleep with the access point under your pillow your only concern should be the client device, which is close you. The AP transmit power plays no role because of the distance.
You didn’t mention health reasons!
There is no reason to increase the power of micro waves beaming through your body 24/7. Especially at night when our cells regenerate and heal. FCC regulations take an exposure average level over time, they don’t account for the burst peak levels of millisecond RF spikes. FCC regulations also assume that a single wireless AP is used in a single home and conduct health studies accordingly, they don’t account for being bathed in 40 of your apartment neighbors’ super gaming AP’s creating an RF ocean of exposure 24/7 in your apartment!! Apartment complexes are ridiculously over-saturated with concentrated RF to a degree which hasn’t been properly studied for health effects.
Ionizing or not, the health studies are not properly conducted to account for these real-world scenarios, and is frankly irresponsible science to rely on!
RF and EMF exposure will be the new smoking as we move foreward. In 10 years we’ll look back and discover all the health studies were improperly conducted by the same industries that produce the technology.
I didn’t propose increasing the power. The title suggests turning it down. In the previous comment I explain that because of the distance the AP transmit power is insignificant when compared to the client device next to the user. If you are worried about RF radiation you should keep your cell phone in flight mode all the time.
There are no bursts or spikes of radio energy in Wi-Fi. The transmit power is at a constant level, which is used when there is data to send. If there is no data there is no transmission. FCC and ETSI regulations prohibit exceeding the maximum transmit power at any time.
You don’t need to worry about your neighbor’s APs because they are even further away. This has been studied extensively and you may look up Free-Space Path Loss (FSPL) yourself. In an apartment complex the paths are not free but there are walls in-between, which will attenuate the radiation even more.
I’m not an expert on data packets but surely if I’m downloading or uploading something chunky, it travels in bits, therefore it will have a power, then no power, then some power, then no power, etc. So even if you say the power is constant when in use, the actual use-or-not status is going to be changing many times per second isn’t it?
No. Wi-Fi is not encoded in on-off. Think of it more like light: red light is one and blue light is zero. The brightness/power is constant. The problem with on-off encoding is that a missing signal is interpreted as a stream of zeros.
Well said.
Thank you for your input.. Now I know why my center with 32 APs is having low signal or no signal at all or areas where signals drops and comes back..
Do you think that
1. reducing the transmission power of all APs at the same level will help?
2.making the distance between APs more consistent will be a factor?
3.how to avoid signal dropping or getting weaker?
4. there are areas where there are a lot of metal pipes where APS are installed…do you think the metal pipes will interfere with the signal?
1) No, reducing transmission power will not help low signal level.
2) By adding more APs you can get a more uniform signal level.
3) See #2.
4) Definitely yes. Do not place the APs behind or between the pipes. Metal will block and reflect signals. Uniform reflections are not a problem, but a pipe array will cause scattering like a disco ball.
Hi Petri, thank you for sharing these very interesting thoughts. I cannot quite understand the point 1. If a typical mobile device does a max TX power of 15mW, and a typical AP does 100mW – what is the reason for such a disparity? Does increasing the TX power of the AP above 15mW only make sense if the receiver is also able to TX 100mW (say a PCI wifi card)?
Short answer: yes. (And the typical default for 5GHz is 200mW)
However, slightly higher AP power makes sense, since often most of the traffic is downloading. In that case it makes sense to have a better connection in one direction. It doesn’t matter if the acknowledgements are transmitted at a lower rate as long as the AP can still receive the acks.
If you have a mixed environment (like most are) you are hurting the laptop users if you set the AP power to 15mW. The laptops get shorter range and worse rates than they would get with higher AP power. This can be solved by adding more APs so the range will always be short, but it costs more money and takes more effort to administer. That’s why Wi-Fi is so challenging to tune.
Hi Petri, thank you for your advice. I have recently bought a “for parts” Linksys WRT1900ACSv2 from ebay, which seems to be functioning well. It is missing all 4 antennas, however. Would you recommend buying four 6dBi antennas, or one/two high gain ones? Thank you!
You’ll need four antennas for the device to function properly. I strongly recommend low gain omni antennas, unless you really need directionality.
Dear Petri, Thank you so much for taking your valuable time to explain all these points. I find your intelligence and manner to be excellent and have learned so much reading all that you have to offer. I am very grateful to you and wish you all the best. And if you can or want to, it would be interesting to create an ethernet–>Wifi super micro adapter that directionally feeds something like an Amazon Echo or an iPad or something similar so that those of us (I am one, especially nowadays in this virus era) who are definitely sensitive in some manner to the frequencies in the tech that has taken over our homes and offices can use Wifi only gizmos without worrying about these frequencies affecting us. Perhaps an adapter with a shield cover that can be velcroed onto something?
You don’t need to worry about the Wi-Fi microwaves. The power levels are very low and there is always some distance. The signal attenuates very quickly with distance. (I don’t think anyone sleeps with an access point under his pillow.) If anything, the only microwave device you carry next to your body, day after day, is your cell phone. Yet, for some reason, people don’t want to give up their cell phones or switch to flight mode, because they want to be connected – wirelessly – all the time. I can’t wrap my head around this reasoning.
There are activist groups in many countries attacking cell towers, because they are afraid of the radiation. Yet they carry their own transmitter next to their bodies. Very few people read and write letters in candlelight.
How?
