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WiFi 7 Multi-link Operation | Advantages of WiFi 7 MLO

This page covers WiFi 7 MLO (Multi-Link Operation) features, MLO modes, MLO architecture and MLO use cases. It mentions benefits or advantages of MLO used in WiFi 7 as per IEEE 802.11be standard and challenges or limitations for MLO implementations.

Introduction: IEEE 802.11be (WiFi-7) is currently under development and draft specifications 1.0/2.0 are available for developers. The standard is planned to be rectified by 2024. IEEE 802.11be is amendment to existing IEEE 802.11 PHY/MAC standards. This WiFi-7 standard is backward compatible with previous WLAN standards and operates in 2.4 GHz, 5 GHz (Lower and higher) and 6 GHz bands. It offers maximum throughput of about 30 Gbps with atleast one operation mode.

Release-1 features include multi-RU per STA, Multi-Link Operation (MLO), low complexity AP coordination, 320 MHz BW channels, 4096 QAM modulation scheme etc. Release 2 features include 16 x 16 MIMO enhancements, HARQ, low latency operations, advanced AP coordination etc.

What is MLO (Multi-Link Operation) ?

Multi-Link operation in 802.11be refers to multi-band and multi-channel. It offers increased data rate, lower latency and increased reliability. It aggregates multiple frequency channels using different frequency bands simultaneously.

WiFi 7 MLO, Multi Link Operation

The figure-1 depicts MLO using three bands 2.4 GHz, 5 GHz and 6 GHz between WiFi AP and STA. It operates in one of the three modes viz. SLO, MLO-STR and MLO-NSTR.

MLO Case Uses

The typical use cases of 802.11be MLO are as follows.
Band Steering/Load Balancing : It helps to mitigate congestion on one link.
Aggregate/Duplicate : It aggregates multiple links to increase data rate. It duplicates critical packets on multiple links to withstand against interference.

MLO Modes

Following are the 802.11be wifi7 operation modes.
SLO (Single Link Operation) : In this mode, only primary channel interface is available.
MLO-STR (Simultaneous Transmission Reception) : In this mode, two radio interface links operate independently and asynchronously. Hence they are capable to transmit and receive simultaneously in different links.
MLO-NSTR (Non-simultaneous Transmission Reception) : NSTR is not capable to transmit/receive simultaneously in different links. In this mode, one interface functions as primary and the other as secondary. Here both the interfaces are available but usage of secondary channel is conditioned on primary also being un-occupied.

Channel access can be done in one of the two ways viz. asynchronous and synchronous. It re-uses link establishment frames and no new frames are added in 802.11be. Discovery and setup follows previous 802.11 standard with some modifications. Power save is done similar to 802.11 TWT aggrements. Target Wake Time (TWT) is designed to minimize contention among STAs in order to save power. It uses new IE (Information Element) in management frames viz. MLE (Multi-Link Element).

MLO Architecture

WiFi 7 MLO device architecture

MLO architecture is implemented with different partition configurations. One such WiFI-7 MLO device architecture is shown in the figure-2. As shown, MAC sub-layer is divided into Lower MAC (LMAC) and Upper MAC (UMAC). UMAC is common for all interfaces to perform link operations. LMAC is individual part for each of the interfaces which perform link specific functionalities such as channel access using its unique parameters. PHY layer will take care of configuring different data rates for various RF bands/channels (2.4 GHz, 5 GHz and 6 GHz).

Benefits or advantages of MLO in Wi-Fi 7

Following are the benefits or advantages of 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.

Some of the challenges of MLO used in WiFI 7 are as follows.
➨Wide channels consume more power which is challenging in mobile device development.
➨There is growth in PAPR (Peak to Average Power Ratio) in wider channels.
➨There is different interference levels and properties on different subchannels.

➨Also refer advantages or benefits of WiFi 7 (802.11be) >>.

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