In all the hype over the multimillion$$ CBTC, I read about a simple train control system that had a RFID device attached to each rail tie…
Could actually be done… even made IoT with use of IPv6 addressing even if we don’t get RFPs specifically for devices, and continually both charged and scanned by passing trains…
Of course, you wouldn’t do that in real life any more than as a (pretty funny) joke. Effective CBTC as an overlay to mandated PTC is little more involved than the approach QNS&L used with locomotives, extended to EOT, some key waysides, and beacons for civil.
Of course at national scale, that’s still multiple millions. That number doesn’t seem so large any more, compared to something like ECP brakes or even dual-mode-lite in early stages…
Is this discussion intended for to Transit?
If it’s for general railroading, does expanding Communication Based Train Control presume that GPS will never be able to do the job?
GPS and tunnels…Oil and water
You just need lower satellites 
Would it work in the Chunnel?
Easily, but with some small algorithm changes.
All GPS really does is detect some differential in the time it takes light to get from a certain number of points of known position to a receiver, then do some quick trig and then map/GIS referencing. This trick is harder inside a tunnel, where a long-baseline constellation within easy RF reception is impossible, but at the same time a very precise fix on entry and exit is possible, and inertial approximation guided by periodic time-aligned beacons can adequately get you longitudinal precision down to cm, and with repeated measurements (which don’t take long) speed and acceleration. That is sufficient as a basis for CBTC position determination in the Chunnel independent of any track sensing.
The beacons you describe would make a system dependent upon something different than direct GPS satellite signals. Thus more time and money. I remember BART tried a similar system using EPLRS technology but it was scrapped. The CBTC systems rely on wireless signals emitted from the lossy lines installed in tunnels for trunk radios and cell phone data…
I think most people understand that GPS does not penetrate tunnels, which is why I was asking for the context for your thread, which you still have not made clear.
I think part of what he’s getting at is that satellite GPS is unavailable, sometimes randomly, in a great many ‘railroad’ places, and unreliable (e.g. from multipath concerns) in a great many more, so if ‘multimillions’ of dollars are to go into mainline CBTC, a better localizing system may be needed. His joke was to use RFID identifying the datum precision of every tie so the head and tail of a train could obtain derived precision quickly and redundantly for “not that much” cost in absolute terms [assuming the RFID tags are passive or externally charged].
As the issue of CBTC is intimately tied to continuously-correct train localization, I think the discussion is not irrelevant.
Note that he says
Most of the current CBTC projects I’ve seen have been geared toward shorter headways for transit and commuter-passenger applications, with the assumption of very limited-sight distance or low-lighting – much of it inherently in tunnels. Radio and other types of EM are easily ‘repeatered’ into tunnels, and easily given appropriate antenna structures including ‘leaky’ or wiggly wires for the ‘communication’ part of CBTC. The fundamental issue is that the only really relevant part of the GPS information – the TOF between transmitter and receiver – is irrecoverably lost in such transversion. So some other method of good localization, be it with beacons or differential localization (no one but an idiot would rely on the ‘usual’ meth
I have read some studies pertaining to driverless freight trains using CBTC…and as far as I know CBTC is presently installed in a few transit applications, such as airport sky trains, etc. The application to transit systems is usually complicated by attempting to add it on to legacy car designs, instead of a completely new wayside and car design…however the RFID device per rail tie is simple and effective…as far as this thread is corncerned, it is a general discussion, so whatever CBTC comments, opinions, facts, studies, etc. are relevant…
Virtually every rail car today has an RFID tag on each side. They are passive, with trackside “interogators” spaced along the lines. There have been incidents of people pirating that information with their own interogators. I believe it’s just the reporting marks.
There are two halves to CBTC. The part referenced in the name is that trains ‘talk’ to each other to stay safely but intelligently apart from each other – this is a combination of short-range radio and ‘networked’ communication including with dispatch, civil, etc. The other, hidden, part of it is that the trains need to know precisely where they are, how they’re actually moving and accelerating, and this has to have ‘high confidence’ regardless of crappy conditions, tunnels, vandalism, Fancy Bear hacking… whatever have you.
Imagine for a moment that I manufacture 10 million transponder tags, each with its rectenna, precoded IPv6 address (look it up in IoT references) and a certain amount of programmable stable NVRAM. I put these things en masse into automated ‘loaders’ that can optically detect ties, slew to a good location, and staple/adhere them the number of ties apart that corresponds to the resolution of your base GPS system (ask MC where the sweet spot of HA-NDGPS with beacons and accurately discriminating track centers or fouling points vs. robustness and redundancy ought to be) – if this is ‘every tie’ for centimetric resolution, so be it. Each of these devices is then scanned via a separate vehicle, running true high-accuracy location, which maps each chip accurately by location and also registers them in sequential order – note that we don’t care if the addresses are in numerical sequence, which simplifies things when ties are replaced, wrecks repaired, etc. Then it programs each chip’s NVRAM with its exact (to ‘beacon-grade’ resolution & jitter budget) coordinate location.
Locomotives can activate and ‘read’ chips, in or out of sequence, and derive position from this in a number of ways. Any one or two failures gave minuscule practical effect on overall location; the chips consume no power when not being used for location and have a very large MTTF and n
Government regulation, FailSafe certification, redundant circuitry, over engineering and contractor greed will determine the complexity…and should we not forget…it will still not be EMP hardened…
The SDRs can be. Certainly GPS cores don’t constitute an irreplaceable showstopping technological obstacle, and there is no electron cascade issue upwards to the GPS constellation. I have not run careful simulation but effective EMP shunting in passive-charged RFID tags doesn’t seem that critical (for the rectenna dimensions involved) either for solar or ‘nuclear’ risetimes. While local EMP probably remains a ‘terrorist-response’ concern, even if air-launched its effect on any great extent of a CBTC-enhanced CTC-like system would not be substantial.
I’m all for massive non-common-mode-failure-susceptible redundancy in critical systems, particularly safety-critical ones putatively run by idiots abd financiers. About government meddling there is little to do but educate the twentysomethings that actually craft the language of the rule details; about contractor greed my answer is much the same as the WOPR’s key insight…