What is Multi-Link Operation (MLO) in Wi-Fi 7?

Multi-Link Operation (MLO) is a Wi-Fi technology that enables devices connected to a Wi-Fi access point (AP) to simultaneously send and/or receive data across different frequency bands and channels. MLO technology is one of the many core features added in Wi-Fi 7 that help enhance the user experience by handling wireless connections more efficiently.

In previous Wi-Fi generations, including Wi-Fi 6 and Wi-Fi 5, a device can only connect to one Wi-Fi band at a time — either the 2.4 GHz band or the 5 GHz band. The latest WiFi 6E products now also connect to the 6 GHz band but can still only connect to one Wi-Fi band at a time. For example,  a typical Wi-Fi 6 router operates on 2.4 and 5 GHz bands, but a smartphone can only connect to it using one of the two bands (2.4 or 5 GHz) at a time. This means that one of the bands will be unused, or one might limit their speeds by choosing the slower band.

The Multi-Link Operation (MLO) of Wi-Fi 7 solves this dilemma. MLO technology aggregates multiple channels on different frequency bands at the same time, negotiating seamless network traffic even if there is interference or congestion. This greatly increases speeds, allows more effective mesh networks, and provides the very latest interference mitigation techniques to ensure wireless devices are always connected fast and reliably, even in dense network environments. With MLO, Wi-Fi 7 can establish multiple links between the device (such as a smartphone) and the Wi-Fi access point (such as a 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.

Both the access point and client device need to support Wi-Fi 7 and MLO to use this feature. 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 devices to connect to all the available Wi-Fi bands at the same time. MLO operates mainly in two modes:

• STR Mode (Simultaneous Transmit and Receive Operation) - STR Mode refers to simultaneous transceiver mode or asynchronous mode. In this mode, two or more links work completely independently, and they don’t interfere with each other. Hence they are capable to transmit and receive simultaneously in different links.
• NSTR Mode (Nonsimultaneous Transmit and Receive Operation) - NSTR Mode refers to non-simultaneous transceiver mode or synchronous mode. In this mode, simultaneous receiving and sending operations are not allowed. At a single time, all links can only receive or all links can send data.

Apart from STR/NSTR modes, there are other MLO modes. Due to the different application scenarios of Wi-Fi 7 MLO, such as Mesh and EasyMesh, sometimes there are multiple links composed of multiple physical IC radios at both ends of the connection (access point and client device). There are also multiple links composed of conventional mobile devices with a single IC.

Benefits of using MLO in Wi-Fi 7

• It increases the data rate (or throughput) by aggregating multiple links at different bands/channels.
• It improves latency using load balancing which mitigates congestion on one link.
• It increases reliability by duplicating packets on multiple links.
• It allows network traffic to flow seamlessly under interference or congestion scenarios.
• It supports traffic separation/differentiation which separates different traffic flows to different links.

Disadvantages of using MLO

• Using wider and more channels consumes more power which is challenging in mobile device development.
• MLO causes an increase in PAPR (Peak to Average Power Ratio) in wider channels.
• There are different interference levels and properties on different subchannels which makes it more complex to deal with them.

Wi-Fi 7 is currently under development and its standard is planned to be rectified by 2024. To keep up with the growing demand for bandwidth and data speeds, Wi-Fi with its MLO technology will be ready to deliver higher WiFi speeds, more stable WiFi, and lower latency, ensuring no bandwidth is wasted.

Click here to read a white paper on Wi-Fi 7 MLO.