Eliminate interference to solve the biggest problem of Wi-Fi

802.11 technology has made great strides over the past 10 years-faster, more powerful, and more scalable. However, there is still a problem that affects the reliability of Wi-Fi.

There is nothing more to complain about than the unstable Wi-Fi performance, poor coverage, and frequent disconnection, which makes the network administrator crash. Solving the invisible and changing environment of Wi-Fi is indeed a problem. RF interference is also the culprit.

RF interference comes from almost all devices that can emit electromagnetic signals-cordless phones, Bluetooth phones, microwave ovens, and even smart meters. However, most enterprises do not realize that the biggest source of Wi-Fi interference is their own Wi-Fi network.

Unlike the authorized spectrum, a certain amount of bandwidth is authorized to a specific service provider. Wi-Fi is a shared medium that anyone can use. It operates in the 2-4 GHz and 5 GHz free-of-Authorization frequencies.

When a 802.11 client device listens for other signals, the device will suspend data transmission regardless of whether the signal is a Wi-Fi signal or not until the signal disappears. Interference during data transmission may cause data packet loss, which forces WiFi to re-transmit data. Retransmission may cause a decrease in data throughput and cause a general impact to users sharing the same AP.

Although the spectrum analysis tools are now integrated in the AP to help IT departments observe and identify Wi-Fi interference, if they do not effectively solve the interference problem, then there is no practical significance.

RF interference has become more serious due to the launch of the new wireless standard 802.11n. 802.11n transmits several Wi-Fi data streams in different directions and directions using multiple RF signals in an AP to achieve higher connection rate. Now, the chance of a problem doubles. If one of these signals is disturbed, as 802.11n is used to significantly improve the data transmission rate, space reuse and channel binding will all become invalid.

Solutions to Interference Problems

Generally, the methods to solve RF interference include reducing the physical data rate, reducing the transmit power of the affected AP, and changing the channel allocation of the AP. Although these methods have their own expertise, none of them directly address RF interference problems.

At present, the market is filled with a large number of APS using omnidirectional bipolar antennas, which send and receive signals in various directions. Because these antennas always send and receive signals regardless of the environment, once there is interference, these systems have no way to fight against interference. They have to reduce the transmission rate of physical data until the acceptable packet loss level is reached. This is too inefficient. In addition, all users who share the AP will feel the intolerable performance decline.

What is incredible is that reducing the AP's data rate actually produces the opposite result as expected. Data Packets stay in the air for a longer time. This means that it takes longer to receive these packets, which increases the risk of packet loss and makes them more vulnerable to periodic interference.

Another common approach for Wi-Fi is to reduce the transmit power of the AP to make better use of the limited number of channels. This reduces the number of devices that share an AP to improve AP performance. However, reducing the transmission power will also reduce the strength of the client to receive signals, which is transformed into a lower data rate and a smaller range of Wi-Fi coverage, leading to the formation of a coverage hole. These holes must be filled by adding more aps. With more aps added, we can imagine that it will produce more interference.

Do not change the channel

Finally, most WLAN vendors want you to believe that the best solution to wi-fi interference is "change the channel ". When the RF interference increases, the AP will automatically select another "clean" channel.

Although changing the channel is an effective method to solve continuous interference at a specific frequency, interference tends to be constantly changing and sometimes absent. By redirecting in a limited channel, it may cause more problems than it solves.

In the most widely used 2.4 GHz Wi-Fi band, there are only three non-interference channels in total. Even in the 5 GHz band, there are only four non-overlapping 40 MHz wide channels after the dynamic frequency selection (DFS) is removed, DFS is a mechanism that allows unauthorized devices to share spectrum with existing radar systems.

Figure: available channels for 802.11 working in 5 GHz band

The AP needs to disconnect the connected client from and associate it again for channel change operations. This will interrupt the speech and video applications and lead to the domino effect caused by the adjacent AP changing the channel to prevent interference from the same channel.

The same channel interference is the interference between devices when different devices use the same channel or use the same wireless band to transmit and receive Wi-Fi signals. To minimize interference with the same channel, network administrators try to better design their networks. For a limited range of available spectrum, the distance between AP deployment is pulled far enough, so that they cannot listen or interfere with each other. However, Wi-Fi signals will not stop or be limited by these architectures.

