Kapsch suggests FCC limit Progeny WAPS to low end of 902-928MHz spectrum, limits to interference

May 3, 2013
By Peter Samuel

2013-05-04: Kapsch has suggested in a submission to the FCC that interference to electronic toll collection transmission could be minimized if NextNav's Progeny, the proposed nationwide wide area positioning service (WAPS) moved its transmissions to the low end of 902-928MHz spread - to 904-909.75MHz. Kapsch is the supplier of E-ZPass toll transponders and readers - the equipment used for some 25 million toll customers in the US between West Virginia and Maine, and from the Atlantic coast west to Illinois.

Also Kapsch suggested the FCC put a clear ceiling level of interference Progeny be allowed to generate for other users of the frequency band. Progeny and a group representing tollers would be negotiated. Rules should require Progeny to mitigate interference by requiring it to adjust its broadcast transmissions - by relocating antennas, using directional rather than broadcast antennas, adjusting their frequencies, or other means.

The supplier of E-ZPass equipment said Progeny's plan to operate without power limits in any part of the 902 to 928MHz band with beacons on high points could result in widespread "denial of use" of electronic tolling: "We conclude therefore that there is real risk of harmful interference from the Progeny system to existing and future (electronic toll) systems."

Toll systems, Kapsch notes, have been designed to avoid interference in other uses of the 902-928MHz band by adopting low signal power, directional antennas, and short range (typically less than 20ft, 6m windshield to gantry antenna.) Very little RF signal is detectable outside the highway right-of-way.

They say: "We find it disturbing that another service which is not primarily intended for vehicular coverage, and has not considered its interference to the NM-LMS (non multilateration location monitoring) services (which includes toll collection), is being permitted in this band without adequate interference assessment."

Kapsch complains that Progeny has not made clear the polarization of antennas apparently because its grant of rights doesn't restrict polarity. This has a major impact on toll collection equipment which uses horizontal polarization. But whichever were used (horizontal, vertical or orthogonal,) Kapsch says, high power levels could generate considerable stray signal ('multipath.')

Progeny plans to operate 919.75 to 921.75Mhz and 925.25 to 927.25MHz. Kapsch in its submission says Progeny in its test report makes very modest claims about avoiding interference saying they showed:

-  "Progeny has engaged in significant efforts to minimize the potential for interference to other users
of the 902-928 MHz band"

- "Taken together, NextNav's technology and network architecture result in a relatively benign signal environment that will not result in unacceptable levels of interference to other users of the 902?928 MHz band."

Kapsch said it found no evidence in Progeny's submission that it had even assessed potential interference to other licensed users like tollers (the readers of which are licensed, though the transponders are unlicensed.)

The E-ZPass equipment supplier says that Progeny's claimed spectrum sharing methodologies don't provide much help to electronic tolling. They don't detract from its wide area, high power broadcasting from multiple often overlapping base stations. Its need to penetrate buildings from multiple broadcast beacons for E911 will require higher power and more signal paths than other uses. This has to generate higher interference than the shortrange uses the rules for the band was designed for, Kapsch's submission says.

Kapsch says claims of low bit data rates are "specious" given the spread spectrum methodology and each unit's need to receive signal from multiple beacons to make its time-difference-of-arrival calculations that are central to its location finding. Base station density will need to be greater than cell phones.

The Progeny plan is for a 20% duty cycle under which within each second there will be two 100ms (milliseconds) bursts.

Kapsch: "We contend these bursts can cause entire loss of service to individual devices in the NM-MLS (tolling is one) services operating in the 909.25-921.75 MHz band."

Because of the need of electronic tolling to complete the read-transponder communications for the very short time that a 65mph vehicle is in the toll zone, the there aren't many opportunities for a good read before the vehicle is gone. By our calculation 65mph = 95ft/second so a 30ft toll zone is traversed in about a third of a second or 333ms. A 100ms interference burst occurring every half second would seem to cause a significantly reduced time to read the tag. Multiple beacons sending a couple of these bursts every second compound the potential interference effect.

NextNav/Progeny in a reply to critics filed with the FCC devotes two pages out of 54 to Kapsch. It rejects or ignores all three of Kapsch's proposals to reduce interference. Going to a lower in the bandwidth to avoid electronic tolling is dismissed on the grounds that 15 years ago the FCC decided all would be free within the full 902-928MHz band. The suggestion that a ceiling be set on interference levels is simply ignored. The third is partially accepted by Progeny:

"Progeny is prepared to cooperate with Kapsch Trafficcom in Progeny's selection of M-LMS transmitter locations. As Kapsch Trafficcom acknowledges, Progeny intends to deploy its beacons primarily at the highest available points on existing broadcast, paging or cellular towers, while (toll readers are) installed primarily "on highways and on access or egresses to highways, bridges, and tunnels."

"Given the significant divergence of these transmitter deployment approaches, it should not be difficult for Progeny and Kapsch Trafficcom to cooperate adequately in their shared use of the spectrum."

E-ZPass Group report

An E-ZPass Group report says that on April 11, 2013  E-ZPass reps PJ Wilkins and Stan Ciszewski along with non-toll members of the Part 15 Coalition had meetings at the 8th floor executive offices of the FCC Commissioners  with Commissioner Ajit Pai, David Goldman, Senior Legislative Advisor to Commissioner Jessica Rosenworcel, and with Chairman Julius Genachowski. Other FCC officials in the meetings were Ruth Milkman, Chief of the Wireless Bureau and Julius Knapp, Chief, Office of Engineering and Technology, and some FCC legal staff.  

Utilities industry reps described the potential for interference with the smart-grid.  Other technologies spoke to the safety aspects of their systems, including silent alarms, personal duress alarms, baby monitors, and emergency services communications devices.  

Wilkins described how the E-ZPass system might be impacted, and also how widespread the 902-928MHz electronic toll collection (ETC) is nationally.  

"We discussed system safety, reliability, customer expectations, financial implications and the like.  We ended by strongly advocating for more testing with Progeny, so that we can understand the potential for interference on our operations."

April 29, 2012, PJ Wilkins, E-ZPass Group; Laura Stefani, Counsel for the Coalition; Michael Fitzpatrick, Senior Counsel, GE; Steve Coran, Counsel for WISPA (Wireless Internet Service Providers Association); and Mike Oldak, General Counsel, Utilities Telecom met with Commissioner Mignon Clyburn.

They covered the same talking points, stressing the  limited testing that Progeny had conducted so far and we again urged that the FCC require more testing of the Progeny system before allowing commercial operations.  

Wilkins writes:  "The bottom line is that the operators in the 900 to 928 MHZ band do not believe there had been sufficient or satisfactory testing of devices that operate in the band.  Progeny has conducted very limited testing with two or three entities, and the results of that testing have been in dispute, with Progeny alleging that the test results showed no "unacceptable" levels of interference, while the other parties tested with claim there was significant interference.  

He notes there has been no testing at all by Progeny of effects of their broadcast WAPS system on electronic toll systems.

"The FCC rules in this case require Progeny to prove that there is no unreasonable interference.  Our position is that Progeny has not yet done so, and must conduct further testing with a wider range of devices before FCC can approve their operations.  We have also taken a position with the FCC that this is a serious matter and should be decided by the Commissioners, rather than 'in bureau' by FCC senior staffers."  

TOLLROADSnews 2013-05-04

Further Reading


Leave a comment: