What is WiFi 7’s Multi-Link Operation (MLO)?
Unless you’re purposefully avoiding living life with the convenience of online connections, chances are you understand how vital fast WiFi is today. In fact, upgrading your WiFi to handle even higher speeds can upgrade your life in terms of work and play.
WiFi 7 — the 7th generation of WiFi — is already on its way. Building off of WiFi 6, WiFi 7 introduces 320 MHz ultra-wide bandwidth, 4096-QAM, Multi-RU, and Multi-Link Operation (MLO) to deliver higher WiFi speeds, more stable WiFi, and lower latency, ensuring no bandwidth is wasted.
Out of all of these, MLO shows great promise in completely revolutionizing connection speeds.
So here’s your in-depth overview of Multi-Link Operation.
What is Multi-Link Operation (MLO)?
In previous WiFi generations, including WiFi 6 and WiFi 5, a device can only connect to one WiFi band — either the 2.4 GHz band or 5 GHz band. The latest WiFi 6E products now also connect to 6 GHz.
However, only one WiFi band is available for a client. Let’s take a typical WiFi 6 AX3000 router, with maximum WiFi speeds of 2402 Mbps on the 5 GHz band and 574 Mbps on the 2.4 GHz band, as an example. If you connect your phone to the WiFi, you’ll find that only the 2402 Mbps on 5 GHz or 574 Mbps on 2.4 GHz are accessible for every connection. This means that one band goes unused, or you might limit your speeds by choosing the slower band.
Multi-Link Operation (MLO) solves this dilemma. It enables devices to simultaneously send and receive data across different frequency bands and channels.
With MLO, WiFi 7 supports establishing multiple links between the Station (STA, such as your phone) and WiFi access point (AP, such as your router). Connecting to the 2.4 GHz, 5 GHz, and 6 GHz bands simultaneously increases throughput, reduces latency, and improves reliability. It is ideal for emerging applications like VR/AR, online gaming, remote office, and cloud computing.
Please refer to the appendix for more about how MLO works.
How Can I Use MLO?
The STA and AP both need to support WiFi 7 and MLO. Notice that the 6 GHz band is not required for MLO. Some WiFi 7 routers may only support one 2.4 GHz band and one or two 5 GHz bands. MLO enables your devices to connect to all the WiFi bands at the same time.
Appendix: How Does MLO Work?
MLO is an improvement on the MAC layer. It uses MLD (Multi-Link Devices) multi-link aggregation to achieve higher throughput, lower latency, and higher reliability. MLO uses MLD multi-link seamless dynamic switching to achieve load balancing and low latency.
1. Operating Mode
WiFi 7 MLO mainly includes two modes: STR Mode and NSTR Mode.
(1) STR Mode (Simultaneous Transmit and Receive Operation)
STR Mode refers to simultaneous transceiver mode or asynchronous mode. That is, two or more links work completely independently, and they don’t interfere with each other.
(2) NSTR Mode (Nonsimultaneous Transmit and Receive Operation)
NSTR Mode refers to non-simultaneous transceiver mode or synchronous mode. That is, simultaneous receiving and sending operations are not allowed. At a single time, all links can only receive or all links can send data.
(3) Others
Apart from STR/NSTR modes, there are other MLO modes. Due to the different application scenarios of WiFi 7 MLO, such as Mesh and EasyMesh, there are multiple links composed of multiple physical IC radios at both ends of the AP-STA connection. There are also multiple links composed of conventional mobile devices with a single IC.
2. Technical Features
The main technical features of MLO can be divided into two aspects — packet-level features and flow-level features. The packet-level aggregation improves latency and peak performance while flow-level routing optimization improves latency and overall throughput.
The main features are:
(1) Packet Level Aggregation
- Packets of the same TID (Traffic Identifier) can be sent on one or more radios
- Helps with low-latency and peak throughput improvement
(2) Cross-Wake-Up Signaling for Power-Saving
- AP indicates a buffering unit on a link that the STA is monitoring
- STA can indicate wake-up of a link using another link
- STA can monitor a link in idle mode to receive BSS/TIM information of other links
(3) Fast Link-Transition
- The active link(s) can be switched dynamically to adapt to load/co-ex conditions
- Beneficial for 11be single-radio STAs
(4) Multi-Primary Channel Access>
- Needed for latency improvements
(5) Shared Single Session Across Links
- Single BA (Block Acknowledgement) session per TID, shared sequence number space
- Single authentication and key derivation for unicast packets
- Separate group keys for broadcast/groupcast packets
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