oliver44 wrote

I tried, the router may have a soft bag or hardware problems!

As your WiFi analysis shows, there are neighboring radios occupying the first 6 WiFi channels. There is even a strong radio ("Tenda_03A388") on the same channel as your family network (channel 6). Thus, the AirTIme available to you and your neighbor is divided between each and every sender using this channel, leaving just a small amount of time for every sending device.

54 Mbit/s wifi speed means your client uses 802.11g. This mode and speed is negotiated dynamically between the device and the AP according to environmental characteristics such as walls in between the link, interferences such as reflections from steel and walls, distance to the AP, etc.

To improve your router's WiFi settings:

Try to use a free (or almost free) channel; this is channel 9 according to your WiFi analyzer. Always use a fixed channel width of 20 MHz. Since each WiFi channel in the 2.4 GHz band spans 5 MHz in width, setting a fixed width of 20 MHz requires as much as 4 channels simultaneously in this band (e.g. channels 7 to 11 if you set it to channel 9).

All 13 available channels are overlapping, so you will hardly find a completely free channel in 2.4 Ghz band nowadays. Anyway, channel 6 is a very bad choice at your place, since there are already two strong senders occupying this channel. Note that only one device - be it your AP, a client device, a neighbor's AP or a neighbor's device - can use the WiFi channel at the same time, so you share the AirTime with the two other wireless networks on channel 6, which greatly reduces maximum throughput theoretically possible with the C2600.

If you are sure your client devices support 802.11n, set fixed 802.11n mode. This uses an improved modulation/coding mechanism. If any client device requires 802.11g, it will be limited to 54 Mbit/s wireless speed in this mode. Only n mode will give you up to 150 to 200 Mbit/s WiFi speed, but only at 40 MHz channel width. The maximum of 800 Mbit/s WiFi speed would need 40 MHz channel width, which would require as many as 8 channels to be used simultaneously in the 2.4 GHz band, and 4 spatial streams to 4 separate client devices each transferring at full 200 Mbit/s wireless speed in MU-MIMO mode. You will never ever reach 800 Mbit/s with only one client device in the 2.4 GHz band.

If you set fixed 40 MHz channel width and n mode only the device will disconnect the WiFi link if it can't allocate the 8 channels needed for this bandwidth in the 2.4 GHz band at any time after going down in speed until the lower limit to ensure a stable connection in this mode.

Be aware that wireless speed is not data speed. In g mode (max. 54 Mbit/s wireless speed), data speed is about 50% of the wireless speed due to the protocol overhead, resulting in 25 to 20 Mbit/s data speed in real life. The data speed is the speed you measure with web-based speed tests.

In n mode you can theoretically get much faster WiFi speeds, but only if the 2.4 GHz band is almost free for use with 40 MHz channel width. Also, if there are obstacles between your device and the AP (such as walls) or interferences (caused by reflections or Bluetooth devices) the WiFi devices will dynamically negotiate lower speeds in order to keep a stable connection (this is what you see when devices change speeds, they constantly negotiate the current WiFi speed according to the actual data traffic: if they are almost idle, WiFi speed goes down, but if data is being sent, WiFi speed increases again.

This being said, getting 40 Mbit/s data speed according to your speed test means that in n mode @ 20 MHz channel width your devices negotiated MCS12, which is 86.7 Mbit/s wireless speed. MCS12 is pretty good in a slightly overcrowded 2.4 GHz band such as shown by your WiFi analyzer. The measures mentioned above for improving the settings can probably increase this speed somewhat, but it all depends on many factors and especially on available AirTime.

So if you get pretty good throughput when using the 5 GHz band (which according to your WiFi analyzer is almost unused at your place and which has no overlapping channels and thus can grant you full AirTime exclusively even in ac mode with 80 MHz channel width), consider to use only the 5 GHz frequency band for devices requiring high speeds.

BTW: For stationary devices like a Smart TV I would use a cable connection if it has an Ethernet port. Unless you take your TV with you when leaving the room, there is no real need to feed it wirelessly IMHO, especially not over the 2.4 GHz band.