8 reasons to turn down the transmit power of your Wi-Fi

By default almost all WiFi access points transmit at full power (100mW on 2.4GHz). This gives maximum coverage and users see a good signal (“full bars”). However, there are good reasons to turn down the transmit power to a fraction of the maximum.

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 it will share the air time with them. 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 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. 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 transfer 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 us, 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.

42 thoughts on “8 reasons to turn down the transmit power of your Wi-Fi”

  1. Great post. Learnt a lot and remembered some almost truly forgotten and valuable and important information.

    Thanks metis.

    AlienC

  2. 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!

    1. 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.

    2. Start at the lowest option and increase power as needed to find the optimal coverage for your apartment.

  3. 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!!

    1. 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.

  4. 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.

    1. 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.

  5. 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.

    1. 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

      1. 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.

  6. Yes. But how do i reduce power on lumia windows phone im asking, huh? Tell me people if you’re so smart.

    1. 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.

      1. 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.

  7. 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. 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.)

  8. 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?

    1. 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.

  9. 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.

    1. 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.

    1. 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.

  10. 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.

  11. 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.

    1. 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.

  12. 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?

    1. 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.

      1. 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.

      2. 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.

  13. You start at 0 and end at 8. Should this be titled _9_ reasons to turn down the transmit power of your Wi-Fi?

    1. 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.

  14. 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”?

    1. 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.

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