The method for changing the channel does not take into account the customer's experience. In these scenarios, interference depends on the favorable position of the AP, but what does the customer see? Is it true to transfer to a clean channel to improve user experience?

Solicitation scheme: stronger signal and lower interference

A technical metric for predicting the performance of a Wi-Fi system is the signal-to-noise ratio (SNR ). SNR is the difference between the received signal level and background noise intensity. Generally, the higher the signal-to-noise ratio, the lower the bit error rate and the higher the throughput. However, once interference occurs, some other problems may concern network administrators, that is, the signal-to-interference-to-noise ratio, also known as SINR.

SINR is the difference between the signal level and the interference level. Because it reflects the negative impact of RF interference on user throughput, SINR is a better indicator to reflect the performance of a Wi-Fi system. The higher the SINR value, the higher the data transmission rate and the larger the spectrum capacity.

Figure: SINR is an important indicator of Wi-Fi system performance.

To obtain higher SINR indicators, the Wi-Fi system must improve signal gain or reduce interference. However, the problem is that the traditional Wi-Fi system can only increase the signal strength in a certain direction by increasing the power or setting up a high-gain oriented antenna on the AP, however, this limits the coverage of small areas. The Adaptive Antenna Array adopted by the latest Wi-Fi innovative technology is a good news for network administrators. It uses the advantages of Oriented antennas to gain and channel, in addition, the same region is overwritten with fewer APs.

Use smarter antennas to solve Interference Problems

The ideal goal of Wi-Fi is to send a Wi-Fi signal directly to a user and monitor the signal to ensure that it is delivered to the user at the maximum rate. It continuously redirects Wi-Fi transmission in the signal path, which is clean and does not need to change the channel.

The new Wi-Fi technology combines dynamic beam forming technology and small smart antenna arrays (the so-called "smart Wi-Fi") to become the solution closest to the ideal Wireless World.

The antenna-based beam technology is a newly developed technology used to change the form and direction of RF energy emitted by the AP. Dynamic beam technology focuses on Wi-Fi signals and automatically guides them around interference only when they need it, that is, when interference occurs.

These systems apply different antenna modes for each client, and change the antenna mode when a problem occurs. For example, in case of interference, a smart antenna can select a signal mode that degrades in the direction of interference, so as to increase SINR and avoid reducing the physical data rate.

The antenna-based beam technology uses multiple targeted antenna elements to provide thousands of antenna modes or paths between the AP and the client. RF energy can be radiated through the optimal path to obtain the highest data rate and the lowest packet loss rate.

The monitoring confirmed by the standard Wi-Fi Media Access Control (MAC) Client determines the signal strength, throughput, and packet loss rate of the selected path. This ensures that the AP can accurately understand the customer experience-and in case of interference, the AP can completely control the selection of the optimal path.

Smart Antenna Arrays also take the initiative to reject interference. Because Wi-Fi only allows one user to be served at a time, these antennas are not used to transmit data to a specified client, but are used by all clients, in this way, the interference signals that normally suppress Wi-Fi transmission can be ignored or rejected. The result is that the signal gain of up to 17dB can be obtained in some cases.

Figure: Automatic interference avoidance using dynamic beam technology

Note: As shown in the figure, by proactively avoiding interference, additional signal gains can be obtained, reaching-17dB; APS integrated with smart antenna arrays; dynamically optimized antenna modes; through beam forming, signal can be enhanced to 10dBi.

Perhaps the biggest benefit of this new technology is that it can run automatically without manual adjustment or manual intervention.

For network administrators, due to the impact of a large number of new Wi-Fi devices on the enterprise network, it is becoming increasingly important to solve the problem of RF interference. At the same time, users have higher and higher requirements for Wi-Fi connection reliability, and demand for supporting streaming media applications is increasing.

Solving the problem of RF interference is the key for enterprises to adapt to these trends in their development. But to implement it, we need to adopt more intelligent and adaptive methods to deal with uncontrolled Wireless frequencies, which are the root cause of all these disturbances.