Difficulties maintaining 160 MHz channel bandwidth

[aru]

In previous firmware versions, even if the bandwidth was set to 20/40/80/160 MHz with DFS channels and auto channel selection enabled, devices could initially connect at 160 MHz. However, after about 5–10 minutes, radar interference would be detected, and the connection would automatically fall back to 80 MHz, never returning to 160 MHz again.

After reading this post, I paid closer attention and noticed that some devices can actually stay connected at 160 MHz for an entire day without issues. This makes me wonder if the new 3006.102.5 firmware, or perhaps the Wi-Fi driver itself, includes specific optimizations for 160 MHz bandwidth.

View Client List, Only with 160 MHz Wi-Fi bandwidth can the network speed exceed 1000 Mbps, and it can remain stable for over 24 hours.

 

[user114514]

There's no need for pointless speculation, as these 160MHz issues aren't caused by DFS. The real problem is TDCS, and simply disabling it will fix the problems.

I advise certain individuals to refrain from giving self-righteous, meaningless opinions without understanding the root cause, as this only misleads everyone unaware of the truth.

 

[bennor]

The real problem is TDCS, and simply disabling it will fix the problems.

To expand the discussion on TDCS; is there anything that indicates what it's value setting, other than zero to disable it, indicates?
And while you suggest disabling wl1_bw_switch_160 and wl2_bw_switch_160, have noticed that on a RT-AX86U Pro (3006.102.5), with the 5Ghz Channel bandwidth set to 20/40/80/160 MHz and 160 MHz set to enabled (PS and no AiMesh), there isn't a wl2_bw_switch_160. Instead there are the following listed in the NVRAM:

wl0_bw_switch_160=2
wl1_bw_switch_160=2
wl_bw_switch_160=2

Would a user with these similar NVRAM entries disable all three if they want to disable the TDCS you mention?
And some may wonder, are there any potential issues or problems by setting the value to "0"?

@user114514 suggested method to disable TDCS when SSH'ing into the Asus router (per their reply one page back):

nvram set wl1_bw_switch_160=0
nvram set wl2_bw_switch_160=0
nvram commit

Note: This assumes the router hardware supports TDCS.

And if anyone cares here is what Brave's search assistant indicates for TDCS on an Asus router (see spoiler tag), take its accuracy and description for what it's worth.

Spoiler: What is Asus Router TDCS

Search Assist
TDCS, or Transmit Data Control System, is a feature in ASUS routers that enhances performance on 80 MHz channels, particularly for WiFi 6 devices. It helps optimize the wireless environment by improving signal quality and overall network efficiency.
shop.adrem.com rog.asus.com

Overview of TDCS in ASUS Routers
TDCS, or Transmit Data Control System, is a feature found in some ASUS routers, particularly those utilizing the latest Broadcom chipsets. This technology enhances the performance of Wi-Fi networks, especially in environments with multiple devices.

Key Benefits of TDCS

• Improved Performance: TDCS optimizes data transmission, ensuring that devices connected to the router experience faster and more reliable connections.
• Enhanced Coverage: By managing how data is transmitted, TDCS helps extend the overall coverage of the Wi-Fi signal, making it more effective in larger spaces.
• Better Channel Utilization: This feature allows for more efficient use of available channels, reducing interference and improving the overall network experience.

Compatibility
TDCS is typically integrated into newer models of ASUS routers that support Wi-Fi 6 (802.11ax) technology. It works alongside other features like TX Shaper to provide a cleaner Wi-Fi environment and optimize performance for devices using 80 MHz channels.

Conclusion
TDCS is a valuable feature for users looking to enhance their wireless network's performance and coverage. It is particularly beneficial in homes or offices with many connected devices, ensuring a smoother and faster internet experience.

 

[user114514]

To expand the discussion on TDCS; is there anything that indicates what it's value setting, other than zero to disable it, indicates?
And while you suggest disabling wl1_bw_switch_160 and wl2_bw_switch_160, have noticed that on a RT-AX86U Pro (3006.102.5), with the 5Ghz Channel bandwidth set to 20/40/80/160 MHz and 160 MHz set to enabled, there isn't a wl2_bw_switch_160. Instead there are the following listed in the NVRAM:

wl0_bw_switch_160=2
wl1_bw_switch_160=2
wl_bw_switch_160=2

Would a user with these similar NVRAM entries disable all three if they want to disable the TDCS you mention?
And some may wonder, are there any potential issues or problems by setting the value to "0"?

@user114514 suggested method to disable TDCS when SSH'ing into the Asus router (per their reply one page back):

nvram set wl1_bw_switch_160=0
nvram set wl2_bw_switch_160=0
nvram commit

Note: This assumes the router hardware supports TDCS.

And if anyone cares here is what Brave's search assistant indicates for TDCS on an Asus router (see spoiler tag), take its accuracy and description for what it's worth.

Spoiler: What is Asus Router TDCS

Search Assist
TDCS, or Transmit Data Control System, is a feature in ASUS routers that enhances performance on 80 MHz channels, particularly for WiFi 6 devices. It helps optimize the wireless environment by improving signal quality and overall network efficiency.
shop.adrem.com rog.asus.com

Overview of TDCS in ASUS Routers
TDCS, or Transmit Data Control System, is a feature found in some ASUS routers, particularly those utilizing the latest Broadcom chipsets. This technology enhances the performance of Wi-Fi networks, especially in environments with multiple devices.

