RFRRU vs. DRU in Wi-Fi 8: Key Differences & Benefits
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Introduction : In the evolution of wireless standards, the way we organize frequency is just as important as the speed of the signal. With the introduction of IEEE 802.11bn (Wi-Fi 8), a new method of tone mapping called DRU (Distributed-tone Resource Unit) has been introduced to be used alongwith traditional RRU method. Let us understand each and understand how they differ.
Regular Resource Unit (RRU)
In an RRU setup, subcarriers (also known as “tones”) are grouped together in a contiguous block of frequency. RRU is the building block of Wi-Fi 6 (IEEE 802.11ax) and Wi-Fi 7 (IEEE 802.11be).
To understand the concept, let us imagine scenario where a single car is assigned single wide lane in which all the data travels together in one solid piece of the spectrum. This is ideal case for high speed data transfer when wi-fi client device is close to AP (Access Point) and signal is also strong. However, in this case as the energy is concentrated in one small area, RRUs often hit regulatory “PSD (Power Spectral Density)” limits set by FCC regulatory standard bodies. This can restrict range of the wi-fi device in the 6 GHz band.
Distributed tone Resource Unit (DRU)
Instead of bunching together, DRU scatters or distributes subcarriers across much wider distribution bandwidth (DBW). It is the major feature of physical layer used in Wi-Fi 8 (IEEE 802.11bn).
For example in 26-tone RU, the total 26 tones remains as is but all these tones are no longer neighbours in frequency domain but spreads out unlike previous wi-fi versions. Due to this, device can transmit at much higher total power without exceeding per-MHz power limits set by regulatory standard bodies such as FCC. Hence DRU performs as range booster which improves uplink reliability and performance for wi-fi client devices that are far away from the AP (Access Point) or router.
Difference between RRU and DRU
Following table mentions comparison between RRU and DRU concepts.
| Feature | Regular Resource Unit (RRU) | Distributed tone RU (DRU) |
|---|---|---|
| Tone arrangement | Contiguous: All tones are grouped in a single frequency block. | Non-Contiguous: Tones are spread across a wider bandwidth. |
| Primary Goal | Maximize Throughput & Efficiency | Maximize Reliability & Uplink Range. |
| Standard Origin | Introduced in Wi-Fi 6 (802.11ax). | Introduced in Wi-Fi 8 (802.11bn). |
| PSD compliance | Higher concentration; hits power limits faster in 6 GHz. | Lower concentration; allows for higher transmit power per tone. |
| Complexity | Low: Simple frequency mapping. | High: Requires complex “Kshift” formulas for indexing. |
| Best Use Case | High speed downloads, streaming, and low range usage. | Long range uplink, IoT sensors and industrial reliability. |
| Spatial Streams | Supports up to 8 spatial streams. | Limited to 1 or 2 spatial streams to reduce complexity. |
| Frequency Logic | Linear tone mapping. | Interleaved/Scattered tone mapping |
Summary
The shift from RRU to DRU represents change of wi-fi’s transition from “speed first” approach to “reliability first” approach. While RRUs remain the king of raw data throughput, the DRU is the solution to the “link budget imbalance” that has long plagued the 6 GHz band, ensuring that Wi-Fi 8 connections remain stable even at the very edge of the coverage area.
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