Circle Line disruptions due to faulty signalling hardware on one ‘rogue train’
ricky l2 seconds ago
RF (Radio Frequency) has a very peculiar characteristics.
A walkie talkie for eg. can jam the whole radio network in the same RF.
Similarly, this rogue train display the same RF peculiar characteristics that jam the whole MRT signal network in the same RF.
One way to resolve this is by having at least dual-frequency RF for signaling and controlling with the Central Transport Management System for eg. one with 2.4Ghz band and one with 5Ghz band.
So if the 2.4Ghz RF band is jam, the MRT trains and the Central Transport Management System can turn off the 2.4Ghz RF band and switch over to 5Ghz RF band.
Then there will be no disruption to the MRT operation.
SG130 minutes ago
That's silly to use a free band in the 2.4Ghz and 5.7Ghz for vital Train signal systems to begin with. Even though the signal is digital coded, the RF carrier is still analog fundamentally. Anyone operating these Band of frequencies are bound to be interfered. Frequency hopping does help, but is limited to how much it can hop. If the place are swamped with the same 2.4Ghz or 5.7Ghz, interference are bound to happen. No ammount of hopping can solve the problem. Critical wireless signal should be assigned a dedicated and guarded RF band . If It is true that the train signal uses any ISM band , are asking for trouble.
ricky l12 seconds ago
Well if I understand correctly, licensed RF is getting scarce and they are mainly reserved for Telcos. military, police, air flight etc.
License RF can even be bid at billions of dollars.
Only 2.4 and 5 Ghz free band are free to use.
Anyway using license guarded RF will not solve this current MRT signaling problem, because as long as a receiver and transmitter jam the guarded RF band, the whole radio signal network will still be jammed.
Thus dual RF signal band is a better solution.
ricky l2 seconds ago
Anyway, there are many techniques to prevent RF interference in the same RF band.
Frequency hopping is just one example.
There are others modulation and demodulation techniques eg.
(1) OFDM (Orthogonal Frequency Division Multiplexing) - where RF band are sliced into smaller band and this smaller band are guarded against interference. Channels are used for auto-negotiation and auto-hopping into other sub-band when interference occur.
(2) DSSS (Direct Sequence Spread Spectrum) - where RF band uses the entire spread spectrum to receive and transmit.
(3) FHSS (Frequency Hopping Spread Spectrum) - where RF hop from frequency to frequency when there are interference.
Many Wifi use the above techniques and even though there are alot of RF interference, they still can receive and transmit RF signals.
Make sense?
No comments:
Post a Comment