MU-MIMO vs. OFDMA: Key Differences Explained

This article breaks down the key distinctions between MU-MIMO (Multi-User Multiple Input Multiple Output) and OFDMA (Orthogonal Frequency Division Multiple Access).

MU-MIMO and OFDMA are techniques used to improve the performance of wireless communication systems. Let’s dive into what makes them different.

MU-MIMO Explained

MU-MIMO stands for Multi-User Multiple Input Multiple Output.

• How it Works: In MU-MIMO, multiple data streams are transmitted simultaneously, as illustrated in Figure 1. Beamforming techniques are used to target individual users, effectively increasing overall capacity.

  

  Image alt: Multi user MIMO

• Advantages:

  • Increases overall capacity.
  • Results in higher speeds for individual users.
  • Ideal for applications requiring high bandwidth.

• Applications:

  • Used in both uplink and downlink of 802.11ax (Wi-Fi 6).
  • Used in the downlink of 802.11ac (Wi-Fi 5).

OFDMA Explained

OFDMA stands for Orthogonal Frequency Division Multiple Access.

• How it Works: OFDMA allocates subcarriers to users based on their specific bandwidth needs. It doesn’t necessarily increase capacity, but it uses the available resources more efficiently.

  

  Image alt: OFDM vs OFDMA

• OFDM vs. OFDMA:

  • In OFDM (Orthogonal Frequency Division Multiplexing), all subcarriers of a symbol are dedicated to a single user at a time. This can lead to wasted resources if the user doesn’t have data to transmit during that time.
  • In OFDMA, multiple users can be multiplexed simultaneously, each with its dedicated set of subcarriers. This allows scheduling multiple users with varying bandwidth requirements. Figure 2 (above) illustrates the difference in frame structures between OFDM and OFDMA.
  • In OFDMA, a Resource Unit (RU), consisting of a subchannel and a number of symbols, is allocated to individual users.

• Advantages:

  • Increases efficiency in resource utilization.
  • Reduces latency.
  • Ideal for low bandwidth applications.

• Applications:

  • Used in cellular wireless technologies like WiMAX (16e), LTE, and 5G.
  • Also used in 802.11ax (Wi-Fi 6).

Conclusion

Both MU-MIMO and OFDMA are valuable techniques that complement each other to improve wireless network performance.