You need to log in to the AP, typically with a browser. The address, admin user and password are typically in the sticker at the bottom of the AP.
Hi Petri, first thanks for all info.
sencond in this current times we would like to be more clarified regarding EMFs.
some of us are interested in reducing them at max.
how can i configure my router for that?
tx power would be better at 100% 40% 20%?
should people use 802.11 /b/g or n?
thanks
and what about using aluminium arround router antenas? thanks
You don’t need to worry about the Wi-Fi microwaves. The power levels are very low and there is always some distance to the AP. The signal attenuates very quickly with distance. For technical reasons described in the post you should run your AP at as low power as is possible while keeping the network functional. Try with 20% and increase the power if necessary.
If you are worried about radiation you should look at what is close to you: your cell phone next to your skin and your laptop at arm’s length. If you wrap aluminium around the AP antennas your client devices will increase power to keep connected to the AP. Completely the opposite of what you are trying to achieve.
Thanks for this excellent, informative, and well-written post. As well for your attentive responses to comments, several of which responses exhibit the patience of a saint!
You’ll perhaps be relieved to know I’m not enquiring about health hazards. Instead, in my case I have discovered that a devious neighbor has hacked into my router. Among other measures I’ve reduced my Tx to 20% and now to 10% to try and attenuate the transmission strength in his direction.
However even 30 metres away from my house I’m still getting three stars or -60dBm and at that point I’m at the fence between the properties. Question: can I go even lower, say to 5%? What might be possible disadvantages to doing so? Needless to say, I have ample speed and coverage in my house and my yard. Is there any downside to removing the router antennae entirely? Thanks
You can go as low as the AP still keeps working. At some point the circuitry will cease functioning. You’ll notice that when you can’t see the SSID any longer. I’ve successfully used 5% when all the clients are in the same room as the AP, but it depends on the quality of the electronic design.
Removing the antenna is a bad idea. You will need to use a 50Ω dummy load or you will risk damaging the RF amplifier.
Lowering the power won’t work as a security mechanism, however. It will help to avoid drawing attention, but if you are targeted, then a directional antenna can pick up the signal. A 2ft/60cm disc costs less than 100€ and will pick up the 5% signal a mile away. Use good passphrases and keep your firmwares up to date instead.
Thanks for the advice. Sounds like I need a new router, since mine hasn’t had a firmware update available for years. I had no idea that weak signals could be targeted like that.
Hello, Petri.
Thank you for this very informative article. If you don’t mind, I would like to post a link to your article in my social media feed: https://mastodon.social/@shahaan
Your article helped me optimize the wifi in my home. I was struggling with thick concrete walls and heavy steel doors separating three rooms where I needed the signal to reach. Thankfully, each room has a wired connection leading back to a single router. So I placed a WAP in each room and lowered the tx power to 2mW. I further optimized the DTIM (10) and ACK TIMING (30) settings, as well as having each wifi on separate, non-overlapping channels (1, 6, 11). Of course, all SSIDs and shared keys are the same so devices can roam easily.
Now all devices have very fast net access! Also, the device batteries do not drain while idle!
One question, if you please: Would having the WAP tx power at 2mW appear to a client as though the AP is too far away, thus showing such a low signal strength, and ultimately causing the client to boost its transmission power high in order to “reach” the AP which is believes to be so far away?
Thank you,
Shahaan
Well done!
As to your question: No, in the same room 2 mW provides a good signal. I presume you have full Wi-Fi bars on your phones? In no case will the client try to increase its transmit power. It will use its hard coded setting or match the WAP transmit power, if your WAPs support 802.11h TPC reporting.
Yes, all clients show full bars. That is good to know, thank you for the quick response!
Hello, Petri.
A quick follow-up, if I may: I have introduced a 5Ghz WAP into my network. Now the 2mW transmission power previously set for 2.4Ghz WAPs seems inadequate. Is there a calculation I can use to find an “equivalent” transmission power for the 5Ghz WAP?
Thanks for your time!
Multiply 2 mW by 4 to get 8 mW. In decibels, add 6 dB for the same effect.
Great, thank you!
Petri,
You are very much appreciated for your valuable advice.
Am I right to assume that the WiFi “signal bars” on an iPhone, indicate signal quality and not just signal strength?
If so, can we use an iPhone to get a general idea of the signal quality in areas we suspect interference from devices or defective appliances? I once had a “quality” stereo headset transmitter that reduced my WiFi reception to 20 feet.
I haven’t figured out what the bars at the top of the screen indicate. They are crude at best, often misleading. Too bad iOS doesn’t allow apps to use the Wi-Fi. The apps can only see a network connection, but no details. That makes iOS a poor platform for Wi-Fi tools. The best app I have used is Wi-Fi Sweetspots. Android doesn’t have any such restrictions so there are plenty of good tools available. If you have an Android phone or table on hand, search for WiFi Analyzer in Google Play.
Newbie here. When I search for Wifi Analyzer, I get products from farproc, VREM, olgor, sladjan, webprovider, and more. Is there a preference? I am ready to search for “best Android wifi analyzer” if your favorite wifi analyzer is not available to me.
The one I meant was by farproc, but it has been a while. Some apps get acquired or changed. Some comment mentions the current version tracking your location, which is totally unnecessary. The app is not complicated so there may be less nosy alternatives. I’m sorry, but I use Macs and iOS, so I am not up to date with Android tools. Too bad Apple rules don’t allow tools like WiFi Analyzer.
Very good article.
In my case I would like to reduce power but can’t . I use my iMac computer as a hot spot, and it always chooses ch 11 as determined by its algorithm., and send full power. There is no control for frequency or power. Unfortunately, my house has internet access by means of a radio link that is fixed to Ch 11 in the 2 Ghz band. Occasionally my local hot spot signal radiates up thru the house and over comes the Internet ch 11. Or rather, when the Internet signal fades due to weather, trees, whatever, my hot spot signal interferes with the Internet radio wave reception, and the link goes down.
You are out of luck unless you want to invest 20€ for an AP. That’s the lowest price around here for 802.11ac/router/firewall device – and Finland is one of the most expensive countries in the world. Unless you live in Switzerland or Norway you should find better bargains.
thank you very much for this awesome article.
Wow. I was sitting in a part of our house with bandwidth issues despite being full bars. I reduced our router transmit power from High to Low. My bars dropped by one level, but my bandwidth went from 4 Mbps to 20 Mpbs. Incredible.
We have an older house with foil backing on the insulation. Maybe all that transmit power was creating echoes that ended up killing bandwidth.
TP-LINK C9, 2.4 Mhz
I’m glad to hear! Your reasoning is probably correct. Most often it isn’t as straightforward but good for you.
Interesting article, found it while searching for some puzzling issue I see around my network, maybe you guys can help me here. While running WIFI scanner I see that couple neighbor AP’s periodically burst signal to almost -4dBm for approximately 1 min and going back to -80dBm. What could it be? Is it scanner reporting wrong data or is it something else? Another strange thing about these AP’s is they have names like xxxSetup-xxx and vendor is unknown.
The first meter from the AP attenuates the signal by 40dB or 47dB (at 2.4GHz and 5GHz). -4dBm signal would mean that there is an AP transmitting at 36dBm or 43dBm one meter away. Those power levels are out of range everywhere. And I assume your neighbors are further away so their transmit levels would be even higher. I would say it is a misreading or meter error.
Those SSID names are common default values.
It isn’t only broadcast strength that affects whether a connection is “symmetrical”. You also have to take into account antenna sensitivity and susceptibility to noise.
Cell phones are tiny devices with tiny antennas packed in closely with dense circuits running at high clock rates. The fact that they can receive any signal at all is a miracle of engineering.
WiFi modems have much larger antennas that are often separated completely from the noisy circuits of the device.
So to achieve the same SNR for both devices, the AP can get by with a weaker signal than the mobile device can.
All gains and losses (antenna, cable, insertion etc.) are equal for transmit and receive. The same goes for noise at the receiver or transmitter.
In smartphones both the Wi-Fi and cellular antennas are both packed inside the same device. Cellular APs (a.k.a. cell towers) have much better antennas than Wi-Fi APs. Still the same rule applies, all gains and losses are equal for both directions.
Hi.
I found this an interesting read. The one thing I haven’t heard you mention was about receive sensitivity of an AP. I know not all APs are created equal. There’s some higher powered APs I’ve used that have better receive sensitivity better than your typical off the shelf AP/Router. These would include EnGenius and TP-Link products. I don’t necessarily use the highest power settings in all of my devices. Your location’s noise floor plays a role in your real world sensitivity. Several years ago at my old house, I was using a EnGenius ECB600 AP at full power which was 600mW, and it was perfectly balanced with my cellphone at that power level when it came to fringe coverage. It’s range very much exceeded the wifi radio on my router. I’ve also used units like a D-Link router at that same location. It had a 50mW transmitter, and I would lose connection when I was still receiving more then a minimal signal strength. I chocked that up to maybe a poor receiver design, or that it’s sensitivity is just not on par with my EnGenius AP.
The sensitivity differences are mainly due to antenna design, which is the trickiest component to design. However, the same antenna is used for both sending and receiving so it is symmetrical, improving transmit efficiency equally. Most of the RF path is symmetrical: antennas, cable attenuation, noise, obstacles, distance, even the RF circuitries. The transmit power is the main factor to balance. Of course it could be that the EnGenius had an optimal receive radio circuitry and a terrible transmit amplifier, but I doubt it.
How did you determine “balanced” with the EnGenius? Beyond the point, where the cell phone lost contact, all coverage just adds to the noise. My ideal is that the coverage areas are equal in size. Basically the incredible receive sensitivity would in effect increase the coverage area of the cell phone.
If your application demands more downlink capacity (the typical scenario), then it makes sense to slightly increase the TX power of the AP. That will improve the downlink MCS index and thus downlink throughput, but it will hurt roaming.
I recommend WiFi man over WiFi analyzer is it also shows every device on your network in the discovery section of the app and has a speed test built in which is nice when you’re checking the speed you get at various distances from the AP.
I found your article very intriguing including all the Q&A.
Thank you. Excellent article, i learnt a whole lot in a short time.
I loved reading this and it really got me wondering about my situation. I recently moved into a townhouse complex. I unfortunately have 5 neighbours that sit wall-to-wall with my unit. Looking at WiFi Analyzer on my phone I can see people are blasting their AP (theirs is stronger through my wall than my AP across the room. There’s on average 5 to 7 SSIDs that I can see on either of the non-DFS spectrums (36-48 and 149-161). This has resulted in pretty bad video calls on Zoom, Google Meet and the like. It usually starts off fine, then suddenly the video gets all choppy (with audio still coming through).