Key Benefits of TDCS

• Improved Performance: TDCS optimizes data transmission, ensuring that devices connected to the router experience faster and more reliable connections.
• Enhanced Coverage: By managing how data is transmitted, TDCS helps extend the overall coverage of the Wi-Fi signal, making it more effective in larger spaces.
• Better Channel Utilization: This feature allows for more efficient use of available channels, reducing interference and improving the overall network experience.

Compatibility
TDCS is typically integrated into newer models of ASUS routers that support Wi-Fi 6 (802.11ax) technology. It works alongside other features like TX Shaper to provide a cleaner Wi-Fi environment and optimize performance for devices using 80 MHz channels.

Conclusion
TDCS is a valuable feature for users looking to enhance their wireless network's performance and coverage. It is particularly beneficial in homes or offices with many connected devices, ensuring a smoother and faster internet experience.

wl2_bw_switch_160 for tri-band models. The specific value depends on your 5GHz radio. For ax86u pro, just set wl1_bw_switch_160.
TDCS is a software feature that doesn't require hardware support. wlx_bw_switch_160=0 just completely disables TDCS without any other side effects.

To summarize the issues people have encountered:
1. The router may sometimes automatically downgrade some 160MHz devices to 80MHz, even though the BSS remains at 160MHz. (This typically occurs in low SNR conditions)
2. The BSS may sometimes abruptly downgrade to 80MHz and fail to recover. This is less likely to occur when the control channel is a DFS channel. (This typically occurs when all 160MHz devices are offline or in sleep mode)

When wl_bw_switch_160 = 2, both of the above scenarios occur.
When wl_bw_switch_160 = 1, only the first scenario occurs.
When wl_bw_switch_160 = 0, TDCS is completely disabled, and the above issue no longer occurs.

 

[user114514]

These issues exist on all routers with Broadcom chipsets, but occur with higher probability on specific models like ax86u. I recommend all users disable TDCS to avoid such problems.

The core idea behind TDCS is that 160MHz should only be used when necessary to improve performance and reliability, but this is fundamentally flawed. According to the Shannon–Hartley theorem, channel capacity C is linearly proportional to bandwidth B and logarithmically proportional to S/N. Therefore, within a given range, a lower MCS and doubled bandwidth will always yield higher rates. This given range is the limit of MCS0.

Each wireless chip contains a lookup table that records the maximum transmit power allowed for each bandwidth and MCS combination.
For 80MHz devices, even if your router has enabled 160MHz, when communicating with 80MHz STAs, it will only use the 80MHz lookup table result. Therefore, 160MHz is not disadvantageous for 80MHz devices.
For 160MHz devices, the Shannon–Hartley theorem ensures that within the MCS0 limit, 160MHz is always the winner. While dropping to 80MHz does extend the absolute range, it's excessive for most users.

 

[user114514]

Additionally, there is an extremely rare scenario that could also cause an unexpected exit from 160MHz: DFS radar misdetection. I'm not sure if anyone has actually encountered this. Generally, modern WiFi chips don't experience this because they typically have precise characteristics of radar waves worldwide already recorded.

If your neighbor also:
1. Uses 160MHz bandwidth
2. Has control channels located on DFS channels
3. Has a high bss basic rate

there exists a possibility that when the neighbor's radio waves reach your router, the SNR is too low to demodulate into a meaningful data, yet the absolute signal strength remains substantial. This scenario could cause poorly designed wireless chips to mistakenly identify it as radar waves, triggering DFS avoidance.
There are workarounds for this situation, but for well-known reasons, I won't share them here.

 

[aru]

There's no need for pointless speculation, as these 160MHz issues aren't caused by DFS. The real problem is TDCS, and simply disabling it will fix the problems.

Thank you for your explanation. I have checked the router’s NVRAM parameters, and wl_bw_switch_160 is set to 2, indicating that TDCS is indeed enabled and has not been modified or disabled. Therefore, the current ability to maintain stable 160 MHz operation is likely not due to TDCS being turned off. It is more probable that the new 3006.102.5 firmware, or the Wi-Fi driver itself, includes certain optimizations for the 160 MHz bandwidth.

Of course, this is just my personal observation, and your explanation may still be applicable to other models or usage environments.

 

[user114514]

Thank you for your explanation. I have checked the router’s NVRAM parameters, and wl_bw_switch_160 is set to 2, indicating that TDCS is indeed enabled and has not been modified or disabled. Therefore, the current ability to maintain stable 160 MHz operation is likely not due to TDCS being turned off. It is more probable that the new 3006.102.5 firmware, or the Wi-Fi driver itself, includes certain optimizations for the 160 MHz bandwidth.

View attachment 67854

Of course, this is just my personal observation, and your explanation may still be applicable to other models or usage environments.

AFAIK BCM4912/4916 devices rarely encounter these issues. You can try changing the control channel to 36-48 to see if it can still stay at 160MHz. Even ax86u typically stays at 160MHz when the control channel is within the DFS channels (52-64, 100-144).