Denial of interference to solve the biggest problem with Wi-Fi

This article reprinted to: Http://www.ciotimes.com/net/rdjs/WI-FI/201006301920.html

RF interference in English: RFI, (Radio Frequency interference)

Japanese: Electronic wave barrier Damage

Summary:
Keywords: Wi-Fi radio frequency interference channel

802.11 technology has grown dramatically over the last 10 years – faster, more powerful, and more scalable. But one problem still haunts Wi-Fi;

There is nothing more than users complaining about Wi-Fi performance is not stable, coverage is not good, often drop the network manager to crash. Addressing Wi-Fi, an invisible and changing environment, is really a problem. and radio frequency interference is also a culprit.

RF interference comes almost from all devices that emit electromagnetic signals – cordless telephones, Bluetooth phones, microwaves and even smart meters. But most businesses are unaware that the biggest source of Wi-Fi interference is their own Wi-Fi network.

Unlike the authorization spectrum, a certain amount of bandwidth is authorized to be used by a particular service provider. Wi-Fi is a shared medium that anyone can use, and it works in both 2.4Ghz and 5Ghz unlicensed bands.

When a 802.11 client device hears other signals, whether or not the signal is a WiFi signal, the device will suspend the transfer of data until the signal disappears. Interference in data transmission can result in packet loss, forcing WiFi to retransmit data. Retransmission results in decreased data throughput and a pervasive impact on users sharing the same AP.

While the spectrum analysis tools are now integrated in the APS to help it monitor and identify Wi-Fi interference, there is no real sense if they don't solve the interference problem effectively.

The problem of radio frequency interference becomes more serious due to the introduction of the new wireless standard 802.11n. 802.11N typically uses multiple RF signals in one AP to transmit several Wi-Fi traffic in different directions and orientations, enabling a higher connection rate. Now, the chance of a problem doubles. If one of these signals is disturbed, the spatial multiplexing and channel bindings are all invalidated as the basic technique of 802.11n for significantly higher data rates.

Common practices for solving interference problems

The usual methods of solving radio frequency interference include reducing the physical data rate, reducing the transmitting power of the affected AP, and changing the channel allocation of the AP by three ways. Although these methods have their own expertise, none of them is directed to the RF interference problem.

The market is awash with APS with omni-directional bipolar antennas that send and receive signals from all directions. Since these antennas are always in the environment, sending and receiving signals in all situations, and in the event of interference, these systems have no alternative but to fight interference. They have to reduce the physical data transfer rate until an acceptable packet drop level is reached. This is simply too inefficient. And with that, all users sharing the AP will feel intolerable performance degradation.

Incredibly, reducing the data rate of the AP actually produces the opposite of the desired result. The packet stays in the air for a longer period of 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 practice for Wi-Fi design is to reduce the transmit power of the AP, thereby making better use of the limited number of channels. Doing so reduces the number of devices that share an AP to improve the performance of the AP. But lowering the transmit power also reduces the strength of the client's received signal, which translates into lower data rates and a smaller range of Wi-Fi coverage, leading to the formation of a cover hole. And these voids have to be filled by adding more APs. and by adding more APS, you can imagine that it would create more distractions.

Please do not change the channel

Finally, most WLAN vendors want you to believe that the best solution for Wi-Fi interference is "change the channel." is that when RF interference increases, the AP automatically chooses another "clean" channel to use.

Although changing the channel is an effective way to resolve persistent disturbances at a specific frequency, the disturbances tend to change and sometimes are not. By jumping in a limited channel, the problem is even more problematic than it solves.

In the most widely used 2.4GHz Wi-Fi band, there are only three non-interfering channels in total. Even in the 5GHz band, there are only 4 non-overlapping 40MHz wide channels after the removal of the dynamic frequency selection (DFS), a mechanism that allows unauthorized devices to share the spectrum with existing radar systems.

　　

Figure: Available channels for 802.11 working in the 5GHz band

The change channel operation performed by the AP requires that the connected client be detached and associated again. This will cause interruptions in speech and video class applications and result in a domino effect caused by the transformation of the channel by neighboring APs to prevent the same channel interference.

