The problem of a sudden communication breakdown or the inability to connect to a free network in underground transport is familiar to many smartphone owners, especially Xiaomi users who notice that other devices in the same car continue to work, and their gadget “capricious”.
Xiaomi’s failure to connect to Wi-Fi in the subway can be caused by a range of factors, from the technical limitations of the transport itself to the specific energy saving settings in the MIUI or HyperOS shell. Unlike a stable home router, public networks are a high-density environment with constant interference.
In this article, we will take a closer look at all possible causes of failure, from antenna hardware to software conflicts, how to set frequency bands correctly, whether to reset network settings, and why the Internet can simply disappear during rush hour.
Technical limitations and network overload in the subway
The first thing to consider is that the subway is an extreme environment for wireless communication, with stations and tunnels shielded with thick layers of concrete and metal, creating the Faraday cage effect, and operators and providers installing powerful access points to provide coverage, but there are limited numbers.
When a thousand people walk into the car, each trying to connect their smartphone to the same access point, there's a tremendous load. IEEE 802.11 simply doesn't have time to distribute data packets to everyone, so your phone can see the network but not receive it. IP-address or permanently lose connection.
Traffic distribution algorithms can prioritize some devices over others, and older or less powerful communication modules in Xiaomi smartphones can lose competition to newer flagships of other brands.
⚠️ Warning: During peak hours, free slots for connecting may simply not be physically available, even if the signal is displayed full.
In addition, the subway system often uses DAS (Distributed Antenna System) systems, which create many small areas of coverage. When a train moves, the phone must constantly switch between antennas, and if this process (roaming between points) occurs too quickly or with errors, mobile Internet or Wi-Fi can break.
Conflicts of frequency bands 2.4 GHz and 5 GHz
One of the key reasons for instability is that it operates in two frequency bands, and most public networks in the subway still use the 2.4 GHz standard because it has better penetration through the walls of the train cars, but it is extremely noisy.
Xiaomi smartphones are set to automatically select the best network by default. If the phone sees a 5GHz signal that is faster but has a shorter range, it will try to connect to it. On a moving train, this signal will disappear every few seconds, causing constant reconnection.
It is recommended to force changes in Wi-Fi settings to give priority to a more stable, albeit slow range, this can be done through an engineering menu or special applications, but often it is enough to simply forget the network with the prefix “5G” and connect to the usual one.
- 📶 2.4 GHz – better through obstacles, but has a low speed and a lot of interference from microwaves and Bluetooth.
- 🚀 5 GHz – high speed, but poor penetration and short range, which is critical in the subway.
- 🔄 Auto-select is a phone feature that often gets it wrong in a dynamic subway environment.
It’s also worth noting that some Redmi and POCO models have a software feature that aggressively shuts down Wi-Fi at a weak signal to save battery.In subway conditions where the signal is constantly “jumping”, this is perceived by the system as lack of network.
How do you know what frequency you are working on?
Power saving settings MIUI and HyperOS
Xiaomi’s shells are known for aggressive power optimization, and the system seeks to extend battery life by shutting down background processes and communication modules if it believes they are not actively used or the signal is unstable.
The battery settings often activate Power Saving mode, which can limit Wi-Fi in the background. When the screen goes out or you turn off the browser, the system may terminate the connection, considering it inappropriate. In the subway, where communication is already unstable, this leads to a complete lack of Internet.
You need to check the settings for the specific application you want to connect to the network (browser, messenger), for which you need to set the resolution to “No restrictions” in the battery section, and you should also turn off the option “Wi-Fi Assistant”, which switches traffic to the mobile network when the Wi-Fi signal is weak, creating the illusion of a failure.
| Parameter | Recommended value | Where to find out. |
|---|---|---|
| Battery mode | Productive / Without restrictions | Settings → Battery |
| Wi-Fi Assistant | Off. | Settings → Wi-Fi → Assistant |
| Background activity | Permission. | Applications → Battery |
Another important thing is Wi-Fi Scan throttling, which in newer versions of Android limits the frequency of network scanning to save power, which prevents the phone from quickly finding a new access point when switching between stations.
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Try to temporarily turn on flight mode for 5-10 seconds and turn it off, which will force all radios to restart and can help you find a more stable access point.
Problems with MAC-addressing and authorization
Many networks in the subway (for example, MT_FREE, Moscow_WiFi) require authorization through SMS Modern Xiaomi smartphones use the function "random". MAC-Address" to enhance privacy, which means that each time you connect, the phone is presented to the network as a new device.
The subway authorization server may not be able to handle the constant change of IDs or block frequent requests from one “virtual” device, considering it an attack. IP-address" or reconnection cycle.
To solve this problem, you need to change the privacy setting for a particular network. MAC-This will make your phone recognizable to the ISP server.
⚠️ Attention: Change MAC-Permanent addresses reduce anonymity in open networks, but are necessary for stable operation in the subway.
To do this, go to Wi-Fi settings, click on the gear next to the name of the metro network and find the Privacy item or «MAC-Select the option "Use" MAC-Address of the device. Then try to re-authorize.
Resetting network settings as a radical method
If software failures accumulate, configuration file conflicts can occur in the phone. DNS cache, erroneous static IPs, or incorrect security profiles can interfere with connection in difficult subway conditions.
Resetting network settings is an effective way to clear up any accumulated errors.This action will remove stored Wi-Fi passwords, Bluetooth settings, and cellular network settings, returning them to factory values. For the subway, this is often the only way to make the phone “see” the network again.
☑️ Preparing for resetting network settings
The procedure is done through the settings menu. The path may vary depending on the version of MIUI, but it's usually in the "Connect and Sharing" or "Additional Settings" section. Once reset, the phone will reboot and you'll have to re-enter your password from your home network, but the subway problem may disappear.
It's important to understand that this method doesn't fix the hardware breakdowns of the antenna, and if Wi-Fi works well elsewhere after resetting, and it doesn't work in the subway, it's probably the provider or the coverage side of the problem.
Influence of covers and hardware features
And the physical impact on antennas is not to be discounted, and some protective covers, especially those with metal inserts, magnets or walls that are too thick, can shield the signal, and even a small additional obstacle becomes critical when there is a strong attenuation in the tunnel.
Also worth mentioning is the hardware difference between the models: Xiaomi’s flagships feature more advanced communication modules with support for multiple MIMO ranges and technologies. Redmi’s budget models can have simplified antenna design, making them more vulnerable in areas of poor reception.
- 🛡️ Thick covers - can weaken the signal on the 20-30%, subway-critical.
- 📱 Hand position – by covering the bottom or top of the phone with your palm, you can block the antennas.
- 🔋 Heating – when overheated, the communication module can reduce radiation power, worsening reception.
If you notice that the problem occurred after the phone fell or the case was replaced, the connector of the antenna module inside the device may have been damaged, in which case software methods will not help, and you will need to diagnose in the service center.
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In the subway, stability is more important than speed, and a forced 2.4GHz switch and power-savings shutdown is better than trying to catch a fast 5GHz.