MU-OFDMA vs MU-MIMO: Key Differences Explained

This article compares MU-OFDMA and MU-MIMO, highlighting their key differences in the context of WLAN 802.11ax.

Introduction:

MU-MIMO (Multi-User Multiple-Input Multiple-Output) enhances overall network capacity by enabling simultaneous transmission of multiple data streams. In contrast, MU-OFDMA (Multi-User Orthogonal Frequency Division Multiple Access) improves efficiency by allocating subcarriers to users based on their individual needs. It’s important to note that MU-OFDMA doesn’t inherently increase capacity like MU-MIMO does. These two technologies are designed to work together, complementing each other in modern Wi-Fi networks.

MU-OFDMA in 802.11ax

Image Courtesy: Aerohive Networks

• OFDMA is essentially a multi-user version of OFDM (Orthogonal Frequency Division Multiplexing), which is used in 802.11a/g/n/ac.
• It enables multiple client devices (users), each with varying bandwidth requirements, to utilize the Wi-Fi network concurrently.
• OFDMA divides the Wi-Fi channel into smaller frequency allocations known as Resource Units (RUs).
• The Access Point (AP) can communicate simultaneously with individually assigned clients due to their unique RU allocations.
• In MU-OFDMA, the channel bandwidth is divided into multiple smaller channels. Each of these channels can be used by multiple clients at different points in time, which is a departure from previous Wi-Fi standards.

MU-MIMO in 802.11ax

Image Courtesy: Aerohive Networks

• MU-MIMO uses different spatial streams to facilitate communication between multiple client devices.
• It employs beamforming techniques to establish unique connections with specific clients.
• The minimum RU size required to use MU-MIMO in 802.11ax is 106 subcarriers or higher.
• The IEEE 802.11ax standard leverages both MU-MIMO and MU-OFDMA to improve network performance. OFDMA provides multi-user access by splitting a single channel into multiple subcarriers, while MU-MIMO offers multi-user access by utilizing different spatial streams.
• MU-MIMO is best suited for scenarios with low client density and applications requiring high bandwidth, where large packets are used for transmission.

Difference between MU-OFDMA and MU-MIMO

The following table summarizes the key differences between MU-OFDMA and MU-MIMO: