In the same environment, should the download speeds for Wi-Fi 2.4G and 5G be the same?

My home telecom broadband is 300 Mbps. When I use 2.4G Wi-Fi, the download speed is 7 Mbps, but when I use 5G Wi-Fi, the download speed is 27 Mbps. Is this situation correct? I feel that the download speed within 100 Mbps should be the same.

Theoretically, the download speed should be the same. With a 20 MHz bandwidth, whether it is carried on a 2.4 GHz carrier or a 5 GHz carrier, using the same modulation technology, the theoretical transmission rate should be identical.

However, the reality is harsh: the actual transmission rates of the two differ significantly. What causes this difference?

When using a wired connection, assuming the cable’s transmission rate is 1 Gbps, the user data packet (Data Packet) transmission rate is also 1 Gbps. This means the cable only transmits Data Packets and does not use the 1 Gbps for any other packets.

But when using wireless, in addition to transmitting user Data Packets, it also needs to transmit management frames (Management Packet), such as Beacon, Probe, etc., and control frames (Control Packet), such as RTS/CTS, ACK, etc.

In a 2.4G network, at what rate is the Beacon frame sent periodically (every 102.4 milliseconds) by default?

1 Mbps.

In a 5G network, at what rate is the Beacon frame sent periodically (every 102.4 milliseconds) by default?

6 Mbps.

This means that the 2.4G network uses 1 Mbps to transmit beacons, which lowers the overall network transmission rate. Although the 5G network’s 6 Mbps beacon transmission also lowers the overall transmission rate, it is much better than the 2.4G network.

In addition to management frames, control frames usually use the lowest rate for transmission to ensure high reliability. After all, control frames like ACK, if transmitted incorrectly, will not be retransmitted. Using a low, robust transmission rate ensures it reaches the receiver.

Readers might say that even if the rates for sending management and control frames differ by 5 Mbps, the effective user data transmission rate should differ by 5 Mbps, not the 20 Mbps mentioned in the question. What other reasons cause this difference?

Although 2.4G has 11 available channels, only three channels are truly non-overlapping (non-interfering): channels 1, 6, and 11. In a home LAN environment, there is no one to coordinate channel usage. In fact, it cannot be coordinated. On one floor, to avoid mutual interference, only three wireless routers can be used, each using one of the three channels. But there are so many households upstairs and downstairs; why can you use it, but I cannot? Isn’t 2.4G available for everyone to use?

Channel interference is an eternal topic for 2.4G. Additionally, devices like Bluetooth headphones, mice, cordless phones, and microwaves also use the 2.4G band. If readers are fortunate enough to observe the entire 2.4G band with a spectrum analyzer or oscilloscope, they will find it exceptionally active and busy.

On the other hand, 5G has at least 10 non-interfering channels. Even in a building, each router can choose a channel without interference. Fortunately, although 5G is also an unlicensed band, industrial devices using this band are much fewer than those using the 2.4G band.

Although 2.4G is very busy, can the router be forced to send packets? Taking others’ paths and leaving them with no path?

Absolutely not. Any wireless product certified by the Wi-Fi Alliance must perform two checks before sending any packet:

• Preamble Detection
• Energy Detection

Preamble detection is used to detect packets sent by 802.11 devices.

Energy detection is used to detect signals from non-802.11 devices, such as microwaves and Bluetooth.

If either of these checks is true, the wireless device cannot send any packets.

Due to busy channel competition, wireless devices must wait a long time before sending packets. Of course, 5G, with relatively idle channels, requires less waiting time than 2.4G, indirectly increasing the overall transmission rate of 5G.

Finally, the 2.4 GHz band only has about 80 MHz of bandwidth space, and 40 MHz of 802.11n cannot be used. However, 40 MHz of 802.11n can be used in the 5G network. This is another important factor that makes the overall speed of 5G higher than that of 2.4G.