Increase/Extend WLAN/Wireless Range HowTo

To connect devices in your home network for internet access, file sharing and video streaming there are three common methods: Ethernet Cables, Powerline Adapter (dLAN, PowerLAN) and Wireless Network (WLAN) with 4GHz and 5GHz.
Here are some Tips to increase your Wireless range so that you have WLAN/WiFi access in every room. I will start with a lot of theory, but after going through the article you will be familiar with several methods to increase your wireless range and the advantages of each.


Receiver Sensitivity

Receiver sensitivity is the lowest power level at which the receiver can detect an RF signal and demodulate data.
The receiver sensitivity is always negative. The more negative the dBm value is, the longer the range. To be more precise, for every -6dBm improvement in receiver sensitivity (like from -90dBm to -96dBm) the range where signals can still be processed will double!
Further, the receiver sensitivity is dependent on the data rate. So a WLAN adapter might have a receiver sensitivity of -91dBm @ 11Mps while for 54Mbps it worsens to -71dBm. (See here) If you want to manually lower your WLAN data rate then you can do the following in Windows. Open the Device Manager, find your Network adapter, click on Properties and then select the Advanced tap. There you can set the Property 'Wireless Mode' to 802.11b/g for 54Mbps or 802.11b for 11Mbps instead of 802.11b/g/n for 65Mbps. The Properties that you can set depend on your adapter. For some adapters you can set a value for speed directly. Now if you go to your Network Connections and check the status of your WLAN connection then you should see a different Speed value. For me, manually changing the Speed did not improve the signal. It might be because the adapter is smart enough to automatically adjust the Speed when the signal is weak. However I did not perform any speed tests with strong signal vs weak signal to verify this.


WLAN Adapter Transmission Power

The transmission power of a WLAN adapter is expressed in milliwatt (mW) or decibel (dB or dBm). Generally, the higher the value the larger the range. Typical values are between 50mW/17dBm and 100mW/20dBm for 802.11b/g adapters. But some adapters even have 316mW/25dBm (see which adapter to choose below). And here is one 802.11b/g/n adapter with 2000mW/33dBm for 802.11n@HT40 and an amazing 1584mW/32dBm for 802.11g.


Antenna Transmission/Reception Power Gain

The gain of an antenna is expressed in milliwatt (mW) or decibel (dB or dBi). It expresses the radiation intensity gain in the direction of maximum radiation, compared to the radiation intensity of an isotropic antenna in that direction. An Isotropic antenna is a hypothetical antenna, that radiates equally in all directions (imagine a sphere).
Because the antenna is a passive device, which does not add power to the signal, a gain is only achieved by changing the direction of the signal. So with a higher gain, the radiation in one direction gets larger while the radiation in other directions gets smaller.
The antenna gain value can be added to the transmission power of the WLAN adapter to get the total transmission power.
There is a relation between the gain in dBi and the increase in radiation distance in that direction. For every 6dBi increase in antenna gain you will double the distance to which signals are spread. So if your existing antenna has a gain of 4dBi and you buy a 16dBi antenna, then you will cover four times the distance compared to the original antenna in the main direction because the gain increased by 2x6dBi (assuming ideal conditions).
According to Wikipedia, "the gain of any antenna when receiving is equal to its gain when transmitting". So this means that the distance can be increased simply by changing the antenna of only a single device.


How Receiver Sensitivity and Transmission Power Work Together

If two persons talk to each other and one does not hear well then the other needs to speak louder to communicate. If only one person speaks louder and has better trained ears then the distance can be increased.
The same applies for WLAN adapters. For example, assume there are two equal WLAN adapters that you want to communicate with each other, but the signal is not strong enough. If you increase the transmission power of the first one, then the second can understand the first, but the first cannot understand the second, because the transmission power of the second is still too low (or because the receiver sensitivity of the first is too low). So one right way would be to increase the transmission power of both. Another way would be to increase the antenna gain of one adapter because, as described above, this will increase the transmission and reception gain.


