Wi-Fi coverage within a train - The "fastest" survey I have ever done

First, a disclosure; unfortunantly I can't give much details about the solution. However there are some info published by diferent manufacturers on out to deploy solutions such as this:

The train had already a Wi-Fi solution for passengers but it's very outdated and unstable.

Coverage
One AP per carriage will suffice.

We can consider 2 APs if a carriage has more passengers but one must not forget the gateway capacity or it would end up deploying something like this:

Noise and Spectrum Availability
I noticed all kind of noise and interference at the 2,4Ghz spectrum, specially when passing through big cargo train terminals.

- Bluetooth
- Motion sensors
- Wi-Fi cameras
- Continuous transmitters
- MW oven used at the bar carriage
- Passengers with their own Wi-Fi equipment. Most of them broadcasting at 20Mhz but there's always one at 40Mhz...

5 Ghz vs 2,4Ghz availability (sorry for my "paint skilz"...)

Not only the air quality was terrible at the 2,4Ghz spectrum, but also most of the passengers were using G and 2,4G N equipment's.

As for 5Ghz spectrum... it was a breeze. No interference, no DFS alarms, no more than 4 equipments registered. We were a team of four engineers, each with 3 Wi-Fi equipment's. There were several times that we noticed connectivity problems in the 2,4G-only equipments while those that were connected to a 5Ghz channel were ok, even at 224 Km/h.

It's hard to have a steady hand wile traveling in a train at such speeds...

The 5Ghz equipments were perfect to detect connectivity issues with the mobile gateways. If a 5Ghz equipment failed, there was always something wrong with the 3G/4G coverage.

So, in conclusion:

- 2,4 Ghz is "abused" by everyone; Wi-Fi and non-Wi-Fi
- 5 Ghz FTW

- Don't forget the capacity of the gateways when planning the throughput of the WiFi network.
- Considerer deploying client managing smart tools.