I’m wondering, if I were to buy a https://store.ui.com/collections/unifi-network-access-points/products/unifi-nanohd-us that has DFS channel access, would this solve my problem you think? I currently have 2 APs, set to the lowest settings possible and one is 5Ghz on 40, and the other 5Ghz on 153 but it seems I’m clashing with others anyway. Just wanted to know your thoughts on the matter.
Lowering your transmit power won’t help in this situation. You need to find a free channel. Get some tool like WiFi Analyzer (Android) or WiFi Explorer (Mac) to see which channels are in use. If you can find a single free 20MHz channel then use it. I am not aware of the current U.S. regulations. Are you certain you can’t set your APs to UNII-II channels? If not, make certain that the NanoHD you are considering can be set.
Yeah unfortunately none of the TP-Link APs I’m using offer any channels in UNII-II. I picked up an Asus RT-AC86U that should support it, so I’ll find out if it helps after I have set it up. Right now none of my neighbours are using anything in DFS so hoping it’ll be a better experience than I’m having now.
You know there will be a one minute delay before your network shows up? The delay is 10 minutes for the weather radar channels. Other than that, it will work fine. See What are WiFi DFS frequencies and should I care?
As others have already mentioned: great article. I came here because I wanted to know how common it is for WAP’s to have a TX power setting. I’m looking for a new one for a project, where I want to have low transmit power because the clients will always be close, no walls, and will be used in venues that already have their own WiFi and I don’t want to cause interference. But I can’t really find “adjustable TX power” in the manufacturer specs I’ve looked at so far. Too bad.
It’s also disappointing that Apple removed the setting from their Airport Utility from version 6 onwards. I cannot reduce the power on my Time Capsules, so they are (probably) working at full blast, unneccessarily. From your article I’ve learnt that in the end, (some, but probably common) WiFi problems would be reduced if everyone would lower their TX power to the minimum needed. Most of my neighbors can’t even figure out how to set the SSID, so unfortunately the chances of them reducing the TX power on their AP’s is zero to none. Wouldn’t it be nice if you could lower the TX Power of your neighbor’s access point 😉
Customers don’t ask about TX power setting so the manufacturers are neglecting it. You need to see the configuration screen to find out. Sometimes it is hidden under Advanced or Professional settings. If you find it, the setting may be in mW, dBm, percentage or just a choice of some preset levels (low/medium/full). “Automatic” means typically full power.
Hi Petri,
So many questions have been explained so thank you!
What is the farthest distance a “typical mobile phone” made in 2020 or close to it, can connect to a current model AP? (Assume the installer is a CWNE #xx9x and did everything perfect and only 1 connection so no interference)
Some AP manufacture’s claim half mile WiFi. But can today’s phones transmit back? 1 watt does not seem sufficient for this. Many point to point devices can blow away a half mile, true. But AP to phone?
It depends solely on the antenna. If you put a 30dBi dish on an AP, it can pick up the signal from a cell phone as far as you can see. For an AP with an omni antenna, you can easily cover a football field if you place the AP in the center. For a phone connection, there is no need to use 1W, 20mW will work just as fine. Both antennas (AP and phone) are symmetrical so equal amount of power on both sides suffices.
This is a great article and very useful – it’s helped me tweak much better performance from my network AND explained why.
I do have one question for you:
Given WiFi is based on sharing airtime, when I dial down my transmit power but my neighbors do not then doesn’t that mean their networks can starve mine out? i.e. in the extreme case, my AP will yield to their traffic but not vice-versa (as my neighbors cannot hear my AP). So their networks can effectively use all the airtime (without even knowing my AP exists).
Particularly I am concerned about the impact that may have on latency (voice/video calls etc.)
The APs share the airtime by taking turns. Your neighbors’ APs will transmit at full power and yours will transmit at lower power when it’s its turn. The power level has nothing to do with the queueing system. The problem is that the AP across the street at full power will use one turn in your block, too. If everyone would turn down the power then everyone would benefit, but blasting at full power won’t gain anything.
Dear Petri,
I have read everything, but I am not quite sure yet. I work with different WiFi systems and try to set up a “standard” method for WiFi measurements for offices with a mixed environment. That TX power of an access point has to be reduced, that is logical. At the same time, you don’t want to sacrifice too much download speed by setting the TX power too low. With all your knowledge, what would you recommend as EIRP levels for 2.4GHz and 5.0GHz? Then I assume a standard network for data and voice applications (~ -65dBm). I am curious how you look at this!
The only answer is the most hated one: “It depends!” In a relatively dense office environment with mixed clients I usually set 15dBm for 5GHz and six less or 9dBm for 2.4GHz to begin with. Then I adjust as needed. In a relatively dense environment I want the clients to roam. I also turn on 2.4GHz on every third AP only – and only if the client requires 2.4GHz. You can easily get -65dBm with low power, if the distance to the nearest AP is short.
If you only have a single AP then you can run it at full power, if you wish. If you only have laptops and desktop computers, then you could design for higher power and deploy less APs. Unless those computers will require a lot of bandwidth, of course. In a mesh environment you should typically use full power for the mesh backbone.
I general I prefer to have plenty of APs and small cells (low power). Then I crank up the required rates to force clients to roam. That will give good overall throughput. Often I design for 20MHz channels to give room for multiple APs. That limits the throughput per device, but who has an actual use case for 1Gbps on a phone? Or even 100Mbps?
I am Brazilian and I would like to congratulate you for the excellent content. I’m using translator to translate this question into your language. I have a doubt! I’m only using the 5ghz network and I would like to know what the ideal power for 5ghz? Because in current routers the power is divided into Low, Medium and High. Thanks for the reply!
I can’t respond in Portuguese so let’s hope the translator can make sense of this. The ideal power depends on your client device mix. If you need to support mobiles (phones and tablets) then I would choose Low. The mobiles will use low power anyway.
It never happen if AP are using adaptative antennas where signal is directed toward clients and not spread all over 360°.
The context was lost. What will never happen?
MU-MIMO spatial differentiation is very challenging. You need a lot of sounding frames the keep track of the clients, that are constantly moving. Just a couple of cm makes a big difference here. Most experts consider MU-MIMO to be a stillborn idea. I don’t know if it will work in the future. The sounding frames eat up a considerable amount of air time in every case.
Hi thanks for this write up, I have implemented this on my wifi with little performance degradation.
But I’m just wondering about what you state that “To minimise power consumption their radios typically max at 15mW (12dBm), while access points max at 100mW (20dBm) on 2.4GHz and 200mW (23dBm) on 5GHz”.
It makes sense for 1x15mW device connecting to an AP, but what if you have several mobile devices connecting to wifi simultaneously, would their combined transmission mW require the equivalent combined output from the wifi AP or does it not work that way?
Thx
In Wi-Fi only one transmits at a time. All devices, including the AP, take turns.
This is the clearest explanation of the AP power issue I’ve seen.
I installed and supported WiFi networks for years. I struggled to convince my users that turning up the power of an AP would not solve most of our performance problems. “Yes, you can shout louder. Can they listen harder?”
I wrote the post after I grew tired of explaining it over and over again 😁
Please name an AP that gives full freedom to set power in dB. I have used modems that let you go to 10% power and no lower, and it was one setting for all channels. Others I know of have no adjustment at all.
Ubiquiti’s UniFi comes to mind first. Of course professional gear like Cisco, Aruba etc. For the consumer gear, it depends. Some have it, some don’t. Some have it hidden behind some advanced settings or you need to turn Pro features on.
The percentage scale is the silliest: Percentage of what? Milliwatts? Decibels? Based on local regulatory maximum or the radio circuitry? Use what you got. 10% sounds like a good start. Increase it to 15% or 20% if you find coverage holes and see if it helps.
UniFi looks like they have lots of good options. Thanks!
If you only need one device (or two at most), you don’t need to have a controller. See How to set up Ubiquiti UniFi WiFi access points with an iOS device (iPhone or iPad) in 5 minutes. The video is a bit dated, but it still works like that. You can also use Android, of course.
Hi Petri, It took me more than a hour to go through article and all the comments and your responses which all are highly informative .
I have one question which if you can help as you said multiple time duering various replies to switch off mobile as it’s most radiating client next to body.
A) What is the Tx power output of mobile device when it is communicating with call tower .
B)Is there any difference in this power when we are browsing on 4G network and when we are making a call ? Which scenario have more mobile phone transmission power and how much ?
C) Is my understanding is correct from this article that if I put my mobile on aircraft mode and then enable only wifi on mobile to communicate with my local AP then max transmission power out of mobile will be 15mW?
A) It depends. Many cell phones can transmit up to 1 Watt. That’s why the phone often heats up during long calls – it is not just your sweaty palms 😁
B) No, 4G is all data. The voice is digitized and sent as bits, just like everything else.
C) You can’t enable WiFi in airplane mode. Airplane mode disables all radios: cell, WiFi, BlueTooth, UWB…
Some may have a weird approach to ‘airplane mode’
Like my iPhone allows turning wifi and bluetooth back on in ‘airplane mode’
Yeah, kind of makes the airplane mode pointless. The reason is that many airlines now offer on-board WiFi and allow passengers to use their BlueTooth earphones.
Hi Petri, You mentioned that maximum Tx power of Wifi shall be close to 15 dBm in mobile. It is difficult to find any information related to Tx power level of Wifi and Bluetooth related to mobile phones or tablets. Do you have an idea from where that kind of information can found?
TL;DR: If the manufacturer doesn’t publish the transmit power, take my word for it.
All devices sold in the US must be approved by FCC and the documents are public. You can search for them at FCC. You need to know the manufacturer code (Apple is “BCG”) and the model number (in iOS Settings>General>About>Model). You get a list of results with frequencies in the rightmost columns. Click on the checkbox in column “Display Grant” to see the maximum power for that frequency range. You will find that the maximum power is different for each channel or group of channels.
However, the devices don’t use the maximum, because it would drain the battery quickly. The software sets the maximum power and that can change in every software update. (Quite often the update promises “better battery life”.) So the actual value is a secret or a moving target at least. Cisco has partnered with Apple to provide best service for Mac and iOS clients. Cisco has published a white paper which says at the bottom of page 5 that the transmit power of iOS devices is typically between 9 and 14 dBm.
Does it still true that mobiles and laptops nowadays still max at 15mW?
If I turn down Tx power to 20%(which is lowest in mine) I see the bar indicator is reduced and the link speed is also reduced. Is this will suffer in my download/upload speed and latency?