WLAN Repeaters

A repeater does not amplify or modify the signal but it creates a second signal. There are three ways to set up multiple WLAN access points that I came across.
A WLAN repeater (WLAN to WLAN), receives the WLAN signal from the router as client and is access point to clients near it. If the repeater is client and access point on the same frequency, as is the case for many repeaters, then the available bandwidth will be halved. Many routers can work as WLAN repeaters.
An access point (LAN to WLAN), receives the LAN signal from the Ethernet wall socket and is WLAN access point to clients. It is a good choice if you have an Ethernet connection in the area where you want to have WLAN. Many routers can work as Access Point.
A Powerline WLAN repeater (dLAN to WLAN) is like an access point but the LAN signal comes from the dLAN.
To set up one of these additional access points, you can use an additional router or a Mini PC like the Raspberry Pi. The Mini PC would need two WLAN adapters to act as WLAN to WLAN repeater. The Mini PC has the advantage that it can perform additional tasks, like measuring the temperature, in the room where it is installed. This set up is called software access point or virtual access point.


Which Adapter to Choose

If range is the key criterion, then you should go for a WiFi device with an external antenna so that you can use a 5dBi or stronger antenna.
Arguably the most important criterion is the receiver sensitivity. Here is a German web-site that lists the receiver sensitivity for some adapters/chipsets. Adapters with good receiver sensitivity are marked in red. From that list, you can see that the adapter with a Realtek RTL8188SU chipset is one of the good ones. My assumption is that WLAN adapters with the newer chipset, namely Realtek RTL8191SU are equally good. The Realtek RTL8187L chipset has an equally good receiver sensitivity of -96dBm @ 1Mbps, -91dBm @ 11Mps and -71dBm @ 54Mbps. (See here) The Realtek RTL8188RU is also equally good. (See here)
BatLink, a company specializing in long-range WiFi equipment sells a long-range USB WLAN dongle with a Ralink RT3070L chipset. The chipset has also equally good receiver sensitivity but with that adapter you can also control the transmission power up to 316mW/25dBm. (See here)


Which External Antenna to Choose

A standard rod antenna, also called dipole or Omni-directional antenna with a gain of 2dBm radiates signals more or less equal in all directions like a sphere. The higher the gain the further it will extend the horizontal area to which it radiates but the vertical beam width will get smaller. Imagine a Doughnut whose radius increases until it becomes a gigantic CD disk. So for best coverage position it upward. The stated gain refers to the length of the horizontal gain.
If used inside, a high-gain (> 6 dBm) Omni-directional antenna might cause reflections of the signal on furniture and thereby create poor signal quality. (See here)
A Directional antenna will give you a higher gain for the direction it points to and almost no transmission and reception to/from all other directions. Because of its direction, that antenna can reduce the noise by ignoring signals that are not in front of it. The higher the gain, the more will the beam extend to the front but the horizontal and vertical beam width will get smaller. The stated gain refers to the length of the beam forward. The shape of the beam is like an American football.
The positioning of the router and its antenna is, of course, also very important and can solve connection difficulties.
TP-Link, for example, has a number of antennas to choose from. (See here)


Conclusions

How to best extend your wireless range at home will depend on your environment and on your requirements. If there is just one PC in one room with a weak signal, then the easiest might be to purchase a new WLAN adapter for that PC with an external antenna. For example this WLAN adapter with 2000mW transmission power. Unfortunately the manufacturer website link states the receiver sensitivity wrong. The web site states for 11b: -96dBm, for 11g: -92dBm and for 11n: -91dBm. But the datasheet from here states more realistic values, namely for 11b: -92dBm , for 11g: -76dBm and for 11n: -73dBm@HT20 and -70dBm@HT40.
If you want to improve the signal from your router, then you could first check if the antenna has a gain of at least 5dBi. Multiple antennas will improve the speed but not the range. If a new antenna is not sufficient then you could add a WLAN repeater.