Co-channel interference is an inter-device interference that occurs when different devices use the same channel or transmit and receive Wi-Fi signals from the same wireless band. To minimize co-channel interference, network administrators are trying to better design their networks. For a limited spectrum of available frequencies, the distance between the APS deployed is pulled far enough to make it impossible for them to listen or interfere with each other. However, Wi-Fi signals do not stop and are not limited by these architectures.

The way the channel is changed does not take into account the customer's perception of how to use it. In these scenarios, the interference depends on the vantage point of the AP, but what does the customer see? Does moving to a clean channel really improve the user experience?

Solicitation Scheme: stronger signal, lower interference

A technical indicator for predicting the performance of a Wi-Fi system is the signal-to-noise ratio (SNR). The SNR is the difference between the received signal level and the background noise intensity. Typically, the higher the signal-to-noise ratio, the lower the error rate and the higher the throughput. However, once the interference occurs, there will be some other problems to make the webmaster worry, that is, signal and interference plus the noise ratio, also known as SINR.

SINR is the difference between the level of signal and the level of interference. Because it reflects the negative impact of RF interference on user throughput, SINR is a better indicator of what performance a Wi-Fi system can achieve. The higher the SINR value, the higher the data transfer rate, and the greater the spectral capacity.

　　

Figure: SINR is an important indicator for determining the performance of Wi-Fi systems

In order to obtain a higher SINR indicator, Wi-Fi systems must be achieved by increasing signal gain or reducing interference. The problem is that traditional Wi-Fi systems can only increase the signal strength in a direction by increasing power or by erecting high-gain directional antennas on the AP, but this limits the coverage of small areas. The latest Wi-Fi innovation technology uses an adaptive antenna array as the webmaster brings the gospel, using the advantages of directional antennas to gain and channel, and with fewer APs to achieve the same area coverage.

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 it is delivered to the user at the maximum rate. It continuously redirects the Wi-Fi transmission on the signal path, which is clean and does not need to transform the channel.

The new Wi-Fi technology combines dynamic beamforming with a small smart antenna array (known as "smart Wi-Fi") as the closest solution to the wireless ideal realm.

Dynamic, antenna-based beamforming is a newly developed technique for changing the form and direction of radio frequency energy emitted by APS. Dynamic beamforming focuses on Wi-Fi signals and automatically "directs" them around the perimeter when they need it, i.e. when interference occurs.

These systems have different antenna patterns applied to each client and change the antenna mode when the problem arises. For example, in the case of interference, the smart antenna can choose a signal mode attenuation in the direction of interference, thereby increasing the SINR and avoiding the use of the method of reducing the physical data rate.

Antenna-based beamforming technology employs multiple directional antennas to provide thousands of antenna modes or paths between the AP and the client. RF energy can be radiated through the best path, resulting in the highest data rates and lowest packet loss rates.

Monitoring of the standard Wi-Fi media access control (MAC) client confirmation determines the strength, throughput, and packet loss rate of the selected path. This ensures that the AP is able to know exactly what the customer's experience is-and that the AP has full control over the selection of the best path when it encounters interference.

Smart antenna arrays will also actively reject interference. Because Wi-Fi allows only one user to be served at the same time, these antennas are not used to transmit data to a specified client, but are used for all clients, in order to ignore or reject interference signals that typically suppress Wi-Fi transmissions. As a result, a signal gain of up to 17dB can be obtained in some cases.

　　

Figure: Using dynamic beamforming technology to automatically avoid interference

Note: The figure shows that by proactively avoiding interference, additional signal gain can be obtained, up to -17db; APs with integrated smart antenna array, dynamically optimized antenna mode, and beam forming, the 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 management personnel, due to the impact of a large number of new Wi-Fi devices on the enterprise network, to solve the problem of radio frequency interference is becoming more and more important. At the same time, users are increasingly demanding the reliability of Wi-Fi connectivity, and the need to support streaming media applications is increasing.

Solving the problem of radio frequency interference is the key to adapt to these trends in enterprise development. But to implement it means a smarter and more adaptable way to handle runaway wireless frequencies, which are the root causes of all these distractions.

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Denial of interference to solve the biggest problem with Wi-Fi