Multi-fold success with Wi-Fi 7 multi-link operation (MLO)

Guest blog by Khushboo Kalyani, Product Marketing, LitePoint

The IEEE 802.11be standard – also known as Wi-Fi 7 – is not just another generation of Wi-Fi standard offering better data rates and improved connectivity. It is also a toolbox of features laying out a flexible framework for adoption across a wide range of end user applications. Here’s an overview of the multiple benefits of MLO – the marquee feature of Wi-Fi 7 by LitePoint’s Khushboo Kalyani. LitePoint is a Wi-Fi NOW Partner.

Wi-Fi is one of the most widely adopted wireless technologies across an array of verticals, such as enterprise, smart home, healthcare, automotive and education. However, as the application use cases evolve, from video conferencing to 3D conferencing or video gaming to real-time cloud gaming, they present distinct key performance indicators (KPIs), whether it in terms of quality of service (QOS), scalability, spectral efficiency, reliability, data rate or latency.

A few ways in which technology could address this demand are by offering new spectrum, increasing transmission channel bandwidth or deploying techniques to improve existing spectrum efficiency. One of the highlight features of Wi-Fi 7 that not only utilizes all of these resources but also optimizes them to service diverse KPI requirements is Multi-Link Operation (MLO).

Disparate global spectrum for Wi-Fi unlicensed use

It may seem like Wi-Fi has an abundant amount of spectrum available for its operation. However, there are a few limitations:

• 2.4 GHz band: Ubiquitously available but offers only three 20 MHz channels, not even close to enough for high resolution, high data rate use cases.
• 5 GHz band: Like 2.4 GHz globally available, theoretically supporting up to six 80 and two 160 MHz wide channels. However, in many instances may only have two usable 80 MHz channels due to the presence of radar systems on the Dynamic Frequency Selection (DFS) channels that limits the overall effective spectrum availability.

• 6 GHz: 1.2 GHz of spectrum, with full 6 GHz band technically supporting seven 160 MHz channels and three 320 MHz channels. Paired with 4096 QAM (Quadrature Amplitude Modulation), the band has the potential to offer extremely high data rates and a seamless user experience. However, the global adoption of this band continues to be fragmented with some countries adopting the entire 6 GHz band, many adopting only the lower portion of the 6 GHz band and a few restricting the use of Wi-Fi in the 6 GHz band entirely.

This disparity in availability of the 6 GHz band across various geographic regions and poor channel availability in the 2.4 and 5 GHz bands leads to inefficiencies in spectrum utilization, limiting the ability of Wi-Fi to support advanced use cases demanding stringent KPIs. Furthermore, despite the end-device’s capability to support multiple bands, the inherent limitation of being able to utilise only single band at a time further limits the true performance potential of Wi-Fi devices.

Higher throughput, deterministic latency, reliability, lower channel congestion:
Not one over the other – but a multifold success with Wi-Fi 7 MLO

MLO is a Wi-Fi 7 feature that allows devices to aggregate multiple channels across different frequency bands into a single connection and efficiently manage it to provide a superior user experience. The deployment flexibility rendered by MLO’s operational versatility offers a way to address several KPIs for next-gen user applications.

• Higher throughput: Multi-channel aggregation with simultaneous Tx/Rx
  One obvious way to increase data rate is by concurrently transmitting/receiving unique streams of data across multiple different channels, thus meetng the demands for data-demanding, real-time applications like video conferencing, over-the-top (OTT) streaming, etc.

• Deterministic latency: Traffic prioritisation
  Uses or availability of multiple channels provides the ability to reserve one of the channels for higher priority data, thus ensuring a predictable latency for sensitive applications like immersive reality, gaming applications, automotive robots, etc. Underneath, the Wi-Fi standard must perform prioritization techniques like traffic classification, packet marking, bandwidth allocation, etc., to ensure effectiveness of multi-link operation.

• Enhanced reliability: Data duplication
  Wi-Fi 7 was developed with consideration of its adoption across not just data heavy or latency critical applications, but also for long range, low power, IoT use cases necessitating link reliability crucial for communication. In such cases, the same data could be transmitted across multiple links to ensure it is received with minimum to no error.

• Reduced channel congestion: Dynamic frequency selection
  During times of network congestion or co-existence issues, especially in the 2.4 and 5 GHz bands from other technologies like Bluetooth or radars, the availability of multiple links enables real-time channel switching to improve the opportunities for transmission and prioritize data transfer.

MLO and its practical implementation

Technically, establishing a multi-link channel communication requires multiple radios on both the access points and client devices (like smartphones, IoT devices, etc.). However, not only does this increase hardware complexit, it also increases the cost of additional antennas and radios to support communication. This added cost and complexity may be justified for products like gateways, access points, customer premise equipment (CPE), which are designed to be feature rich, future proof, but not for smaller form factors like mobile phones or smart home devices, where hardware dimensions or cost are key factors of the purchase decision.

To ensure MLO is usable across varied applications, it primarily supports two different modes of operation – Enhanced Multi-Link Single Radio (eMLSR) & Multi-Link Multi-Radio (MLMR). As the name suggests, within MLMR mode devices use multiple radios to establish multiple spatially multiplexed links.  In contrast, within eMLSR the device’s single radio dynamically switches between multiple links.

Spectrum Flexibility: Asymmetric channel utilisation

As noted above, despite the availability of spectrum the disparity in adoption of the 6 GHz band and/or presence of DFS channels in the 5 GHz band causes an inescapable challenge of limited availability of wider data pipes.

MLO proves to be a perfect solution to tackle the problem, since it allows channels from different bands and varied bandwidth to be aggregated for achieving any of the above-mentioned KPIs. This is especially beneficial in markets with limited to no 6 GHz band availability to efficiently utilize the non-DFS channels in the 5 and 2.4 GHz band for increased bandwidth.[AS1] [KK2]

Conclusion

Unlike previous generations of technologies, Wi-Fi 7 was designed with an underlying motive to support a diverse array of use cases with its rich feature set including support for 320 MHz channels, 4096 QAM, Multi-RU, and preamble puncturing. MLO is a feature which – when paired with any of the above features – will multiply the gains observed even if the spectrum availability is non-contiguous and sparse.

/Khushboo.