Resource Unit

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

802.11ax WLAN is the first WLAN standard to use OFDMA to enable transmissions with multiple users simultaneously (it is called High Efficiency Multi Users [HE-MU] Access). In OFDMA, a 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]

Maximum number of RUs for each Channel Bandwidth (CBW)[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

Resource Units allocation is also used in MIMO transmission to enable multiple users to use MIMO at the same time.

See also

References

  1. 1 2 3 802.11 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. |access-date= requires |url= (help)
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