How Does DL OFDMA Works ?
OFDMA is solely used for 802.11 knowledge body exchanges between APs and purchasers. It isn’t utilised for administration or management frames.
AP should first contend for the medium and safe a TXOP earlier than initiating a DL-OFDMA body trade. The AP might transmit a multi-user request-to-send (MU-RTS) body to optimize medium entry and scale back interference. The AP dynamically divides the channel into RUs of various sizes (e.g., 26-tone, 52-tone, 106-tone, 242-tone, 484-tone, 996-tone, and a pair of×996-tone RUs) primarily based on knowledge demand. Wi-Fi 7 permits purchasers to be assigned a number of RUs, permitting them to obtain knowledge over non-contiguous RUs, rising knowledge throughput. Following the simultaneous CTS responses from the purchasers, the AP initiates multi-user DL-PPDU transmissions to the OFDMA-capable purchasers. Word that the AP has determined learn how to allocate the 20 MHz channel into a number of RUs. After receiving their knowledge by the assigned RUs, the purchasers should ship a Block ACK to the AP. The AP first transmits a Block ACK Request (BAR) body, prompting purchasers to reply with Block ACKs concurrently. Alternatively, purchasers might ship an computerized Block ACK in parallel.
Downlink OFDMA.
Analyzing RU allocation in HE MU PPDU:-
Word:- HE-MU: MU-PPDU is used for DL MU-OFDMA transmission.
1. HE-SIG-A subject:
HE-SIG-A subject carries data essential to interpret HE PPDU’s. HE-SIG-A has totally different content material relying on the kind of body.
For instance, HE SU PPDU, HE ER SU PPDU and HE MU PPDU’s may have totally different content material in HE-SIG-A subject. We’ll solely think about MU PPDU’s that are a part of MU-OFDMA transmission.
2. HE-SIG-B subject:
SIG-B subject gives essential data concerning OFDMA and DL MU-MIMO useful resource allocation.This subject solely exists in multi-user transmission.
So, it’s protected to say most of HE data knowledge within the PCAP belongs to SIG-A.
Single-user transmission has solely HE data subject within the PPDU as proven within the determine under.
Single consumer PPDU
HE-MU data, which is simply out there in MU-PPDU. So, most of this knowledge represents SIG-B as proven within the determine under.
Multi Person PPDU
Guidelines governing HE SIG-B fields associated to OFDMA:-
An AP that transmits an HE MU PPDU shall set the UL/DL subject within the HE-SIG-A subject to 0.
The HE-SIG-B subject consists of 1 or two HE-SIG-B content material channels, with every HE-SIG-B content material channel conveying consumer allocation for a number of 20 MHz subchannels. A 20 MHz HE MU PPDU has one HE-SIG-B content material channel, whereas an HE MU PPDU with larger than 20 MHz PPDU bandwidth has two HE-SIG-B content material channels.
If the worth of the HE-SIG-B Compression subject within the HE-SIG-A subject is 0, then the RU Allocation subfield within the Widespread subject in every HE-SIG-B content material channel signifies the mix of RUs within the present PPDU and the variety of Person fields included within the corresponding HE-SIG-B content material channel for every RU.
The RU allocation for the above determine is 484 RU and we will additionally see the supported bandwidth, ie,. bandwidth from Bandwidth subject in SIG-A: 3 if it units the worth 3 means 160Mhz
Multi Useful resource Unit (MRU) Help in EHT PPDUs: Small and Massive MRU Configurations in OFDMA
Now, let’s discover Wi-Fi 7’s MRU (A number of Useful resource Unit) function in OFDMA, a newly launched enhancement in Wi-Fi 7
The EHT PHY permits the usage of MRUs in an EHT PPDU. An MRU is fashioned by combining a number of RUs, together with 26-tone, 52-tone, 106-tone, 242-tone, 484-tone, 996-tone, and a pair of×996-tone RUs.
RUs which can be the identical measurement as or bigger than 242-tone RUs are outlined as massive measurement RUs and RUs which can be smaller than 242-tone RUs are outlined as small measurement RUs.
1. Small measurement MRUs
The small measurement MRUs outlined for DL and UL OFDMA transmissions are as follows: 52+26-tone MRU and 106+26-tone MRU.
The 52+26-tone MRU is fashioned by combining a 52-tone RU and an adjoining 26-tone RU throughout the identical 20 MHz channel. Its knowledge subcarriers are the mixed knowledge subcarriers of each RUs, whereas its pilot subcarriers are the union of the pilot subcarriers from the 52-tone and 26-tone RUs.
Allowed 52+26-tone MRUs in an OFDMA 20 MHz EHT PPDU
The 106+26-tone MRU is fashioned by combining a 106-tone RU and an adjoining 26-tone RU throughout the identical 20 MHz channel. Its knowledge subcarriers are the mixed knowledge subcarriers of each RUs, whereas its pilot subcarriers are the union of the pilot subcarriers from the 106-tone and 26-tone RUs.
Allowed 106+26-tone MRUs in an OFDMA 20 MHz EHT PPDU
2. Massive measurement MRUs
The massive measurement MRU outlined for DL and UL OFDMA transmissions are as follows: 484+242-tone MRU,996+484-tone MRU, 2×996+484-tone MRU, 3×996-tone MRU, and three×996+484-tone MRU.
The 484+242-tone MRU is permitted in OFDMA 80 MHz, 160 MHz, and 320 MHz EHT PPDUs. It’s fashioned by combining a 484-tone RU and a 242-tone RU inside an 80 MHz frequency subblock. Its knowledge subcarriers are the mixed knowledge subcarriers of each RUs, whereas its pilot subcarriers are the union of the pilot subcarriers from the 484-tone and 242-tone RUs.
Allowed 484+242-tone MRUs in a non-OFDMA 80 MHz EHT PPDU
Analyzing RU allocations in EHT PPDU:-
- Guidelines governing the allocation in 11be:-
If the UL/DL subfield within the U-SIG is about to 0, then it signifies the PPDU is distributed to a STA. If a worth of 1 signifies the PPDU is distributed to an AP.
And likewise within the EHT MU PPDU, if the PPDU Sort and Compression Mode are set the worth to 0, then it signifies a DL OFDMA transmission.
Word:- The under tables clarify the bits wanted to set in EHT MU PPDU’s for OFDMA, MUMIMO and so forth..
U-SIG subject of an EHT MU PPDU
