What is MU-OFDMA in WiFi (802.11 ax) Wireless Communication ?

Introduction: WiFi technology continues to evolve, delivering faster speeds and improved efficiency to meet the growing demand for high performance wireless connectivity. One key innovation in the WiFi 6 (802.11 ax) standard is Multi User Orthogonal Frequency Division Multiple Access (MU-OFDMA). This advanced feature revolutionizes the way data is transmitted, enhancing network efficiency and reducing latency, especially in dense environments. In this guide, we'll explore what MU-OFDMA is, how it works and its impact on wireless communication.

What is OFDMA?

We already know about OFDM which stands for Orthogonal Frequency Division Multiplexing. In OFDM, all the subcarriers are assigned to individual client all the time during its time interval. In OFDMA, total subcarriers are divided into groups which is known as subchannel. The one or more subchannels are assigned to the clients based on bandwidth requirement. OFDM has been used in previous WLAN standards such as 802.11a/g/n/ac as well as fixed wimax (16d). OFDMA has been used in mobile wimax (16e), LTE and 5G cellular systems. First time OFDMA has been adopted in WLAN 802.11ax standard in order to increase efficiency of the wifi system. IEEE 802.11ax is the latest in series of wifi standards.

What is MU-OFDMA?

• OFDMA is multi-user version of OFDM used in 802.11a/g/n/ac.
• It allows multiple client devices (i.e. users) with varying BW to use wifi network simultaneously.
• OFDMA divides wifi channel into small frequency allocations known as RUs (Resource Units).
• AP communicates with individually assigned clients simultaneously due to their unique allocations of RUs.
• The figure-1 depicts MU-OFDMA in which channel bandwidth is divided into number of channels. Each of these channels can be used by multiple clients at different time instants unlike previous wifi standards.

• OFDM divides single channel into multiple subcarriers using IFFT. Subcarriers are orthogonal and hence they do not interfere with one another. Moreover it prevents ICI (Intercarrier Interference).
• OFDM has been employed in 802.11ac with 20 MHz Bw. This 20 MHz has 64 subcarriers with 312.5 kHz spacing between them. It has symbol duration of about 3.2 microsecond. OFDMA in 802.11ax uses larger symbol duration of about 12.8 µs. It has subcarrier spacing of about 78.125 KHz.

Advantages of MU-OFDMA

Following are some of the benefits of MU-OFDMA.
1. It helps in better frequency reuse in the wifi network across broad region.
2. It helps in reducing latency between wifi client and Access Point (AP).
3. It helps to increase network efficiency.
4. Narrow subcarrier spacing in 802.11ax allows better equalization and enhanced channel robustness.
5. Due to 78.125 kHz channel spacing, OFDMA with 20 MHz BW consists of total of 256 subcarriers as shown in the figure-2. Subcarriers are categorized into three types based on their functionalities viz. data subcarriers, pilot subcarriers and unused subcarriers.

Conclusion

MU-OFDMA is a cornerstone feature of WiFi 6 (802.11ax), designed to meet the challenges of modern wireless communication. By enabling simultaneous data transmission for multiple users, it significantly enhances network performance and user experience. Whether it's streaming, gaming, or supporting IoT devices, MU-OFDMA ensures efficient, low latency communication. As WiFi technology advances, features like MU-OFDMA will continue to shape the future of wireless connectivity.
➨Also refer difference between OFDM and OFDMA >>.

WiFi 6 Resources as per IEEE 802.11ax

WiFi 7 Resources as per IEEE 802.11be

WiFi Technology RELATED LINKS

Useful Links to Legacy WLAN Standards

RF and Wireless Terminologies