A WiFi RU, or Resource Unit, is a fundamental building block used in Wi-Fi 6 (802.11ax) technology to efficiently allocate spectrum for data transmission.
In the context of 802.11ax Wireless Local Area Networks (WLAN), a Resource Unit (RU) is defined as:
A unit in OFDMA terminology used in 802.11ax WLAN to denote a group of 78.125 kHz bandwidth subcarriers (tones) used in both DownLink (DL) and UpLink (UL) transmissions.
This definition highlights the core concept: RUs divide the available channel bandwidth into smaller, distinct segments that can be assigned to different users simultaneously.
Understanding Resource Units (RUs)
RUs are central to Orthogonal Frequency-Division Multiple Access (OFDMA), the multi-user version of the OFDM technology used in previous Wi-Fi standards. Instead of having one user occupy the entire channel bandwidth at a time, OFDMA allows an access point (like your router) to communicate with multiple devices concurrently by assigning each device one or more RUs.
- Composition: An RU is formed by grouping specific frequencies, or subcarriers, each having a bandwidth of 78.125 kHz. The smallest possible RU consists of a set number of these subcarriers. Larger RUs are made up of more of these subcarriers grouped together.
- Direction: RUs are used for both:
- Downlink (DL): Data transmitted from the access point to client devices.
- Uplink (UL): Data transmitted from client devices to the access point.
- Power Allocation: As noted in the reference, "different transmit powers may be applied to different RUs." This allows the Wi-Fi system to optimize performance for each user or transmission by adjusting power levels based on channel conditions or distance.
Why RUs Matter in WiFi 6
The introduction of RUs via OFDMA significantly improves Wi-Fi efficiency, especially in environments with many connected devices and mixed traffic types (like web browsing, streaming, and IoT data).
Key Benefits of Using RUs:
- Increased Efficiency: Multiple devices can transmit or receive data concurrently using their assigned RUs within the same channel. This is much more efficient than the "one device at a time" method used in older Wi-Fi standards.
- Lower Latency: By allowing simultaneous small transmissions, OFDMA reduces the time devices have to wait to send or receive data, leading to lower latency, particularly for applications sensitive to delay.
- Improved Performance in Crowded Networks: In homes or offices with many connected devices, RUs help manage traffic flow better, ensuring a smoother experience for all users.
- Optimized Resource Allocation: RUs can be allocated dynamically based on device needs, ensuring bandwidth is used effectively.
In essence, RUs are the key to how Wi-Fi 6 can serve more devices more efficiently than its predecessors, by finely slicing the available spectrum and assigning these slices (the RUs) to different users as needed.
