The world is hungrier than ever for faster, more reliable Wi-Fi. That’s why the arrival of Wi-Fi 7 (802.11be), or Extreme High Throughput (EHT), is such a big deal. While everyone talks about the lightning-fast 320 MHz channels, the real genius of Wi-Fi 7 lies in a mandatory, game-changing feature that protects that speed: Punctured Transmission (often called Preamble Puncturing).
This simple but powerful innovation is the secret weapon that ensures we can actually use those wide channels efficiently, dramatically improving spectrum efficiency and overall network performance.
1. The Bottleneck: Why Wide Channels Failed in Wi-Fi 6
The evolution of Wi-Fi has always followed a simple path: wider channel equals higher speed. Wi-Fi 5 (802.11ac) and Wi-Fi 6 (802.11ax) pushed channel widths up to 160 MHz.
But there was a critical flaw in this “all-or-nothing” approach.
The Catastrophic Collapse
Imagine you’re trying to use a huge, 160 MHz channel to stream 8K video. If even a tiny piece of narrow-band interference (like a radar signal in the 5 GHz band or a non-Wi-Fi device) pops up in a small 20 MHz segment of that channel, the entire transmission would catastrophically fail.
- Wasted Spectrum: A small interferer, maybe less than 20 MHz wide, could make the whole 160 MHz channel unusable. The system would be forced to revert to the tiny, inefficient primary 20 MHz channel.
- Unacceptable Overhead: In the new 6 GHz band, where Wi-Fi 7 supports channels up to 320 MHz, that tiny bit of interference could invalidate a huge block of spectrum, leading to severe throughput loss.
Prior generations essentially said, “If one part of the road is blocked, we must close the whole highway.”
2. Punctured Transmission: The Granular Solution
Punctured Transmission is Wi-Fi 7’s answer to this waste. It transforms channel usage from a rigid, contiguous block into a resilient, adaptive composite. While it was an optional feature in 802.11ax, it is a mandatory component of 802.11be.
This feature allows the Access Point (AP) and its associated clients to identify, “carve out”, and simply ignore (or “puncture”) unusable 20 MHz sub-channels within a wider composite channel.
| How Puncturing Works | ||
| #1 | Identification: | The AP detects the narrow-band interferer affecting a specific 20 MHz segment of, say, a 160 MHz wide channel. |
| #2 | Puncture Application: | The AP quickly notifies all connected stations to puncture that specific, unusable segment. The segment is completely skipped over for data transmission. |
| #3 | Dynamic Utilization: | Stations are then permitted to use the remaining clean spectrum—whether it’s contiguous or non-contiguous. |
| The result? | A 160 MHz channel affected by a 20 MHz interferer can still operate effectively at 140 MHz (160 MHz minus the 20 MHz puncture). The network avoids a complete channel downgrade and maintains high performance. | |
3. Impact & Benefits: Higher Speed, Lower Latency
The performance benefits of dynamically recovering substantial portions of an otherwise unusable channel are enormous, especially for the high-demand applications Wi-Fi 7 is built to support.
| Benefit | Description |
| Sustained Throughput | The data rate is reduced only proportionally to the size of the puncture (e.g., 20/160), not forced down to the baseline 20 MHz rate. |
| Low Latency | Maintaining a wider effective channel frees up airtime much faster for other devices in the network, preserving the critical low-latency performance that defines EHT. |
| Modulation Stability | Even with a reduced bandwidth, the preserved spectrum segments can continue to utilize Wi-Fi 7’s high-efficiency 4096-QAM, minimizing overall performance degradation. |
4. The Testing Challenge
While Puncturing is a boon for users, it introduces new layers of complexity for device manufacturers and compliance testing. Regulatory bodies, like the FCC, must ensure that even with a channel puncture, the device still meets strict requirements, including:
- Bandwidth Spectral Mask: The device must meet the mask requirements for the total nominal bandwidth, even if the puncture is at the edge or in the middle.
- Band Edges: Test data is required for configurations where the puncture is specifically located at the outer edge of the nominal bandwidth.
- Output Power: The power transmitted within the remaining (un-punctured) regions must adhere to the permitted power levels for that specific bandwidth.
- PSD: A 6 dB reduction is required on the PSD and the conducted power for a client device connected to a standard power access point
Conclusion
Punctured Transmission is more than just a feature; it’s the insurance policy for Wi-Fi 7’s high-speed promise.
By mandating the capability for this fine-grained spectrum carving, 802.11be protects the significant investment in wider channel technology (up to 320 MHz) against common narrow-band interference. This resilience is absolutely paramount to delivering the promised multi-Gigabits-per-second speeds and ultra-low latency required by next-generation applications like AR/VR and cloud gaming.