In this article, we will dive into everything you need to know about Transmit Power and Transmit Power Control in Wi-Fi. If you are interested in something more, you can check out our article about the most important warehouse Wi-Fi design tips, after you read this article.
What is Transmit Power in Wi-Fi?
Transmit Power is the amount of radio frequency energy given out by a wireless transmitter.
What is Transmit Power Control?
Transmit Power Control is a feature in 802.11h, in which wireless access points can define local parameters for their maximum transmit power.
Essentially, it reduces the power of a radio transmitter to the minimum necessary to maintain the link within a certain quality. It is also used to avoid interference with other devices and/or extend the battery life.
What is Dynamic Transmit Power Control? (TPC)
Dynamic Transmit Power Control is the ability to dynamically change the transmit power of the wireless access point to accommodate itself to the wireless environment.
This is based on certain parameters such as the amount of unwanted interference, channel usage, and signal strength of neighboring wireless access points, etc.
How does Dynamic Transmit Power Control Work For Wireless Access Points?
Dynamic Transmit Power Control automatically calculates the amount of transmit power to be used, by calculating different environmental parameters such as the signal strength from neighboring access points (APs), channel usage, and the number of access points.
From this calculation, the Dynamic Transmit Power Control algorithm will compute a suitable transmit power level to be used by the wireless access points.
What is a Good Transmit Power For Wi-Fi?
A good transmit power for Wi-Fi is around 10-14 dBm (decibels relative to milliwatt) also known as 10-25 milliwatts, as a general rule of thumb.
What is the Best Transmit Power in 5 GHz Wi-Fi?
The best transmit power in 5 GHz Wi-Fi is 10-17 dBm (decibel milliwatts) aka 10-50 milliwatts. This is because the 2.4 GHz band tends to operate between 8-13 dBm; so we’ll want to be around 4-6 dBm above the 2.4 GHz band. This will ensure client devices will ‘prefer’ the 5 GHz band over the 2.4 GHz.
Does Wi-Fi Transmit Power Affect Speed?
Yes, Wi-Fi transmit power does somewhat affect speed. If the transmit power is too low, the signal strength will also be reduced. This will affect the data rate of your wireless connection, thereby affecting your speeds.
What is the Maximum Transmit Power for 2.4 GHz Wi-Fi?
The maximum transmit power for 2.4 GHz Wi-Fi is around 20-30 dBm, depending on the manufacturer of your choosing.
What is the Maximum Transmit Power for 5 GHz Wi-Fi?
The maximum transmit power for 5 GHz Wi-Fi is around 20-30 dBm as well, depending on your wireless access point manufacturer. As per 802.11H, different regions will have different maximum allowed transmit power on the 5 GHz channel for both indoor and outdoor environments.
Do I enable or disable 802.11H?
You should generally enable 802.11h for scalability and manageability of enterprise wireless networks. By enabling 802.11h, almost 16 additional DFS channels will be enabled.
Should I enable or disable 802.11D?
802.11D is always enabled by default, and you cannot disable it without potentially breaking local laws. 802.11D is the country regulation for your wireless network. Different countries and regions permit different channels in the 5 GHz band to be used.
For example, Australia prohibits the use of channels 124 to 128 on Wi-Fi because these specific channels are reserved for weather radars. If you are using these channels, you could get in trouble as you might be interrupting the weather radar channels.
Should You Turn Up Transmit Power on your Wi-Fi Router?
You can turn up the transmit power if you do not have enough coverage or range in your environment; as turning up the transmit power often leads to positive results, that will improve the Receive Signal Strength of client devices.
This also depends on the distance from your access points to your networking devices, or if you have thick walls or anything between them, whereby if the transmit power is turned up too much, you can run into a scenario whereby the client device is able to ‘hear’ the AP but the AP is unable to ‘hear’ the client device.
This can cause high amounts of retransmissions in your Wi-Fi network which would lead to slower speeds and lower reliability. So, having a proper Wi-Fi design is pretty important to avoid situations like this.
What are the Different Types of Transmit Power?
There are 2 types of transmit power: active gain and passive gain.
Active gain uses an increase in transmit power level to subsequently increase signal strength, and sometimes performance, assuming everything is done properly. A signal amplifier can even be used, if necessary.
Passive gain achieves better signal strength by using an antenna that has a higher gain. The higher the gain, the more concentrated the signal will be in a certain direction. Additionally, this also increases the receive sensitivity of the radios.
What Happens if Transmit Power is Too High?
When Transmit Power is too high, it can lead to lower data rates; this will translate to slower speeds, as shown on the diagram above. This is because the laptop is able to ‘hear’ the AP very well, but the AP isn’t able to ‘hear’ the laptop well enough.
This is a great example of what happens when the access point has a transmit power that is too high. As you can see from the diagram, the receive signal strength is excellent, at -57 dBm. However, the wireless AP isn’t able to ‘hear’ the signal very well, and leads to data not being able to be acknowledge. This will in turn lead to the transmitter needing to retransmit the same data.
Each time data is retransmitted, the data rate and modulation get shifted progressively lower, so that the data will be comprehensible and simple enough to be acknowledged. Low data rates means slow and sluggish Wi-Fi speed, that leads to bad user experience.
For more information regarding data and modulation rates, you can check it out here.
What Happens When Transmit Power is at a Good Level?
When Transmit Power is at the perfect level, the received signal strength and data rates should more or less tally each other as per the MCS Index chart. This means that both the AP and your laptop can ‘hear’ each other at similar levels, which will result in faster speeds, more reliable connection and lower latency.
How Do You Check Transmit Power on Mac OS?
- Hold down the ‘Option’ key
- Left Click on the Wi-Fi icon on the top right.
How Do You Check Transmit Power on Windows?
- Open Command Prompt (Hold Down Windows Key + Press R; and type ‘cmd’, without the quotation marks).
- Type in this command into the box: netsh wlan show interface
Notice that the signal readings will be in percentages. This is the formula to convert the percentage signal reading from percentages to dBM:
Here’s a chart that illustrates the conversion from windows signal percentage to dBm:
| Percentage | dBm |
| 100% | -50 dBm or more |
| 90% | -55 dBm |
| 80% | -60 dBm |
| 70% | -65 dBm |
| 60% | -70 dBm |
| 50% | -75 dBm |
Is Higher Transmit Power Better?
Higher Transmit Power isn’t necessarily better. If your transmit power is too low, the signal strength will also be low, which will result in lower speeds. On the other hand, if transmit power is too high, channel interference will significantly increase and can cause hidden node problems and ‘sticky’ clients. A good general rule of thumb for a recommended transmit power should be 10-17 dBm, averaging 14 dBm.
This makes it so that the wireless access point might have a hard time detecting the signal coming out of the client device. This phenomenon is called Asymmetric Transmit Power.
The Network Guys 
Leave a Reply