OFDMA improves efficiency for WiFi networks from the “spectrum” perspective, and UL & DL OFDMA is one of the most notable and well-known WiFi 6 features among service providers. Its variant applications are now running over WiFi network, however some of the services such as AR/VR and 4K/8K streaming need higher throughputs while some services like gaming and VoIP need lower latency. Some services like IoT require higher reliability. To most services, large spectrum bandwidths such as 80/160 MHz are often more than necessary. With SU-MIMO/MU-MIMO, the whole “spectrum” bandwidth only serves a single STA at a time, which is inefficient utilizing the large spectrum in many application scenarios. OFDMA can divide a large spectrum bandwidth into several smaller RUs (resource units) to carry multiple services for different needs simultaneously. The 11ax defines seven RU sizes constructed by “26”, “52”, “106”, “242”, “484”, “996” or “2x996” SCs (sub-carriers). With the combinations of OFDMA, 8x8 MIMO, different MCS rates and GI (Guard Interval), the 11ax can support a range of data rates from 0.4 Kbps to 9.6 Gbps for different application needs. It is flexible to dynamically allocate RUs in different sizes within the large-spectrum bandwidth according to the STA needs to be fulfilled.
The 11ax defines a maximum of 74 RUs (26-SC) in a 160 MHz channel bandwidth, which means that as many as 74 STAs of different services can be served simultaneously by an AP. Comparing to SU-MIMO/MU-MIMO, the OFDMA can significantly improve the utilization efficiency of the large spectrum a WiFi network can offer. In addition, OFDMA brings other improvements such as lower latency and better reliability as well.
Higher allocation hit-rates can reduce latency.
Smaller RUs with narrower bandwidth can natively provide better SINR (Signal-to-Interference-plus-Noise Ratio). In general, better SINR means wider service coverage or more reliable communications with less retransmissions. It also benefits IoT applications and reliable “ACK” confirmations that don’t require high bandwidths.
For some real-time applications like gaming, lower latency is usually more important than large bandwidth from the user experience perspective. From the technology viewpoint, OFDMA is more capable of having higher grouping/scheduling hit rates per time slot for STAs running time-sensitive services; along with the better SINR thanks to the smaller RUs, the 11ax by OFDMA is expected to significantly improve the latency issue comparing to SU-MIMO/MU-MIMO.
Smaller RUs with narrower bandwidth can natively provide better SINR (Signal-to-Interference-plus-Noise Ratio). In general, better SINR means wider service coverage or more reliable communications with less retransmissions. It can benefit IoT applications with less power consumption.
Similar to DL & UL MU-MIMO, the “DL OFDMA” operations are “Point to Multi-points”, however the “UL OFDMA” operations are “Multi-points to Point”. In synchronization with “CFO”, the “received power variance” in AP and “timing” is also necessary for “UL OFDMA”. Just like “UL MU-MIMO”, “UL OFDMA” can especially improve uplink efficiency by grouped “ACK” confirmations from multiple STAs simultaneously and reserve more air time for effective data transmissions.