The new Wifi equipment installed in late 2016 brings real improvement to the Amtrak Acela Express Wifi performance.
First WiFi deployment
Amtrak WiFi was first deployed in 1Q2010 by GBS Group and Nomad Digital, with 3G cellular connectivity. This connection was shared among the passenger cars from the central cellular modem in the cafe car via wired 150 Mbps between the 802.11n 2.4 GHz Wifi APs, which was a new standard feature on smartphones (at least 802.11g for phones and 802.11n for laptops). Typical data throughput was under 1 Mbps, but this was adequate for basic Internet use. At the time, the mobile internet had not moved much past the state it was in when I started using it in the early 2000s. That is, highly reduced text-only with tiny graphics, maybe a Little bit of form entry. Many media-heavy websites such as Federal New Radio were simply blocked. All connections went through a central Amtrak server for this purpose like a VPN and proxy.
As the mobile internet and social media become more the norm, the original Amtrak Wifi system become so overloaded as to become useless. I simply used my phone’s 4G connection (I was on the first 4G network, WiMax from Sprint) even though the 2.5 GHz signal frequently dipped back to the 1.9 GHz 3G signal. By 3Q2013, Amtrak had refreshed its Wifi fleet with LTE cellular connections, bringing another burst of relief, making the Wifi system useful again–briefly. The total train data throughput, despite the multi-modem, carrier-aggregating system was on the order of 10 Mbps, far too inadequate for social media and video was still blocked.
The Wifi equipment remained the same–central cafe car cellular modem and 150 Mbps wired link to 802.11n 2.4 GHz APs. This meant as savvy travelers used their own LTE/Wifi hotspots on 2.4 GHz the meager train Wifi was jammed with CSMA/CA, a problem well known in urban environments. The Wifi became nearly as useless as the first-generation system, and as inexpensive buses and even passenger cars brought ubiquitous Wifi, Amtrak’s Wifi was widely ridiculed and reviled.
next generation Wifi (Acela only)
Passengers on Acela Express (only Acela as of Fall 2017) benefit from the late 2016 install of 802.11ac Wifi (implicitly 5 GHz) along with 802.11n for 2.4 GHz. Gigabit links to the cafe car have also been installed on Acela. At the same time, south of New York City is having trackside links installed in the 5 GHz band to the train, helping overcome problems with weak/constantly changing LTE towers.
The Acela Express Wifi is 2x2 antenna, MCS-9, 40 MHz as of Fall 2017. This yields a 400 Mbps raw connection rate. The connection is throttled to approximately 3 Mbps downlink and 2 Mbps uplink. Latency is 50-300 ms typically. VPN connections do drop periodically, which might be annoying for you. This implies you can (just) watch 1080p compressed streaming video, which does indeed work via YouTube on Amtrak Acela Express. I do not recommend using HD video, to be neighborly, I would watch SD (240p or 480p) video to avoid sucking up too much of the train LTE/trackside bandwidth.
Non-Acela Wifi is the old WiFi system
As of fall 2017, the Northeast Regional and other Amtrak trains are stuck with the old Wifi system, which is often not useful for more than basic text emails. As a side note, in 2015-2016 some of the long distance routes had Verizon Mifi portable routers in the sleeper cars, but this may have been only an experiment–one that actually did work in the sleeper cars, but not sure if this has been continued for non-listed Amtrak Wifi trains.