Hi umaryaqub,
OFDM
In telecommunications, orthogonal frequency-division multiplexing (OFDM) is a type of digital transmission and a method of encoding digital data on multiple carrier frequencies. OFDM has developed into a popular scheme for wideband digital communication, used in applications such as digital television and audio broadcasting, DSL internet access, wireless networks, power line networks, and 4G/5G mobile communications.
OFDMA
Before 802.11ax, the OFDM mode is used for data transmission, and users are distinguished by time segment. In each time segment, a user completely occupies all subcarriers and sends a complete data packet. 802.11ax introduces a more efficient data transmission mode, namely, OFDMA (because 802.11ax supports the uplink and downlink multi-user mode, this mode can also be called MU-OFDMA). This mode implements multi-user multiplexing of channel resources by allocating subcarriers to different users and adding multiple access in the OFDM system.
Compared with OFDM, OFDMA has the following advantages:
1. Finer channel resource allocation. Particularly, in a case in which a channel state of some nodes is not good, transmit power may be allocated according to channel quality, so as to allocate a channel time-frequency resource in a more refined manner.
2. Better QoS. 802.11ac and earlier standards occupy the entire channel to transmit data. If a QoS data packet needs to be sent, the packet can be sent only after the previous sender releases the entire channel. Therefore, a long delay occurs. In OFDMA mode, one sender occupies only some resources of the entire channel. Therefore, data of multiple users can be sent at a time. This reduces the access delay of QoS nodes.
3. More concurrent users and higher user bandwidth. OFDMA divides the entire channel resource into multiple subcarriers (also called sub-channels). The subcarriers are further divided into several groups based on different RU types. Each user may occupy one or more groups of RUs to meet different bandwidth requirements.
For more information of OFDMA, you can refer to https://forum.huawei.com/enterprise/en/wlan-from-beginner-to-expert-wi-fi-6-post-2-how-ofdma-makes-a-difference/thread/644187-869
I hope it helps!
