Hello, everyone!
As a supplement to the ONT basic knowledge, I begin to introduce a series of basic Wi-Fi knowledge.
Today, I will share knowledge about OFDMA.
In Wi-Fi standards earlier than Wi-Fi 6, data is transmitted in orthogonal frequency division multiplexing (OFDM) mode, and users are allocated different time slots. In each time slot, a user occupies all subcarriers and sends a complete data packet.
Wi-Fi 6 introduces a more efficient data transmission mode, which is called orthogonal frequency division multiple access (OFDMA). As Wi-Fi 6 supports the upstream and downstream multi-user mode, this mode can also be called MU-OFDMA. It achieves multi-user multiplexing of channel resources by assigning subcarriers to different users and adding multiple access to the OFDM system. Similar to LTE, the smallest sub-channel is referred to as a resource unit (RU) in Wi-Fi 6. Each RU includes at least 26 subcarriers, and a user is distinguished based on a time-frequency RU. First, the resources of an entire channel are divided into small time-frequency RUs of a fixed size. In this mode, user data is carried on each RU. Therefore, in terms of the total time-frequency resources, multiple users can send data at the same time in each time slot, as shown in the following figure.
Orders are delivered separately, it is highly possible that trucks are not fully loaded.
The OFDMA technology aggregates multiple orders so that trucks on the road are as full as possible. In this way, the transportation efficiency is greatly improved.
Although Wi-Fi 6 allows OFDMA and MU-MIMO to be used at the same time, do not confuse OFDMA and MU-MIMO. OFDMA improves concurrency efficiency by subdividing channels (subchannels) in multi-user concurrent access scenarios, while MU-MIMO improves throughput by using different spatial streams in such scenarios. The following table compares OFDMA and MU-MIMO.
OFDMA | MU-MIMO |
Higher efficiency | Higher capacity |
Lower latency | Higher rate per user |
Suitable for low-bandwidth applications | Suitable for bandwidth-hungry applications |
Suitable for small-packet transmission | Suitable for large-packet transmission |
In Wi-Fi 6, MU-MIMO and OFDMA can be used separately.
OFDMA increases the air interface efficiency and greatly reduces the application latency. It transmits small data packets at higher efficiency within the working signal-to-noise ratio (SNR) range and is suitable for wireless voice or similar application scenarios. MU-MIMO improves the system capacity and efficiency of transmitting large data packets in high SNR scenarios and is applicable to video, web browsing, and office applications.
That's all for today's basic knowledge sharing.
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