If i connect to wifi with poor strength (say 1 bar) will it cause more battery in using device? What about also speed?
And if i increase Tx power, will I get more signal strength than previous caes (within range but poor signal strength)?
Mobiles: yes. This won’t change, because the transmit power eats up battery life. Most consumers value battery life over other properties. Laptops typically can use more power because they have heavier batteries. The ideal transmit power thus depends on your client device mix.
The decrease in signal strength you see now shows what your AP has already been experiencing. The signal at the AP has been poor, even though the signal that your mobile has displayed has been good. In many cases the mobile device can’t even connect though “the signal is good”. The AP can’t receive the signal from the mobile.
Yes, poor signal will decrease battery life. The mobile device will use its maximum power and will need to retransmit often. If you move the AP closer to the device it can decrease tx power and still transmit successfully the first time. Increasing the tx power at the AP won’t help. The solution is typically to add more low-power APs to the design.
Hello,
I’m not sure if you’re still keeping up with this post, but I just found it today and was pretty surprised about the sharing airspace vs competing for it. Upon learning that, I am now re-thinking my whole approach to my home wifi situation. If you would be so kind, could you provide any insights you might have on my situation?
Initially I had 3 Google OnHub routers in bridge mode (single whole home router), I placed one on each floor of my home, and they just happened to be somewhat vertical section of the home. The OnHub’s were auto setup on channels and power, and had both 2.4 and 5Ghz bands enabled.
Around December this past year I bought a new 3-pack of TP-Link Deco AP’s that were WiFi6 hoping to upgrade and future-proof the house a bit, especially as the family had been recently complaining about our wifi performance. I ended up renaming the old OnHubs “backbone” and put all our smart-home devices solely on that network, and then left the new “Deco” AP’s to manage all our TV’s, smart phones, and other devices. I was thinking that I was keeping down competition for bandwidth on the AP’s since I thought AP’s max bandwidth is X, but when it’s shared across 10 devices, and two are actively streaming content, then the bandwidth is like 20% of that expected X. I basically chained the old OnHub units into their new Deco replacements on each floor (all AP’s are wired).
We started noticing problems with the new “deco” network, devices are dropping for short periods, completely interrupting usage of our phones and TV’s. So I bit the bullet and bought 3 new Ubiquiti WiFi6 AP’s, I have already been using a Ubiquiti router for years and figured these would be much better… and now I’m running Wifi Analyzer to see all these wifi networks in my own home and thinking, maybe I should just get rid of all my old AP’s and just use the new Ubiquiti ones solely.
1: is there a difference/reason to try and put smart home devices on a separate wifi network? I know some devices only work on 2.4Ghz, so I could setup the 2.4Ghz band to be named “backbone” and leave the 5Ghz band as my main wifi (basically my current setup) but this would mean only 6 broadcasting in the home, 3 at 2.4Ghz and 3 and 5Ghz? Does having 2.4 and 5Ghz bandwidths each up more connection “bandwidth” across the devices connected to the AP? (sorry i’m rambling, is there any benefit to having a separate AP for just the “backbone” or is that making my house wifi worse?)
2: having all the AP’s somewhat vertically in the home probably doesn’t help much with turning down the power (the Ubiquiti AP’s do have a high, med, low, auto setting). Should I find a way to space the AP’s to different sides of the home for each floor? Like, basement is far east side of home, mid floor is far west side of home, and upstairs is back to far east again? I do think that many phones aren’t switching to the closest AP as I walk thru the house and I wasn’t sure how to fix that.
3: Would I just be better off naming all my AP’s “upstairs”, “main”, “basement” so that when connecting you would have to manually switch networks (that was annoying, so I named them all the same to avoid that)
Thank you so much for your time.
Cheers,
Gordon
Get rid of the other APs and go with the UniFis is my recommendation. You shouldn’t have multiple AP networks (on 2.4 at least). You’ll get a good network since all your APs are wired.
Browse through my other articles on 2.4GHz and 5GHz channels, UniFi Controller on GCP, DFS channels etc.
Thank you very much Petri. This really helps !
This is a very thought-provoking and smart analysis! I will use it in my career servicing wireless locations. It does require mt to do a bit of a rethink.
I have a small problem with the comparison made in #6: Distortion. While what you are saying about car audio is persuasive and verifiable, there are many variables and radio and audible sound observe different limitations entirely. Wi-fi can exist in an airless vacuum, for example. I fear you may have made an error in associating the limitations of overdriven speakers to amplification in general – there is no immediate reason to believe electromagnetic radiation should suffer distortion as a result of being amplified – It only has to move through space, whereas sound has to move through all the properties of matter.
If you are indeed sure that electromagnetic signals such as light and radio become distorted as they are amplified as a property of amplification itself, I’d ask you to lay it out for us instead of the common experience you refer to.
The distortion doesn’t happen in the medium. It happens in the amplifier and antennas/speakers. Think of a pure sine wave, when you overdrive the amplifiers (and antennas/speakers) the tops and bottoms “go over the edge” and are clipped. A clipped sine wave is transmitted. A clipped sine wave is kind of a combination of sine and square waves with sharp corners where the tops and bottoms flatten. These sharp corners introduce high frequency components to the signal (think about applying a Fourier transformation). That is why an overdriven car radio-amplifier has ear-shattering high-pitched noise in it. I can’t include an image here, but do a Google image search for clipped sine wave. You can also search for square wave fourier series to see where the high frequencies come from. The medium plays no role.
