Hi, everyone! Today I’m going to introduce wifi 6 lossless roaming.
With the development of automation, the global logistics IT investment amount keeps increasing rapidly. Warehousing logistics is one of the most important parts of the logistics industry and is also the logistics sub-scenario that has the most network requirements. The IT investment in warehousing accounts for 47% of the total investment in the logistics industry. From the perspective of industry trends, the warehousing and logistics industry is developing towards informatization automation and intelligentization. It has the following characteristics:
Driving force: E-commerce promotes the rapid growth of the logistics market space, and the CAGR exceeds 12%.
Increasing labor costs and demands drive the logistics industry to develop towards automation and intelligentization.
Third-party logistics service providers in the logistics industry are increasing, up to more than 70% in Europe and the United States, and increasing professionalism.
E-commerce promotes the construction of cold chains and has higher requirements for the device environment.
Except for the rapid development of industry requirements, automatic robot control and scheduling pose unprecedented requirements on the real-time, reliability, and concurrency capabilities of WLAN communication. The existing network for traditional Internet access or manual warehousing applications cannot meet the feature and specification requirements.
Typical problems with these scenarios are:
The terminal and WLAN are provided by different vendors. As the WLAN protocol does not specify the roaming status of the STA, therefore, the roaming behavior of the terminal depends on the default conservative configuration provided by the chip vendor. That is, the STA roams in the worst case. In this case, the SNR is extremely low.
Protocols such as 802.11v and 802.11r are not mandatory for improving the roaming speed. And a large proportion of terminals does not support 802.11v and 802.11r. As a result, the terminal is disconnected from the previous BSS. Before roaming, the terminal needs to perform full-channel scanning. This is disastrous for continuous and delay-sensitive network services.
The following key technologies will solve the preceding pain points in multiple aspects.
This solution is based on the AC+Fit architecture and uses the tunnel forwarding mode. Central APs and Fat APs are not involved.
Lossless scanning
The roaming timeliness depends on scanning efficiency. There are 13 channels on the 2.4 GHz frequency band and 25 channels on the 5 GHz frequency band (different country codes). If the scanning time of a single channel is 100 ms, the long-term scanning (100 ms x 13 or even 100 ms x 25) will bring great negative gains to network reliability.
The lossless scanning technology improves the scanning efficiency of the terminal from the actual network topology. According to the network topology, a proper neighboring channel is selected to transmit the channel set to be scanned to the terminal.
The scanning result is timely and reliable, which greatly improves the scanning efficiency.
Before the terminal switches to the channel for scanning, the terminal informs the AP that the AP will delay the sending of buffered packets. This ensures that no packet loss occurs during STA scanning.
Efficient roaming
To ensure the timeliness of roaming and the reliability of the network, the roaming algorithm can be divided into two parts: the generation of roaming target and the determination of roaming time. The roaming target generation algorithm generates a roaming target AP list based on historical scanning results. Then, the roaming time determination algorithm determines the optimal AP that meets the roaming conditions as the target AP for roaming.
The STA instructs the network side to buffer packets before roaming. After the roaming is successful, the cached packets are sent back.
This algorithm ensures that an STA can roam to a BSSID with good quality and service continuity.
Note: This scenario is applicable to the tunnel forwarding mode.
Strong anti-interference capability
The anti-interference capability of the air interface for packet transmission is improved in the following aspects to meet the requirements for high packet reliability in the case of light AGV application traffic:
When the environment deteriorates, the AMC algorithm of AGV VAP needs to reduce the transmit rate to improve the anti-interference capability.
The priority of service packets associated with AGV terminals is increased to the VO level. The dynamic EDCA parameter is enabled to further improve the priority of V0 services and the capability of concurrent multi-service processing. This effect has been demonstrated in voice and video functions.
WMM defines EDCA in 802.11e. EDCA divides data packets into four AC queues. A high-priority AC is more likely to occupy channels than a low-priority AC. Each AC queue is assigned a set of channel contention EDCA parameters. The parameter combination defines the channel occupation capability of the corresponding AC queue. The following figure shows the logical diagram of the AC queue to channel contention.
1. Higher roaming reliability, lower latency, and lower packet loss rate, greatly improving network service capacity.
2. The reliability of network links is greatly improved, and the AGV data link is more stable. This effectively improves the usage capability in complex air interface environments and ensures service quality.
3. This greatly reduces the number of parking faults caused by network disconnection of small vehicles, ensures orderly AGV scheduling, and significantly improves network load.
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