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 will give other APs on the same channel equal access to the radio. 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 hear the AP if the AP can’t hear 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 antennas and amplifiers work symmetrically in both directions.

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.

8 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.

  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.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.