Amtrak’s waiver request for Wi-Fi network rankles Wi-Fi Alliance, IEEE committee

Amtrak is asking the FCC for a waiver on certain conditions for the Wi-Fi network it plans to build along the Northeast Corridor, but Wi-Fi proponents are concerned that a waiver might adversely affect other users of Wi-Fi.

Specifically, Amtrak is seeking a conditional waiver to permit operation of its trackside network (TSN) as a fixed point-to-point network in the U-NII-1 and U-NII-3 bands, which it says is similar to a waiver the FCC’s Office of Engineering and Technology (OET) granted to Deere & Company. The FCC’s OET is currently reviewing Amtrak’s waiver request and accepting public comments.

The Northeast Corridor is Amtrak’s most heavily traveled route, connecting Washington, D.C., to Boston, and about 750,000 Amtrak and commuter passenger trips are taken every day in the corridor. But Amtrak’s Wi-Fi service hasn’t kept up with demand.

Since its inception, Amtrak’s Wi-Fi service relied on commercial network service providers, with each train containing a communications control unit (CCU) located within a single car that acts as the “brain car.” The CCU uses multiple concurrent 3G and 4G cellular links supplied by the four major U.S. wireless operators.

Those connections are then distributed wirelessly to Wi-Fi access points located throughout the train so that passengers have connectivity in every car, Amtrak explained in its waiver request. The aggregated traffic is sent from the train via antennas mounted on the rooftop of the “brain car” over the commercial cellular networks to servers at Amtrak’s East Coast data center, where packets are reassembled and sent to the internet.

Besides risking poor performance due to over-used airwaves, Amtrak told the commission that continued reliance on commercial cellular networks forces Amtrak to face the real possibility that grandfathered “unlimited” data plans may cease, exposing the company to unacceptably high monthly charges that could force the closure of its AmtrakConnect service or require Amtrak to impose significant limitations on use of its Wi-Fi. The only effective way to guarantee the long-term viability of its Wi-Fi service is to construct its own dedicated, private TSN, according to rail provider.

But Amtrak has determined that if it uses the U-NII-1 band under current commission rules, it would be required to deploy three times as many trackside access points in order to operate as efficiently as it currently does in the U-NII-3 band, thereby undermining the business case for the project.

Amtrak doesn’t claim that its TSN operates as a fixed network, but points out that like a fixed point-to-point network, the location of Amtrak’s transmitting devices is always known—trains can’t and do not travel outside of Amtrak’s right-of-way, so it’s “not inappropriate to characterize Amtrak’s TSN as having characteristics typical of fixed operations,” according to Amtrak's filing (PDF).

The Wi-Fi Alliance (WFA) says Amtrak’s waiver request contains a brief examination of the potential interference to satellite operations caused by its proposed system, but “it does not meaningfully consider potential interference to U-NII- devices.” Instead, Amtrak asserts that its proposed system will cause only de minimis interference because of the use of directional antennas with a narrow beamwidth. But that’s not good enough, according to the alliance.

“Amtrak must conduct testing of interference potential, perhaps using the ‘proof-of-concept’ TSN Amtrak has already constructed in Delaware, and provide that data to the Commission and to the public to ensure that existing operations are protected,” the Wi-Fi Alliance wrote (PDF). Such field tests should include coexistence measurement of existing Wi-Fi systems placed at distances representative of the “worst case scenario” in which train tracks pass very close to residential and commercial structures. The tests also could present an opportunity to evaluate Amtrak’s claim that the as-proposed TSN would produce less interference than a system that would comply with the rules.

The WFA is not the only one concerned about the impact to other users. The IEEE 802 LAN/MAN Standards Committee also submitted comments to the FCC asking that the commission require an impact study before granting the waiver. “If no study exists, the Commission should not proceed if and until such a study is done, and reviewed and evaluated by IEEE 802,” the filing said.

Globalstar is authorized to operate mobile satellite service MSS feeder links at 5096- 5250 MHz, which overlaps with the U-NII-1 band at 5.15-5.25 GHz.2 But the company said it does not object (PDF) to Amtrak’s waiver request so long as the commission adopts Amtrak’s proposed waiver conditions, ensuring that Amtrak’s operations remain extremely limited in scale and not harm Globalstar’s licensed feeder link operations.

The FCC's deadline for comment was Feb. 27, and reply comments on the matter are due March 15.