Thanks for responding, Petri. This info is changing the way I operate and I am sharing it with my team. You’ve changed my mind!
thanks alot of information
Petri,
Thank you so much for this clear and detailed information! Your patience and tactfulness is clearly seen in your answers to some of the comments / questions. Thank you.
Hello!
I use 2.4GHz with 5 devices connected at the same time with the 11n for all and has a lot of interference in the automatic channel mode, I’m not sure which to use the power low, middle or high.
If you have just a single access point, you can’t do anything about the interference except to look for the least occupied channel. Setting your power to medium won’t hurt you, but it will make everyone else’s life a little easier. Let’s hope your neighbors will find this post and turn down their tx power as well.
I put it on channel 6 and it decreases to low, the signal has improved in relation to the area of the apartment 🙂
Even though the signal was at -64dBm
Is there a word or terminology that best describes #1 of this article. (Great write up btw!)
There is no generally accepted buzzword that you could easily google up. If you want a single word, then reciprocity would be my choice. WiFi is always bidirectional, each unicast frame has to be acknowledged. Therefore it is important to have a functional bidirectional connection. In practice much of the traffic is downloading, so the ACKs may be sent at a lower bitrate without affecting throughput, but that is splitting hairs.
Petri,
You are very knowledgeable on this topic so I thought you could address my question about adjusting the transmit power of APs so that 2.4 and 5.0GHz have the same reach. Starting from the premise that the client has limited transmit power for both 2.4 & 5.0 of ~12dBm, if the AP is adjusted to transmit 12dBM for 2.4GHz and 19dbm (12+7) for 5.0GHz, doesn’t that create a situation where the 5.0GHz signal reaches the client device with sufficient power that the client will associate with the 5.0GHz radio, but then, having only 12dBm of transmit power to go back to the AP, the AP is unable to receive the weak signal. To summarize, in a case where it required 19dBm to have the signal reach the client and the client only has 12dBm to go back the other way, wouldn’t there be a deficit that would prevent proper bidirectional communication?
Thank you-
In that case you’d want to set the transmit power of the AP to 12dBm for 5GHz and to 5dBm for 2.4GHz.
What I have learnt from many documents that I have gone through and from your points is, to deploy more APs with lowest Tx-Power supported at high-client-dense areas. is that right?
Yes. Also make certain to keep the APs on different channels. Use 20 MHz channel widths to maximize the number of separate channels.
This article is absolutely excellent. It was so helpful for me in my thinking, especially as we are researching what a move to WiFi 6E would look like for our organization. Thank you Petri!
Just stumbled across this post as I was reconfiguring my router. I’ve always got about 40mbps over Wifi even with an advertised 300mbps speeds. Just recently upgraded to 500mbps and was looking around my router settings, decided to turn down transmit power to medium instead of high. I’m now getting 580mbps consistently.
Not sure if this is just coincidence but I appreciate the article.
Great write up, thank you.
Utility Routers e.g. Verizon FIOS are set at 100% Power by Default, so all my Neighbors are needlessly blasting 2.4Ghz from their one and two bedroom apartments. Mine is set comfortably at 5%. I wish Utilities like Verizon would put “Power Setting” at the TOP of their Quick Start Guides. I’ve also been told Time Warner Spectrum may not allow you to set Power. Perhaps an online Petition to change this ? Thanks for a great article
Some people argue that it is better to use all the power you are allowed to. That takes one variable off the equation. The reason providers set their devices to 100% is to give the users “full bars”.
Hey Petri, important advice needed !
You seem to know a lot and my scenario is totally opposite of the discussion here. I plan to transmit a very long distance 2.4Ghz Wifi , and took 2W power amplifer with RF in and RF out.
On the RF in I’ve attached one of the router SMA ports. On RF out I’ve attached 5Dbi antenna.
This is the amplifier https://www.aliexpress.com/item/1005001897211946.html?spm=a2g0o.order_list.order_list_main.55.2d5818027eiU9W
I’ve tried powering it with 8volts to 20 volts by voltage regulator. Even though the amplifier diode is glowing green and the amplifier does heat especially at 20 volts, the remote device signal is always showing the same. On or Off it is always the same and I benefit nothing. It makes no sense even if the amplifier is one way only. It had to amplify when router switches to TX isn’t it ? I have no idea when it switches on RX on that SMA port where it is connected.
How come 2W and absolutely no difference when attached to one of the antennas ?
Is it possible that it is damaged ? I know that it consumes power and there’s some voltage on the RF out circuit until it reaches a condensor C12 and after it the multimeter shows 0V. This is also something that I wonder. I know that multimeter catches direct current (DC) at 0Hz. If this amplifier indeed made 2 Watts at 8 volts for example then those 8 volts are now direct current of ~2400Hz (converted into radiated radio frequency) and thus the multimeter can’t catch it on DC mode ?
Like what’s your opinion, why nothing changed for TX 🙁 ?
RF amps are illegal here so I have no experience with them. The reason why DC multimeter shows 0V is that it is showing the average of a signal oscillating around 0V. You need a rectifier or switch your multimeter to AC mode.
