Resource Unit
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Resource Unit (RU) is a unit in OFDMA terminology used in 802.11ax WLAN to denote a group of subcarriers (tones) used in both DownLink (DL) and UpLink (UL) transmissions. With OFDMA, different transmit powers may be applied to different RUs. There are maximum of 9 RUs for 20 MHz, 18 in case of 40 MHz and more in case of 80 or 160 MHz.[1] The RUs enables an Access Point station to allow multi-users to access it simultaneously and efficiently.
Description
In OFDMA, an OFDM symbol is constructed of subcarriers where the total number defines a Physical Layer PDU bandwidth. Each user is assigned different subsets of subcarriers to achieve simultaneous data transmission in MU (Multi-Users) environment. The more subcarriers are used, the longer their symbol rate is, which means that the overall rate of information remains the same.
There are a few RUs currently defined: 26-tone RU, 52-tone RU, 106-tone RU, 242-tone RU, 484-tone RU, 996-tone RU and 2x996-tone RU. For example, for basic 20 MHz bandwidth, nine 26-tone RUs can be used, but only four with 52-tone RUs.[1]
| RU Type | CBW20 | CBW40 | CBW80 | CBW80+80 and CMW160 |
|---|---|---|---|---|
| 26-Tone RU | 9 | 18 | 37 | 74 |
| 52-Tone RU | 4 | 8 | 16 | 32 |
| 106-Tone RU | 2 | 4 | 8 | 16 |
| 242-Tone RU | 1 | 2 | 4 | 8 |
| 484-Tone RU | N/A | 1 | 2 | 4 |
| 996-Tone RU | N/A | N/A | 1 | 2 |
| 2x996 Tone RU | N/A | N/A | N/A | 1 |
See also
- Frequency-division multiple access
- Single-carrier FDMA (SC-FDMA), a.k.a. linearly precoded OFDMA (LP-OFDMA)
References
- ^ a b c 802.11 Working Group, IEEE (October 2017). IEEE P802.11ax™/D2.0 Draft Standard for Information technology— Telecommunications and information exchange between systems Local and metropolitan area networks—Specific requirements: Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications; Amendment 6: Enhancements for High Efficiency WLAN. New York, New York 10016-5997, USA: IEEE. pp. 357–360.
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