Exploring high-density WLAN deployment technology (1)

Exploring high-density WLAN deployment technology (1)

Statistics show that at least two or three wireless terminals are currently used at the same time (mainly laptops, tablets, mobile phones, and smart wearable devices ). Users enjoy the convenience brought about by mobile payment, mobile social networking, and mobile marketing. manufacturers need to provide wireless signals anytime, anywhere. This involves a problem: how to solve WLAN coverage at a high population density?

I. High-density coverage

The density of terminals in real high-density scenarios is far greater than normal imagination. It neither has several people meeting in a conference room, nor has some people watching videos, Weibo, or chatting in a cafe. The so-called high-density coverage scenario usually refers to a similar application scenario.

The high-density scenarios of the waiting hall are characterized by difficult deployment, large space, high user mobility, poor channel quality, and complicated business types.

In comparison, high-density applications for large-scale conferences are deployed flexibly and relatively closed, and users are relatively stable. channels are of good quality, can be coordinated, and business types can be controlled. According to the deployment practices, there are mature and reliable solutions for large-scale conferences with high-density WLAN coverage. For example, the number of Internet Security Conferences is more than 3000, many conferences have more than people, and on-site access has a good wireless experience.

The deployment difficulty of high-density scenarios is mainly related to two factors. The first is that 802.11 of the protocols have defects, and the second is due to the lack of wireless spectrum resources. The details are as follows:

● Multi-Channel Access/conflict avoidance by carrier listeners (CSMA/CA)

The IEEE 802.11 standard uses a method called carrier-based multi-channel access/conflict avoidance (CSMA/CA) to avoid conflict.

To avoid conflicts, all workstations are required to listen before each frame is transmitted. When a workstation has frames to send, it will face one of the following situations:

○ If no other device is transmitting data, the workstation can transmit its frames immediately. The receiving workstation must send a confirmation frame to confirm that the original frame has arrived without conflict.

○ Another device is being transmitted, and the workstation must wait. After the current frame is transmitted, it will wait for a random period of time before transmitting its own frame.

That is to say, each AP can only communicate with one terminal at a time. When the number of terminals is large, a large number of APs need to be deployed to carry the business traffic. In the future, the 802.11ac protocol will improve this defect. A single AP can communicate with up to four terminals at the same time, greatly improving the communication efficiency. To some extent, it will reduce the difficulty of high-density coverage.

● Same-frequency interference

The greatest difficulty for large-scale AP deployment is how to plan frequency and control power. We deploy enough aps in a limited space based on the maximum number of users to access and the minimum bandwidth required for network services. But the core of the problem is how to solve the same frequency interference.

02.11 B/g/n operates in the GHz band. The 2.4 GHz frequency band ranges from 2.483 GHz to GHz. According to China's frequency planning, there are only 1, 6, and 11 non-interference channels, with a bandwidth of 20 MHz for each channel. Therefore, in the past GHz WLAN coverage scheme, using 3 or less APS can completely avoid interference. When the number of APS is greater than 3, frequent mutual interference will inevitably occur. The more users, the more APs are required, and the more severe the same frequency interference, wireless resources of the entire network are exhausted.

II. Key Technologies for high-density coverage

The high-density coverage solution is not implemented by one or two technologies, but by integrating dozens of Wireless Access optimization technologies. It also involves innovative technologies developed by manufacturers based on their own practices. For example, the package-by-package power control technology was developed by H3C and applied for a national patent. Next, we will analyze the key mainstream technologies of high-resolution coverage.

● Large-capacity AP

Generally, the maximum number of terminals included in the AP published by the manufacturer is based on the parameters in the MAC address table. In actual use, the user's traffic is not considered. The traffic is measured at 4 Mbps per user, the maximum number of users of a single AP in many manufacturers is up to 30, each AP can be deployed at a high-key level and can support up to 100 users online at the same time ).

● Intelligent Multi-Vibrator antenna system and Selection Algorithm

An array antenna is composed of multiple antennas. Different antennas are formed through the combination of different antennas during working, virtual antennas with different directions, angles, and gains are implemented to adapt to different working environments and locations of different users and avoid unnecessary interference. The adaptive array antenna can quickly calculate the optimal antenna combination mode by judging the working environment and perception of the user's location during work and processing the internal chip, the purpose of coverage. Wireless access devices can form up to 4096 different kinds of Ripple modes through combinations of different antennas, which can easily adapt to various indoor environments and increase coverage to achieve stable network quality.

● Channel Reuse Technology

As mentioned above, deploying a WLAN Network in a high-density environment should minimize the visibility between APs. To solve this problem, you can use the AP channel Reuse Technology and adjust the ap rf parameters to filter out the interference of neighboring weak signals of the same frequency, reduce conflicting domains and increase throughput.

● Empty port message Suppression

The biggest factor affecting coverage is empty port utilization. If the utilization rate of the blank port has reached 60% or above before deployment, then WLAN coverage will be almost ineffective. In addition to the user usage rate, the empty port usage mainly comes from the following aspects:

● Use of other Wi-Fi signals, such as self-built Wi-Fi hotspots;

● Non-Wi-Fi signals or air ports unavailable due to increased noise, such as Bluetooth and microwave ovens;

● The occupation of empty ports by unrelated messages of associated and non-associated user data.

According to practical experience, other Wi-Fi signals usually occupy about 15%, and non-Wi-Fi signals occupy about 12% of the channel. The first two points cannot be adjusted or changed by our own devices. Therefore, we need to perform very fine-grained Optimization on the third point. The empty port message suppression function allows you to independently manage data frames, management frames, and control frames in the empty port.