How Wi-Fi 7 adaptive puncturing in DFS channels can maximize mesh performance in the 5GHz band

Wi-Fi mesh networks are incredibly popular with consumers today, providing an easily deployable solution for high-speed whole-house Wi-Fi coverage. An exemplary 5GHz band Wi-Fi coverage comparison (Figure 1), demonstrates the significant improvement a Wi-Fi mesh system can have in a typical home.

An essential requirement to deliver on the promise of sufficient Wi-Fi performance for each client within a mesh network area are high-throughput backhaul links with a consistent channel capacity to serve all connected clients accordingly from each mesh node. This implies that the mesh nodes’ backhaul links have access to wide channels with sufficient radio frequency (RF) power to bridge the distance in-between and provide the required link capacity.

The 5GHz spectrum and DFS requirements

A sometimes overlooked aspect of the 5GHz unlicensed band is its significant bandwidth of 480MHz to 560MHz in most geolocations as outlined in Figure 2. The center piece of this spectrum (U-NII-2C, 5470MHz to 5725MHz) offers a contiguous 240MHz channel and relatively high RF power levels that can provide significant throughput as part of a backhaul link. 

However, since Wi-Fi was not the first radio system operating in this spectrum, most regulatory bodies impose some well manageable restrictions on parts of the bandwidth in the U-NII2A and U-NII-2C bands prioritizing incumbents’ access rights, typically through dynamic frequency selection (DFS) and/or transmit power control (TPC) mechanisms.

The DFS operation

A DFS incumbent detection mechanism is mandatory only on access points (APs) and mesh nodes¹ since these exercise control over the operating channels of their connected clients. This helps to keep system cost and implementation complexity reasonable. Additionally, some countries may require Wi-Fi APs and mesh nodes to either operate indoors at lower power levels. To avoid any interference altogether, some countries, such as China, prohibit Wi-Fi APs to access these channels.

Before entering a DFS mandating channel, each AP and mesh node will scan the related 5GHz spectrum for a specified amount of time before it actively engages. Once operating on a DFS channel, the AP continues to monitor for radar pulses and must vacate the parts of the spectrum in which radar activity is detected within a mandated time. Once a slither of spectrum has been marked as exposed to radar signals, the system will wait between 30 minutes to multiple hours before re-engaging in that specific frequency range.

Minimizing the impact of incumbent occupied channels

To minimize the impact of a detected radar system on the total accessible bandwidth, we use Adaptive Interference Puncturing, which is based on a new Wi-Fi 7 method for efficient in-band interference mitigation. It can be used in conjunction with the DFS scanner to continuously use the widest-possible channel bandwidth even in the presence of radar signals.

In case a mesh node detects an incumbent radar signal, the Qualcomm Immersive Home platforms and Qualcomm Networking Pro Series platforms use Adaptive Interference Puncturing, slicing out the incumbent occupied sub-channel(s) from the wideband channel in use (see Figure 3) and continuing to operate in the remaining spectrum, reducing the usable bandwidth in 20MHz or 40MHz increments only, depending on the total channel bandwidth and the nature of the radar system.

Using the maximum available 5GHz spectrum — including the DFS channels — is a key feature of Qualcomm Technologies’ mesh networking solutions based on flexible hardware building blocks, and available turn-key control solutions intelligently providing sufficient backhaul bandwidth to support necessary throughput, latency, and jitter and can dynamically adjust to changing conditions

Qualcomm Technologies’ networking solutions offer a bouquet of different measures to optimize mesh networking performance including an advanced network scheduler², Orthogonal Frequency Division Multiple Access (OFDMA), Multi-Link Operation, and Multi-User Multiple-Input, Multiple-Output (MU-MIMO) to serve a multitude of connected devices, while deploying client connections and backhaul links in a manner that provides sufficient throughput and required latency in most use cases.

Qualcomm Networking Pro Series Wi-Fi 7 Platforms and Qualcomm Immersive Home Wi-Fi 7 Platforms support DFS, Qualcomm Multi-Link Mesh, above-mentioned Wi-Fi 7 features, and more.

 1: We will not address SRD (Short Range Devices) in this context.

 2: See Whitepaper: High performance scheduling unlocks Wi-Fi 6 potential