Without amplifiers the trick is to use directive antennas. You can easily set up 30dBi antennas to transmit over long distances within legal power limits. The only problem is that you need to align the antennas carefully. Laser pointers may be useful.
There are so many wrong things with this article:
The link power is calculated downlink + uplink. If you transmit more power on your router then you’d need to amplify the signal less in your device. Equally amplifiers in the router have a higher gain since they are wall plugged so that’s why the device can transmit less power.
first of all, your wifi front end will be designed to work with maximum power without distorting. – your car audio only distorts if the amplifier you use is too power full for your driver but if they are designed toghether ( which in rf design you have to ) this will never happen.
Secondly wifi is split into channels. The standard is designed to handle the interference at the specified tx power that why there is a maximum and you can’t blast 30dbm of wifi power.
Whoever wrote this clearly has no understanding of rf design and principles.
Thank you for your time. However, there are some points I would like to clarify. If you are referring link power budget then it is calculated downlink + uplink, that is correct. However, amplifying the received client signal at the AP amplifies also the noise, which doesn’t improve signal to noise ratio (SNR) at all. Increasing transmit power at the AP does improve download speeds, but causes problems in roaming and client connectivity.
In car audio, the standard radios with integrated amplifiers are designed together and they still distort. RF circuits should be designed as a unit, but I don’t trust most designs, so I like to leave some margin.
The problem with channels is that there are too few of them. Keeping the TX power low you can reuse channels at a shorter distance. Also, the RF filters aren’t perfect, adjacent channel interference (ACI) does affect nearby transmitters – especially at high power.
Hello Petri,
My question might be irrelevant but I’m just curious, since nowadays we have our phones all the time, is there a risk in making it a hotspot so other devices can connect?
You mentioned that it’s not risky since we are a bit far from AP and it’s only risky if we have the AP under our pillow, what if we use phone as a hotspot, will it act like how the AP does?
I’m not sure how to explain my question but I hope you get my point, hehhee
Yes, you can turn your phone into a hotspot, but its WiFi transmit power is still limited to around 14dBm (or 25mW). Actually, the cellular radio uses much more power, but even that is regulated to a safe level.
Your article on lowering Wi-Fi transmit power is spot on! I’ve experienced firsthand the benefits, from enhanced security to improved device battery life. The emphasis on creating a more localized network is genius – it’s like customizing your Wi-Fi for optimal performance. This advice is a game-changer in a world where connectivity is everything. Kudos for shedding light on this often-overlooked aspect of Wi-Fi management.
Is it also true lowering txpower will cause slower MCS rate to be selected, thereby impacting network performance?
I can’t recall where I saw it, but there was mention that above or below a certain dBm, different MCS rate will be set between STA and AP.
Yes, you are right. Both the STA and the AP will independently keep trying better MCS rates and fall back if it doesn’t work (as the devices may move or the environment may change at any time). Close to the AP you will have good rates at any reasonable power. A little further away higher AP power may help download speeds as AP->STA MCS is higher. However, at the edge you will have problems when the STA receives the AP but not the other way. The solution is to apply as low power as practical (but no less!) 🙂
I am constantly called to troubleshoot odd Wi-Fi behavior. The users are frustrated and the devices don’t roam properly. By balancing the AP power with the typical clients the problems disappear. Yes, in some cases there is slight penalty for downloads, but if you are downloading a huge update you can move closer to the AP.
Very informative, thx a lot
Hello Petri.
The information provided by you is very helpful, thank you for that. But I still have some questions:
1. If band steering is not being used, should I still make 2.4GHz 6-7 db lower than 5Ghz?
2. What is the max acceptable transmit power for 2.4GHz and 5GHz respectively?
1. That would cause “more natural” band steering towards 5GHz.
2. That depends. If you have a sparse deployment (APs far apart) and AC powered client devices then use full power. If you have a dense deployment and/or low power client devices, then use lower tx power. Usually you have a mix of both, so you need to decide which one is more important. Most often I use less than 20dBm. In a dense cell phone environment I might go a lot lower, even below 10dBm
Thanks for your time and answers. Highly appreciate it.
Great information, thank you !
I have some questions. In a residential area, on 2.4Ghz, let’s say there a are 2 to 4 networks per usable channel 1,6,11
All these networks are classic ISP boxes with almost full power and beaconing at 1 mbps, and, on my side, my network on one of these channels with 12 mbps as minimum bitrate and 14 dbm output power
1) Does CCI works the same ? I mean do my “ERP-OFDM” perturbates in any way the HR-DSSS neighborhood wifi ?
2) If a neighbor network frequently switch from 20 to 40 Mhz, allegedly automatically, will my network be more detectable if beaconing at 1mbprs instead of 12 (in order for this neighbor’s AP NOT to switch to 40 mhz width)
3) Is 12 mbps as min bitrate realist at all in a residential, unpredictable environment ?
1) Yes, there is a preamble in front of every transmission that will be detected by older devices, too.
2) Minimum bitrate doesn’t affect the preamble. Transmission power does. In theory if your tx power is very low it is possible that the neighbor AP doesn’t detect it and transmits its high power signal over it. In practice the detection is very sensitive, it doesn’t need to decode the bits. Just receiving a signal marks the channel as occupied.
3) 12 Mbps bitrate works just as well as any other in this respect. All it requires is that you have good enough signal from your APs at all areas of your house.
Thank you very much Petri for the detailed answers !