Wi-Fi 6 Acceleration for Latency-Sensitive Services

Release Date:2021-07-26  Author:By Chen Daowei  Click:

With the arrival of Wi-Fi 6 comes the massive deployment of gigabit fixed networks. The increasing adoption of gigabit broadband promotes rapid development of virtual reality (VR) service. The VR technology is characterized by immersion, interaction and conception, and its applications mainly include livestreaming and gaming. The development of the Internet and the widespread use of smartphones have generated an exponential growth in mobile gaming. There are currently more than 2.2 billion mobile gamers worldwide, with around 60% of the gaming devices connected to games via Wi-Fi. Peak latency between stations (STAs) and access points (APs) produces over 60% of game buffering. The recently emerging cloud VR games demand that home Wi-Fi networks provide high bandwidth and low latency.

Network Requirements of Latency-Sensitive Services
Multiplayer online battle arena (MOBA) is a genre of games that is currently in vogue. MOBA games generally require a latency of no greater than 50 ms, a bandwidth of 1 Mbps, and packet loss of less than 10-5. VR games are rendered locally or in the cloud. For locally-rendered VR games, the network requirements are similar to those of MOBA. For cloud-rendered VR games, the network requirements are higher, with latency no longer than 15 ms, bandwidth at 260 Mbps, and packet loss smaller than 10-5.
To accelerate MOBA and cloud VR games, they first have to be identified from the many services carried over the Internet pipeline. For MOBA games, the AP or gateway uses the game server domain name request originated by the gaming terminal to determine what type of game is being played, and utilizes the media access control (MAC) address of the terminal to decide what data traffic is generated by the game. Cloud VR games have high requirements for the entire network including the home, access, and upper-layer networks. The games are usually configured with dedicated channels that can be used to identify them.

Wi-Fi 6 Acceleration for MOBA Games 
To enable low-latency, low-bandwidth MOBA games, ZTE has developed wireless routers that support MOBA game acceleration technologies. Lab test data shows that, under the same interference environment, the acceleration technologies drastically reduce bi-directional latency from 12 ms to 5 ms.
Intelligently identifying MOBA games and changing their service priority: The router uses deep packet inspection technology (DPI) or domain name requests to identify MOBA games, tags their service priority, and maps their traffic to the access category of voice (AC-VO) of Wi-Fi multimedia (WMM). This avoids MOBA games competing with other Internet services in the same channel for air time and helps gaming traffic better contend for air time.
Increasing the number of retransmissions to reduce packet loss: Loss of MOBA game packets is not allowed. On the router, a high number of retransmissions can be configured for WMM AC-VO so that services like video and download do not cause Wi-Fi buffer overflows, thereby cutting the packet loss of MOBA games.
Disabling A-MSDU to boost transmission efficiency: A Wi-Fi chip aggregates packets and then sends the aggregated packet to improve transmission efficiency. When a transmission error occurs, the aggregate MAC service data unit (A-MSDU) frame needs to retransmit the entire packet, which will greatly impair transmission efficiency in an interference-heavy environment. Disabling the A-MSDU function slashes the probability of aggregating the usually small packets of MOBA service. This not only decreases the retransmissions of the aggregate packet due to local packet errors, but also shrinks the waiting time experienced by the aggregate MOBA packet.
Lowering the modulation rate of gaming terminals to raise Wi-Fi coverage: The router allows the initial modulation rate of game packets to be cut. For example, a modulation rate with 20 MHz bandwidth and a low modulation and coding scheme (MCS) can be configured to obtain a higher transmission gain to reduce packet errors and burst latencies. If the gaming terminal supports dual carrier modulation (DCM), which is a new feature of Wi-Fi 6, having DCM enabled on the router will further increase the transmission gain.

Wi-Fi 6 Acceleration for Cloud VR Games
To implement low-latency, high-bandwidth cloud VR games, ZTE has developed wireless routers that support cloud VR game acceleration technologies. Lab test data shows that, under the same interference environment, the acceleration technologies significantly decrease bi-directional latency from 21 ms to 7 ms. 
Built-in mini-content distribution network (CDN): To reduce latency, the home gateway or router can cache in advance the high-bitrate and large field-of-view (FOV) images of cloud VR games. When the user turns the VR headset, the cached images can be retrieved from the home gateway or router. This mechanism can reduce the latency between the home gateway or router and the cloud VR server by about 8 ms.
WMM priority mapping of cloud VR games: Considering that cloud VR games are of high bandwidth and low latency, game traffic should be classified into control traffic and video traffic, and the two types of traffic should be tagged with different priorities at both the server and client. Control traffic takes up little bandwidth but does not allow packet loss, while video traffic uses much bandwidth but tolerates a small amount of packet loss. Therefore, the router maps control traffic to the AC-VO and video traffic to the access category of video (AC-VI). In this way, control traffic can obtain Wi-Fi air time more easily, while video traffic can have more transmission opportunities (TXOPs) and more data can be sent.
Smart QoS based on Wi-Fi 6: Wi-Fi 6 supports orthogonal frequency-division multiple access (OFDMA), enabling an AP to send data to multiple STAs simultaneously to enhance transmission efficiency at the air interface and lessen the packet latency. When one access category (AC) covers multiple STAs and services, priority scheduling can be performed to give a higher priority to VR game packets to ensure the quality of service (QoS) of VR games. When there are multiple ACs, different bandwidths can be allocated to them and the AP can schedule multiple ACs each time it sends data. Each time data is transmitted, VR game packets can be sent, thus increasing the throughput and reducing the packet latency of VR games.
Preamble puncturing based on Wi-Fi 6: The preamble puncturing feature of Wi-Fi 6 allows the router to avoid an occupied bandwidth of 20 MHz in the middle of the channel. The router can switch among the 20, 40, 60, and 80 MHz bandwidths, which considerably improves switching flexibility. In addition, to reduce the interference conflict at the primary 20 MHz channel, a Wi-Fi 6 AP can obtain the channel information of the neighboring AP(s) through channel scanning and select a 20 MHz channel with the least interference as its primary channel. The router can use the dynamic frequency selection (DFS) function to notify the connected STA(s) to dynamically switch channels.
Intelligent packet discarding for video traffic of VR games: Interference always exists at the Wi-Fi air interface, so low-probability packet loss is unavoidable. When packet loss occurs, some packets of the video traffic of VR games should be discarded. Different types of video frames are given different discarding priorities to ensure the transmission of key video frames and curtail the transmission of video frames that cannot be decoded. This technique improves video transmission efficiency and cuts video stuttering. When the video media server or CDN encodes videos to generate video packets, it tags different types of video frames with different differentiated services code point (DSCP) priorities. To distinguish different types of video frames, video transmission devices only need to identify their DSCP priority tags, thus accelerating the process of recognizing and discarding video packets.

ZTE employs a series of Wi-Fi 6 acceleration technologies to optimize latency-sensitive services such as MOBA games and cloud VR games. The acceleration technologies not only improve user experience of the games, but also provide comprehensive service assurance capabilities like easy installation and maintenance and efficient deployment, helping operators upgrade home networks from being bandwidth-centric to being experience-centric and make a strategic transformation.

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